THERE is no phase of the art of flying more important than the fore and aft control of an airship. Lateral stability is secondary to this feature, for reasons which will appear as we develop the subject.
THE BIRD TYPE OF FORE AND AFT CONTROL.— Every aeroplane follows the type set by nature in the particular that the body is caused to oscillate on a vertical fore and aft plane while in flight. The bird has one important advantage, however, in structure. Its wing has a flexure at the joint, so that its body can so oscillate independently of the angle of the wings.
The aeroplane has the wing firmly fixed to the body, hence the only way in which it is possible to effect a change in the angle of the wing is by changing the angle of the body. To be consistent the aeroplane should be so constructed that the angle of the supporting surfaces should be movable, and not controllable by the body.
The bird, in initiating flight from a perch, darts downwardly, and changes the angle of the body to correspond with the direction of the flying start. When it alights the body is thrown so that its breast banks against the air, but in ordinary flight its wings only are used to change the angle of flight.
ANGLE AND DIRECTION OF FLIGHT.—In order to become familiar with terms which will be frequently used throughout the book, care should be taken to distinguish between the terms angle and direction of flight. The former has reference to the up and down movement of an aeroplane, whereas the latter is used to designate a turning movement to the right or to the left.
WHY SHOULD THE ANGLE OF THE BODY CHANGE? —The first question that presents itself is, why should the angle of the aeroplane body change? Why should it be made to dart up and down and produce a sinuous motion? Why should its nose tilt toward the earth, when it is descending, and raise the forward part of the structure while ascending?
The ready answer on the part of the bird-form advocate is, that nature has so designed a flying structure. The argument is not consistent, because in this respect, as in every other, it is not made to conform to the structure which they seek to copy.
CHANGING ANGLE OF BODY NOT SAFE.—Furthermore, there is not a single argument which can be advanced in behalf of that method of building, which proves it to be correct. Contrariwise, an analysis of the flying movement will show that it is the one feature which has militated against safety, and that machines will never be safe so long as the angle of the body must be depended upon to control the angle of flying.
Fig. 11a Monoplane in Flight.
In Fig. 11a three positions of a monoplane are shown, each in horizontal flight. Let us say that the first figure A is going at 40 miles per hour, the second, B, at 50, and the third, C, at 60 miles. The body in A is nearly horizontal, the angle of the plane D being such that, with the tail E also horizontal, an even flight is maintained.
When the speed increases to 50 miles an hour, the angle of incidence in the plane D must be decreased, so that the rear end of the frame must be raised, which is done by giving the tail an angle of incidence, otherwise, as the upper side of the tail should meet the air it would drive the rear end of the frame down, and thus defeat the attempt to elevate that part.
Fig. 12. Angles of Flight.
As the speed increases ten miles more, the tail is swung down still further and the rear end of the frame is now actually above the plane of flight. In order, now, to change the angle of flight, without altering the speed of the machine, the tail is used to effect the control.
Examine the first diagram in Fig. 12. This shows the tail E still further depressed, and the air striking its lower side, causes an upward movement of the frame at that end, which so much decreases the angle of incidence that the aeroplane darts downwardly.
In order to ascend, the tail, as shown in the second diagram, is elevated so as to depress the rear end, and now the sustaining surface shoots upwardly.
Suppose that in either of the positions 1 or 2, thus described, the aviator should lose control of the mechanism, or it should become deranged or "stick," conditions which have existed in the history of the art, what is there to prevent an accident?
In the first case, if there is room, the machine will loop the loop, and in the second case the machine will move upwardly until it is vertical, and then, in all probability, as its propelling power is not sufficient to hold it in that position, like a helicopter, and having absolutely no wing supporting surface when in that position, it will dart down tail foremost.
A NON-CHANGING BODY.—We may contrast the foregoing instances of flight with a machine having the sustaining planes hinged to the body in such a manner as to make the disposition of its angles synchronous with the tail. In other words, see how a machine acts that has the angle of flight controllable by both planes,—that is, the sustaining planes, as well as the tail.
Fig. 13. Planes on Non-changing Body.
In Fig. 13 let the body of the aeroplane be horizontal, and the sustaining planes B disposed at the same angle, which we will assume to be 15 degrees, this being the imaginary angle for illustrative purposes, with the power of the machine to drive it along horizontally, as shown in position 1.
In position 2 the angles of both planes are now at 10 degrees, and the speed 60 miles an hour, which still drives the machine forward horizontally.
In position 3 the angle is still less, being now only 5 degrees but the speed is increased to 80 miles per hour, but in each instance the body of the machine is horizontal.
Now it is obvious that in order to ascend, in either case, the changing of the planes to a greater angle would raise the machine, but at the same time keep the body on an even keel.
Fig. 14. Descent with Non-changing Body.
DESCENDING POSITIONS BY POWER CONTROL.—In Fig. 14 the planes are the same angles in the three positions respectively, as in Fig. 13, but now the power has been reduced, and the speeds are 30, 25, and 20 miles per hour, in positions A, B and C.
Suppose that in either position the power should cease, and the control broken, so that it would be impossible to move the planes. When the machine begins to lose its momentum it will descend on a curve shown, for instance, in Fig. 15, where position 1 of Fig. 14 is taken as the speed and angles of the plane when the power ceased.
Fig. 15. Utilizing Momentum.
CUTTING OFF THE POWER.—This curve, A, may reach that point where momentum has ceased as a forwardly-propelling factor, and the machine now begins to travel rearwardly. (Fig. 16.) It has still the entire supporting surfaces of the planes. It cannot loop-the-loop, as in the instance where the planes are fixed immovably to the body.
Carefully study the foregoing arrangement, and it will be seen that it is more nearly in accord with the true flying principle as given by nature than the vaunted theories and practices now indulged in and so persistently adhered to.
The body of a flying machine should not be oscillated like a lever. The support of the aeroplane should never be taken from it. While it may be impossible to prevent a machine from coming down, it can be prevented from overturning, and this can be done without in the least detracting from it structurally.
Fig. 16. Reversing Motion.
The plan suggested has one great fault, however. It will be impossible with such a structure to cause it to fly upside down. It does not present any means whereby dare-devil stunts can be performed to edify the grandstand. In this respect it is not in the same class with the present types.
THE STARTING MOVEMENT.—Examine this plan from the position of starting, and see the advantages it possesses. In these illustrations we have used, for convenience only, the monoplane type, and it is obvious that the same remarks apply to the bi-plane.
