CHAPTER XII DETAILS OF FUSELAGE CONSTRUCTION

CHAPTER XII DETAILS OF FUSELAGE CONSTRUCTIONClassification of types. While there are a number of methods adopted in building up the fuselage structure, the common type is the "wire truss" in which wood compression members are used in connection with steel wire or cable tension members. Four wooden "longerons" or "longitudinals" run the entire length of the body and are bent to its general outline. The longitudinals are spaced at the correct distance by wood compression members, which in turn are held in place by wire cross bracing. This method of trussing forms a very strong and light structure, although rather complicated, and difficult to build. The cross-section is rectangular, although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame.Another well known type is the "Monocoque" body, first used on the Gordon-Bennett Deperdussin monoplane. This fuselage is a circular shell built up of three-ply tulip wood, thus forming a single piece body of great strength. The three-ply shell is really a veneer, the layers proceeding spirally around the body, each layer being securely glued to its neighbor. Between each layer is a scrim layer of treated silk, and another fabric layer is generally glued to the outside of the shell. The shell is very thin, the total thickness of the three layers of wood and fabric in modern machines being rather less than 1.5 millimeters (about 1/16 inch). In the original "Deps" this was somewhat greater, 0.15 inch. Monocoque construction as a rule is heavy and expensive, but offers the great advantage of strength, perfect alignment at all times, and of offering resistance to rifle and shell fire. If the longitudinals of a truss type are struck with a bullet, or shell fragment, the entire fuselage is likely to fail, but a monocoque body may be well perforated before failure is likely to take place.The American L. W. F. Tractor Biplane has a monocoque body in which spruce laminations are used instead of hardwood. One ply runs longitudinally while the other two layers are spiralled to the right and left respectively. Between each layer is a scrim layer of treated silk, the whole construction being covered with a final layer of fabric, several coats of waterproof compound, and four final coats of spar varnish. When used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness. Since spruce is used in place of hardwood, the construction is lighter than in European models, and the L. W. F. Company claim that it is lighter than the usual truss construction. An additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush.Another form of monocoque construction was adopted by the French builder, Bleriot, at the beginning of the war. The fuselage of this machine was covered with papier-mache, the ash longitudinals being buried in this mixture. The papier-mache is built up with glue and silk threads. This construction is very light and strong, but is expensive and difficult to protect against moisture. The front of the fuselage is protected with a 3 millimeter steel armor plate to protect the pilot against bullets and shrapnel. The papier-mache portion of the body is not easily splintered by bullets.A third form of monocoque, experimented upon by the author, is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell. This outer shell is strengthened by suitable stiffener angles. With a shell thickness of 0.013 inch, the strength is equal to the strength of a wood shell and is slightly less in weight. It has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture. It cannot splinter, will not catch fire and offers a maximum resistance against penetration. There is yet much experimental work to be done before the construction is perfected.About midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern German aeroplanes. In general, this may be described as being a veneer shell fastened to the conventional wood longitudinals. Stay wires are not in general use, the veneer taking the shear due to the bending movement. Six longerons are used instead of four, the two additional members being located midway on the vertical sides. Transverse wood frames take the place of the transverse stay wires used in the truss type. Examples of this type are met with in the "Albatros de Chasse" and in the "Gotha" bomb dropper. The single seater, "Roland," has a fuselage of circular section, with a true monocoque veneer construction, but German-like, reinforces the construction with a number of very small longitudinals. In this machine there are 6 layers, or plies, of wood reinforced by fabrics. The entire thickness of the wood and fabric is only 1.5 millimeters (1/16 inch).Steel tube fuselage dates back to the beginning of the aeroplane industry. In this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes, the cross struts being also of this material. The diagonal bracing may be either of steel wire, as in the wood frames, or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts. For the greatest weight-efficiency, a steel tube body should be triangular in section rather than square. A triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary. Connections on a steel tube fuselage are difficult to make and are heavy. They require much brazing and welding with the result that the strength is uncertain and the joint is heavy.A very modern type of steel construction is that developed by the Sturtevant Company. The members of the Sturtevant fuselage are in the form of steel angles and channels, similar in many respects to the sections used in steel buildings and bridges. The joints are riveted and pinned as in steel structural work. The longitudinals are angles and the struts are channels. Crystallization of the steel members is prevented by the use of special pin-connected joints provided with shock absorbing washers. Owing to the simplicity of the riveted joints, there is practically no weight due to connections, and since the weight of connections is a large item in the total weight of a fuselage, the Sturtevant is a very light structure. According to G. C. Loening, engineer of the company, the fittings of a large wood fuselage weigh at least 60 pounds. This is almost entirely saved with the riveted connections.Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.A novel type of wood fuselage has been described by Poulsen in "Flight." Eight small longitudinals are used which are held in place by three-ply wooden formers or diaphragms. Wire bracing is used in a longitudinal direction, but not transversely in the plane of the diaphragms. The cross-section is octagonal, and the completed structure is covered with fabric. For the amateur this offers many advantages since the wiring is reduced to a minimum and all of the members are small and easily bent to shape. It is fully as light as any type of body, for the connections are only thin strips of steel bolted to the diaphragms with small machine screws. No formers are needed for the deck, and the machine can be given a close approximation to the ideal stream-line form with little trouble.Truss Type Fuselage. We will now take up the construction of the truss type of fuselage in more detail, and investigate the merits of the different types of connections used in fastening the frame together. Like every part of the aeroplane, the fuselage must either be right or wrong, there is no middle course. Fig. 23 shows a side elevation of a typical truss type fuselage built up with wood longitudinals and struts, the tension members being high tensile strength steel wire and cable. L and L’ are the upper and lower longitudinals, S-S-S are the vertical struts, and T-T-T are the horizontal cross struts which run across the frame. The engine bed is the timber marked B at the front of the body. The upper wing is attached to the body through the "cabane" struts C, and the chassis connections are shown at D. The stern post E closes the rear end of the body in a knife edge and acts as a support for the rudder and the rear end of the stabilizer. F is the seat rail which carries the seats and supports the control yokes.All cross bracing is of high tensile strength steel wire, or of high strength aviation cable, these strands taking the tensile stresses while the wood struts are in compression. In the forward portion, double stranded cables are generally used, with solid wire applied to the after portions. The longitudinals are of ash from the motor to the rear of the pilot's seat, while the rear longitudinals are generally of spruce. In some machines, however, the entire length of the longitudinals is ash. The latter arrangement makes a heavier, but stronger body. The struts are usually of spruce as this material is stiffer than ash and much lighter.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Both the struts and longitudinals are frequently channelled out for lightness, as shown by Fig. 27, the wooden member being left rectangular in section only at the points where the connections are made with the struts and cables. The channelling-out process, if correctly followed, gives very strong stiff members with a minimum of cross-sectional area and weight. Many captured German machines, on the contrary, have solid longitudinals of rectangular section, wrapped with linen fabric. This fabric strengthens the construction and at the same time reduces the chances of splintering the wooden members in a hard landing. The fabric is glued to the wood and the entire wrapping is then given several coats of a moisture repelling varnish. In the older types of fuselage, the longitudinals were often of the "laminated" class, that is, were built up of several layers of wood glued together in a single rectangular mass. This reduced the tendency toward splitting, but was very unreliable because of the uncertainty of the glued joints when exposed to the effects of heat and moisture. Laminated longitudinals are now seldom used, particularly in the region of the motor where water and oil are certain to wreck havoc with the glued up members.As the stresses rapidly diminish toward the tail, it is the general practice to taper down the section of the longitudinal toward the rear and to reduce the section of the struts. The longitudinals are generally kept constant in section from the motor to the rear of the pilot's seat, the taper starting at the latter point and continuing to the rear end. For example, if the longitudinal section at the motor is 1 1/4" x 1 1/2", the section at the rear will be 1" x 1", the width of the struts corresponding to this taper. While tapering is very desirable from the weight standpoint, it makes the fitting problem very difficult since each fitting must be of a different dimension unless the connections can be designed so that they are adjustable to changes in the section of the longitudinals. In one machine, the width and depth of the longitudinals are kept constant, the variation in weight and section being accomplished by increasing the depth of the channelling as the rear is approached. With this design, the same fittings can be applied from one end to the other.Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.Since the loading of the struts is comparatively light, they can be much reduced in section by channelling or by chamfering, as shown by Fig. 28. If the width and thickness is maintained, much of the interior material can be removed without danger of reducing the strength. Sketch (A) in Fig. 28 shows a very common method of strut reduction, the strut being of rectangular section throughout its length, but tapered in such a way that it is thickest at the center (d) and thinnest at the two ends (e). To obtain the correct relation between the center end thickness requires very careful calculation. As shown, the strut is attached to the upper and lower longitudinals by sheet steel fittings or "sockets." Sketch (B) shows a simple method, the rectangular strut being chamfered off at each of the four corners, and left full size at either end where the fittings connect it with the longitudinals. This form is not correct from a technical standpoint, but is generally good enough for lightly loaded struts, and has the advantage of being cheaply and easily constructed. In sketch (C) a channelled strut is shown, the center portion being channelled out in a manner similar to the channelling of the longitudinals. This lightening process is most commonly adopted with the large heavily loaded struts in the front portion of the fuselage, and at the points where the motor bed is suspended or where the wings and chassis are attached to the body. The black dots at the ends of the struts indicate the bolt holes for the fittings, it being permissible to drill holes in the ends of the struts but not in the longitudinal members. If the strut is large enough to resist the bending stresses at the center it will generally allow of holes being drilled near the ends without danger of strength reduction. Again, the struts are always in compression and hence the bolts may be depended upon to partly take the place of the removed material in carrying the compressive stresses.Holes should never be drilled in the longitudinals since these members may be either in tension or compression, depending upon the angle at which the elevator flaps are set. The hole not only destroys the strength at the point at which it is drilled, but this reduction also extends to a considerable distance on either side of the hole, owing to the fibrous nature of the wood. In steel members the effect of the hole is purely local and does not usually extend much beyond the edge of the hole. Considering the wood beam as consisting of a series of parallel fibers, it will be seen that severing any one of the fibers will decrease the strength of the wood through a distance equal to the length of the cut fiber, or at least through a distance equal to the natural shear value of the resins that bind the fibers together.Fuselage fittings are almost numberless in the variety of design. They must be very light and strong, must be applied without drilling the longerons, and should be simple and cheap to construct. They are usually made of sheet steel of from 0.20 to 0.30 point carbon, and may be either bent or pressed into shape. At the points where the struts are joined to the longitudinals, the fittings connect struts and wires in three planes, the vertical struts and fore and aft wires; the transverse wires and horizontal struts, and the top and bottom wires that lie in a horizontal plane. There are at least 6 connections at every strut, four of the connections being made to the stay wires or cables. A simple connection is therefore very hard to design.Fig. 29 shows a typical fuselage "panel" and the interconnected members in their usual relation. LU and LL are the top and bottom longitudinals at the right, while LU' and LL’ are the longitudinals at the right hand side. The vertical struts SV and SV’ separate the top and bottom longitudinals, while the horizontal struts SH and SH’ separate the right and left hand sides of the fuselage body. The wires w-w-w-w brace the body fore and aft in a vertical plane. The wires t-t lie in a horizontal plane, produce compression in the horizontal struts SH-SH', and stiffen the frame against side thrust. The transverse rectangle SV-SH-SV’-SH' is held in shape by the transverse stay wires W-W, this rectangle, and the stays resisting torsional stress (twisting), act against the struts composing the sides of the rectangle. In some European machines, the wires WW are eliminated, and are replaced by thin veneer panels, or short wood knee braces as shown by Fig. 30. The section shows the longitudinals L-L-L-L and the struts SV-SV’-SH-SH’ braced by the veneer sheet or diaphragm D. This diaphragm is well perforated by lightening holes and effectually resists any torsional stress that may be due to motor torque, etc. Since the transverse wires W-W in Fig. 29 are rather inaccessible and difficult to adjust, the veneer diaphragm in Fig. 27 has a great advantage. In this regard it may be stated that wire bracing is not a desirable construction, and the substitution of solid veneer is a step in advance.Wire bracing has always seemed like a makeshift to the author. The compression and tension members being of materials of widely different characteristics are not suitable in positions where a strict alignment must be maintained under different conditions of temperature and moisture. The difference in expansion between wire and the wood compression members produces alternate tightness and slackness at the joints, and as this is not a uniform variation at the different joints, the frame is always weaving in and out of line. Under the influence of moisture the wood either swells or contracts, while the wire and cable maintain their original lengths and adjustments. The result is that a frame of this kind must be given constant attention if correct alignment is desired.The adjustment of a wire braced wood fuselage should be performed only by a skilled mechanic, as it is easily possible to strain the members beyond the elastic limit by careless or ignorant handling of the wire straining turnbuckles. In the endeavor to bring an old warped fuselage back into line it is certain that the initial tension in the wires can be made greater than the maximum working stress for which the wires were originally intended. Shrinkage of the wood also loosens the bond between the wooden members and the steel fittings unless this is continually being taken up. Some form of unit construction, such as the monocoque body, is far more desirable than the common form of wire trussed wood body.Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.Fuselage Fittings. In the early days of aviation the fuselage fittings on many machines were made of aluminum alloy. This metal, while light, was uncertain in regard to strength, hence the use of the alloy was gradually abandoned. At present the greater part of the fittings are stamped steel, formed out of the sheet, and are of a uniform strength for similar designs and classes of material.The steel best adapted for the fittings has a carbon content of from 0.20 to 0.30, with an ultimate strength of 60,000 pounds per square inch, and a 15 per cent elongation. The steel as received from the mill should be annealed before stamping or forming to avoid fracture. After the forming it can be given a strengthening heat treatment. A lower steel lying between 0.10 and 0.15 carbon is softer and can be formed without annealing before the forming process. This material is very weak, however, the tensile strength being about 40,000 pounds per square inch. Fittings made of the 0.15 carbon steel will therefore be heavier than with the 0.30 carbon steel for the same strength. The thickness of the metal will vary from 1/32" to 1/16", depending upon the load coming on the fitting.A typical fuselage strut fitting is shown by Fig. 31-A in which L-L-L are the longerons, d is the fitting strap passing over the longerons, S and So are the vertical and horizontal struts respectively. The stay wires are fastened to ears (b) bent out of the fitting, the wires being attached through the adjustable turnbuckles (t). The struts are provided with the sheet steel ferrules marked (F). There are no bolts passing through the longitudinals L-L', the fitting being clamped to the wooden member. This is very simple and light fitting. Fig. 31-B is a similar type, so simple that further discussion is unnecessary.Fig. 32 shows a fuselage strut fitting as used on the Standard Type H-3 Biplane. We are indebted to "Aerial Age" for this illustration. This consists of a sheet metal strap of "U" form which is bent over the longitudinal and is bolted to the vertical strut. At either side of the strut are through bolts to which bent straps attach the turnbuckles. These straps are looped around the bolts and form a clevis for the male ends of the turnbuckles.Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.An old form of fuselage connection used on the Nieuport monoplane is shown by Fig. 33, an example of a type in which the bolts are passed through the longeron member. This fitting is very light but objectionable because of the piercing of the longeron.An Austrian aeroplane, the Hansa-Brandenberg, has a wood fuselage in which no stay wires are used. This fuselage is shown by Fig. 23a. Both the vertical and inclined members are wood struts. The outer covering of wood veneer makes the use of stay wires unnecessary since the sheath takes up all horizontal stresses, and hence forms a sort of plate girder construction. The German Albatros also employs a wireless veneer fuselage, the construction being shown in detail by Figs. 36 and 36a. Three longerons are located on either side of the body, the third member being placed at about the center of the vertical side. As will be seen, the veneer makes the use of wire bracing and metal connections unnecessary. The veneer also insures perfect alignment.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Wing Connections. The lower wings are attached to the lower longitudinals by a special sheet steel fitting which also generally connects to a vertical strut at this point, and to an extra heavy horizontal strut. A sheet metal clevis, or socket, on the wing spar is pinned to the fuselage half of the fitting so that the wing can be easily detached when the machine is to be dissembled. At this point a connection is also provided for the end of the inner interplane stay wires. The horizontal strut at the point of wing attachment is really a continuation of the wing spar and takes up the thrust due to the inclination of the interplane stays. In the majority of cases the horizontal thrust strut is a steel tube, with the hinged connection brazed to its outer ends. This is one of the most important and heavily loaded connections on the machine and should be designed accordingly.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 37 shows a typical wing to fuselage connection of the hinge type. The wing spar (G) is covered with a sheet steel ferrule (A) at its inner end. Two eye bars (B) are bolted to the wing spar, and over the ferrule, the eyes of the bar projecting beyond the end of the spar. This forms the wing half of the connecting hinge. The eyes are fastened to the fuselage hinge member (H) by means of the pin (E). This pin has a tapered end for easy entry into the joint, and is pierced with holes at the outer end for cotter pins or a similar retaining device. The fuselage hinge member (H) is brazed to the end of the steel tube strut (T). This tube runs across the fuselage from wing spar end to wing spar end.Strut tube (T) lies on, and is fastened to, the fuselage longeron (L), and also lies between the two halves of the vertical strut (S). The vertical strut is cut out at its lower end for the receipt of the steel tube (T). A steel plate is brazed to the tube, is wrapped about the longeron (L) and is bolted to the vertical strut (S). The interplane stay (F) is attached to the pin (E) at the point of juncture of the wing spar eye and the fuselage member of the hinge. A collar (I) is brazed to the tube, and forms a means of attaching the fuselage stays (D). The drift wires (C) of the wings are attached to an eye at the end of one of the wing spar bolts. As shown, the fitting (H) is a steel forging, very carefully machined and reduced in weight. The inside wing ribs are indicated by (K), from which it will be seen that there is a gap between the end of the wings and the outside face of the fuselage.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.Fig. 36-a shows the construction of the wing joint of the German Albatros machine. The fuselage is of monocoque construction which allows of a simple attachment to the outer shell. This is a very sturdy and simple connection. Fig. 38-Z is the wing attachment detail of the English London and Provincial Biplane (1916), the fuselage in this case being of the wire trussed wood type. We are indebted to "Flight" for this illustration.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.In some machines the interplane stay wires are attached to a lug formed from the attachment plate, but we do not consider that this construction is as good as the type in which the wire is attached directly to the wing spar pin. While the former may be easier to assemble, the attachment of the wire to the pin eliminates any eccentricity, or bending moment, due to the pull of the interplane stay. The attachment in the L. W. F. insures against any eccentricity in the stay attachment, and at the same time makes the assembly and dismounting a very simple matter.Fig. 37. Wing Connection to Fuselage.Fig. 37. Wing Connection to Fuselage.Chassis Member Attachment. The attachment of the chassis struts generally involves some difficulty as these members usually intersect the line of the longerons at a very awkward angle. If the wing attachment is near the same point, as it generally is, the detail is made doubly difficult. The chassis must be pin connected as in the case of the wing joint so that the chassis members can be easily and quickly removed. A detail of a chassis to body connection is shown by Fig. 39. In this figure (L) is the lower longeron, (S) is the vertical fuselage strut, and (C) is one of the chassis members. The upper end of the chassis member is enveloped in a sheet steel ferrule (D) which is bolted in place, and which is provided with a clevis at its upper end for the attachment pin (P).A plate (E) is bolted to the fuselage strut (S) and is passed around the lower longeron (L), a hinge joint (H) being provided for attachment to the chassis ferrule through the pin (P). Ears or lugs are left at (G-G) for the attachment of the fuselage stays (B-B). On the inner side of the plate (E) are attachment lugs for the horizontal strut (H). It will be noted that the plate (E) is well provided with lightening holes so that the weight can be kept down to a minimum. The pin is tapered at the end, and is provided with cotter pin holes. The fitting in general is small, and does not produce any great degree of head resistance, the small part exposed being of good streamline form.Wing ConnectionsFig. 38x. Wing Connection of the Albatros Reconnaissance Biplane. Fig. 38y. Wing Attachment of Albatros Fighter with Pin Joint. Fig. 38z. Wing Connection of London and Provincial Biplane.Great care should be taken in brazing or welding these fittings, since the heat changes the structure of the metal and greatly reduces its strength. The brazing temperature varies from 1,500 to 1,700 degrees, a point well above the tempering heat of steel. Attempts have been made to heat treat the metal after the brazing operation, but with very little success, owing to the fact that the heat treating temperature is generally at or above the melting point of the brazing spelter, hence is likely to cause holes and openings in the brazed joints. With acetylene welded joints the parts can, and should be, heat treated after the welding. While this is an apparent advantage of acetylene welding, all parts cannot be successfully handled in this manner. The welding torch can only join edges, while the brazing spelter can be applied over almost any area of surface. Welding is very successful in joining thin steel tubes while in many fittings made of sheet metal, brazing is the only feasible operation.Fig. 39. Chassis Connection.Fig. 39. Chassis Connection.Both methods have a common fault, in that they are unreliable. Imperfect welds and brazing are not always apparent from the outside, actual breakage of the part being necessary to determine the true nature of the joint.FUSELAGE WEIGHTS.Distribution of Weight. The weight of a fuselage depends upon the span of the wings, upon the seating capacity, and upon the weight and type of the power plant. The weight also varies considerably with the type of construction, that is, whether of truss, veneer, or monocoque construction. A heavily powered machine, or one carrying more than a single person, requires heavier structural members and hence weighs more than a small single seater. The amount of fuel carried also has a considerable bearing on the fuselage weight.Probably the best method of treating this subject is to give the fuselage weights of several types of well known machines. The reader will then have at least a comparative basis for determining the approximate weight. (Truss type only.)Fuselage Weights TableThere are so many variables that the weight cannot be determined by any set rule or formula. Alexander Klemin in his "Course in Aerodynamics and Airplane Design" says that the approximate weight of a bare wood truss type fuselage is about 150 pounds for a machine having a total weight of 2,500 pounds. For small biplane and monoplane scouts weighing approximately 1,200 pounds total, the bare fuselage frame will weigh about 70 pounds. These figures are for the bare frame alone and without seats, controls, tail skids or other fittings. The weights given under the column headed "Wt. Bare" include the engine beds, tail skids, flooring, cowling and body covering, and hence exceed the "bone bare" estimate of Klemin by a considerable amount.The all-steel fuselage of the large Sturtevant battle-plane (Model A) weighs 165 pounds inclusive of the steel engine bed. A wooden, wire braced fuselage of the same size and strength weighs well over 200 pounds, the metal fittings and wires weighing about 60 pounds alone. Ash is used in the wood example for the longerons. The struts and diagonal members in the Sturtevant metal fuselage are riveted directly to the longitudinals, without fittings or connection plates. The safety factor for air loads is 8, and for the ground loads due to taxi-ing over the ground, a safety factor of 4 is used.After a minute comparison of the items comprising the fuselage of the Curtiss JN4-B and the Standard H-3, Klemin finds that the fuselage assembly of the Standard H-3 amounts to 13.6 per cent of the total loaded weight, and that the fuselage of the Curtiss JN4-B is 15.5 per cent of the total. Tanks, piping and controls are omitted in both cases. For machines weighing about 2,500 pounds, Dr. J. C. Hunsaker finds the body weight averaging 8.2 per cent of the total, this figure being the average taken from a number of machines.On careful examination it will be found that the fuselage assembly (bare) amounts to a trifle less than the wing group for biplanes having a total weight of from 1,900 to 2,500 pounds. The relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights. We will set these different relations forth in the following table:PERCENTAGE OF FUSELAGE WEIGHTName of Plane or InvestigatorFuselage Weight as Percentage of the Total LoadWing Weight As Percentage of Total WeightBody Assembly BareBody Assembly and EquipmentBody Assembly and Power PlantCurtiss JN4-B15.50%17.86%43.96%14.15%Standard H-313.60%17.70%45.40%14.52%J.C. Hunsaker8.20%11.50%34.30%16.50%Author's Experience14.96%17.62%46.66%14.60%Average of Above13.06%16.17%42.58%14.94%In the above table, the column headed "Body Assembly and Equipment" includes the body frame, controls, tanks and piping. In the fourth column, the radiator, motor, propeller, water, and exhaust pipe have been added. For the average value it will be seen that the bare fuselage is about 1.88 per cent lower than the weight of the wings. It should be noted that the wing weight given is the weight of the surfaces alone, and does not include the weight of the interplane struts, wires and fittings. The weight of the wing surfaces as above will average about 0.75 pounds per square foot.Based on the above figures, we can obtain a rough rule for obtaining the approximate weight of the fuselage, at least accurate enough for a preliminary estimate. If A = the total area of the wings, then the total weight of the wings will be expressed by w = 0.75A. The weight (f) of the fuselage can be shown as f = 13.06/1494 x w = 0.65A.Example. The area of the Standard H-4 is 542 square feet total. Find the approximate weight of the fuselage. By the formula, f = 0.65A = 0.65 x 542 = 352 pounds. The actual bare weight is 302.0 pounds. For several other machines, the actual weight is greater than the weight calculated by the formula, so that the rule can be taken as a fair average, especially for a new type that is not as refined in detail as the H-3.SIZE OF LONGERONSThe size of the longerons, that is, the section, is influenced by many factors. As these members must resist flying loads, the leverage of elevator flaps, stresses due to control wires, landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members. This latter method is a method for a trained engineer, but an exhaustive description of the method of procedure will be found in books on the subject of "Strength of Materials." For the practical man, I give the following list of longeron dimensions so that he will have at least a guide in the selection of his material.The length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison, although this is a crude and inaccurate method. As the longerons taper from front to back, the sizes of the section are given at the motor end, and also at the tail. The size of the front members depends principally upon the weight of the motor and the passenger load, while the rear longerons carry the elevator loads and the tail skid shock. If the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance. The loads on the stabilizer, elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping, and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress. In the front of the fuselage, the motor exerts a steady torque (twist) in addition to the stress due to its weight, and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight. The combination of these forces acting at different times makes the calculation very difficult.Longeron Dimensions TableIn the case of the Curtiss R-4, the front longerons taper down from the motor 1.63" x 1.25" to a point directly behind the pilot's seat, the section at the latter point being 1.25" x 1.25". From this point the rear longerons taper down to 1" x 1" at the tail. At the motor, the section is 1.63" x 1.25". The longitudinals of the Bleriot monoplane are laminated and are built up of alternate layers of spruce and ash. This is an old type of machine and this practice has since been discontinued. It will be noted that as the power is increased, the size of the front longerons is generally increased, although this is not always the case in speed machines. The Chicago Aero Works’ "Star" fuselage could easily carry a 90 horsepower motor, although this size is not regularly installed.Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.

