GERMAN DIRIGIBLESEarly Zeppelin Airships.At the same time that Santos-Dumont was carrying on his hazardous experiments, the problem was being attacked along slightly different lines by Count Zeppelin.It will be remembered that Dumont experienced much trouble on account of the envelope of his balloon being too flexible, causing it to crumple in the middle and to become distorted in shape from the pressure of the air. His efforts to overcome this by the employment of air bags did not meet with great success, even in his later types.Fig. 15. Zeppelin Dirigible Rising from Lake ConstanceFig. 15. Zeppelin Dirigible Rising from Lake ConstanceConstruction.Zeppelin employed a very rigid construction. His first balloon, which was built in 1898, was the largest which had ever been made. It is illustrated in Fig. 15, which shows his first design slightly improved. It was about 40 feet in diameter and 420 feet long—an air craft as large as many an ocean vessel. The envelope consisted of two distinct bags, an outer and an inner one, with an air space between. The air space between the inner and outer envelopes acted as a heat insulator and prevented the gas within from being affected by rapid changes of temperature. The inner bag contained the gas, and the outer one served as a protective covering. In the construction of this outer bag lies the novelty of Zeppelin’s design. A rigid framework of strongly braced aluminum rings was provided and this was covered with linen and silk which had been specially treated to prevent leakage of gas. The inner envelope consisted of seventeen gas-tight compartments which could be filled or emptied separately. In the event of the puncture of one of them, the balloon would remain afloat. An aluminum keel was provided to further increase the rigidity. A sliding weight could be moved backward or forward along the keel and cause the nose of the airship to point upward or downward as desired. This would make the craft move upward or downward without throwing out ballast or losing gas. Lender each end of the balloon a light aluminum car was rigidly fastened and in each was a 16-horsepower Daimler gasoline engine. The two engines could be worked either independently of each other or together. Each engine drove a vertical and horizontal propeller. The propellers each had four aluminum blades. As will be seen from Fig. 15, the ears were too far apart for ordinary means of communication and so speaking tubes, electric bells, and an electric telegraph system were installed.First Trials.Very little was known as to the effects of alighting on the ground with such a rigid affair as this vessel, therefore the cars were made like boats so that the airship could alight and float on the water. The first trials were made over Lake Constance in July, 1900. The mammoth craft was housed in a huge floating shed, and the vessel emerged from it with the gas bag floating above and the two cars touching the water. She rose easily from the water, and then began a series of mishaps such as usually fall to the lot of experimenters. The upper cross stay proved too weak for the long body of the balloon and bent upward about 10 inches during the flight. This prevented the propeller shafts from working properly. Then the winch which worked the sliding weight was broken and, finally, the steering ropes to the rudders became entangled. In spite of all this, a speed of 13 feet per second, or about 9 miles per hour, was obtained. These breakages made it necessary to descend to the lake for repairs and in alighting the framework was further damaged by running into a pile in the lake. The airship was repaired and another flight was made later in the year, during which a speed of 30 feet per second, or 20 miles per hour, was obtained.Second Airship.Zeppelin had sunk his own private fortune and that of his supporters in his first venture, and it was not till five years later that he succeeded in raising enough money to construct a second airship. No radical changes in construction were made in the new model, but there were slight improvements made in all its details. The balloon was about 8 feet shorter than the original and the propellers were enlarged. Three vertical rudders were placed in front and three behind the balloon, and below the end of the craft horizontal rudders were installed to assist in steering upward or downward. The steering was taken care of from the front car.The most important change was made possible by the improvement in gasoline engines during the preceding five years. Where, in the earlier model, he had two 16-horsepower engines, he now used an 85-horsepower engine in each car, with practically the same weight. In fact, the total weight of the vessel was only 9 tons, while his first airship weighed 10 tons.His new craft made many successful flights. One was made at the rate of 38 miles per hour and continued for seven hours, covering a total distance of 266 miles.Later Zeppelins.The later Zeppelins embody no remarkable changes in design, the principal alteration being in size. One of these is illustrated in Fig. 16. In this the gas bag was increased to 446 feet in length and it held over 460,000 cubic feet of gas. This gave it a total lifting power of 16 tons. With this, Zeppelin made a voyage of over 375 miles. He was in the air for twenty hours on this trip and carried eleven passengers with him.Fig. 16. Zeppelin Airship in FlightFig. 