Fig. 17 shows the starting position of the stock monoplane, in position 1, while it is being initially run over the ground, preparatory to launching. Position 2 represents the negative angle at which the tail is thrown, which movement depresses the rear end of the frame and thus gives the supporting planes the proper angle to raise the machine, through a positive angle of incidence, of the plane.
Fig. 17. Showing changing angle of body.
THE SUGGESTED TYPE.—In Fig. 18 the suggested type is shown with the body normally in a horizontal position, and the planes in a neutral position, as represented in position 1. When sufficient speed had been attained both planes are turned to the same angle, as in position 2, and flight is initiated without the abnormal oscillating motion of the body.
But now let us see what takes place the moment the present type is launched. If, by any error on the part of the aviator, he should fail to readjust the tail to a neutral or to a proper angle of incidence, after leaving the ground, the machine would try to perform an over-head loop.
The suggested plan does not require this caution. The machine may rise too rapidly, or its planes may be at too great an angle for the power or the speed, or the planes may be at too small an angle, but in either case, neglect would not turn the machine to a dangerous position.
These suggestions are offered to the novice, because they go to the very foundation of a correct understanding of the principles involved in the building and in the manipulation of flying machines and while they are counter to the beliefs of aviators, as is shown by the persistency in adhering to the old methods, are believed to be mechanically correct, and worthy of consideration.
THE LOW CENTER OF GRAVITY.—But we have still to examine another feature which shows the wrong principle in the fixed planes. The question is often asked, why do the builders of aeroplanes place most of the weight up close to the planes? It must be obvious to the novice that the lower the weight the less liability of overturning.
FORE AND AFT OSCILLATIONS.—The answer is, that when the weight is placed below the planes it acts like a pendulum. When the machine is traveling forward, and the propeller ceases its motion, as it usually does instantaneously, the weight, being below, and having a certain momentum, continues to move on, and the plane surface meeting the resistance just the same, and having no means to push it forward, a greater angle of resistance is formed.
In Fig. 19 this action of the two forces is illustrated. The plane at the speed of 30 miles is at an angle of 15 degrees, the body B of the machine being horizontal, and the weight C suspended directly below the supporting surfaces.
The moment the power ceases the weight continues moving forwardly, and it swings the forward end of the frame upwardly, Fig. 20, and we now have, as in the second figure, a new angle of incidence, which is 30 degrees, instead of 12. It will be understood that in order to effect a change in the position of the machine, the forward end ascends, as shown by the dotted line A.
Fig. 20. Action when Propeller ceases to pull.
The weight a having now ascended as far as possible forward in its swing, and its motion checked by the banking action of the plan it will again swing back, and again carry with it the frame, thus setting up an oscillation, which is extremely dangerous.
The tail E, with its unchanged angle, does not, in any degree, aid in maintaining the frame on an even keel. Being nearly horizontal while in flight, if not at a negative angle, it actually assists the forward end of the frame to ascend.
APPLICATION OF THE NEW PRINCIPLE.—Extending the application of the suggested form, let us see wherein it will prevent this pendulous motion at the moment the power ceases to exert a forwardly- propelling force.
Fig. 21. Synchronously moving Planes.
In Fig. 21 the body A is shown to be equipped with the supporting plane B and the tail a, so they are adjustable simultaneously at the same angle, and the weight D is placed below, similar to the other structure.
At every moment during the forward movement of this type of structure, the rear end of the machine has a tendency to move upwardly, the same as the forward end, hence, when the weight seeks, in this case to go on, it acts on the rear plane, or tail, and causes that end to raise, and thus by mutual action, prevents any pendulous swing.
LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY-MOVING WINGS. —A little reflection will convince any one that if the two wings move in harmony, the weight does not have to be placed low, and thus still further aid in making a compact machine. By increasing the area of the tail, and making that a true supporting surface, instead of a mere idler, the weight can be moved further back, the distance transversely across the planes may be shortened, and in that way still further increase the lateral stability.
THERE are three distinct types of heavier-than- air machines, which are widely separated in all their characteristics, so that there is scarcely a single feature in common.
Two of them, the aeroplane, and the orthopter, have prototypes in nature, and are distinguished by their respective similarities to the soaring birds, and those with flapping wings.
The Helicopter, on the other hand, has no antecedent type, but is dependent for its raising powers on the pull of a propeller, or a plurality of them, constructed, as will be pointed out hereinafter.
AEROPLANES.—The only form which has met with any success is the aeroplane, which, in practice, is made in two distinct forms, one with a single set of supporting planes, in imitation of birds, and called a monoplane; and the other having two wings, one above the other, and called the bi-plane, or two-planes.
All machines now on the market which do not depend on wing oscillations come under those types.
THE MONOPLANE.—The single plane type has some strong claims for support. First of these is the comparatively small head resistance, due to the entire absence of vertical supporting posts, which latter are necessary with the biplane type. The bracing supports which hold the outer ends of the planes are composed of wires, which offer but little resistance, comparatively, in flight.
ITS ADVANTAGES.—Then the vertical height of the machine is much less than in the biplane. As a result the weight, which is farther below the supporting surface than in the biplane, aids in maintaining the lateral stability, particularly since the supporting frame is higher.
Usually, for the same wing spread, the monoplane is narrower, laterally, which is a further aid to prevent tilting.
ITS DISADVANTAGES.—But it also has disadvantages which must be apparent from its structure. As all the supporting surface is concentrated in half the number of planes, they must be made of greater width fore and aft, and this, as we shall see, later on, proves to be a disadvantage.
It is also doubted whether the monoplane can be made as strong structurally as the other form, owing to the lack of the truss formation which is the strong point with the superposed frame. A truss is a form of construction where braces can be used from one member to the next, so as to brace and stiffen the whole.
THE BIPLANE.—Nature does not furnish a type of creature which has superposed wings. In this particular the inventor surely did not follow nature. The reasons which led man to employ this type may be summarized as follows:
In experimenting with planes it is found that a broad fore and aft surface will not lift as much as a narrow plane. This subject is fully explained in the chapter on The Lifting Surfaces of Planes. In view of that the technical descriptions of the operation will not be touched upon at this place, except so far as it may be necessary to set forth the present subject.
This peculiarity is due to the accumulation of a mass of moving air at the rear end of the plane, which detracts from its lifting power. As it would be a point of structural weakness to make the wings narrow and very long, Wenham many years ago suggested the idea of placing one plane above the other, and later on Chanute, an engineer, used that form almost exclusively, in experimenting with his gliders.
It was due to his influence that the Wrights adopted that form in their gliding experiments, and later on constructed their successful flyers in that manner. Originally the monoplane was the type generally employed by experimenters, such as Lilienthal, and others.