CHAPTER XII DETAILS OF FUSELAGE CONSTRUCTIONClassification of types. While there are a number of methods adopted in building up the fuselage structure, the common type is the "wire truss" in which wood compression members are used in connection with steel wire or cable tension members. Four wooden "longerons" or "longitudinals" run the entire length of the body and are bent to its general outline. The longitudinals are spaced at the correct distance by wood compression members, which in turn are held in place by wire cross bracing. This method of trussing forms a very strong and light structure, although rather complicated, and difficult to build. The cross-section is rectangular, although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame.Another well known type is the "Monocoque" body, first used on the Gordon-Bennett Deperdussin monoplane. This fuselage is a circular shell built up of three-ply tulip wood, thus forming a single piece body of great strength. The three-ply shell is really a veneer, the layers proceeding spirally around the body, each layer being securely glued to its neighbor. Between each layer is a scrim layer of treated silk, and another fabric layer is generally glued to the outside of the shell. The shell is very thin, the total thickness of the three layers of wood and fabric in modern machines being rather less than 1.5 millimeters (about 1/16 inch). In the original "Deps" this was somewhat greater, 0.15 inch. Monocoque construction as a rule is heavy and expensive, but offers the great advantage of strength, perfect alignment at all times, and of offering resistance to rifle and shell fire. If the longitudinals of a truss type are struck with a bullet, or shell fragment, the entire fuselage is likely to fail, but a monocoque body may be well perforated before failure is likely to take place.The American L. W. F. Tractor Biplane has a monocoque body in which spruce laminations are used instead of hardwood. One ply runs longitudinally while the other two layers are spiralled to the right and left respectively. Between each layer is a scrim layer of treated silk, the whole construction being covered with a final layer of fabric, several coats of waterproof compound, and four final coats of spar varnish. When used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness. Since spruce is used in place of hardwood, the construction is lighter than in European models, and the L. W. F. Company claim that it is lighter than the usual truss construction. An additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush.Another form of monocoque construction was adopted by the French builder, Bleriot, at the beginning of the war. The fuselage of this machine was covered with papier-mache, the ash longitudinals being buried in this mixture. The papier-mache is built up with glue and silk threads. This construction is very light and strong, but is expensive and difficult to protect against moisture. The front of the fuselage is protected with a 3 millimeter steel armor plate to protect the pilot against bullets and shrapnel. The papier-mache portion of the body is not easily splintered by bullets.A third form of monocoque, experimented upon by the author, is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell. This outer shell is strengthened by suitable stiffener angles. With a shell thickness of 0.013 inch, the strength is equal to the strength of a wood shell and is slightly less in weight. It has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture. It cannot splinter, will not catch fire and offers a maximum resistance against penetration. There is yet much experimental work to be done before the construction is perfected.About midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern German aeroplanes. In general, this may be described as being a veneer shell fastened to the conventional wood longitudinals. Stay wires are not in general use, the veneer taking the shear due to the bending movement. Six longerons are used instead of four, the two additional members being located midway on the vertical sides. Transverse wood frames take the place of the transverse stay wires used in the truss type. Examples of this type are met with in the "Albatros de Chasse" and in the "Gotha" bomb dropper. The single seater, "Roland," has a fuselage of circular section, with a true monocoque veneer construction, but German-like, reinforces the construction with a number of very small longitudinals. In this machine there are 6 layers, or plies, of wood reinforced by fabrics. The entire thickness of the wood and fabric is only 1.5 millimeters (1/16 inch).Steel tube fuselage dates back to the beginning of the aeroplane industry. In this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes, the cross struts being also of this material. The diagonal bracing may be either of steel wire, as in the wood frames, or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts. For the greatest weight-efficiency, a steel tube body should be triangular in section rather than square. A triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary. Connections on a steel tube fuselage are difficult to make and are heavy. They require much brazing and welding with the result that the strength is uncertain and the joint is heavy.A very modern type of steel construction is that developed by the Sturtevant Company. The members of the Sturtevant fuselage are in the form of steel angles and channels, similar in many respects to the sections used in steel buildings and bridges. The joints are riveted and pinned as in steel structural work. The longitudinals are angles and the struts are channels. Crystallization of the steel members is prevented by the use of special pin-connected joints provided with shock absorbing washers. Owing to the simplicity of the riveted joints, there is practically no weight due to connections, and since the weight of connections is a large item in the total weight of a fuselage, the Sturtevant is a very light structure. According to G. C. Loening, engineer of the company, the fittings of a large wood fuselage weigh at least 60 pounds. This is almost entirely saved with the riveted connections.Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.A novel type of wood fuselage has been described by Poulsen in "Flight." Eight small longitudinals are used which are held in place by three-ply wooden formers or diaphragms. Wire bracing is used in a longitudinal direction, but not transversely in the plane of the diaphragms. The cross-section is octagonal, and the completed structure is covered with fabric. For the amateur this offers many advantages since the wiring is reduced to a minimum and all of the members are small and easily bent to shape. It is fully as light as any type of body, for the connections are only thin strips of steel bolted to the diaphragms with small machine screws. No formers are needed for the deck, and the machine can be given a close approximation to the ideal stream-line form with little trouble.Truss Type Fuselage. We will now take up the construction of the truss type of fuselage in more detail, and investigate the merits of the different types of connections used in fastening the frame together. Like every part of the aeroplane, the fuselage must either be right or wrong, there is no middle course. Fig. 23 shows a side elevation of a typical truss type fuselage built up with wood longitudinals and struts, the tension members being high tensile strength steel wire and cable. L and L’ are the upper and lower longitudinals, S-S-S are the vertical struts, and T-T-T are the horizontal cross struts which run across the frame. The engine bed is the timber marked B at the front of the body. The upper wing is attached to the body through the "cabane" struts C, and the chassis connections are shown at D. The stern post E closes the rear end of the body in a knife edge and acts as a support for the rudder and the rear end of the stabilizer. F is the seat rail which carries the seats and supports the control yokes.All cross bracing is of high tensile strength steel wire, or of high strength aviation cable, these strands taking the tensile stresses while the wood struts are in compression. In the forward portion, double stranded cables are generally used, with solid wire applied to the after portions. The longitudinals are of ash from the motor to the rear of the pilot's seat, while the rear longitudinals are generally of spruce. In some machines, however, the entire length of the longitudinals is ash. The latter arrangement makes a heavier, but stronger body. The struts are usually of spruce as this material is stiffer than ash and much lighter.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Both the struts and longitudinals are frequently channelled out for lightness, as shown by Fig. 27, the wooden member being left rectangular in section only at the points where the connections are made with the struts and cables. The channelling-out process, if correctly followed, gives very strong stiff members with a minimum of cross-sectional area and weight. Many captured German machines, on the contrary, have solid longitudinals of rectangular section, wrapped with linen fabric. This fabric strengthens the construction and at the same time reduces the chances of splintering the wooden members in a hard landing. The fabric is glued to the wood and the entire wrapping is then given several coats of a moisture repelling varnish. In the older types of fuselage, the longitudinals were often of the "laminated" class, that is, were built up of several layers of wood glued together in a single rectangular mass. This reduced the tendency toward splitting, but was very unreliable because of the uncertainty of the glued joints when exposed to the effects of heat and moisture. Laminated longitudinals are now seldom used, particularly in the region of the motor where water and oil are certain to wreck havoc with the glued up members.As the stresses rapidly diminish toward the tail, it is the general practice to taper down the section of the longitudinal toward the rear and to reduce the section of the struts. The longitudinals are generally kept constant in section from the motor to the rear of the pilot's seat, the taper starting at the latter point and continuing to the rear end. For example, if the longitudinal section at the motor is 1 1/4" x 1 1/2", the section at the rear will be 1" x 1", the width of the struts corresponding to this taper. While tapering is very desirable from the weight standpoint, it makes the fitting problem very difficult since each fitting must be of a different dimension unless the connections can be designed so that they are adjustable to changes in the section of the longitudinals. In one machine, the width and depth of the longitudinals are kept constant, the variation in weight and section being accomplished by increasing the depth of the channelling as the rear is approached. With this design, the same fittings can be applied from one end to the other.Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.Since the loading of the struts is comparatively light, they can be much reduced in section by channelling or by chamfering, as shown by Fig. 28. If the width and thickness is maintained, much of the interior material can be removed without danger of reducing the strength. Sketch (A) in Fig. 28 shows a very common method of strut reduction, the strut being of rectangular section throughout its length, but tapered in such a way that it is thickest at the center (d) and thinnest at the two ends (e). To obtain the correct relation between the center end thickness requires very careful calculation. As shown, the strut is attached to the upper and lower longitudinals by sheet steel fittings or "sockets." Sketch (B) shows a simple method, the rectangular strut being chamfered off at each of the four corners, and left full size at either end where the fittings connect it with the longitudinals. This form is not correct from a technical standpoint, but is generally good enough for lightly loaded struts, and has the advantage of being cheaply and easily constructed. In sketch (C) a channelled strut is shown, the center portion being channelled out in a manner similar to the channelling of the longitudinals. This lightening process is most commonly adopted with the large heavily loaded struts in the front portion of the fuselage, and at the points where the motor bed is suspended or where the wings and chassis are attached to the body. The black dots at the ends of the struts indicate the bolt holes for the fittings, it being permissible to drill holes in the ends of the struts but not in the longitudinal members. If the strut is large enough to resist the bending stresses at the center it will generally allow of holes being drilled near the ends without danger of strength reduction. Again, the struts are always in compression and hence the bolts may be depended upon to partly take the place of the removed material in carrying the compressive stresses.Holes should never be drilled in the longitudinals since these members may be either in tension or compression, depending upon the angle at which the elevator flaps are set. The hole not only destroys the strength at the point at which it is drilled, but this reduction also extends to a considerable distance on either side of the hole, owing to the fibrous nature of the wood. In steel members the effect of the hole is purely local and does not usually extend much beyond the edge of the hole. Considering the wood beam as consisting of a series of parallel fibers, it will be seen that severing any one of the fibers will decrease the strength of the wood through a distance equal to the length of the cut fiber, or at least through a distance equal to the natural shear value of the resins that bind the fibers together.Fuselage fittings are almost numberless in the variety of design. They must be very light and strong, must be applied without drilling the longerons, and should be simple and cheap to construct. They are usually made of sheet steel of from 0.20 to 0.30 point carbon, and may be either bent or pressed into shape. At the points where the struts are joined to the longitudinals, the fittings connect struts and wires in three planes, the vertical struts and fore and aft wires; the transverse wires and horizontal struts, and the top and bottom wires that lie in a horizontal plane. There are at least 6 connections at every strut, four of the connections being made to the stay wires or cables. A simple connection is therefore very hard to design.Fig. 29 shows a typical fuselage "panel" and the interconnected members in their usual relation. LU and LL are the top and bottom longitudinals at the right, while LU' and LL’ are the longitudinals at the right hand side. The vertical struts SV and SV’ separate the top and bottom longitudinals, while the horizontal struts SH and SH’ separate the right and left hand sides of the fuselage body. The wires w-w-w-w brace the body fore and aft in a vertical plane. The wires t-t lie in a horizontal plane, produce compression in the horizontal struts SH-SH', and stiffen the frame against side thrust. The transverse rectangle SV-SH-SV’-SH' is held in shape by the transverse stay wires W-W, this rectangle, and the stays resisting torsional stress (twisting), act against the struts composing the sides of the rectangle. In some European machines, the wires WW are eliminated, and are replaced by thin veneer panels, or short wood knee braces as shown by Fig. 30. The section shows the longitudinals L-L-L-L and the struts SV-SV’-SH-SH’ braced by the veneer sheet or diaphragm D. This diaphragm is well perforated by lightening holes and effectually resists any torsional stress that may be due to motor torque, etc. Since the transverse wires W-W in Fig. 29 are rather inaccessible and difficult to adjust, the veneer diaphragm in Fig. 27 has a great advantage. In this regard it may be stated that wire bracing is not a desirable construction, and the substitution of solid veneer is a step in advance.Wire bracing has always seemed like a makeshift to the author. The compression and tension members being of materials of widely different characteristics are not suitable in positions where a strict alignment must be maintained under different conditions of temperature and moisture. The difference in expansion between wire and the wood compression members produces alternate tightness and slackness at the joints, and as this is not a uniform variation at the different joints, the frame is always weaving in and out of line. Under the influence of moisture the wood either swells or contracts, while the wire and cable maintain their original lengths and adjustments. The result is that a frame of this kind must be given constant attention if correct alignment is desired.The adjustment of a wire braced wood fuselage should be performed only by a skilled mechanic, as it is easily possible to strain the members beyond the elastic limit by careless or ignorant handling of the wire straining turnbuckles. In the endeavor to bring an old warped fuselage back into line it is certain that the initial tension in the wires can be made greater than the maximum working stress for which the wires were originally intended. Shrinkage of the wood also loosens the bond between the wooden members and the steel fittings unless this is continually being taken up. Some form of unit construction, such as the monocoque body, is far more desirable than the common form of wire trussed wood body.Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.Fuselage Fittings. In the early days of aviation the fuselage fittings on many machines were made of aluminum alloy. This metal, while light, was uncertain in regard to strength, hence the use of the alloy was gradually abandoned. At present the greater part of the fittings are stamped steel, formed out of the sheet, and are of a uniform strength for similar designs and classes of material.The steel best adapted for the fittings has a carbon content of from 0.20 to 0.30, with an ultimate strength of 60,000 pounds per square inch, and a 15 per cent elongation. The steel as received from the mill should be annealed before stamping or forming to avoid fracture. After the forming it can be given a strengthening heat treatment. A lower steel lying between 0.10 and 0.15 carbon is softer and can be formed without annealing before the forming process. This material is very weak, however, the tensile strength being about 40,000 pounds per square inch. Fittings made of the 0.15 carbon steel will therefore be heavier than with the 0.30 carbon steel for the same strength. The thickness of the metal will vary from 1/32" to 1/16", depending upon the load coming on the fitting.A typical fuselage strut fitting is shown by Fig. 31-A in which L-L-L are the longerons, d is the fitting strap passing over the longerons, S and So are the vertical and horizontal struts respectively. The stay wires are fastened to ears (b) bent out of the fitting, the wires being attached through the adjustable turnbuckles (t). The struts are provided with the sheet steel ferrules marked (F). There are no bolts passing through the longitudinals L-L', the fitting being clamped to the wooden member. This is very simple and light fitting. Fig. 31-B is a similar type, so simple that further discussion is unnecessary.Fig. 32 shows a fuselage strut fitting as used on the Standard Type H-3 Biplane. We are indebted to "Aerial Age" for this illustration. This consists of a sheet metal strap of "U" form which is bent over the longitudinal and is bolted to the vertical strut. At either side of the strut are through bolts to which bent straps attach the turnbuckles. These straps are looped around the bolts and form a clevis for the male ends of the turnbuckles.Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.An old form of fuselage connection used on the Nieuport monoplane is shown by Fig. 33, an example of a type in which the bolts are passed through the longeron member. This fitting is very light but objectionable because of the piercing of the longeron.An Austrian aeroplane, the Hansa-Brandenberg, has a wood fuselage in which no stay wires are used. This fuselage is shown by Fig. 23a. Both the vertical and inclined members are wood struts. The outer covering of wood veneer makes the use of stay wires unnecessary since the sheath takes up all horizontal stresses, and hence forms a sort of plate girder construction. The German Albatros also employs a wireless veneer fuselage, the construction being shown in detail by Figs. 36 and 36a. Three longerons are located on either side of the body, the third member being placed at about the center of the vertical side. As will be seen, the veneer makes the use of wire bracing and metal connections unnecessary. The veneer also insures perfect alignment.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Wing Connections. The lower wings are attached to the lower longitudinals by a special sheet steel fitting which also generally connects to a vertical strut at this point, and to an extra heavy horizontal strut. A sheet metal clevis, or socket, on the wing spar is pinned to the fuselage half of the fitting so that the wing can be easily detached when the machine is to be dissembled. At this point a connection is also provided for the end of the inner interplane stay wires. The horizontal strut at the point of wing attachment is really a continuation of the wing spar and takes up the thrust due to the inclination of the interplane stays. In the majority of cases the horizontal thrust strut is a steel tube, with the hinged connection brazed to its outer ends. This is one of the most important and heavily loaded connections on the machine and should be designed accordingly.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 37 shows a typical wing to fuselage connection of the hinge type. The wing spar (G) is covered with a sheet steel ferrule (A) at its inner end. Two eye bars (B) are bolted to the wing spar, and over the ferrule, the eyes of the bar projecting beyond the end of the spar. This forms the wing half of the connecting hinge. The eyes are fastened to the fuselage hinge member (H) by means of the pin (E). This pin has a tapered end for easy entry into the joint, and is pierced with holes at the outer end for cotter pins or a similar retaining device. The fuselage hinge member (H) is brazed to the end of the steel tube strut (T). This tube runs across the fuselage from wing spar end to wing spar end.Strut tube (T) lies on, and is fastened to, the fuselage longeron (L), and also lies between the two halves of the vertical strut (S). The vertical strut is cut out at its lower end for the receipt of the steel tube (T). A steel plate is brazed to the tube, is wrapped about the longeron (L) and is bolted to the vertical strut (S). The interplane stay (F) is attached to the pin (E) at the point of juncture of the wing spar eye and the fuselage member of the hinge. A collar (I) is brazed to the tube, and forms a means of attaching the fuselage stays (D). The drift wires (C) of the wings are attached to an eye at the end of one of the wing spar bolts. As shown, the fitting (H) is a steel forging, very carefully machined and reduced in weight. The inside wing ribs are indicated by (K), from which it will be seen that there is a gap between the end of the wings and the outside face of the fuselage.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.Fig. 36-a shows the construction of the wing joint of the German Albatros machine. The fuselage is of monocoque construction which allows of a simple attachment to the outer shell. This is a very sturdy and simple connection. Fig. 38-Z is the wing attachment detail of the English London and Provincial Biplane (1916), the fuselage in this case being of the wire trussed wood type. We are indebted to "Flight" for this illustration.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.In some machines the interplane stay wires are attached to a lug formed from the attachment plate, but we do not consider that this construction is as good as the type in which the wire is attached directly to the wing spar pin. While the former may be easier to assemble, the attachment of the wire to the pin eliminates any eccentricity, or bending moment, due to the pull of the interplane stay. The attachment in the L. W. F. insures against any eccentricity in the stay attachment, and at the same time makes the assembly and dismounting a very simple matter.Fig. 37. Wing Connection to Fuselage.Fig. 37. Wing Connection to Fuselage.Chassis Member Attachment. The attachment of the chassis struts generally involves some difficulty as these members usually intersect the line of the longerons at a very awkward angle. If the wing attachment is near the same point, as it generally is, the detail is made doubly difficult. The chassis must be pin connected as in the case of the wing joint so that the chassis members can be easily and quickly removed. A detail of a chassis to body connection is shown by Fig. 39. In this figure (L) is the lower longeron, (S) is the vertical fuselage strut, and (C) is one of the chassis members. The upper end of the chassis member is enveloped in a sheet steel ferrule (D) which is bolted in place, and which is provided with a clevis at its upper end for the attachment pin (P).A plate (E) is bolted to the fuselage strut (S) and is passed around the lower longeron (L), a hinge joint (H) being provided for attachment to the chassis ferrule through the pin (P). Ears or lugs are left at (G-G) for the attachment of the fuselage stays (B-B). On the inner side of the plate (E) are attachment lugs for the horizontal strut (H). It will be noted that the plate (E) is well provided with lightening holes so that the weight can be kept down to a minimum. The pin is tapered at the end, and is provided with cotter pin holes. The fitting in general is small, and does not produce any great degree of head resistance, the small part exposed being of good streamline form.Wing ConnectionsFig. 38x. Wing Connection of the Albatros Reconnaissance Biplane. Fig. 38y. Wing Attachment of Albatros Fighter with Pin Joint. Fig. 38z. Wing Connection of London and Provincial Biplane.Great care should be taken in brazing or welding these fittings, since the heat changes the structure of the metal and greatly reduces its strength. The brazing temperature varies from 1,500 to 1,700 degrees, a point well above the tempering heat of steel. Attempts have been made to heat treat the metal after the brazing operation, but with very little success, owing to the fact that the heat treating temperature is generally at or above the melting point of the brazing spelter, hence is likely to cause holes and openings in the brazed joints. With acetylene welded joints the parts can, and should be, heat treated after the welding. While this is an apparent advantage of acetylene welding, all parts cannot be successfully handled in this manner. The welding torch can only join edges, while the brazing spelter can be applied over almost any area of surface. Welding is very successful in joining thin steel tubes while in many fittings made of sheet metal, brazing is the only feasible operation.Fig. 39. Chassis Connection.Fig. 39. Chassis Connection.Both methods have a common fault, in that they are unreliable. Imperfect welds and brazing are not always apparent from the outside, actual breakage of the part being necessary to determine the true nature of the joint.FUSELAGE WEIGHTS.Distribution of Weight. The weight of a fuselage depends upon the span of the wings, upon the seating capacity, and upon the weight and type of the power plant. The weight also varies considerably with the type of construction, that is, whether of truss, veneer, or monocoque construction. A heavily powered machine, or one carrying more than a single person, requires heavier structural members and hence weighs more than a small single seater. The amount of fuel carried also has a considerable bearing on the fuselage weight.Probably the best method of treating this subject is to give the fuselage weights of several types of well known machines. The reader will then have at least a comparative basis for determining the approximate weight. (Truss type only.)Fuselage Weights TableThere are so many variables that the weight cannot be determined by any set rule or formula. Alexander Klemin in his "Course in Aerodynamics and Airplane Design" says that the approximate weight of a bare wood truss type fuselage is about 150 pounds for a machine having a total weight of 2,500 pounds. For small biplane and monoplane scouts weighing approximately 1,200 pounds total, the bare fuselage frame will weigh about 70 pounds. These figures are for the bare frame alone and without seats, controls, tail skids or other fittings. The weights given under the column headed "Wt. Bare" include the engine beds, tail skids, flooring, cowling and body covering, and hence exceed the "bone bare" estimate of Klemin by a considerable amount.The all-steel fuselage of the large Sturtevant battle-plane (Model A) weighs 165 pounds inclusive of the steel engine bed. A wooden, wire braced fuselage of the same size and strength weighs well over 200 pounds, the metal fittings and wires weighing about 60 pounds alone. Ash is used in the wood example for the longerons. The struts and diagonal members in the Sturtevant metal fuselage are riveted directly to the longitudinals, without fittings or connection plates. The safety factor for air loads is 8, and for the ground loads due to taxi-ing over the ground, a safety factor of 4 is used.After a minute comparison of the items comprising the fuselage of the Curtiss JN4-B and the Standard H-3, Klemin finds that the fuselage assembly of the Standard H-3 amounts to 13.6 per cent of the total loaded weight, and that the fuselage of the Curtiss JN4-B is 15.5 per cent of the total. Tanks, piping and controls are omitted in both cases. For machines weighing about 2,500 pounds, Dr. J. C. Hunsaker finds the body weight averaging 8.2 per cent of the total, this figure being the average taken from a number of machines.On careful examination it will be found that the fuselage assembly (bare) amounts to a trifle less than the wing group for biplanes having a total weight of from 1,900 to 2,500 pounds. The relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights. We will set these different relations forth in the following table:PERCENTAGE OF FUSELAGE WEIGHTName of Plane or InvestigatorFuselage Weight as Percentage of the Total LoadWing Weight As Percentage of Total WeightBody Assembly BareBody Assembly and EquipmentBody Assembly and Power PlantCurtiss JN4-B15.50%17.86%43.96%14.15%Standard H-313.60%17.70%45.40%14.52%J.C. Hunsaker8.20%11.50%34.30%16.50%Author's Experience14.96%17.62%46.66%14.60%Average of Above13.06%16.17%42.58%14.94%In the above table, the column headed "Body Assembly and Equipment" includes the body frame, controls, tanks and piping. In the fourth column, the radiator, motor, propeller, water, and exhaust pipe have been added. For the average value it will be seen that the bare fuselage is about 1.88 per cent lower than the weight of the wings. It should be noted that the wing weight given is the weight of the surfaces alone, and does not include the weight of the interplane struts, wires and fittings. The weight of the wing surfaces as above will average about 0.75 pounds per square foot.Based on the above figures, we can obtain a rough rule for obtaining the approximate weight of the fuselage, at least accurate enough for a preliminary estimate. If A = the total area of the wings, then the total weight of the wings will be expressed by w = 0.75A. The weight (f) of the fuselage can be shown as f = 13.06/1494 x w = 0.65A.Example. The area of the Standard H-4 is 542 square feet total. Find the approximate weight of the fuselage. By the formula, f = 0.65A = 0.65 x 542 = 352 pounds. The actual bare weight is 302.0 pounds. For several other machines, the actual weight is greater than the weight calculated by the formula, so that the rule can be taken as a fair average, especially for a new type that is not as refined in detail as the H-3.SIZE OF LONGERONSThe size of the longerons, that is, the section, is influenced by many factors. As these members must resist flying loads, the leverage of elevator flaps, stresses due to control wires, landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members. This latter method is a method for a trained engineer, but an exhaustive description of the method of procedure will be found in books on the subject of "Strength of Materials." For the practical man, I give the following list of longeron dimensions so that he will have at least a guide in the selection of his material.The length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison, although this is a crude and inaccurate method. As the longerons taper from front to back, the sizes of the section are given at the motor end, and also at the tail. The size of the front members depends principally upon the weight of the motor and the passenger load, while the rear longerons carry the elevator loads and the tail skid shock. If the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance. The loads on the stabilizer, elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping, and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress. In the front of the fuselage, the motor exerts a steady torque (twist) in addition to the stress due to its weight, and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight. The combination of these forces acting at different times makes the calculation very difficult.Longeron Dimensions TableIn the case of the Curtiss R-4, the front longerons taper down from the motor 1.63" x 1.25" to a point directly behind the pilot's seat, the section at the latter point being 1.25" x 1.25". From this point the rear longerons taper down to 1" x 1" at the tail. At the motor, the section is 1.63" x 1.25". The longitudinals of the Bleriot monoplane are laminated and are built up of alternate layers of spruce and ash. This is an old type of machine and this practice has since been discontinued. It will be noted that as the power is increased, the size of the front longerons is generally increased, although this is not always the case in speed machines. The Chicago Aero Works’ "Star" fuselage could easily carry a 90 horsepower motor, although this size is not regularly installed.Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.