16. Zeppelin Airship in FlightIn August, 1908, the Zeppelin left its great iron house at Friedrichshafen and sailed in a great circle over Lake Constance. The day after it started, however, it was destroyed by a storm, and sudden destruction from one cause or another has ended the existence of practically every one of the Zeppelins built since, usually after a very brief period of service.Shape and Framing.In the early days of dirigible design the data upon which the shape and proportions of the envelope were based were purely empirical. Schwartz, Germany’s pioneer in this field, adopted the projectile as representing the form offering the least air resistance and accordingly designed his envelope with a sharply pointed bow and a rounded-off stern, giving it a length four times its diameter. Zeppelin did not agree with these conclusions and adopted a pencil form, rounded at the nose and tapering to a sharp point at the stern, making the length nine to ten times the diameter. Subsequent research work in the aerodynamic laboratory has demonstrated that the most efficient form for air penetration is one having a length six times its maximum diameter with the latter situated at a point four-tenths of the total length from the bow. It has likewise been proved that an ellipse is more efficient than either the projectile or pencil form and that tapering to a sharp point at the stern offers no particular advantage. As a result, the most approved form resembles the shape of a perfecto cigar, the nose being somewhat blunter than the after end. This form is likewise that of the swiftest-swimming fishes and has been shown to have the least head resistance as well as the minimum skin friction; it results in a section to which the termstream-linehas been applied, and it is now employed on all exposed non-supporting surfaces on aeroplanes, such as the struts and even the bracing cables. Laboratory research has demonstrated that it is worth while to reduce the head resistance of even such apparently negligible surfaces as those presented by these wires and cables and, therefore, they are stream-lined by attaching recessed triangular strips of wood to their forward sides.Framing Details.Despite this, the builders of the Zeppelins have adhered to the original pencil shape with but slight modifications at the bow and stern, probably because that shape is much easier to build and assemble from standard girders. The form of girder employed is shown in Fig. 17, while the complete assembly of the frame is illustrated in Fig. 18. The girders form the longerons, or longitudinal beams, running the entire length of the rigid frame and supported at equidistant points by ring members built of similar girder sections. The fourth ring from the nose and each alternate ring after that are further braced by being trussed to the longitudinal beams around their entire circumferences, as shown in Fig. 18. The larger V-shaped truss at the bottom forms the gangway, which is now placed inside the envelope instead of being suspended beneath it, as formerly. This is done to eliminate the head resistance set up by the additional surface thus exposed. In the first instance in which this gangway was incorporated in the envelope, no provision was made for ventilation, and the ship was wrecked by a gas explosion. Regardless of how tight the fabric is made, gas is always oozing out through it to a greater or less extent. This fact is now met by providing ventilating shafts leading from the gangway to the upper surface of the envelope. Additional shafts through the envelope lead to gun platforms, forward, amidships, and aft, and are reached by aluminum ladders.Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 18. Aluminum Frame Construction of Zeppelin HullFig. 18. Aluminum Frame Construction of Zeppelin HullFraming of Schutte-Lanz Type.It has become customary to refer to all large German airships as Zeppelins, but many of those used during the past three years have been of the Schutte-Lanz build, which is also a rigid frame type of dirigible but has been designed with a view of overcoming some of the disadvantages of the aluminum frame construction encountered in the use of the Zeppelin. The length and diameter of the latter airships are such that, no matter how rigidly the framing is assembled, there is more or less sag. When the sag exceeds a certain amount, the frame is apt to buckle at the point where it occurs, involving expensive repairs or wrecking the airship altogether. To overcome this difficulty, the Schutte-Lanz type employs a rigid frame of flexible material, namely, laminated wood in strip form, held together at joints and crossings by aluminum fittings and braced inside by cables. As shown by Fig. 19, no rigid longitudinal beams are employed, the only girders used being rings, to which a network built of the wood strips is attached. Starting at the nose, each continuous strip follows an open spiral path such as would be traced in the air by a screw of very large pitch, in fact, approximating the rifling of a gun barrel. It will also be noted from the illustration that the form of the Schutte-Lanz airship is the cigar-shape, which laboratory research has shown to be the most efficient.Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsFig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsThe use of wood in conjunction with the spiral construction of the supporting members of the framing affords the maximum degree of flexibility, since the displacement of any of these members under stresses of either tension or compression would have to be very great to cause damage to the frame as a whole. The frame not being rigid, strictly speaking, either as units or as a complete assembly, stress at any particular point would simply cause all the members near that point to give in the direction of the strain, and the rest of the frame would accommodate itself to their change of position by either elongating or shortening slightly. In addition to these advantages, the Schutte-Lanz type of construction is said to be lighter than the Zeppelin for an airship of the same load-carrying capacity.Power Plant.Compared with their successors of war times, the early Zeppelins were mere pigmies where power is concerned. Many of these pioneers were driven by less than 100 horsepower all told, whereas in the later types no single motor unit as small as this total has been employed. The motors used most largely have been the 160-horsepower Mercedes and the 200-horsepower Maybach, both of which are described in detail under the title "Aviation Motors." From five to ten of these units have been used on a single ship, giving an aggregate in some of the latest types of close to 2,000 horsepower. Power has been applied through five or six propellers to limit their diameter and to guard against the breakdown of any one of the units putting the power plant out of commission as a whole. To distribute the weight of the engines equally and to insure each propeller a position in which it can work in undisturbed air, the engines have been placed at widely separated points on the airship and in different planes so that no two are coaxial. The main engine room is usually located in a cabin just back of the operating bridge and wireless room, while the remaining motors are suspended in independent gondolas at different points along the sides. Where more than 1,000 horsepower has been used, each of these gondolas' has been fitted with two motors placed side by side and so coupled that either one or both may be employed to drive the single propeller carried by the propelling car. All the more recent propellers have been of the two-bladed type.Control Surfaces.The numerous expedients formerly resorted to by various designers in providing for stabilizing, steering, and elevating surfaces have been abandoned for forms that are practically a duplication of aeroplane practice. Experience demonstrated that the different types of multiplane rudders, elevators, and stabilizing surfaces employed in earlier days not only offered no operating advantages but were actually detrimental, in that they increased the head resistance unnecessarily. Moreover, their complication meant increased weight and weaker construction. They have accordingly been displaced by monoplane surfaces which are of exactly the same type of construction as those used on the aeroplane and the location and proportions of which are very evidently based on aeroplane practice. Both the horizontal and vertical stabilizers are of approximately triangular form and have the steering and elevating surfaces hinged to them at their after ends, so that, except for the pointed extremity of the envelope which extends beyond them, the tail unit of the later Zeppelins is practically the same as the empennage of an aeroplane. The horizontal surfaces are apparently depended on entirely to effect the ascent and descent, there being no evidence of swiveling propellers by means of which the power of the engines could be employed to draw the airship up or down. The great weight of ballast carried is, of course, in the form of water, but this is discarded in order to ascend only when the power of the engines exerted against the elevating planes is no longer capable of keeping the airship at the altitude desired. In the low temperatures encountered in night flights, however, the contraction of the hydrogen gas is so great that the crew has found it necessary to reduce the weight by discarding not only every pound of ballast but, as far as possible, everything portable. Despite this, several airships have fallen when their fuel supply was exhausted, one coming to the ground in Scotland, two dropping into the North Sea, and three or four falling in France.Operating Controls.All the operating controls are centered at the navigating bridge, which is inclosed to form the commander’s cabin. By means of push buttons, switches, levers, and wheels every operating function required is set into motion from this central point. Whether auxiliary motors are carried for the purpose of pumping air into the balloonets or this is one of the duties of the main engine just back of the wireless room does not appear, but with the aid of a push button board the amount of air in any of the balloonets may be increased or decreased at will. There is a control button for each operation, or two for each balloonet, which fact necessitates a rather forbidding looking board, since the more recent Zeppelins have seventeen to nineteen gas bags within each of which is incorporated an air balloonet.The amount of fuel supplied to any one of the motor units can likewise be controlled from a central board, and this is also true of the ballast release apparatus, so that water can be emptied from any one of the ballast tanks at will, thus facilitating ascent or descent by lightening one end or the other. Elevating and steering surfaces are operated by small hand-steering wheels with cables passing around their drums, a member of the crew being stationed at each of these controlling wheels. Owing to the number of motors used, the instrument board is the most formidable appearing piece of apparatus on the