STABILITY IN BIPLANES.—Biplanes are not naturally as stable laterally as the monoplane. The reason is, that a downward tilt has the benefit of only a narrow surface, comparable with the monoplane, which has broadness of wing.
To illustrate this, let us assume that we have a biplane with planes five feet from front to rear, and thirty-six feet in length. This would give two planes with a sustaining surface of 360 square feet. The monoplane would, probably, divide this area into one plane eight and a half feet from front to rear, and 42 feet in length.
In the monoplane each wing would project out about three feet more on each side, but it would have eight and a half feet fore and aft spread to the biplane's five feet, and thus act as a greater support.
THE ORTHOPTER.—The term orthopter, or ornithopter, meaning bird wing, is applied to such flying machines as depend on wing motion to support them in the air.
Unquestionably, a support can be obtained by beating on the air but to do so it is necessary to adopt the principle employed by nature to secure an upward propulsion. As pointed out elsewhere, it cannot be the concaved type of wing, or its shape, or relative size to the weight it must carry.
As nature has furnished such a variety of data on these points, all varying to such a remarkable degree, we must look elsewhere to find the secret. Only one other direction offers any opportunity, and that is in the individual wing movement.
NATURE'S TYPE NOT UNIFORM.—When this is examined, the same obscurity surrounds the issue. Even the speeds vary to such an extent that when it is tried to differentiate them, in comparison with form, shape, and construction, the experimenter finds himself wrapt in doubt and perplexity.
But birds do fly, notwithstanding this wonderful array of contradictory exhibitions. Observation has not enabled us to learn why these things are so. High authorities, and men who are expert aviators, tell us that the bird flies because it is able to pick out ascending air currents.
THEORIES ABOUT FLIGHT OF BIRDS.—Then we are offered the theory that the bird has an instinct which tells it just how to balance in the air when its wings are once set in motion. Frequently, what is taken for instinct, is something entirely different.
It has been assumed, for instance, that a cyclist making a turn at a rapid speed, and a bird flying around a circle will throw the upper part of the body inwardly to counteract the centrifugal force which tends to throw it outwardly.
Experiments with the monorail car, which is equipped with a gyroscope to hold it in a vertical position, show that when the car approaches a curve the car will lean inwardly, exactly the same as a bird, or a cyclist, and when a straight stretch is reached, it will again straighten up.
INSTINCT.—Now, either the car, so equipped possesses instinct, or there must be a principle in the laws of nature which produces the similarity of action.
In like manner there must be some principle that is entirely independent of the form of matter, or its arrangement, which enables the bird to perform its evolutions. We are led to believe from all the foregoing considerations that it is the manner or the form of the motion.
MODE OF MOTION.—In this respect it seems to be comparable in every respect to the great and universal law of the motions in the universe. Thus, light, heat and electricity are the same, the manifestations being unlike only because they have different modes of motion.
Everything in nature manifests itself by motion. It is the only way in which nature acts. Every transformation from one thing to another, is by way of a movement which is characteristic in itself.
Why, then, should this great mystery of nature, act unlike the other portions of which it is a part?
THE WING STRUCTURE.—The wing structure of every flying creature that man has examined, has one universal point of similarity, and that is the manner of its connection with the body. It is a sort of universal joint, which permits the wing to swing up and down, perform a gyratory movement while doing so, and folds to the rear when at rest.
Some have these movements in a greater or less degree, or capable of a greater range; but the joint is the same, with scarcely an exception. When the stroke of the wing is downwardly the rear margin is higher than the front edge, so that the downward beat not only raises the body upwardly, but also propels it forwardly.
THE WING MOVEMENT.—The moment the wing starts to swing upwardly the rear end is depressed, and now, as the bird is moving forwardly, the wing surface has a positive angle of incidence, and as the wing rises while the forward motion is taking place, there is no resistance which is effective enough to counteract the momentum which has been set up.
The great problem is to put this motion into a mechanical form. The trouble is not ascribable to the inability of the mechanic to describe this movement. It is an exceedingly simple one. The first difficulty is in the material that must be used. Lightness and strength for the wing itself are the first requirements. Then rigidity in the joint and in the main rib of the wing, are the next considerations.
In these respects the ability of man is limited. The wing ligatures of flying creatures is exceedingly strong, and flexible; the hollow bone formation and the feathers are extremely light, compared with their sustaining powers.
THE HELICOPTER MOTION.—The helicopter, or helix-wing, is a form of flying machine which depends on revolving screws to maintain it in the air. Many propellers are now made, six feet in length, which have a pull of from 400 to 500 pounds. If these are placed on vertically-disposed shafts they would exert a like power to raise a machine from the earth.
Obviously, it is difficult to equip such a machine with planes for sustaining it in flight, after it is once in the air, and unless such means are provided the propellers themselves must be the mechanism to propel it horizontally.
This means a change of direction of the shafts which support the propellers, and the construction is necessarily more complicated than if they were held within non-changeable bearings.
This principle, however, affords a safer means of navigating than the orthopter type, because the blades of such an instrument can be forced through the air with infinitely greater speed than beating wings, and it devolves on the inventor to devise some form of apparatus which will permit the change of pull from a vertical to a horizontal direction while in flight.
THIS subject includes the form, shape and angle of planes, used in flight. It is the direction in which most of the energy has been expended in developing machines, and the true form is still involved in doubt and uncertainty.
RELATIVE SPEED AND ANGLE.—The relative speed and angle, and the camber, or the curved formation of the plane, have been considered in all their aspects, so that the art in this respect has advanced with rapid strides.
NARROW PLATES MOST EFFECTIVE.—It was learned, in the early stages of the development by practical experiments, that a narrow plane, fore and aft, produces a greater lift than a wide one, so that, assuming the plane has 100 square feet of sustaining surface, it is far better to make the shape five feet by twenty than ten by ten.
However, it must be observed, that to use the narrow blade effectively, it must be projected through the air with the long margin forwardly. Its sustaining power per square foot of surface is much less if forced through the air lengthwise.
Experiments have shown why a narrow blade has proportionally a greater lift, and this may be more clearly understood by examining the illustrations which show the movement of planes through the air at appropriate angles.
Fig. 22. Stream lines along a plane.
STREAM LINES ALONG A PLANE.—In Fig. 22, A is a flat plane, which we will assume is 10 feet from the front to the rear margin. For convenience seven stream lines of air are shown, which contact with this inclined surface. The first line 1, after the contact at the forward end, is driven downwardly along the surface, so that it forms what we might term a moving film.