CHAPTER XII DETAILS OF FUSELAGE CONSTRUCTIONClassification of types. While there are a number of methods adopted in building up the fuselage structure, the common type is the "wire truss" in which wood compression members are used in connection with steel wire or cable tension members. Four wooden "longerons" or "longitudinals" run the entire length of the body and are bent to its general outline. The longitudinals are spaced at the correct distance by wood compression members, which in turn are held in place by wire cross bracing. This method of trussing forms a very strong and light structure, although rather complicated, and difficult to build. The cross-section is rectangular, although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame.Another well known type is the "Monocoque" body, first used on the Gordon-Bennett Deperdussin monoplane. This fuselage is a circular shell built up of three-ply tulip wood, thus forming a single piece body of great strength. The three-ply shell is really a veneer, the layers proceeding spirally around the body, each layer being securely glued to its neighbor. Between each layer is a scrim layer of treated silk, and another fabric layer is generally glued to the outside of the shell. The shell is very thin, the total thickness of the three layers of wood and fabric in modern machines being rather less than 1.5 millimeters (about 1/16 inch). In the original "Deps" this was somewhat greater, 0.15 inch. Monocoque construction as a rule is heavy and expensive, but offers the great advantage of strength, perfect alignment at all times, and of offering resistance to rifle and shell fire. If the longitudinals of a truss type are struck with a bullet, or shell fragment, the entire fuselage is likely to fail, but a monocoque body may be well perforated before failure is likely to take place.The American L. W. F. Tractor Biplane has a monocoque body in which spruce laminations are used instead of hardwood. One ply runs longitudinally while the other two layers are spiralled to the right and left respectively. Between each layer is a scrim layer of treated silk, the whole construction being covered with a final layer of fabric, several coats of waterproof compound, and four final coats of spar varnish. When used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness. Since spruce is used in place of hardwood, the construction is lighter than in European models, and the L. W. F. Company claim that it is lighter than the usual truss construction. An additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush.Another form of monocoque construction was adopted by the French builder, Bleriot, at the beginning of the war. The fuselage of this machine was covered with papier-mache, the ash longitudinals being buried in this mixture. The papier-mache is built up with glue and silk threads. This construction is very light and strong, but is expensive and difficult to protect against moisture. The front of the fuselage is protected with a 3 millimeter steel armor plate to protect the pilot against bullets and shrapnel. The papier-mache portion of the body is not easily splintered by bullets.A third form of monocoque, experimented upon by the author, is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell. This outer shell is strengthened by suitable stiffener angles. With a shell thickness of 0.013 inch, the strength is equal to the strength of a wood shell and is slightly less in weight. It has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture. It cannot splinter, will not catch fire and offers a maximum resistance against penetration. There is yet much experimental work to be done before the construction is perfected.About midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern German aeroplanes. In general, this may be described as being a veneer shell fastened to the conventional wood longitudinals. Stay wires are not in general use, the veneer taking the shear due to the bending movement. Six longerons are used instead of four, the two additional members being located midway on the vertical sides. Transverse wood frames take the place of the transverse stay wires used in the truss type. Examples of this type are met with in the "Albatros de Chasse" and in the "Gotha" bomb dropper. The single seater, "Roland," has a fuselage of circular section, with a true monocoque veneer construction, but German-like, reinforces the construction with a number of very small longitudinals. In this machine there are 6 layers, or plies, of wood reinforced by fabrics. The entire thickness of the wood and fabric is only 1.5 millimeters (1/16 inch).Steel tube fuselage dates back to the beginning of the aeroplane industry. In this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes, the cross struts being also of this material. The diagonal bracing may be either of steel wire, as in the wood frames, or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts. For the greatest weight-efficiency, a steel tube body should be triangular in section rather than square. A triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary. Connections on a steel tube fuselage are difficult to make and are heavy. They require much brazing and welding with the result that the strength is uncertain and the joint is heavy.A very modern type of steel construction is that developed by the Sturtevant Company. The members of the Sturtevant fuselage are in the form of steel angles and channels, similar in many respects to the sections used in steel buildings and bridges. The joints are riveted and pinned as in steel structural work. The longitudinals are angles and the struts are channels. Crystallization of the steel members is prevented by the use of special pin-connected joints provided with shock absorbing washers. Owing to the simplicity of the riveted joints, there is practically no weight due to connections, and since the weight of connections is a large item in the total weight of a fuselage, the Sturtevant is a very light structure. According to G. C. Loening, engineer of the company, the fittings of a large wood fuselage weigh at least 60 pounds. This is almost entirely saved with the riveted connections.Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.A novel type of wood fuselage has been described by Poulsen in "Flight." Eight small longitudinals are used which are held in place by three-ply wooden formers or diaphragms. Wire bracing is used in a longitudinal direction, but not transversely in the plane of the diaphragms. The cross-section is octagonal, and the completed structure is covered with fabric. For the amateur this offers many advantages since the wiring is reduced to a minimum and all of the members are small and easily bent to shape. It is fully as light as any type of body, for the connections are only thin strips of steel bolted to the diaphragms with small machine screws. No formers are needed for the deck, and the machine can be given a close approximation to the ideal stream-line form with little trouble.Truss Type Fuselage. We will now take up the construction of the truss type of fuselage in more detail, and investigate the merits of the different types of connections used in fastening the frame together. Like every part of the aeroplane, the fuselage must either be right or wrong, there is no middle course. Fig. 23 shows a side elevation of a typical truss type fuselage built up with wood longitudinals and struts, the tension members being high tensile strength steel wire and cable. L and L’ are the upper and lower longitudinals, S-S-S are the vertical struts, and T-T-T are the horizontal cross struts which run across the frame. The engine bed is the timber marked B at the front of the body. The upper wing is attached to the body through the "cabane" struts C, and the chassis connections are shown at D. The stern post E closes the rear end of the body in a knife edge and acts as a support for the rudder and the rear end of the stabilizer. F is the seat rail which carries the seats and supports the control yokes.All cross bracing is of high tensile strength steel wire, or of high strength aviation cable, these strands taking the tensile stresses while the wood struts are in compression. In the forward portion, double stranded cables are generally used, with solid wire applied to the after portions. The longitudinals are of ash from the motor to the rear of the pilot's seat, while the rear longitudinals are generally of spruce. In some machines, however, the entire length of the longitudinals is ash. The latter arrangement makes a heavier, but stronger body. The struts are usually of spruce as this material is stiffer than ash and much lighter.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Both the struts and longitudinals are frequently channelled out for lightness, as shown by Fig. 27, the wooden member being left rectangular in section only at the points where the connections are made with the struts and cables. The channelling-out process, if correctly followed, gives very strong stiff members with a minimum of cross-sectional area and weight. Many captured German machines, on the contrary, have solid longitudinals of rectangular section, wrapped with linen fabric. This fabric strengthens the construction and at the same time reduces the chances of splintering the wooden members in a hard landing. The fabric is glued to the wood and the entire wrapping is then given several coats of a moisture repelling varnish. In the older types of fuselage, the longitudinals were often of the "laminated" class, that is, were built up of several layers of wood glued together in a single rectangular mass. This reduced the tendency toward splitting, but was very unreliable because of the uncertainty of the glued joints when exposed to the effects of heat and moisture. Laminated longitudinals are now seldom used, particularly in the region of the motor where water and oil are certain to wreck havoc with the glued up members.As the stresses rapidly diminish toward the tail, it is the general practice to taper down the section of the longitudinal toward the rear and to reduce the section of the struts. The longitudinals are generally kept constant in section from the motor to the rear of the pilot's seat, the taper starting at the latter point and continuing to the rear end. For example, if the longitudinal section at the motor is 1 1/4" x 1 1/2", the section at the rear will be 1" x 1", the width of the struts corresponding to this taper. While tapering is very desirable from the weight standpoint, it makes the fitting problem very difficult since each fitting must be of a different dimension unless the connections can be designed so that they are adjustable to changes in the section of the longitudinals. In one machine, the width and depth of the longitudinals are kept constant, the variation in weight and section being accomplished by increasing the depth of the channelling as the rear is approached. With this design, the same fittings can be applied from one end to the other.Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.Since the loading of the struts is comparatively light, they can be much reduced in section by channelling or by chamfering, as shown by Fig. 28. If the width and thickness is maintained, much of the interior material can be removed without danger of reducing the strength. Sketch (A) in Fig. 28 shows a very common method of strut reduction, the strut being of rectangular section throughout its length, but tapered in such a way that it is thickest at the center (d) and thinnest at the two ends (e). To obtain the correct relation between the center end thickness requires very careful calculation. As shown, the strut is attached to the upper and lower longitudinals by sheet steel fittings or "sockets." Sketch (B) shows a simple method, the rectangular strut being chamfered off at each of the four corners, and left full size at either end where the fittings connect it with the longitudinals. This form is not correct from a technical standpoint, but is generally good enough for lightly loaded struts, and has the advantage of being cheaply and easily constructed. In sketch (C) a channelled strut is shown, the center portion being channelled out in a manner similar to the channelling of the longitudinals. This lightening process is most commonly adopted with the large heavily loaded struts in the front portion of the fuselage, and at the points where the motor bed is suspended or where the wings and chassis are attached to the body. The black dots at the ends of the struts indicate the bolt holes for the fittings, it being permissible to drill holes in the ends of the struts but not in the longitudinal members. If the strut is large enough to resist the bending stresses at the center it will generally allow of holes being drilled near the ends without danger of strength reduction. Again, the struts are always in compression and hence the bolts may be depended upon to partly take the place of the removed material in carrying the compressive stresses.Holes should never be drilled in the longitudinals since these members may be either in tension or compression, depending upon the angle at which the elevator flaps are set. The hole not only destroys the strength at the point at which it is drilled, but this reduction also extends to a considerable distance on either side of the hole, owing to the fibrous nature of the wood. In steel members the effect of the hole is purely local and does not usually extend much beyond the edge of the hole. Considering the wood beam as consisting of a series of parallel fibers, it will be seen that severing any one of the fibers will decrease the strength of the wood through a distance equal to the length of the cut fiber, or at least through a distance equal to the natural shear value of the resins that bind the fibers together.Fuselage fittings are almost numberless in the variety of design. They must be very light and strong, must be applied without drilling the longerons, and should be simple and cheap to construct. They are usually made of sheet steel of from 0.20 to 0.30 point carbon, and may be either bent or pressed into shape. At the points where the struts are joined to the longitudinals, the fittings connect struts and wires in three planes, the vertical struts and fore and aft wires; the transverse wires and horizontal struts, and the top and bottom wires that lie in a horizontal plane. There are at least 6 connections at every strut, four of the connections being made to the stay wires or cables. A simple connection is therefore very hard to design.Fig. 29 shows a typical fuselage "panel" and the interconnected members in their usual relation. LU and LL are the top and bottom longitudinals at the right, while LU' and LL’ are the longitudinals at the right hand side. The vertical struts SV and SV’ separate the top and bottom longitudinals, while the horizontal struts SH and SH’ separate the right and left hand sides of the fuselage body. The wires w-w-w-w brace the body fore and aft in a vertical plane. The wires t-t lie in a horizontal plane, produce compression in the horizontal struts SH-SH', and stiffen the frame against side thrust. The transverse rectangle SV-SH-SV’-SH' is held in shape by the transverse stay wires W-W, this rectangle, and the stays resisting torsional stress (twisting), act against the struts composing the sides of the rectangle. In some European machines, the wires WW are eliminated, and are replaced by thin veneer panels, or short wood knee braces as shown by Fig. 30. The section shows the longitudinals L-L-L-L and the struts SV-SV’-SH-SH’ braced by the veneer sheet or diaphragm D. This diaphragm is well perforated by lightening holes and effectually resists any torsional stress that may be due to motor torque, etc. Since the transverse wires W-W in Fig. 29 are rather inaccessible and difficult to adjust, the veneer diaphragm in Fig. 27 has a great advantage. In this regard it may be stated that wire bracing is not a desirable construction, and the substitution of solid veneer is a step in advance.Wire bracing has always seemed like a makeshift to the author. The compression and tension members being of materials of widely different characteristics are not suitable in positions where a strict alignment must be maintained under different conditions of temperature and moisture. The difference in expansion between wire and the wood compression members produces alternate tightness and slackness at the joints, and as this is not a uniform variation at the different joints, the frame is always weaving in and out of line. Under the influence of moisture the wood either swells or contracts, while the wire and cable maintain their original lengths and adjustments. The result is that a frame of this kind must be given constant attention if correct alignment is desired.The adjustment of a wire braced wood fuselage should be performed only by a skilled mechanic, as it is easily possible to strain the members beyond the elastic limit by careless or ignorant handling of the wire straining turnbuckles. In the endeavor to bring an old warped fuselage back into line it is certain that the initial tension in the wires can be made greater than the maximum working stress for which the wires were originally intended. Shrinkage of the wood also loosens the bond between the wooden members and the steel fittings unless this is continually being taken up. Some form of unit construction, such as the monocoque body, is far more desirable than the common form of wire trussed wood body.Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.Fuselage Fittings. In the early days of aviation the fuselage fittings on many machines were made of aluminum alloy. This metal, while light, was uncertain in regard to strength, hence the use of the alloy was gradually abandoned. At present the greater part of the fittings are stamped steel, formed out of the sheet, and are of a uniform strength for similar designs and classes of material.The steel best adapted for the fittings has a carbon content of from 0.20 to 0.30, with an ultimate strength of 60,000 pounds per square inch, and a 15 per cent elongation. The steel as received from the mill should be annealed before stamping or forming to avoid fracture. After the forming it can be given a strengthening heat treatment. A lower steel lying between 0.10 and 0.15 carbon is softer and can be formed without annealing before the forming process. This material is very weak, however, the tensile strength being about 40,000 pounds per square inch. Fittings made of the 0.15 carbon steel will therefore be heavier than with the 0.30 carbon steel for the same strength. The thickness of the metal will vary from 1/32" to 1/16", depending upon the load coming on the fitting.A typical fuselage strut fitting is shown by Fig. 31-A in which L-L-L are the longerons, d is the fitting strap passing over the longerons, S and So are the vertical and horizontal struts respectively. The stay wires are fastened to ears (b) bent out of the fitting, the wires being attached through the adjustable turnbuckles (t). The struts are provided with the sheet steel ferrules marked (F). There are no bolts passing through the longitudinals L-L', the fitting being clamped to the wooden member. This is very simple and light fitting. Fig. 31-B is a similar type, so simple that further discussion is unnecessary.Fig. 32 shows a fuselage strut fitting as used on the Standard Type H-3 Biplane. We are indebted to "Aerial Age" for this illustration. This consists of a sheet metal strap of "U" form which is bent over the longitudinal and is bolted to the vertical strut. At either side of the strut are through bolts to which bent straps attach the turnbuckles. These straps are looped around the bolts and form a clevis for the male ends of the turnbuckles.Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.An old form of fuselage connection used on the Nieuport monoplane is shown by Fig. 33, an example of a type in which the bolts are passed through the longeron member. This fitting is very light but objectionable because of the piercing of the longeron.An Austrian aeroplane, the Hansa-Brandenberg, has a wood fuselage in which no stay wires are used. This fuselage is shown by Fig. 23a. Both the vertical and inclined members are wood struts. The outer covering of wood veneer makes the use of stay wires unnecessary since the sheath takes up all horizontal stresses, and hence forms a sort of plate girder construction. The German Albatros also employs a wireless veneer fuselage, the construction being shown in detail by Figs. 36 and 36a. Three longerons are located on either side of the body, the third member being placed at about the center of the vertical side. As will be seen, the veneer makes the use of wire bracing and metal connections unnecessary. The veneer also insures perfect alignment.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Wing Connections. The lower wings are attached to the lower longitudinals by a special sheet steel fitting which also generally connects to a vertical strut at this point, and to an extra heavy horizontal strut. A sheet metal clevis, or socket, on the wing spar is pinned to the fuselage half of the fitting so that the wing can be easily detached when the machine is to be dissembled. At this point a connection is also provided for the end of the inner interplane stay wires. The horizontal strut at the point of wing attachment is really a continuation of the wing spar and takes up the thrust due to the inclination of the interplane stays. In the majority of cases the horizontal thrust strut is a steel tube, with the hinged connection brazed to its outer ends. This is one of the most important and heavily loaded connections on the machine and should be designed accordingly.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 37 shows a typical wing to fuselage connection of the hinge type. The wing spar (G) is covered with a sheet steel ferrule (A) at its inner end. Two eye bars (B) are bolted to the wing spar, and over the ferrule, the eyes of the bar projecting beyond the end of the spar. This forms the wing half of the connecting hinge. The eyes are fastened to the fuselage hinge member (H) by means of the pin (E). This pin has a tapered end for easy entry into the joint, and is pierced with holes at the outer end for cotter pins or a similar retaining device. The fuselage hinge member (H) is brazed to the end of the steel tube strut (T). This tube runs across the fuselage from wing spar end to wing spar end.Strut tube (T) lies on, and is fastened to, the fuselage longeron (L), and also lies between the two halves of the vertical strut (S). The vertical strut is cut out at its lower end for the receipt of the steel tube (T). A steel plate is brazed to the tube, is wrapped about the longeron (L) and is bolted to the vertical strut (S). The interplane stay (F) is attached to the pin (E) at the point of juncture of the wing spar eye and the fuselage member of the hinge. A collar (I) is brazed to the tube, and forms a means of attaching the fuselage stays (D). The drift wires (C) of the wings are attached to an eye at the end of one of the wing spar bolts. As shown, the fitting (H) is a steel forging, very carefully machined and reduced in weight. The inside wing ribs are indicated by (K), from which it will be seen that there is a gap between the end of the wings and the outside face of the fuselage.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.Fig. 36-a shows the construction of the wing joint of the German Albatros machine. The fuselage is of monocoque construction which allows of a simple attachment to the outer shell. This is a very sturdy and simple connection. Fig. 38-Z is the wing attachment detail of the English London and Provincial Biplane (1916), the fuselage in this case being of the wire trussed wood type. We are indebted to "Flight" for this illustration.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.In some machines the interplane stay wires are attached to a lug formed from the attachment plate, but we do not consider that this construction is as good as the type in which the wire is attached directly to the wing spar pin. While the former may be easier to assemble, the attachment of the wire to the pin eliminates any eccentricity, or bending moment, due to the pull of the interplane stay. The attachment in the L. W. F. insures against any eccentricity in the stay attachment, and at the same time makes the assembly and dismounting a very simple matter.Fig. 37. Wing Connection to Fuselage.Fig. 37. Wing Connection to Fuselage.Chassis Member Attachment. The attachment of the chassis struts generally involves some difficulty as these members usually intersect the line of the longerons at a very awkward angle. If the wing attachment is near the same point, as it generally is, the detail is made doubly difficult. The chassis must be pin connected as in the case of the wing joint so that the chassis members can be easily and quickly removed. A detail of a chassis to body connection is shown by Fig. 39. In this figure (L) is the lower longeron, (S) is the vertical fuselage strut, and (C) is one of the chassis members. The upper end of the chassis member is enveloped in a sheet steel ferrule (D) which is bolted in place, and which is provided with a clevis at its upper end for the attachment pin (P).A plate (E) is bolted to the fuselage strut (S) and is passed around the lower longeron (L), a hinge joint (H) being provided for attachment to the chassis ferrule through the pin (P). Ears or lugs are left at (G-G) for the attachment of the fuselage stays (B-B). On the inner side of the plate (E) are attachment lugs for the horizontal strut (H). It will be noted that the plate (E) is well provided with lightening holes so that the weight can be kept down to a minimum. The pin is tapered at the end, and is provided with cotter pin holes. The fitting in general is small, and does not produce any great degree of head resistance, the small part exposed being of good streamline form.Wing ConnectionsFig. 38x. Wing Connection of the Albatros Reconnaissance Biplane. Fig. 38y. Wing Attachment of Albatros Fighter with Pin Joint. Fig. 38z. Wing Connection of London and Provincial Biplane.Great care should be taken in brazing or welding these fittings, since the heat changes the structure of the metal and greatly reduces its strength. The brazing temperature varies from 1,500 to 1,700 degrees, a point well above the tempering heat of steel. Attempts have been made to heat treat the metal after the brazing operation, but with very little success, owing to the fact that the heat treating temperature is generally at or above the melting point of the brazing spelter, hence is likely to cause holes and openings in the brazed joints. With acetylene welded joints the parts can, and should be, heat treated after the welding. While this is an apparent advantage of acetylene welding, all parts cannot be successfully handled in this manner. The welding torch can only join edges, while the brazing spelter can be applied over almost any area of surface. Welding is very successful in joining thin steel tubes while in many fittings made of sheet metal, brazing is the only feasible operation.Fig. 39. Chassis Connection.Fig. 39. Chassis Connection.Both methods have a common fault, in that they are unreliable. Imperfect welds and brazing are not always apparent from the outside, actual breakage of the part being necessary to determine the true nature of the joint.FUSELAGE WEIGHTS.Distribution of Weight. The weight of a fuselage depends upon the span of the wings, upon the seating capacity, and upon the weight and type of the power plant. The weight also varies considerably with the type of construction, that is, whether of truss, veneer, or monocoque construction. A heavily powered machine, or one carrying more than a single person, requires heavier structural members and hence weighs more than a small single seater. The amount of fuel carried also has a considerable bearing on the fuselage weight.Probably the best method of treating this subject is to give the fuselage weights of several types of well known machines. The reader will then have at least a comparative basis for determining the approximate weight. (Truss type only.)Fuselage Weights TableThere are so many variables that the weight cannot be determined by any set rule or formula. Alexander Klemin in his "Course in Aerodynamics and Airplane Design" says that the approximate weight of a bare wood truss type fuselage is about 150 pounds for a machine having a total weight of 2,500 pounds. For small biplane and monoplane scouts weighing approximately 1,200 pounds total, the bare fuselage frame will weigh about 70 pounds. These figures are for the bare frame alone and without seats, controls, tail skids or other fittings. The weights given under the column headed "Wt. Bare" include the engine beds, tail skids, flooring, cowling and body covering, and hence exceed the "bone bare" estimate of Klemin by a considerable amount.The all-steel fuselage of the large Sturtevant battle-plane (Model A) weighs 165 pounds inclusive of the steel engine bed. A wooden, wire braced fuselage of the same size and strength weighs well over 200 pounds, the metal fittings and wires weighing about 60 pounds alone. Ash is used in the wood example for the longerons. The struts and diagonal members in the Sturtevant metal fuselage are riveted directly to the longitudinals, without fittings or connection plates. The safety factor for air loads is 8, and for the ground loads due to taxi-ing over the ground, a safety factor of 4 is used.After a minute comparison of the items comprising the fuselage of the Curtiss JN4-B and the Standard H-3, Klemin finds that the fuselage assembly of the Standard H-3 amounts to 13.6 per cent of the total loaded weight, and that the fuselage of the Curtiss JN4-B is 15.5 per cent of the total. Tanks, piping and controls are omitted in both cases. For machines weighing about 2,500 pounds, Dr. J. C. Hunsaker finds the body weight averaging 8.2 per cent of the total, this figure being the average taken from a number of machines.On careful examination it will be found that the fuselage assembly (bare) amounts to a trifle less than the wing group for biplanes having a total weight of from 1,900 to 2,500 pounds. The relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights. We will set these different relations forth in the following table:PERCENTAGE OF FUSELAGE WEIGHTName of Plane or InvestigatorFuselage Weight as Percentage of the Total LoadWing Weight As Percentage of Total WeightBody Assembly BareBody Assembly and EquipmentBody Assembly and Power PlantCurtiss JN4-B15.50%17.86%43.96%14.15%Standard H-313.60%17.70%45.40%14.52%J.C. Hunsaker8.20%11.50%34.30%16.50%Author's Experience14.96%17.62%46.66%14.60%Average of Above13.06%16.17%42.58%14.94%In the above table, the column headed "Body Assembly and Equipment" includes the body frame, controls, tanks and piping. In the fourth column, the radiator, motor, propeller, water, and exhaust pipe have been added. For the average value it will be seen that the bare fuselage is about 1.88 per cent lower than the weight of the wings. It should be noted that the wing weight given is the weight of the surfaces alone, and does not include the weight of the interplane struts, wires and fittings. The weight of the wing surfaces as above will average about 0.75 pounds per square foot.Based on the above figures, we can obtain a rough rule for obtaining the approximate weight of the fuselage, at least accurate enough for a preliminary estimate. If A = the total area of the wings, then the total weight of the wings will be expressed by w = 0.75A. The weight (f) of the fuselage can be shown as f = 13.06/1494 x w = 0.65A.Example. The area of the Standard H-4 is 542 square feet total. Find the approximate weight of the fuselage. By the formula, f = 0.65A = 0.65 x 542 = 352 pounds. The actual bare weight is 302.0 pounds. For several other machines, the actual weight is greater than the weight calculated by the formula, so that the rule can be taken as a fair average, especially for a new type that is not as refined in detail as the H-3.SIZE OF LONGERONSThe size of the longerons, that is, the section, is influenced by many factors. As these members must resist flying loads, the leverage of elevator flaps, stresses due to control wires, landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members. This latter method is a method for a trained engineer, but an exhaustive description of the method of procedure will be found in books on the subject of "Strength of Materials." For the practical man, I give the following list of longeron dimensions so that he will have at least a guide in the selection of his material.The length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison, although this is a crude and inaccurate method. As the longerons taper from front to back, the sizes of the section are given at the motor end, and also at the tail. The size of the front members depends principally upon the weight of the motor and the passenger load, while the rear longerons carry the elevator loads and the tail skid shock. If the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance. The loads on the stabilizer, elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping, and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress. In the front of the fuselage, the motor exerts a steady torque (twist) in addition to the stress due to its weight, and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight. The combination of these forces acting at different times makes the calculation very difficult.Longeron Dimensions TableIn the case of the Curtiss R-4, the front longerons taper down from the motor 1.63" x 1.25" to a point directly behind the pilot's seat, the section at the latter point being 1.25" x 1.25". From this point the rear longerons taper down to 1" x 1" at the tail. At the motor, the section is 1.63" x 1.25". The longitudinals of the Bleriot monoplane are laminated and are built up of alternate layers of spruce and ash. This is an old type of machine and this practice has since been discontinued. It will be noted that as the power is increased, the size of the front longerons is generally increased, although this is not always the case in speed machines. The Chicago Aero Works’ "Star" fuselage could easily carry a 90 horsepower motor, although this size is not regularly installed.Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.