bridge, since there is a revolution counter for each power unit in addition to the numerous other instruments required. Some of these instruments are the aneroid barometer for indicating the altitude, transverse and longitudinal clinometers to show the amount of heel and the angle at which the airship is traveling with relation to the horizontal, the anemometer, or air-speed indicator, manometers, or pressure gauges, for each one of the gas bags, fuel and ballast supply gauges, drift indicators, electric bomb releasers, mileage recorders, and the like. In addition to these, there are a large chart and a compass, so the navigating bridge of a Zeppelin combines in small space all the instruments to be found in the engine room and on the bridge of an ocean liner besides several which the latter does not require. That the proper coordination of all the functions mentioned is an exceedingly difficult task for one man seems evident from the numerous Zeppelins that have apparently wrecked themselves.Crew Carried.In the various Zeppelins that have been captured or shot down by the British or French, the personnel has varied from fifteen to thirty men but in the majority of instances has not exceeded twenty. The positions and duties are about as follows: The commander, lieutenant-commander, and chief engineer, and possibly a navigating officer are stationed at the bridge. Two or three of the crew are also stationed there to work the manually operated controls. In the cabin just back of the bridge are two wireless operators and one or two engine attendants for the motors in the engine room behind the wireless room. A similar number of engine attendants are stationed in the after engine room and there is at least one attendant for each of the other motor units. One man is stationed at each machine gun, of which there are three to five on the "roof" and two in each car, and at least as many bombers are needed to load the "droppers." As a reserve there are usually an additional gun pointer for each gun and an extra engine attendant, since to run continuously most of the crew would have to stand watch and watch as in marine practice. The sleeping accommodations consist of canvas hammocks slung in the gangway.Explosives Carried.In addition to a liberal supply of ammunition for the machine guns, a large weight of bombs is carried, though the quantity as well as the size of the bombs themselves has been exaggerated in the same or even greater ratio than that which has proved characteristic of the German military press-agency service. The bombs are carried suspended in racks amidships, and the bomb droppers are also located at that part of the ship so that the release of the bombs will not upset the longitudinal equilibrium of the craft. The bomb-dropping apparatus is controlled electrically from the navigating bridge but may also be operated by hand from the same point. It has been reported by the Germans that their latest types of Zeppelins are capable of dropping bombs weighing 1 ton each. In view of the effect that the sudden release of a weight of 1 ton would have on the airship itself, this is manifestly very much of an exaggeration. Zeppelin bombs that have failed to explode have never exceeded 200 to 300 pounds and many of those employed are doubtless still lighter. So far as the total amount carried is concerned, many of the later airships doubtless are capable of transporting 2 to 3 tons and still carrying sufficient fuel, though adverse conditions would prevent their return, as has frequently happened.
GERMAN DIRIGIBLESEarly Zeppelin Airships.At the same time that Santos-Dumont was carrying on his hazardous experiments, the problem was being attacked along slightly different lines by Count Zeppelin.It will be remembered that Dumont experienced much trouble on account of the envelope of his balloon being too flexible, causing it to crumple in the middle and to become distorted in shape from the pressure of the air. His efforts to overcome this by the employment of air bags did not meet with great success, even in his later types.Fig. 15. Zeppelin Dirigible Rising from Lake ConstanceFig. 15. Zeppelin Dirigible Rising from Lake ConstanceConstruction.Zeppelin employed a very rigid construction. His first balloon, which was built in 1898, was the largest which had ever been made. It is illustrated in Fig. 15, which shows his first design slightly improved. It was about 40 feet in diameter and 420 feet long—an air craft as large as many an ocean vessel. The envelope consisted of two distinct bags, an outer and an inner one, with an air space between. The air space between the inner and outer envelopes acted as a heat insulator and prevented the gas within from being affected by rapid changes of temperature. The inner bag contained the gas, and the outer one served as a protective covering. In the construction of this outer bag lies the novelty of Zeppelin’s design. A rigid framework of strongly braced aluminum rings was provided and this was covered with linen and silk which had been specially treated to prevent leakage of gas. The inner envelope consisted of seventeen gas-tight compartments which could be filled or emptied separately. In the event of the puncture of one of them, the balloon would remain afloat. An aluminum keel was provided to further increase the rigidity. A sliding weight could be moved backward or forward along the keel and cause the nose of the airship to point upward or downward as desired. This would make the craft move upward or downward without