The second air stream 2, strikes the first stream, followed successively by the other streams, 3, 4, and so on, each succeeding stream being compelled to ride over, or along on the preceding mass of cushioned air, the last lines, near the lower end, being, therefore, at such angles, and contacting with such a rapidly-moving column, that it produces but little lift in comparison with the 1st, 2d and 3d stream lines. These stream lines are taken by imagining that the air approaches and contacts with the plane only along the lines indicated in the sketch, although they also in practice are active against every part of the plane.
THE CENTER OF PRESSURE.—In such a plane the center of pressure is near its upper end, probably near the line 3, so that the greater portion of the lift is exerted by that part of the plane above line 3.
AIR LINES ON THE UPPER SIDE OF THE PLANE.— Now, another factor must be considered, namely, the effect produced on the upper side of the plane, over which a rarefied area is formed at certain points, and, in practice, this also produces, or should be utilized to effect a lift.
RAREFIED AREA.—What is called a rarefied area, has reference to a state or condition of the atmosphere which has less than the normal pressure or quantity of air. Thus, the pressure at sea level, is about 14 3/4 per square inch
As we ascend the pressure grows less, and the air is thus rarer, or, there is less of it. This is a condition which is normally found in the atmosphere. Several things tend to make a rarefied condition. One is altitude, to which we have just referred.
Then heat will expand air, making it less dense, or lighter, so that it will move upwardly, to be replaced by a colder body of air. In aeronautics neither of these conditions is of any importance in considering the lifting power of aeroplane surfaces.
RAREFACTION PRODUCED BY MOTION.—The third rarefied condition is produced by motion, and generally the area is very limited when brought about by this means. If, for instance, a plane is held horizontally and allowed to fall toward the earth, it will be retarded by two forces, namely, compression and rarefaction, the former acting on the under side of the plane, and the latter on the upper side.
Of the two rarefaction is the most effectual, and produces a greater effect than compression. This may be proven by compressing air in a long pipe, and noting the difference in gauge pressure between the ends, and then using a suction pump on the same pipe.
When a plane is forced through the air at any angle, a rarefied area is formed on the side which is opposite the one having the positive angle of incidence.
If the plane can be so formed as to make a large and effective area it will add greatly to the value of the sustaining surface.
Unfortunately, the long fiat plane does not lend any aid in this particular, as the stream line flows down along the top, as shown in Fig. 23, without being of any service.
Fig. 23. Air lines on the upper side of a Plane.
THE CONCAVED PLANE.—These considerations led to the adoption of the concaved plane formation, and for purposes of comparison the diagram, Fig. 24, shows the plane B of the same length and angle as the straight planes.
In examining the successive stream lines it will be found that while the 1st, 2d and 3d lines have a little less angle of impact than the corresponding lines in the straight plane, the last lines, 5, 6 and 7, have much greater angles, so that only line 4 strikes the plane at the same angle.
Such a plane structure would, therefore, have its center of pressure somewhere between the lines 3 and 4, and the lift being thus, practically, uniform over the surface, would be more effective.
THE CENTER OF PRESSURE.—This is a term used to indicate the place on the plane where the air acts with the greatest force. It has reference to a point between the front and rear margins only of the plane.
Fig. 24. Air lines below a concaved Plane.
UTILIZING THE RAREFIED AREA.—This structure, however, has another important advantage, as it utilizes the rarefied area which is produced, and which may be understood by reference to Fig. 25.
The plane B, with its upward curve, and at the same angle as the straight plane, has its lower end so curved, with relation to the forward movement, that the air, in rushing past the upper end, cannot follow the curve rapidly enough to maintain the same density along C, hence this exerts
an upward pull, due to the rarefied area, which serves as a lifting force, as well as the compressed mass beneath the plane.
CHANGING CENTER OF PRESSURE.—The center of pressure is not constant. It changes with the angle of the plane, but the range is considerably less on a concave surface than on a flat plane.
Fig. 25. Air lines above a convex Plane.
In a plane disposed at a small angle, A, as in Fig. 26, the center of pressure is nearer the forward end of the plane than with a greater positive angle of incidence, as in Fig. 27, and when the plane is in a normal flying angle, it is at the center, or at a point midway between the margins.
PLANE MONSTROSITIES.—Growing out of the idea that the wing in nature must be faithfully copied, it is believed by many that a plane with a pronounced thickness at its forward margin is one of the secrets of bird flight.
Accordingly certain inventors have designed types of wings which are shown in Figs. 28 and 29.
Fig. 28 Changing centers of Pressures.
Fig 29. Bird-wing structures.
Both of these types have pronounced bulges, designed to "split" the air, forgetting, apparently, that in other parts of the machine every effort is made to prevent head resistance.
THE BIRD WING STRUCTURE.—The advocates of such construction maintain that the forward edge of the plane must forcibly drive the air column apart, because the bird wing is so made, and that while it may not appear exactly logical, still there is something about it which seems to do the work, and for that reason it is largely adopted.
WHY THE BIRD'S WING HAS A PRONOUNCED BULGE.—Let us examine this claim. The bone which supports the entire wing surface, called the (pectoral), has a heavy duty to perform. It is so constructed that it must withstand an extraordinary torsional strain, being located at the forward portion of the wing surface. Torsion has reference to a twisting motion.
In some cases, as in the bat, this primary bone has an attachment to the rear of the main joint, where the rear margin of the wing is attached to the leg of the animal, thus giving it a support and the main bone is, therefore, relieved of this torsional stress.
THE BAT'S WING.—An examination of the bat's wing shows that the pectoral bone is very small and thin, thus proving that when the entire wing support is thrown upon the primary bone it must be large enough to enable it to carry out its functions. It is certainly not so made because it is a necessary shape which best adapts it for flying.
If such were the case then nature erred in the case of the bat, and it made a mistake in the housefly's wing which has no such anterior enlargement to assist (?) it in flying.
AN ABNORMAL SHAPE.—Another illustration is shown in Fig. 30, which has a deep concave directly behind the forward margin, as at A, so that when the plane is at an angle of about 22 degrees, a horizontal line, as B, passing back from the nose, touches the incurved surface of the plane at a point about one-third of its measurement back across the plane.
Fig. 30. One of the Monstrosities
This form is an exact copy of the wing of an actual bird, but it belongs, not to the soaring, but to the class which depends on flapping wings, and as such it cannot be understood why it should be used for soaring machines, as all aeroplanes are.
The foregoing instances of construction are cited to show how wildly the imagination will roam when it follows wrong ideals.