Classification of types. While there are a number of methods adopted in building up the fuselage structure, the common type is the "wire truss" in which wood compression members are used in connection with steel wire or cable tension members. Four wooden "longerons" or "longitudinals" run the entire length of the body and are bent to its general outline. The longitudinals are spaced at the correct distance by wood compression members, which in turn are held in place by wire cross bracing. This method of trussing forms a very strong and light structure, although rather complicated, and difficult to build. The cross-section is rectangular, although in many cases the body is converted into a circular or elliptical section by the use of light wood formers fastened to the main frame.

Another well known type is the "Monocoque" body, first used on the Gordon-Bennett Deperdussin monoplane. This fuselage is a circular shell built up of three-ply tulip wood, thus forming a single piece body of great strength. The three-ply shell is really a veneer, the layers proceeding spirally around the body, each layer being securely glued to its neighbor. Between each layer is a scrim layer of treated silk, and another fabric layer is generally glued to the outside of the shell. The shell is very thin, the total thickness of the three layers of wood and fabric in modern machines being rather less than 1.5 millimeters (about 1/16 inch). In the original "Deps" this was somewhat greater, 0.15 inch. Monocoque construction as a rule is heavy and expensive, but offers the great advantage of strength, perfect alignment at all times, and of offering resistance to rifle and shell fire. If the longitudinals of a truss type are struck with a bullet, or shell fragment, the entire fuselage is likely to fail, but a monocoque body may be well perforated before failure is likely to take place.