throwing out ballast or losing gas. Lender each end of the balloon a light aluminum car was rigidly fastened and in each was a 16-horsepower Daimler gasoline engine. The two engines could be worked either independently of each other or together. Each engine drove a vertical and horizontal propeller. The propellers each had four aluminum blades. As will be seen from Fig. 15, the ears were too far apart for ordinary means of communication and so speaking tubes, electric bells, and an electric telegraph system were installed.First Trials.Very little was known as to the effects of alighting on the ground with such a rigid affair as this vessel, therefore the cars were made like boats so that the airship could alight and float on the water. The first trials were made over Lake Constance in July, 1900. The mammoth craft was housed in a huge floating shed, and the vessel emerged from it with the gas bag floating above and the two cars touching the water. She rose easily from the water, and then began a series of mishaps such as usually fall to the lot of experimenters. The upper cross stay proved too weak for the long body of the balloon and bent upward about 10 inches during the flight. This prevented the propeller shafts from working properly. Then the winch which worked the sliding weight was broken and, finally, the steering ropes to the rudders became entangled. In spite of all this, a speed of 13 feet per second, or about 9 miles per hour, was obtained. These breakages made it necessary to descend to the lake for repairs and in alighting the framework was further damaged by running into a pile in the lake. The airship was repaired and another flight was made later in the year, during which a speed of 30 feet per second, or 20 miles per hour, was obtained.Second Airship.Zeppelin had sunk his own private fortune and that of his supporters in his first venture, and it was not till five years later that he succeeded in raising enough money to construct a second airship. No radical changes in construction were made in the new model, but there were slight improvements made in all its details. The balloon was about 8 feet shorter than the original and the propellers were enlarged. Three vertical rudders were placed in front and three behind the balloon, and below the end of the craft horizontal rudders were installed to assist in steering upward or downward. The steering was taken care of from the front car.The most important change was made possible by the improvement in gasoline engines during the preceding five years. Where, in the earlier model, he had two 16-horsepower engines, he now used an 85-horsepower engine in each car, with practically the same weight. In fact, the total weight of the vessel was only 9 tons, while his first airship weighed 10 tons.His new craft made many successful flights. One was made at the rate of 38 miles per hour and continued for seven hours, covering a total distance of 266 miles.Later Zeppelins.The later Zeppelins embody no remarkable changes in design, the principal alteration being in size. One of these is illustrated in Fig. 16. In this the gas bag was increased to 446 feet in length and it held over 460,000 cubic feet of gas. This gave it a total lifting power of 16 tons. With this, Zeppelin made a voyage of over 375 miles. He was in the air for twenty hours on this trip and carried eleven passengers with him.Fig. 16. Zeppelin Airship in FlightFig. 16. Zeppelin Airship in FlightIn August, 1908, the Zeppelin left its great iron house at Friedrichshafen and sailed in a great circle over Lake Constance. The day after it started, however, it was destroyed by a storm, and sudden destruction from one cause or another has ended the existence of practically every one of the Zeppelins built since, usually after a very brief period of service.Shape and Framing.In the early days of dirigible design the data upon which the shape and proportions of the envelope were based were purely empirical. Schwartz, Germany’s pioneer in this field, adopted the projectile as representing the form offering the least air resistance and accordingly designed his envelope with a sharply pointed bow and a rounded-off stern, giving it a length four times its diameter. Zeppelin did not agree with these conclusions and adopted a pencil form, rounded at the nose and tapering to a sharp point at the stern, making the length nine to ten times the diameter. Subsequent research work in the aerodynamic laboratory has demonstrated that the most efficient form for air penetration is one having a length six times its maximum diameter with the latter situated at a point four-tenths of the total length from the bow. It has likewise been proved that an ellipse is more efficient than either the projectile or pencil form and that tapering to a sharp point at the stern offers no particular advantage. As a result, the most approved form resembles the shape of a perfecto cigar, the nose being somewhat blunter than the after end. This form is likewise that of the swiftest-swimming fishes and has been shown to have the least head resistance as well as the minimum skin friction; it results in a section to which the termstream-linehas been applied, and it is now employed on all exposed non-supporting surfaces on aeroplanes, such as the struts and even the bracing cables. Laboratory research has demonstrated that it is worth while to reduce the head resistance of even such apparently negligible surfaces as those presented by these wires and cables and, therefore, they are stream-lined