THE TAIL AS A MONITOR.—The tendency of the center of pressure to change necessitates a correctional means, which is supplied in the tail of the machine, just as the tail of a kite serves to hold it at a correct angle with respect to the wind and the pull of the supporting string.
"PEQUOD, a Frenchman, yesterday repeatedly performed the remarkable feat of flying with the machine upside down. This exhibition shows that the age of perfection has arrived in flying machines, and that stability is an accomplished fact."—News item.
This is quoted to show how little the general public knows of the subject of aviation. It correctly represents the achievement of the aviator, and it probably voiced the sentiment of many scientific men, as well as of the great majority of aviators.
A few days afterwards, the same newspaper published the following:
"Lieutenant ——, while experimenting yesterday morning, met his death by the overturning of his machine at an altitude of 300 meters. Death was instantaneous, and the machine was completely destroyed."
The machines used by the two men were of the same manufacture, as Pequod used a stock machine which was strongly braced to support the inverted weight, but otherwise it was not unlike the well known type of monoplane.
Beachy has since repeated the experiment with a bi-plane, and it is a feat which has many imitators, and while those remarkable exhibitions are going on, one catastrophe follows the other with the same regularity as in the past.
Let us consider this phase of flying. Are they of any value, and wherein do they teach anything that may be utilized,
LACK OF IMPROVEMENTS IN MACHINES.—It is remarkable that not one single forward step has been taken to improve the type of flying machines for the past five years. They possess the same shape, their stabilizing qualities and mechanism for assuring stability are still the same.
MEN EXPEDITED, AND NOT THE MACHINE.—The fact is, that during this period the man has been exploited and not the machine. Men have learned, some few of them, to perform peculiar stunts, such as looping the loop, the side glide, the drop, and other features, which look, and are, hazardous, all of which pander to the sentiments of the spectators.
ABNORMAL FLYING OF NO VALUE.—It would be too broad an assertion to say that it has absolutely no value, because everything has its use in a certain sense, but if we are to judge from the progress of inventions in other directions, such exhibitions will not improve the art of building the device, or make a fool-proof machine.
Indeed, it is the very thing which serves as a deterrent, rather than an incentive. If machines can be handled in such a remarkable manner, they must be, indeed, perfect! Nothing more is needed! They must represent the highest structural type of mechanism!
That is the idea sought to be conveyed in the first paragraph quoted. It is pernicious, instead of praiseworthy, because it gives a false impression, and it is remarkable that even certain scientific journals have gravely discussed the perfected (?) type of flying machine as demonstrated by the experiments alluded to.
THE ART OF JUGGLING.—We may, occasionally, see a cyclist who understands the art of balancing so well that he can, with ease, ride a machine which has only a single wheel; or he can, with a stock bicycle, ride it in every conceivable attitude, and make it perform all sorts of feats.
It merely shows that man has become an expert at juggling with a machine, the same as he manipulates balls, and wheels, and other artifices, by his dexterity.
PRACTICAL USES THE BEST TEST.—The bicycle did not require such displays to bring it to perfection. It has been the history of every invention that improvements were brought about, not by abnormal experiments, but by practical uses and by normal developments.
The ability of an aviator to fly with the machine in an inverted position is no test of the machine's stability, nor does it in any manner prove that it is correctly built. It is simply and solely a juggling feat—something in the capacity of a certain man to perform, and attract attention because they are out of the ordinary.
CONCAVED AND COXVEX PLANES:—They were performed as exhibition features, and intended as such, and none of the exponents of that kind of flying have the effrontery to claim that they prove anything of value in the machine itself, except that it incidentally has destroyed the largely vaunted claim that concaved wings for supporting surfaces are necessary.
HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.— When flying "upside down," the convex side of the plane takes the pressure of the air, and maintains, so it is asserted, the weight of the machine. This is true during that period when the loop is being made. The evolution is made by first darting down, as shown in Fig. 31, from the horizontal position, 1, to the position 2, where the turn begins.
Fig. 31. Flying upside down.
TURNING MOVEMENT.—Now note the characteristic angles of the tail, which is the controlling factor. In position 1 the tail is practically horizontal. In fact, in all machines, at high flight, the tail is elevated so as to give little positive angle of incidence to the supporting planes.
In position No. 2, the tail is turned to an angle of incidence to make the downward plunge, and when the machine has assumed the vertical, as in position 3, the tail is again reversed to assume the angle, as in 1, when flying horizontally.
At the lower turn, position 4, the tail is turned similar to the angle of position 2, which throws the rear end of the machine down, and as the horizontal line of flight is resumed, in an inverted position, as in position 4, the tail has the same angle, with relation to the frame, as the supporting planes.
During this evolution the engine is running, and the downward plunge develops a tremendous speed, and the great momentum thus acquired, together with the pulling power of the propeller while thus in flight, is sufficient to propel it along horizontally, whatever the plane surface curve, or formation may be.
It is the momentum which sustains it in space, not the air pressure beneath the wings, for reasons which we have heretofore explained. Flights of sufficient duration have thus been made to prove that convex, as well as concave surfaces are efficient; nevertheless, in its proper place we have given an exposition of the reasoning which led to the adoption of the concaved supporting surfaces.
WHEN CONCAVED PLANES ARE DESIRABLE.— Unquestionably, for slow speeds the concaved wing is desirable, as will be explained, but for high speeds, surface formation has no value. That is shown by Pequod's feat.
THE SPEED MANIA.—This is a type of mania which pervades every field of activity in the building of aeroplanes. Speed contests are of more importance to the spectators on exhibition grounds than stability or durability. Builders pander to this, hence machines are built on lines which disregard every consideration of safety while at normal flight.
USES OF FLYING MACHINES.—The machine as now constructed is of little use commercially. Within certain limitations it is valuable for scouting purposes, and attempts have been made to use it commercially. But the unreliable character of its performances, due to the many elements which are necessary to its proper working, have operated against it.
PERFECTION IN MACHINES MUST COME BEFORE SPEED.—Contrary to every precept in the building of a new article, the attempt is made to make a machine with high speed, which, in the very nature of things, operates against its improvement. The opposite lack of speed—is of far greater utility at this stage of its development.
THE RANGE OF ITS USE.—The subject might be illustrated by assuming that we have a line running from A to Z, which indicates the range of speeds in aeroplanes. The limits of speeds are fairly stated as being within thirty and eighty- five miles per hour. Less than thirty miles are impossible with any type of plane, and while some have made higher speeds than eighty-five miles it may be safe to assume that such flights took place under conditions where the wind contributed to the movement.