The American L. W. F. Tractor Biplane has a monocoque body in which spruce laminations are used instead of hardwood. One ply runs longitudinally while the other two layers are spiralled to the right and left respectively. Between each layer is a scrim layer of treated silk, the whole construction being covered with a final layer of fabric, several coats of waterproof compound, and four final coats of spar varnish. When used for seaplanes the wood plies are stitched together with strong wires to prevent separation due to dampness. Since spruce is used in place of hardwood, the construction is lighter than in European models, and the L. W. F. Company claim that it is lighter than the usual truss construction. An additional advantage of the monocoque construction is that the pilot is protected against splinters or penetration by the limbs of trees when making a forced landing in the brush.

Another form of monocoque construction was adopted by the French builder, Bleriot, at the beginning of the war. The fuselage of this machine was covered with papier-mache, the ash longitudinals being buried in this mixture. The papier-mache is built up with glue and silk threads. This construction is very light and strong, but is expensive and difficult to protect against moisture. The front of the fuselage is protected with a 3 millimeter steel armor plate to protect the pilot against bullets and shrapnel. The papier-mache portion of the body is not easily splintered by bullets.

A third form of monocoque, experimented upon by the author, is the steel shell type in which the three-ply wood veneer is supplanted by a thin steel shell. This outer shell is strengthened by suitable stiffener angles. With a shell thickness of 0.013 inch, the strength is equal to the strength of a wood shell and is slightly less in weight. It has the advantage of being easily and cheaply formed into shape and is absolutely proof against the influences of heat and moisture. It cannot splinter, will not catch fire and offers a maximum resistance against penetration. There is yet much experimental work to be done before the construction is perfected.

About midway between the truss fuselage and the monocoque is the veneer construction used on many of the modern German aeroplanes. In general, this may be described as being a veneer shell fastened to the conventional wood longitudinals. Stay wires are not in general use, the veneer taking the shear due to the bending movement. Six longerons are used instead of four, the two additional members being located midway on the vertical sides. Transverse wood frames take the place of the transverse stay wires used in the truss type. Examples of this type are met with in the "Albatros de Chasse" and in the "Gotha" bomb dropper. The single seater, "Roland," has a fuselage of circular section, with a true monocoque veneer construction, but German-like, reinforces the construction with a number of very small longitudinals. In this machine there are 6 layers, or plies, of wood reinforced by fabrics. The entire thickness of the wood and fabric is only 1.5 millimeters (1/16 inch).

Steel tube fuselage dates back to the beginning of the aeroplane industry. In this type the wood longitudinals of the wood truss type are replaced with thin gage steel tubes, the cross struts being also of this material. The diagonal bracing may be either of steel wire, as in the wood frames, or may be made up of inclined steel tube members that perform both the duty of the stay wires and struts. For the greatest weight-efficiency, a steel tube body should be triangular in section rather than square. A triangular section saves one longitudinal and a multitude of wire struts and connections since no transverse bracing is necessary. Connections on a steel tube fuselage are difficult to make and are heavy. They require much brazing and welding with the result that the strength is uncertain and the joint is heavy.

A very modern type of steel construction is that developed by the Sturtevant Company. The members of the Sturtevant fuselage are in the form of steel angles and channels, similar in many respects to the sections used in steel buildings and bridges. The joints are riveted and pinned as in steel structural work. The longitudinals are angles and the struts are channels. Crystallization of the steel members is prevented by the use of special pin-connected joints provided with shock absorbing washers. Owing to the simplicity of the riveted joints, there is practically no weight due to connections, and since the weight of connections is a large item in the total weight of a fuselage, the Sturtevant is a very light structure. According to G. C. Loening, engineer of the company, the fittings of a large wood fuselage weigh at least 60 pounds. This is almost entirely saved with the riveted connections.

Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.

Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.

Truss Type Fuselage of Curtiss R-4 BiplaneTruss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.

Truss Type Fuselage of Curtiss R-4 Biplane, Showing Motor and Front Radiator Mounted in Place. It Will Be Noted That the Upper and Lower Longerons Are Channeled Out for Lightness and Hence These Members Are of the "I" Beam or Channel Form. Propeller Flange Is Shown Projecting Through the Radiator Opening.

A novel type of wood fuselage has been described by Poulsen in "Flight." Eight small longitudinals are used which are held in place by three-ply wooden formers or diaphragms. Wire bracing is used in a longitudinal direction, but not transversely in the plane of the diaphragms. The cross-section is octagonal, and the completed structure is covered with fabric. For the amateur this offers many advantages since the wiring is reduced to a minimum and all of the members are small and easily bent to shape. It is fully as light as any type of body, for the connections are only thin strips of steel bolted to the diaphragms with small machine screws. No formers are needed for the deck, and the machine can be given a close approximation to the ideal stream-line form with little trouble.

Truss Type Fuselage. We will now take up the construction of the truss type of fuselage in more detail, and investigate the merits of the different types of connections used in fastening the frame together. Like every part of the aeroplane, the fuselage must either be right or wrong, there is no middle course. Fig. 23 shows a side elevation of a typical truss type fuselage built up with wood longitudinals and struts, the tension members being high tensile strength steel wire and cable. L and L’ are the upper and lower longitudinals, S-S-S are the vertical struts, and T-T-T are the horizontal cross struts which run across the frame. The engine bed is the timber marked B at the front of the body. The upper wing is attached to the body through the "cabane" struts C, and the chassis connections are shown at D. The stern post E closes the rear end of the body in a knife edge and acts as a support for the rudder and the rear end of the stabilizer. F is the seat rail which carries the seats and supports the control yokes.

All cross bracing is of high tensile strength steel wire, or of high strength aviation cable, these strands taking the tensile stresses while the wood struts are in compression. In the forward portion, double stranded cables are generally used, with solid wire applied to the after portions. The longitudinals are of ash from the motor to the rear of the pilot's seat, while the rear longitudinals are generally of spruce. In some machines, however, the entire length of the longitudinals is ash. The latter arrangement makes a heavier, but stronger body. The struts are usually of spruce as this material is stiffer than ash and much lighter.

Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)

Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)

Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.

Diagram of Typical Truss Type Fuselage, Showing Principal Members in Place.

Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)

Fuselage of Hansa-Brandenburg Fighting Biplane. See Page 268. Figs. 27-28-29-30. Fuselage Details. (Truss Type)

Both the struts and longitudinals are frequently channelled out for lightness, as shown by Fig. 27, the wooden member being left rectangular in section only at the points where the connections are made with the struts and cables. The channelling-out process, if correctly followed, gives very strong stiff members with a minimum of cross-sectional area and weight. Many captured German machines, on the contrary, have solid longitudinals of rectangular section, wrapped with linen fabric. This fabric strengthens the construction and at the same time reduces the chances of splintering the wooden members in a hard landing. The fabric is glued to the wood and the entire wrapping is then given several coats of a moisture repelling varnish. In the older types of fuselage, the longitudinals were often of the "laminated" class, that is, were built up of several layers of wood glued together in a single rectangular mass. This reduced the tendency toward splitting, but was very unreliable because of the uncertainty of the glued joints when exposed to the effects of heat and moisture. Laminated longitudinals are now seldom used, particularly in the region of the motor where water and oil are certain to wreck havoc with the glued up members.

As the stresses rapidly diminish toward the tail, it is the general practice to taper down the section of the longitudinal toward the rear and to reduce the section of the struts. The longitudinals are generally kept constant in section from the motor to the rear of the pilot's seat, the taper starting at the latter point and continuing to the rear end. For example, if the longitudinal section at the motor is 1 1/4" x 1 1/2", the section at the rear will be 1" x 1", the width of the struts corresponding to this taper. While tapering is very desirable from the weight standpoint, it makes the fitting problem very difficult since each fitting must be of a different dimension unless the connections can be designed so that they are adjustable to changes in the section of the longitudinals. In one machine, the width and depth of the longitudinals are kept constant, the variation in weight and section being accomplished by increasing the depth of the channelling as the rear is approached. With this design, the same fittings can be applied from one end to the other.

Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.

Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.

Figs. 27-28-29-30. Fuselage Framing Members and Details.Figs. 27-28-29-30. Fuselage Framing Members and Details.

Figs. 27-28-29-30. Fuselage Framing Members and Details.

Since the loading of the struts is comparatively light, they can be much reduced in section by channelling or by chamfering, as shown by Fig. 28. If the width and thickness is maintained, much of the interior material can be removed without danger of reducing the strength. Sketch (A) in Fig. 28 shows a very common method of strut reduction, the strut being of rectangular section throughout its length, but tapered in such a way that it is thickest at the center (d) and thinnest at the two ends (e). To obtain the correct relation between the center end thickness requires very careful calculation. As shown, the strut is attached to the upper and lower longitudinals by sheet steel fittings or "sockets." Sketch (B) shows a simple method, the rectangular strut being chamfered off at each of the four corners, and left full size at either end where the fittings connect it with the longitudinals. This form is not correct from a technical standpoint, but is generally good enough for lightly loaded struts, and has the advantage of being cheaply and easily constructed. In sketch (C) a channelled strut is shown, the center portion being channelled out in a manner similar to the channelling of the longitudinals. This lightening process is most commonly adopted with the large heavily loaded struts in the front portion of the fuselage, and at the points where the motor bed is suspended or where the wings and chassis are attached to the body. The black dots at the ends of the struts indicate the bolt holes for the fittings, it being permissible to drill holes in the ends of the struts but not in the longitudinal members. If the strut is large enough to resist the bending stresses at the center it will generally allow of holes being drilled near the ends without danger of strength reduction. Again, the struts are always in compression and hence the bolts may be depended upon to partly take the place of the removed material in carrying the compressive stresses.

Holes should never be drilled in the longitudinals since these members may be either in tension or compression, depending upon the angle at which the elevator flaps are set. The hole not only destroys the strength at the point at which it is drilled, but this reduction also extends to a considerable distance on either side of the hole, owing to the fibrous nature of the wood. In steel members the effect of the hole is purely local and does not usually extend much beyond the edge of the hole. Considering the wood beam as consisting of a series of parallel fibers, it will be seen that severing any one of the fibers will decrease the strength of the wood through a distance equal to the length of the cut fiber, or at least through a distance equal to the natural shear value of the resins that bind the fibers together.

Fuselage fittings are almost numberless in the variety of design. They must be very light and strong, must be applied without drilling the longerons, and should be simple and cheap to construct. They are usually made of sheet steel of from 0.20 to 0.30 point carbon, and may be either bent or pressed into shape. At the points where the struts are joined to the longitudinals, the fittings connect struts and wires in three planes, the vertical struts and fore and aft wires; the transverse wires and horizontal struts, and the top and bottom wires that lie in a horizontal plane. There are at least 6 connections at every strut, four of the connections being made to the stay wires or cables. A simple connection is therefore very hard to design.

Fig. 29 shows a typical fuselage "panel" and the interconnected members in their usual relation. LU and LL are the top and bottom longitudinals at the right, while LU' and LL’ are the longitudinals at the right hand side. The vertical struts SV and SV’ separate the top and bottom longitudinals, while the horizontal struts SH and SH’ separate the right and left hand sides of the fuselage body. The wires w-w-w-w brace the body fore and aft in a vertical plane. The wires t-t lie in a horizontal plane, produce compression in the horizontal struts SH-SH', and stiffen the frame against side thrust. The transverse rectangle SV-SH-SV’-SH' is held in shape by the transverse stay wires W-W, this rectangle, and the stays resisting torsional stress (twisting), act against the struts composing the sides of the rectangle. In some European machines, the wires WW are eliminated, and are replaced by thin veneer panels, or short wood knee braces as shown by Fig. 30. The section shows the longitudinals L-L-L-L and the struts SV-SV’-SH-SH’ braced by the veneer sheet or diaphragm D. This diaphragm is well perforated by lightening holes and effectually resists any torsional stress that may be due to motor torque, etc. Since the transverse wires W-W in Fig. 29 are rather inaccessible and difficult to adjust, the veneer diaphragm in Fig. 27 has a great advantage. In this regard it may be stated that wire bracing is not a desirable construction, and the substitution of solid veneer is a step in advance.

Wire bracing has always seemed like a makeshift to the author. The compression and tension members being of materials of widely different characteristics are not suitable in positions where a strict alignment must be maintained under different conditions of temperature and moisture. The difference in expansion between wire and the wood compression members produces alternate tightness and slackness at the joints, and as this is not a uniform variation at the different joints, the frame is always weaving in and out of line. Under the influence of moisture the wood either swells or contracts, while the wire and cable maintain their original lengths and adjustments. The result is that a frame of this kind must be given constant attention if correct alignment is desired.

The adjustment of a wire braced wood fuselage should be performed only by a skilled mechanic, as it is easily possible to strain the members beyond the elastic limit by careless or ignorant handling of the wire straining turnbuckles. In the endeavor to bring an old warped fuselage back into line it is certain that the initial tension in the wires can be made greater than the maximum working stress for which the wires were originally intended. Shrinkage of the wood also loosens the bond between the wooden members and the steel fittings unless this is continually being taken up. Some form of unit construction, such as the monocoque body, is far more desirable than the common form of wire trussed wood body.

Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.

Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.

Fuselage Details of De Havilland V. Single Seat Chaser.Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.

Fuselage Details of De Havilland V. Single Seat Chaser. A Rotary Le Rhone Motor Is Used in a Circular Cowl. The Diagonal Bracing in the Front Section is Reinforced by Laminated Wood Plates Instead of by Wires. Dimensions in Millimeters.

Fuselage Fittings. In the early days of aviation the fuselage fittings on many machines were made of aluminum alloy. This metal, while light, was uncertain in regard to strength, hence the use of the alloy was gradually abandoned. At present the greater part of the fittings are stamped steel, formed out of the sheet, and are of a uniform strength for similar designs and classes of material.

The steel best adapted for the fittings has a carbon content of from 0.20 to 0.30, with an ultimate strength of 60,000 pounds per square inch, and a 15 per cent elongation. The steel as received from the mill should be annealed before stamping or forming to avoid fracture. After the forming it can be given a strengthening heat treatment. A lower steel lying between 0.10 and 0.15 carbon is softer and can be formed without annealing before the forming process. This material is very weak, however, the tensile strength being about 40,000 pounds per square inch. Fittings made of the 0.15 carbon steel will therefore be heavier than with the 0.30 carbon steel for the same strength. The thickness of the metal will vary from 1/32" to 1/16", depending upon the load coming on the fitting.

A typical fuselage strut fitting is shown by Fig. 31-A in which L-L-L are the longerons, d is the fitting strap passing over the longerons, S and So are the vertical and horizontal struts respectively. The stay wires are fastened to ears (b) bent out of the fitting, the wires being attached through the adjustable turnbuckles (t). The struts are provided with the sheet steel ferrules marked (F). There are no bolts passing through the longitudinals L-L', the fitting being clamped to the wooden member. This is very simple and light fitting. Fig. 31-B is a similar type, so simple that further discussion is unnecessary.

Fig. 32 shows a fuselage strut fitting as used on the Standard Type H-3 Biplane. We are indebted to "Aerial Age" for this illustration. This consists of a sheet metal strap of "U" form which is bent over the longitudinal and is bolted to the vertical strut. At either side of the strut are through bolts to which bent straps attach the turnbuckles. These straps are looped around the bolts and form a clevis for the male ends of the turnbuckles.

Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.

Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.

Fig. 31. Typical Fuselage Strut Fittings.Fig. 31. Typical Fuselage Strut Fittings.

Fig. 31. Typical Fuselage Strut Fittings.

An old form of fuselage connection used on the Nieuport monoplane is shown by Fig. 33, an example of a type in which the bolts are passed through the longeron member. This fitting is very light but objectionable because of the piercing of the longeron.

An Austrian aeroplane, the Hansa-Brandenberg, has a wood fuselage in which no stay wires are used. This fuselage is shown by Fig. 23a. Both the vertical and inclined members are wood struts. The outer covering of wood veneer makes the use of stay wires unnecessary since the sheath takes up all horizontal stresses, and hence forms a sort of plate girder construction. The German Albatros also employs a wireless veneer fuselage, the construction being shown in detail by Figs. 36 and 36a. Three longerons are located on either side of the body, the third member being placed at about the center of the vertical side. As will be seen, the veneer makes the use of wire bracing and metal connections unnecessary. The veneer also insures perfect alignment.

Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.

Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.

Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.

Fig. 32. Fuselage Strut Fittings of the Standard H-3 Training Biplane.

Wing Connections. The lower wings are attached to the lower longitudinals by a special sheet steel fitting which also generally connects to a vertical strut at this point, and to an extra heavy horizontal strut. A sheet metal clevis, or socket, on the wing spar is pinned to the fuselage half of the fitting so that the wing can be easily detached when the machine is to be dissembled. At this point a connection is also provided for the end of the inner interplane stay wires. The horizontal strut at the point of wing attachment is really a continuation of the wing spar and takes up the thrust due to the inclination of the interplane stays. In the majority of cases the horizontal thrust strut is a steel tube, with the hinged connection brazed to its outer ends. This is one of the most important and heavily loaded connections on the machine and should be designed accordingly.

Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.

Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.

Fig. 33. Fuselage Fittings of the Nieuport Monoplane.Fig. 33. Fuselage Fittings of the Nieuport Monoplane.

Fig. 33. Fuselage Fittings of the Nieuport Monoplane.

Fig. 37 shows a typical wing to fuselage connection of the hinge type. The wing spar (G) is covered with a sheet steel ferrule (A) at its inner end. Two eye bars (B) are bolted to the wing spar, and over the ferrule, the eyes of the bar projecting beyond the end of the spar. This forms the wing half of the connecting hinge. The eyes are fastened to the fuselage hinge member (H) by means of the pin (E). This pin has a tapered end for easy entry into the joint, and is pierced with holes at the outer end for cotter pins or a similar retaining device. The fuselage hinge member (H) is brazed to the end of the steel tube strut (T). This tube runs across the fuselage from wing spar end to wing spar end.

Strut tube (T) lies on, and is fastened to, the fuselage longeron (L), and also lies between the two halves of the vertical strut (S). The vertical strut is cut out at its lower end for the receipt of the steel tube (T). A steel plate is brazed to the tube, is wrapped about the longeron (L) and is bolted to the vertical strut (S). The interplane stay (F) is attached to the pin (E) at the point of juncture of the wing spar eye and the fuselage member of the hinge. A collar (I) is brazed to the tube, and forms a means of attaching the fuselage stays (D). The drift wires (C) of the wings are attached to an eye at the end of one of the wing spar bolts. As shown, the fitting (H) is a steel forging, very carefully machined and reduced in weight. The inside wing ribs are indicated by (K), from which it will be seen that there is a gap between the end of the wings and the outside face of the fuselage.

Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.

Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.

Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout.Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.

Fig. 36. Veneer Fuselage Construction of the German "Albatros" Speed Scout. Body Outline Is Obtained by Veneer Diaphragms and no Stay Wires Are Used.

Fig. 36-a shows the construction of the wing joint of the German Albatros machine. The fuselage is of monocoque construction which allows of a simple attachment to the outer shell. This is a very sturdy and simple connection. Fig. 38-Z is the wing attachment detail of the English London and Provincial Biplane (1916), the fuselage in this case being of the wire trussed wood type. We are indebted to "Flight" for this illustration.

Fig. 36-a. Details of Albatros Veneer Fuselage Construction.Fig. 36-a. Details of Albatros Veneer Fuselage Construction.

Fig. 36-a. Details of Albatros Veneer Fuselage Construction.

In some machines the interplane stay wires are attached to a lug formed from the attachment plate, but we do not consider that this construction is as good as the type in which the wire is attached directly to the wing spar pin. While the former may be easier to assemble, the attachment of the wire to the pin eliminates any eccentricity, or bending moment, due to the pull of the interplane stay. The attachment in the L. W. F. insures against any eccentricity in the stay attachment, and at the same time makes the assembly and dismounting a very simple matter.

Fig. 37. Wing Connection to Fuselage.Fig. 37. Wing Connection to Fuselage.

Fig. 37. Wing Connection to Fuselage.

Chassis Member Attachment. The attachment of the chassis struts generally involves some difficulty as these members usually intersect the line of the longerons at a very awkward angle. If the wing attachment is near the same point, as it generally is, the detail is made doubly difficult. The chassis must be pin connected as in the case of the wing joint so that the chassis members can be easily and quickly removed. A detail of a chassis to body connection is shown by Fig. 39. In this figure (L) is the lower longeron, (S) is the vertical fuselage strut, and (C) is one of the chassis members. The upper end of the chassis member is enveloped in a sheet steel ferrule (D) which is bolted in place, and which is provided with a clevis at its upper end for the attachment pin (P).

A plate (E) is bolted to the fuselage strut (S) and is passed around the lower longeron (L), a hinge joint (H) being provided for attachment to the chassis ferrule through the pin (P). Ears or lugs are left at (G-G) for the attachment of the fuselage stays (B-B). On the inner side of the plate (E) are attachment lugs for the horizontal strut (H). It will be noted that the plate (E) is well provided with lightening holes so that the weight can be kept down to a minimum. The pin is tapered at the end, and is provided with cotter pin holes. The fitting in general is small, and does not produce any great degree of head resistance, the small part exposed being of good streamline form.

Wing ConnectionsFig. 38x. Wing Connection of the Albatros Reconnaissance Biplane. Fig. 38y. Wing Attachment of Albatros Fighter with Pin Joint. Fig. 38z. Wing Connection of London and Provincial Biplane.

Fig. 38x. Wing Connection of the Albatros Reconnaissance Biplane. Fig. 38y. Wing Attachment of Albatros Fighter with Pin Joint. Fig. 38z. Wing Connection of London and Provincial Biplane.

Great care should be taken in brazing or welding these fittings, since the heat changes the structure of the metal and greatly reduces its strength. The brazing temperature varies from 1,500 to 1,700 degrees, a point well above the tempering heat of steel. Attempts have been made to heat treat the metal after the brazing operation, but with very little success, owing to the fact that the heat treating temperature is generally at or above the melting point of the brazing spelter, hence is likely to cause holes and openings in the brazed joints. With acetylene welded joints the parts can, and should be, heat treated after the welding. While this is an apparent advantage of acetylene welding, all parts cannot be successfully handled in this manner. The welding torch can only join edges, while the brazing spelter can be applied over almost any area of surface. Welding is very successful in joining thin steel tubes while in many fittings made of sheet metal, brazing is the only feasible operation.

Fig. 39. Chassis Connection.Fig. 39. Chassis Connection.

Fig. 39. Chassis Connection.

Both methods have a common fault, in that they are unreliable. Imperfect welds and brazing are not always apparent from the outside, actual breakage of the part being necessary to determine the true nature of the joint.

FUSELAGE WEIGHTS.Distribution of Weight. The weight of a fuselage depends upon the span of the wings, upon the seating capacity, and upon the weight and type of the power plant. The weight also varies considerably with the type of construction, that is, whether of truss, veneer, or monocoque construction. A heavily powered machine, or one carrying more than a single person, requires heavier structural members and hence weighs more than a small single seater. The amount of fuel carried also has a considerable bearing on the fuselage weight.Probably the best method of treating this subject is to give the fuselage weights of several types of well known machines. The reader will then have at least a comparative basis for determining the approximate weight. (Truss type only.)Fuselage Weights TableThere are so many variables that the weight cannot be determined by any set rule or formula. Alexander Klemin in his "Course in Aerodynamics and Airplane Design" says that the approximate weight of a bare wood truss type fuselage is about 150 pounds for a machine having a total weight of 2,500 pounds. For small biplane and monoplane scouts weighing approximately 1,200 pounds total, the bare fuselage frame will weigh about 70 pounds. These figures are for the bare frame alone and without seats, controls, tail skids or other fittings. The weights given under the column headed "Wt. Bare" include the engine beds, tail skids, flooring, cowling and body covering, and hence exceed the "bone bare" estimate of Klemin by a considerable amount.The all-steel fuselage of the large Sturtevant battle-plane (Model A) weighs 165 pounds inclusive of the steel engine bed. A wooden, wire braced fuselage of the same size and strength weighs well over 200 pounds, the metal fittings and wires weighing about 60 pounds alone. Ash is used in the wood example for the longerons. The struts and diagonal members in the Sturtevant metal fuselage are riveted directly to the longitudinals, without fittings or connection plates. The safety factor for air loads is 8, and for the ground loads due to taxi-ing over the ground, a safety factor of 4 is used.After a minute comparison of the items comprising the fuselage of the Curtiss JN4-B and the Standard H-3, Klemin finds that the fuselage assembly of the Standard H-3 amounts to 13.6 per cent of the total loaded weight, and that the fuselage of the Curtiss JN4-B is 15.5 per cent of the total. Tanks, piping and controls are omitted in both cases. For machines weighing about 2,500 pounds, Dr. J. C. Hunsaker finds the body weight averaging 8.2 per cent of the total, this figure being the average taken from a number of machines.On careful examination it will be found that the fuselage assembly (bare) amounts to a trifle less than the wing group for biplanes having a total weight of from 1,900 to 2,500 pounds. The relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights. We will set these different relations forth in the following table:PERCENTAGE OF FUSELAGE WEIGHTName of Plane or InvestigatorFuselage Weight as Percentage of the Total LoadWing Weight As Percentage of Total WeightBody Assembly BareBody Assembly and EquipmentBody Assembly and Power PlantCurtiss JN4-B15.50%17.86%43.96%14.15%Standard H-313.60%17.70%45.40%14.52%J.C. Hunsaker8.20%11.50%34.30%16.50%Author's Experience14.96%17.62%46.66%14.60%Average of Above13.06%16.17%42.58%14.94%In the above table, the column headed "Body Assembly and Equipment" includes the body frame, controls, tanks and piping. In the fourth column, the radiator, motor, propeller, water, and exhaust pipe have been added. For the average value it will be seen that the bare fuselage is about 1.88 per cent lower than the weight of the wings. It should be noted that the wing weight given is the weight of the surfaces alone, and does not include the weight of the interplane struts, wires and fittings. The weight of the wing surfaces as above will average about 0.75 pounds per square foot.Based on the above figures, we can obtain a rough rule for obtaining the approximate weight of the fuselage, at least accurate enough for a preliminary estimate. If A = the total area of the wings, then the total weight of the wings will be expressed by w = 0.75A. The weight (f) of the fuselage can be shown as f = 13.06/1494 x w = 0.65A.Example. The area of the Standard H-4 is 542 square feet total. Find the approximate weight of the fuselage. By the formula, f = 0.65A = 0.65 x 542 = 352 pounds. The actual bare weight is 302.0 pounds. For several other machines, the actual weight is greater than the weight calculated by the formula, so that the rule can be taken as a fair average, especially for a new type that is not as refined in detail as the H-3.

Distribution of Weight. The weight of a fuselage depends upon the span of the wings, upon the seating capacity, and upon the weight and type of the power plant. The weight also varies considerably with the type of construction, that is, whether of truss, veneer, or monocoque construction. A heavily powered machine, or one carrying more than a single person, requires heavier structural members and hence weighs more than a small single seater. The amount of fuel carried also has a considerable bearing on the fuselage weight.

Probably the best method of treating this subject is to give the fuselage weights of several types of well known machines. The reader will then have at least a comparative basis for determining the approximate weight. (Truss type only.)

Fuselage Weights Table

There are so many variables that the weight cannot be determined by any set rule or formula. Alexander Klemin in his "Course in Aerodynamics and Airplane Design" says that the approximate weight of a bare wood truss type fuselage is about 150 pounds for a machine having a total weight of 2,500 pounds. For small biplane and monoplane scouts weighing approximately 1,200 pounds total, the bare fuselage frame will weigh about 70 pounds. These figures are for the bare frame alone and without seats, controls, tail skids or other fittings. The weights given under the column headed "Wt. Bare" include the engine beds, tail skids, flooring, cowling and body covering, and hence exceed the "bone bare" estimate of Klemin by a considerable amount.

The all-steel fuselage of the large Sturtevant battle-plane (Model A) weighs 165 pounds inclusive of the steel engine bed. A wooden, wire braced fuselage of the same size and strength weighs well over 200 pounds, the metal fittings and wires weighing about 60 pounds alone. Ash is used in the wood example for the longerons. The struts and diagonal members in the Sturtevant metal fuselage are riveted directly to the longitudinals, without fittings or connection plates. The safety factor for air loads is 8, and for the ground loads due to taxi-ing over the ground, a safety factor of 4 is used.

After a minute comparison of the items comprising the fuselage of the Curtiss JN4-B and the Standard H-3, Klemin finds that the fuselage assembly of the Standard H-3 amounts to 13.6 per cent of the total loaded weight, and that the fuselage of the Curtiss JN4-B is 15.5 per cent of the total. Tanks, piping and controls are omitted in both cases. For machines weighing about 2,500 pounds, Dr. J. C. Hunsaker finds the body weight averaging 8.2 per cent of the total, this figure being the average taken from a number of machines.