Fig. 32. Chart showing Range of Uses
COMMERCIAL UTILITY.—Before machines can be used successfully they must be able to attain slower speeds. Alighting is the danger factor. Speed machines are dangerous, not in flight or at high speeds, but when attempting to land. A large plane surface is incompatible with speed, which is another illustration that at high velocities supporting surfaces are not necessary.
Commercial uses require safety as the first element, and reliability as the next essential. For passenger service there must be an assurance that it will not overturn, or that in landing danger is not ever-present. For the carrying of freight interrupted service will militate against it.
How few are the attempts to solve the problem of decreased speed, and what an eager, restless campaign is being waged to go faster and faster, and the addition of every mile above the record is hailed as another illustration of the perfection (?) of the flying machine.
To be able to navigate a machine at ten, or fifteen miles an hour, would scarcely be interesting enough to merit a paragraph; but such an accomplishment would be of far more value than all of Pequod's feats, and be more far-reaching in its effects than a flight of two hundred miles per hour.
KITES are of very ancient origin, and in China, Japan, and the Malayan Peninsula, they have been used for many years as toys, and for the purposes of exhibiting forms of men, animals, and particularly dragons, in their periodical displays.
THE DRAGON KITE.—The most noted of all are the dragon kites, many of them over a hundred feet in length, are adapted to sail along majestically, their sinuous or snake-like motions lending an idea of reality to their gorgeously-colored appearance in flight.
ITS CONSTRUCTION.—It is very curiously wrought, and as it must be extremely light, bamboo and rattan are almost wholly used, together with rice paper, in its construction.
Fig. 33 shows one form of the arrangement, in which the bamboo rib, A, in which only two sections are shown, as B, B, form the backbone, and these sections are secured together with pivot pins C. Each section has attached thereto a hoop, or circularly-formed rib, D, the rib passing through the section B, and these ribs are connected together loosely by cords E, which run from one to the other, as shown.
These circular ribs, D, are designed to carry a plurality of light paper disks, F, which are attached at intervals, and they are placed at such angles that they serve as small wing surfaces or aeroplanes to hold the structure in flight.
Fig. 33. Ribs of Dragon Kite
THE MALAY KITE.—The Malay kite, of which Fig. 34 shows the structure, is merely made up of two cross sticks, A, B, the vertical strip, A, being bent and rigid, whereas the cross stick, B, is light and yielding, so that when in flight it will bend, as shown, and as a result it has wonderful stability due to the dihedral angles of the two surfaces. This kite requires no tail to give it stability.
Fig. 34. The Malay Kite.
DIHEDRAL ANGLES.—This is a term to designate a form of disposing of the wings which has been found of great service in the single plane machines. A plane which is disposed at a rising angle, as A, A, Fig. 35, above the horizontal line, is called dihedral, or diedral.
Fig. 35. Dihedral Angle.
This arrangement in monoplanes does away with the necessity of warping the planes, or changing them while in flight. If, however, the angle is too great, the wind from either quarter is liable to raise the side that is exposed.
THE COMMON KITE.—While the Malay kite has only two points of cord attachment, both along the vertical rib, the common kite, as shown in Fig. 36, has a four-point connection, to which the flying cord is attached. Since this form has no dihedral angle, it is necessary to supply a tail, which thus serves to keep it in equilibrium, while in flight.
Fig. 36. Common Kite.
Various modifications have grown out of the Malay kite. One of these forms, designed by Eddy, is exactly like the Malay structure, but instead of having a light flexible cross piece, it is bent to resemble a bow, so that it is rigidly held in a bent position, instead of permitting the wind to give it the dihedral angle.
THE BOW KITE.—Among the different types are the bow kite, Fig. 37, and the sexagonal structure, Fig. 38, the latter form affording an especially large surface.
_Fig. 37. Bow Kite.-
Fig. 38. Hexagonal Kite.
THE BOX KITE.—The most marked improvement in the form of kites was made by Hargreaves, in 1885, and called the box kite. It has wonderful stability, and its use, with certain modifications, in Weather Bureau experiments, have proven its value.
It is made in the form of two boxes, A, B, open at the ends, which are secured together by means of longitudinal bars, C, that extends from one to the other, so that they are held apart a distance, approximately, equal to the length of one of the boxes.
Fig. 39. Hargreave Kite.
Their fore and aft stability is so perfect that the flying cord D is attached at one point only, and the sides of the boxes provide lateral stability to a marked degree.
THE VOISON BIPLANE.—This kind of kite furnished the suggestion for the Voison biplane, which was one of the earlier productions in flying machines.
Fig. 40 shows a perspective of the Voison plane, which has vertical planes A, A, at the ends, and also intermediate curtains B, B. This was found to be remarkably stable, but during its turning movements, or in high winds, was not satisfactory, and for that reason was finally abandoned.
LATERAL STABILITY IN KITES NOT CONCLUSIVE AS TO PLANES.—This is instanced to show that while such a form is admirably adapted for kite purposes, where vertical curtains are always in line with the wind movement, and the structure is held taut by a cord, the lateral effect, when used on a machine which does not at all times move in line with the moving air current. A condition is thus set up which destroys the usefulness of the box kite formation.
Fig. 40. Voison Biplane.
THE SPEAR KITE.—This is a novel kite, with remarkable steadiness and is usually made with the wings on the rear end larger than those on the forward end (Fig. 41), as thereby the cord A can be attached to the spear midway between the two sets of wings.
Fig. 41. Spear Kite.
THE CELLULAR KITE.—Following out the suggestion of the Hargreaves kite, numerous forms embodying the principle of the box structure were made and put on the market before the aeroplane became a reality.
Fig. 42. Cellular Kite.
A structure of this form is illustrated in Fig. 42. Each box, as A, B, has therein a plurality of vertical and horizontal partitions, so that a number of cells are provided, the two cell-like boxes being held apart by a bar C, axially arranged.
This type is remarkably stable, due to the small cells, and kites of this kind are largely used for making scientific experiments.
THE TETRAHEDRAL KITE.—Prof. Bell, inventor of the telephone, gave a great deal of study to kites, which resulted in the tetrahedral formation, as shown in Fig. 43.
Fig. 43. Tetrahedral Kite.
The structure, apparently, is somewhat complicated, but an examination of a single pair of blades, as shown at A, shows that it is built up of triangularly-formed pieces, and that the openings between the pieces are equal to the latter, thereby providing a form of kite which possesses equilibrium to a great degree.
It has never been tried with power, and it is doubtful whether it would be successful as a sustaining surface for flying machines, for the same reasons that caused failure with the box-like formation of the Voison Machine.
THE DELTOID.—The deltoid is the simplest, and the most easily constructed of all the kites. It is usually made from stiff cardboard, A-shaped in outline, as shown in Figs. 44 and 45, and bent along a central line, as at A, forming two wings, each of which is a right-angled triangle.
Fig. 44. and 45. Deltoid Formation.
The peculiarity of this formation is, that it has remarkable stability when used as a kite, with either end foremost. If a small weight is placed at the pointed end, and it is projected through the air, it will fly straight, and is but little affected by cross currents.
THE DUNNE FLYING MACHINE.—A top view of this biplane is shown in Fig. 46. The A-shaped disposition of the planes, gives it good lateral stability, but it has the disadvantage under which all aeroplanes labor, that the entire body of the machine must move on a fore and aft vertical plan in order to ascend or descend.
Fig. 46. The Dunne Bi-plane.
This is a true deltoid formation, as the angle of incidence of the planes is so disposed that when the planes are horizontal from end to end, the inclination is such as to make it similar to the deltoid kite referred to.
ROTATING KITE.—A type of kite unlike the others illustrated is a rotating structure, which gives great stability, due to the gyroscopic action on the supporting surfaces.
Fig. 47 shows a side view with the top in section. The supporting surface is umbrella-shaped. In fact, the ordinary umbrella will answer if not dished too much. An angularly-bent piece of wire A, provided with loops B, B, at the ends, serve as bearings for the handle of the umbrella.
At the bend of the wire loop C, the cord D is attached. The lower side of the umbrella top has cup-shaped pockets E, near the margin, so arranged that their open ends project in the same direction, and the wind catching them rotates the circular plane.
Fig. 47. Rotable Umbrella Kite.
KITE PRINCIPLES.—A careful study of the examples here given, will impress the novice with one important fact, which, in its effect has a more important bearing on successful flight, than all the bird study and speculations concerning its mysteries.
This fact, in essence, is, that the angle of the kite is the great factor in flight next to the power necessary to hold it. Aside from this, the comparison between kites and aeroplanes is of no practical value.
Disregarding the element of momentum, the drift of a machine against a wind, is the same, dynamically, as a plane at rest with the wind moving past it. But there is this pronounced difference: The cord which supports the kite holds it so that the power is in one direction only.
When a side gust of wind strikes the kite it is moved laterally, in sympathy with the kite, hence the problem of lateral displacement is not the same as with the aeroplane.
LATERAL STABILITY IN KITES.—In the latter the power is definitely fixed with relation to the machine itself, and if we should assume that a plane with a power on it sufficient to maintain a flight of 40 miles an hour, should meet a wind moving at the same speed, the machine would be stationary in space.
Such a condition would be the same, so far as the angles of the planes are concerned, with a kite held by a string, but there all similarity in action ends.
The stabilizing quality of the kite may be perfect, as the wind varies from side to side, but the aeroplane, being free, moves to the right or to the left, and does not adjust itself by means of a fixed point, but by a movable one.
SIMILARITY OF FORE AND AFT CONTROL.—Fore and aft, however, the kite and aeroplane act the same. Fig. 48 shows a diagram which illustrates the forces which act on the kite, and by means of which it adjusts its angle automatically.
Let us assume that the kite A is flown from a cord B, so that its angle is 22 1/2 degrees, the wind being 15 miles per hour to maintain the cord B at that angle. When the wind increases to 20 miles an hour there is a correspondingly greater lift against the kite.
Fig. 48. Action of Wind forces on Kite.
As its angle is fixed by means of the loop C, it cannot change its angle with reference to the cord, or independently of it, and its only course is to move up higher and assume the position shown by the figure at D, and the angle of incidence of the kite is therefore changed to 15 degrees, or even to 10 degrees.
In the case of the aeroplane the effect is similar from the standpoint of power and disposition of the planes. If it has sufficient power, and the angle of the planes is not changed, it will ascend; if the planes are changed to 15 degrees to correspond with the kite angle it will remain stationary.
GLIDING FLIGHT.—The earliest attempt to fly by gliding is attributed to Oliver, a Monk of Malmesbury who, in 1065 prepared artificial wings, and with them jumped from a tower, being injured in the experiment.
Nearly 700 years later, in 1801, Resnier, aFrenchman, conducted experiments with varyingresults, followed by Berblinger, in 1842, andLeBris, a French sailor, in 1856.
In 1884, J. J. Montgomery, of California, designed a successful glider, and in 1889 Otto and Gustav Lilienthal made the most extended tests, in Germany, and became experts in handling gliders.
Pilcher, in England, was the next to take up the subject, and in 1893 made many successful glides, all of the foregoing machines being single plane surfaces, similar to the monoplane.
Long prior to 1896 Octave Chanute, an engineer, gave the subject much study, and in that year made many remarkable flights, developing the double plane, now known as the biplane.
He was an ardent believer in the ability of man to fly by soaring means, and without using power for the purpose.
It is doubtful whether gliders contributed much to the art in the direction of laterally stabilizing aeroplanes. They taught useful lessons with respect to area and fore and aft control.
The kite gave the first impulse to seek out a means for giving equilibrium to planes, and Montgomery made a kite with warping wings as early as 1884.
Penaud, a Frenchman, in 1872, made a model aeroplane which had the stabilizing means in the tail. All these grew out of kite experiments; and all gliders followed the kite construction, or the principles involved in them, so that, really, there is but one intervening step between the kite and the flying machine, as we know it, the latter being merely kites with power attached, as substitutes for the cords.
ONE OF THE USES OF GLIDER EXPERIMENTS.— There is one direction in which gliders are valuable to the boy and to the novice who are interested in aviation. He may spend a lifetime in gliding and not advance in the art. It is questionable whether in a scientific way it will be of any service to him; but experiments of this character give confidence, the ability to quickly grasp a situation, and it will thus teach self reliance in emergencies.
When in a glider quick thinking is necessary. The ability to shift from one position to another; to apply the weight where required instantaneously; to be able during the brief exciting moment of flight to know just what to do, requires alertness.
Some are so wedded to the earth that slight elevation disturbs them. The sensation in a glider while in flight is unlike any other experience. It is like riding a lot of tense springs, and the exhilaration in gliding down the side of a hill, with the feet free and body suspended, is quite different from riding in an aeroplane with power attached.
HINTS IN GLIDING.—It seems to be a difficult matter to give any advice in the art of gliding. It is a feat which seems to necessitate experiment from first to last. During the hundreds of tests personally made, and after witnessing thousands of attempts, there seems to be only a few suggestions or possible directions in which caution might be offered.