On careful examination it will be found that the fuselage assembly (bare) amounts to a trifle less than the wing group for biplanes having a total weight of from 1,900 to 2,500 pounds. The relation between the wing weight and the fuselage weight seems to bear a closer relation than between the fuselage and total weights. We will set these different relations forth in the following table:

Name of Plane or Investigator

Fuselage Weight as Percentage of the Total Load

Wing Weight As Percentage of Total Weight

Body Assembly Bare

Body Assembly and Equipment

Body Assembly and Power Plant

Curtiss JN4-B

15.50%

17.86%

43.96%

14.15%

Standard H-3

13.60%

17.70%

45.40%

14.52%

J.C. Hunsaker

8.20%

11.50%

34.30%

16.50%

Author's Experience

14.96%

17.62%

46.66%

14.60%

Average of Above

13.06%

16.17%

42.58%

14.94%

In the above table, the column headed "Body Assembly and Equipment" includes the body frame, controls, tanks and piping. In the fourth column, the radiator, motor, propeller, water, and exhaust pipe have been added. For the average value it will be seen that the bare fuselage is about 1.88 per cent lower than the weight of the wings. It should be noted that the wing weight given is the weight of the surfaces alone, and does not include the weight of the interplane struts, wires and fittings. The weight of the wing surfaces as above will average about 0.75 pounds per square foot.

Based on the above figures, we can obtain a rough rule for obtaining the approximate weight of the fuselage, at least accurate enough for a preliminary estimate. If A = the total area of the wings, then the total weight of the wings will be expressed by w = 0.75A. The weight (f) of the fuselage can be shown as f = 13.06/1494 x w = 0.65A.

Example. The area of the Standard H-4 is 542 square feet total. Find the approximate weight of the fuselage. By the formula, f = 0.65A = 0.65 x 542 = 352 pounds. The actual bare weight is 302.0 pounds. For several other machines, the actual weight is greater than the weight calculated by the formula, so that the rule can be taken as a fair average, especially for a new type that is not as refined in detail as the H-3.

SIZE OF LONGERONSThe size of the longerons, that is, the section, is influenced by many factors. As these members must resist flying loads, the leverage of elevator flaps, stresses due to control wires, landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members. This latter method is a method for a trained engineer, but an exhaustive description of the method of procedure will be found in books on the subject of "Strength of Materials." For the practical man, I give the following list of longeron dimensions so that he will have at least a guide in the selection of his material.The length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison, although this is a crude and inaccurate method. As the longerons taper from front to back, the sizes of the section are given at the motor end, and also at the tail. The size of the front members depends principally upon the weight of the motor and the passenger load, while the rear longerons carry the elevator loads and the tail skid shock. If the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance. The loads on the stabilizer, elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping, and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress. In the front of the fuselage, the motor exerts a steady torque (twist) in addition to the stress due to its weight, and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight. The combination of these forces acting at different times makes the calculation very difficult.Longeron Dimensions TableIn the case of the Curtiss R-4, the front longerons taper down from the motor 1.63" x 1.25" to a point directly behind the pilot's seat, the section at the latter point being 1.25" x 1.25". From this point the rear longerons taper down to 1" x 1" at the tail. At the motor, the section is 1.63" x 1.25". The longitudinals of the Bleriot monoplane are laminated and are built up of alternate layers of spruce and ash. This is an old type of machine and this practice has since been discontinued. It will be noted that as the power is increased, the size of the front longerons is generally increased, although this is not always the case in speed machines. The Chicago Aero Works’ "Star" fuselage could easily carry a 90 horsepower motor, although this size is not regularly installed.Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.

The size of the longerons, that is, the section, is influenced by many factors. As these members must resist flying loads, the leverage of elevator flaps, stresses due to control wires, landing stresses and the weight of the motor and personnel it is always advisable to itemize the loading and then prepare a diagram to obtain the stresses in the different members. This latter method is a method for a trained engineer, but an exhaustive description of the method of procedure will be found in books on the subject of "Strength of Materials." For the practical man, I give the following list of longeron dimensions so that he will have at least a guide in the selection of his material.

The length of the fuselage and power of motor are given so that the reader can obtain sizes by comparison, although this is a crude and inaccurate method. As the longerons taper from front to back, the sizes of the section are given at the motor end, and also at the tail. The size of the front members depends principally upon the weight of the motor and the passenger load, while the rear longerons carry the elevator loads and the tail skid shock. If the rudder is high above the fuselage it introduces a twisting movement that may be of considerable importance. The loads on the stabilizer, elevators and the vertical rudder are very severe when straightening out after a steep dive or in looping, and the pull on the control wires exerted by the aviator at this time greatly adds to the total stress. In the front of the fuselage, the motor exerts a steady torque (twist) in addition to the stress due to its weight, and to this must be added the gyroscopic force caused by the propeller when the machine is suddenly changed in the direction of flight. The combination of these forces acting at different times makes the calculation very difficult.

Longeron Dimensions Table

In the case of the Curtiss R-4, the front longerons taper down from the motor 1.63" x 1.25" to a point directly behind the pilot's seat, the section at the latter point being 1.25" x 1.25". From this point the rear longerons taper down to 1" x 1" at the tail. At the motor, the section is 1.63" x 1.25". The longitudinals of the Bleriot monoplane are laminated and are built up of alternate layers of spruce and ash. This is an old type of machine and this practice has since been discontinued. It will be noted that as the power is increased, the size of the front longerons is generally increased, although this is not always the case in speed machines. The Chicago Aero Works’ "Star" fuselage could easily carry a 90 horsepower motor, although this size is not regularly installed.

Pusher Type Fuselage (Nacelle). Compared with the tractor biplane and the monoplane fuselage, the body of the pusher is very short and light. The latter body simply acts as a support for the motor and personnel since the tail loads are carried by the outriggers or tail booms. The motor is located at the rear end of the body and may be either of the air or water-cooled type. The accompanying figure shows a typical pusher type body, or "Nacelle" as it is sometimes called.

The advantages of the pusher type for military service are obvious. The observer or gunner can be placed immediately in the front where his vision is unobstructed, and where the angle of fire is at a maximum.

Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.

Typical Pusher Body Showing Wings, and Outrigger to Tail Surfaces.

Twin Motored Fuselage. Twin motored aeroplanes generally have the power plants mounted at a point about midway between the fuselage and tips of the wings. In almost every case, the power plants are of unit construction, that is to say, consist of the motor, radiator and propeller complete on one support, only the fuel and oil tanks being mounted in the fuselage. The fuselage of the twin may be similar in length and general construction to that of the tractor biplane, or it may be a short "nacelle" similar to that used in the pusher type. In any case, the observer can be located in the extreme front of the body.

An interesting and unusual construction is the body of the Caproni Biplane (1916). A center nacelle carries the passengers, a pusher screw being located at the rear of the central body as in the case of the pusher biplane. On either side of the center are the motors driving the tractor screws, each motor being encased in a long tractor type fuselage that also supports the tail surfaces. The latter fuselage serves to streamline the motors and takes the place of the usual outrigger construction. There are three bodies, two tractor screws, and one pusher screw. Somewhat similar in design is the famous German "Billy Two-Tails," this machine being equipped with two tractor type bodies. A motor is located in the front of each body. Each fuselage is provided with accommodations for passengers, and is long enough to support the tail surfaces. The Caproni and the German machine are both very large machine and heavily powered.

U.S.A. Sea-Plane Specifications (1916). These government specifications cover a twin motored sea-plane with a central nacelle. The body is arranged so that the forward man (observer) can operate the forward machine gun through a horizontal arc of at least 150°, and through a vertical arc of at least 270°, with the gun at an angle of about 75° with the center line of the body. The muzzle must be forward of the propeller plane. The rear man (pilot) operates a machine gun through a vertical arc of at least 150° to the rear, and through a vertical arc of at least 180°, with the gun at an angle of about 105° with the fuselage center line. The muzzle must be to the rear of the plane of propeller rotation.

The number of stays and other important connections which extend across the plane of propeller rotation shall be reduced to a minimum. It is considered advisable to incorporate in the design of the body such a structure (in the plane and 8 inches forward of propeller plane) as will prevent a broken propeller blade from severing the main body. The system used in the construction of the cage masts used on battleships is suggested, with a number of spruce compression members in place of stay-wires. The clearance of the propeller tips from the sides of the central body shall be from 5 to 12 inches. No part of the gas tanks shall lie in the plane of propeller rotation, nor within a space 6 inches ahead of this plane.

A space extending at least 9 inches back from the rear of the observer's seat, and entirely across the body, must be left open and unoccupied in order that any desired instruments can be installed therein. In the center line of the body, a circular hole 9 inches in diameter shall be cut in the floor of the observer's cock-pit, the rear of the hole being 5 inches forward of the forward edge of the observer's seat. The flooring of the pilot's and observer's cockpits shall consist of spruce strips 1/2" x 1/2 " spaced at 1/2" intervals along the longerons. No flooring is to be placed under the seats.

The safety factor of the body and tail structure shall not be less than 2.5, the air speed being taken at 100 miles per hour with the elevator at an angle of 20° and the fixed stabilizer surface at 6°. All wire tension members not readily accessible for inspection and adjustment are to be single strand high tensile steel wire. All tension stays that are easily accessible shall be of non-flexible stranded steel cable. For turnbuckle safetying No. 20 semi-hard copper wire shall be used. All cable shall be well stretched before making up the connections. A load equal to 20 or 30 per cent of the breaking load shall be applied for a period of from two to three hours. The hard wire must undergo a bending test by bending at a right angle turn over a radius equal to the diameter of the wire, back and forth four times each way. No more than four sizes of turnbuckles shall be used on the entire aeroplane structure. The strengths and size numbers of the turnbuckles will be as follows: No. 1 = 8,000 lbs. No. 2 = 4,600 lbs. No. 3 = 2,100 lbs. No. 4 = 1,100 lbs. Controls and fittings in the vicinity of the compasses shall, as much as possible, be of non-magnetic material. All steel plate and forged fittings shall be protected against the action of salt water by baking enamel, the best standard three coat process being used. All covered wiring and turnbuckles shall be coated by at least two coats of Flexible Compound.

All steel tubing shall be thoroughly cleaned, slushed with mineral oil inside, and plugged at both ends by wood plugs impregnated with mineral oil or paraffine. All steel nuts, bolts, pins and cotter pins shall be protected by heavy nickel plating over copper. All wood members, especially faying surfaces, end grain butts, scarfs and joints, shall be protected against the access of moisture before final assembly by the best grade of varnish, or by impregnation by paraffine. All wood shall be straight grained, well seasoned, of uniform weight, and free of knots, pitch pockets, checks or cracks. Spruce to be of the very highest grade of selected straight, even grained, clear spruce. It shall be air seasoned, preferably for two years. Kiln dried wood is not acceptable.

It is highly desirable to have all bolts, pins, plate fittings and turnbuckle ends made of chrome vanadium steel (S. A. E. Specification 6.130), heat treated to obtain the best physical characteristics. All parts and fittings that must be bent shall be heat treated after all bending operations are completed, and by such a sequence of treatment as will produce the desired grain and toughness, and relieve all stresses due to the bending. This includes sheet and forged steel fittings, turnbuckle ends and bolts and pins. All steel parts and fittings submitted to stress or vibration shall be heat treated in such a manner as to produce the highest possible refinement of grain and give the greatest possible resistance to alternating and vibratory stresses. Where plate fittings are in contact with wooden members, sharp edges next to the wood shall be removed. In making up and connecting steel fittings, welding shall be used wherever possible. If impracticable to weld, and in such cases only, brazing will be used, proper heat treatment to be employed to restore strength and toughness of metal after such welding or brazing. Extreme care should be taken to avoid nicking or kinking any wire, cable or fitting. Fittings, sheet or forged, must be free from sharp corners and supplied with generous fillets.

In general the S.A.E. Standards will be acceptable, and these standards for screw threads shall be used wherever possible. U.S. Standard threads will be accepted where threaded into cast iron, cast aluminum or copper alloys. All nuts and pins must be provided with one or more positive and durable safety devices. In general, where it must be expected that a structural fitting will be disassembled a number of times during the life of the aeroplane, castellated nuts with split pins, in accordance with S.A.E. Standards, shall be used. Wherever this is not the case, pins or bolts shall be riveted in a workmanlike manner.

Seats shall be securely braced against both horizontal and vertical stresses. Arrangement and dimensions of cock-pits shall be as nearly as practicable to that indicated by the drawings (not published in this chapter). In addition, if practicable, the pilot should be provided with quick release arm rests. Sections of best grade of khaki on each side of seats, in which pockets are made, should be fastened to longerons and vertical posts in such a way as to be securely in place and yet readily detachable for inspection of structural wiring and fittings. Safety belts shall be provided for both seats and securely fastened. The belts shall safely support at any point a load of 2,000 pounds applied as in practice. Rubber shock absorbers in the safety belt system are considered to be an advantage. The quick release device shall be as indicated in drawings and shall reliably and quickly function. Seat pads shall be quickly detachable in order that they may be used as life preservers. They will be filled with Kapok or other similar material and covered with real leather to protect it against the action of salt water.

Suitable covers shall be provided over the top of the rear end of the fuselage. These must be easily removed and capable of being securely fastened in place during flight. Space shall be allowed in the body directly in the rear of the observer's seat for the stowage of the sea anchor. When in use, the sea anchor shall be attached by suitable and convenient fastening hooks to the two points along the lower longerons, and at the junction of the two vertical struts in the rear of the front seat. The structure must be such that it will successfully withstand the stresses imposed by the sea anchor. Controls shall be of the standard Deperdussin type, installed in the rear cock-pit only. The tanks for the main supply of gasoline shall be in the fuselage and located so that the longitudinal balance will not be disturbed by the emptying of the tank during flight.

The above data is not in the exact form of the original specifications and is not complete, but gives only the specifications that affect the design of the body. These were picked out part by part from the original.

Army Specification 1003 (Speed Scout). These specifications cover the design of land machines, the extracts given here referring only to the safety factor. Body forward of the cockpit shall be designed for safety factor of 10 over static conditions, with the propeller axis horizontal. Body in rear of cockpit shall be designed to fail under loads not less than those imposed under the following conditions:

(a) Dynamic loading of 5 as the result of quick turns in pulling out of a dive. (b) Superposed on the above dynamic loading shall be the load which it is possible to impose upon the elevators, computed by the following formula: L = 0.005AV², where A is the total area of the stabilizing surface (elevators and fixed surface), and V is the horizontal high speed of the machine. The units are all in the metric system. (c) Superposed on this loading shall be the force in the control cables producing compression in the longerons.

Fuselage Covering. Disregarding the monocoque and veneer constructed types of fuselage, the most common method of covering consists of a metal shell in the forward end, and a doped linen covering for that portion of the body that lies to the rear of the rear seat. The metal sheathing, which may be of sheet steel or sheet aluminum, generally runs from the extreme front end to the rear of the pilot's cockpit. Sheet steel is more common than aluminum because of its stiffness. Military machines are usually protected in the forward portions of the fuselage by a thin armor plate of about 3 millimeters in thickness. This is a protection against rifle bullets and shrapnel fragments, but is of little avail against the heavier projectiles. Armor is nearly always omitted on speed scouts because of its weight. Bombers of the Handley-Page type are very heavily plated and this shell can resist quite large calibers.

The fabric used on the rear portion of the fuselage is of linen similar to the wing covering, and like the wing fabric is well doped with some cellulose compound to resist moisture and to produce shrinkage and tautness. On the sides and bottom the fabric is supported by very thin, light stringers attached to the fuselage struts. On the top, the face is generally curved by supporting a number of closely spaced stringers on curved wooden formers. The formers are generally arranged so that they can be easily removed for the inspection of the wire stay connections and the control leads. On some machines the top of the fuselage consists entirely of sheet metal supported on formers, while in others the metal top only extends from the motor to the rear of the rear cockpit.

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