First, in respect to the position of the body at the moment of launching. The glider is usually so made that in carrying it, preparatory to making the run and the leap required to glide, it is held so that it balances in the hands.
Now the center of air pressure in gliding may not be at the same point as its sustaining weight when held by the hand, and furthermore, as the arm-pits, by which the body of the experimenter are held while gliding, are not at the same point, but to the rear of the hands, the moment the glider is launched too great a weight is brought to the rear margin of the planes, hence its forward end lifts up.
This condition will soon manifest itself, and be corrected by the experimenter; but there is another difficulty which is not so easy to discover and so quick to remedy, and that is the swing of the legs the moment the operator leaves the ground.
The experimenter learns, after many attempts, that gliding is a matter of a few feet only, and he anticipates landing too soon, and the moment he leaps from the ground the legs are swung forwardly ready to alight.
This is done unconsciously, just as a jumper swings his legs forwardly in the act of alighting. Such a motion naturally disturbs the fore and aft stability of the gliding machine, by tilting up the forward margin, and it banks against the air, instead of gliding.
The constant fear of all gliders is, that the machine will point downwardly, and his motion, as well as the position of the body, tend to shoot it upwardly, instead.
As may be inferred from the foregoing statements, there are no definite rules for the construction of either type of flying machine, as the flying models vary to such an extent that it is difficult to take either of them as a model to represent the preferred type of construction.
LATERAL, AND FORE AND AFT.—The term lateral should be understood, as applied to aeroplanes. It is always used to designate the direction at right angles to the movement of the machine. Fore and aft is a marine term meaning lengthwise, or from front to rear, hence is always at right angles to the lateral direction.
The term transverse is equivalent to lateral, in flying machine parlance, but there is this distinction: Transverse has reference to a machine or object which, like the main planes of an aeroplane, are broader, (that is,—from end to end) than their length, (from front to rear).
On the other hand, lateral has reference to side branches, as, for instance, the monoplane wings, which branch out from the sides of the fore and aft body.
STABILITY AND STABILIZATION.—These terms constantly appear in describing machines and their operations. If the flying structure, whatever it may be, has means whereby it is kept from rocking from side to side, it has stability, which is usually designated as lateral stability. The mechanism for doing this is called a stabilizer.
THE WRIGHT SYSTEM.—The Wright machine has reference solely to the matter of laterally controlling the flying structure, and does not pertain to the form or shape of the planes.
In Fig. 49 A designates the upper and lower planes of a Wright machine, with the peculiar rounded ends. The ends of the planes are so arranged that the rear margins may be raised or lowered, independently of the other portions of the planes, which are rigid. This movement is indicated in sketch 1, where the movable part B is, as we might say, hinged along the line C.
The dotted line D on the right hand end, shows how the section is depressed, while the dotted lines E at the left hand end shows the section raised. It is obvious that the downturned ends, as at D, will give a positive angle at one end of the planes, and the upturned wings E at the other end will give a negative angle, and thus cause the right hand end to raise, and the other end to move downwardly, as the machine moves forwardly through the air.
CONTROLLING THE WARPING ENDS.—Originally the Wrights controlled these warping sections by means of a cradle occupied by the aviator, so that the cradle would move or rock, dependent on the tilt of the machine. This was what was termed automatic control. This was found to be unsatisfactory, and the control has now been placed so that it connects with a lever and is operated by the aviator, and is called Manually-operated control.
In all forms of control the wings on one side are depressed on one side and correspondingly elevated on the other.
THE CURTIS WINGS.—Curtis has small wings, or ailerons, intermediate the supporting surfaces, and at their extremities, as shown in sketch 2. These are controlled by a shoulder rack or swinging frame operated by the driver, so that the body in swinging laterally will change the two wings at the same time, but with angles in different directions.
THE FARMAN AILERONS.—Farman's disposition is somewhat different, as shown in sketch 3. The wings are hinged to the upper planes at their rear edges, and near the extremities of the planes. Operating wires lead to a lever within reach of the aviator, and, by this means, the wings are held at any desired angle, or changed at will.
The difficulty of using any particular model, is true, also, of the arrangement of the fore and aft control, as well as the means for laterally stabilizing it. In view of this we shall submit a general form, which may be departed from at will.
FEATURES WELL DEVELOPED.—Certain features are fairly well developed, however. One is the angle of the supporting plane, with reference to the frame itself; and the other is the height at which the tail and rudder should be placed above the surface of the ground when the machine is at rest.
DEPRESSING THE REAR END.—This latter is a matter which must be taken into consideration, because in initiating flight the rear end of the frame is depressed in order to give a sufficient angle to the supporting planes so as to be able to inaugurate flight.
In order to commence building we should have some definite idea with respect to the power, as this will, in a measure, determine the area of the supporting surfaces, as a whole, and from this the sizes of the different planes may be determined.
DETERMINING THE SIZE.—Suppose we decide on 300 square feet of sustaining surface. This may require a 30, a 40 or a 50 horse power motor, dependent on the speed required, and much higher power has been used on that area.
However, let us assume that a forty horse power motor is available, our 300 square feet of surface may be put into two planes, each having 150 square feet of surface, which would make each 5' by 30' in size; or, it may be decided to make the planes narrower, and proportionally longer. This is immaterial. The shorter the planes transversely, the greater will be the stability, and the wider the planes the less will be the lift, comparatively.
RULE FOR PLACING THE PLANES.—The rule for placing the planes is to place them apart a distance equal to the width of the planes themselves, so that if we decide on making them five feet wide, they should be placed at least five feet apart. This rule, while it is an admirable one for slow movements or when starting flight, is not of any advantage while in rapid flight.
If the machine is made with front and rear horizontally-disposed rudders, or elevators, they also serve as sustaining surfaces, which, for the present will be disregarded.
Lay off a square A, Fig. 49a, in which the vertical lines B, B, and the horizontal lines C, C, are 5' long, and draw a cross D within this, the lines running diagonally from the corners.
Now step off from the center cross line D, three spaces, each five feet long, to a point E, and join this point by means of upper and lower bars F, G, with the upper and lower planes, so as to form the tail frame.
Fig. 49a. Rule for spacing Planes.
As shown in Fig. 50, the planes should now be indicated, and placed at an angle of about 8 degrees angle, which are illustrated, H being the upper and I the lower plane. Midway between the forward edges of the two planes, is a horizontal line J, extending forwardly, and by stepping off the width of two planes, a point K is made, which forms the apex of a frame L, the rear ends of the bars being attached to the respective planes H, I, at their forward edges.
Fig. 50. Frame of Control Planes.