by attaching recessed triangular strips of wood to their forward sides.Framing Details.Despite this, the builders of the Zeppelins have adhered to the original pencil shape with but slight modifications at the bow and stern, probably because that shape is much easier to build and assemble from standard girders. The form of girder employed is shown in Fig. 17, while the complete assembly of the frame is illustrated in Fig. 18. The girders form the longerons, or longitudinal beams, running the entire length of the rigid frame and supported at equidistant points by ring members built of similar girder sections. The fourth ring from the nose and each alternate ring after that are further braced by being trussed to the longitudinal beams around their entire circumferences, as shown in Fig. 18. The larger V-shaped truss at the bottom forms the gangway, which is now placed inside the envelope instead of being suspended beneath it, as formerly. This is done to eliminate the head resistance set up by the additional surface thus exposed. In the first instance in which this gangway was incorporated in the envelope, no provision was made for ventilation, and the ship was wrecked by a gas explosion. Regardless of how tight the fabric is made, gas is always oozing out through it to a greater or less extent. This fact is now met by providing ventilating shafts leading from the gangway to the upper surface of the envelope. Additional shafts through the envelope lead to gun platforms, forward, amidships, and aft, and are reached by aluminum ladders.Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 18. Aluminum Frame Construction of Zeppelin HullFig. 18. Aluminum Frame Construction of Zeppelin HullFraming of Schutte-Lanz Type.It has become customary to refer to all large German airships as Zeppelins, but many of those used during the past three years have been of the Schutte-Lanz build, which is also a rigid frame type of dirigible but has been designed with a view of overcoming some of the disadvantages of the aluminum frame construction encountered in the use of the Zeppelin. The length and diameter of the latter airships are such that, no matter how rigidly the framing is assembled, there is more or less sag. When the sag exceeds a certain amount, the frame is apt to buckle at the point where it occurs, involving expensive repairs or wrecking the airship altogether. To overcome this difficulty, the Schutte-Lanz type employs a rigid frame of flexible material, namely, laminated wood in strip form, held together at joints and crossings by aluminum fittings and braced inside by cables. As shown by Fig. 19, no rigid longitudinal beams are employed, the only girders used being rings, to which a network built of the wood strips is attached. Starting at the nose, each continuous strip follows an open spiral path such as would be traced in the air by a screw of very large pitch, in fact, approximating the rifling of a gun barrel. It will also be noted from the illustration that the form of the Schutte-Lanz airship is the cigar-shape, which laboratory research has shown to be the most efficient.Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsFig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsThe use of wood in conjunction with the spiral construction of the supporting members of the framing affords the maximum degree of flexibility, since the displacement of any of these members under stresses of either tension or compression would have to be very great to cause damage to the frame as a whole. The frame not being rigid, strictly speaking, either as units or as a complete assembly, stress at any particular point would simply cause all the members near that point to give in the direction of the strain, and the rest of the frame would accommodate itself to their change of position by either elongating or shortening slightly. In addition to these advantages, the Schutte-Lanz type of construction is said to be lighter than the Zeppelin for an airship of the same load-carrying capacity.Power Plant.Compared with their successors of war times, the early Zeppelins were mere pigmies where power is concerned. Many of these pioneers were driven by less than 100 horsepower all told, whereas in the later types no single motor unit as small as this total has been employed. The motors used most largely have been the 160-horsepower Mercedes and the 200-horsepower Maybach, both of which are described in detail under the title "Aviation Motors." From five to ten of these units have been used on a single ship, giving an aggregate in some of the latest types of close to 2,000 horsepower. Power has been applied through five or six propellers to limit their diameter and to guard against the breakdown of any one of the units putting the power plant out of commission as a whole. To distribute the weight of the engines equally and to insure each propeller a position in which it can work in undisturbed air, the engines have been placed at widely separated points on the airship and in different planes so that no two are coaxial. The main engine room is usually located in a cabin just back of the operating bridge and wireless room, while the remaining motors are suspended in independent gondolas at different points along the sides. Where more than 1,000 horsepower has been used, each of these gondolas' has been fitted with two motors placed side by side and so coupled that either one or both may be employed to drive the single propeller carried by the propelling car. All the more recent propellers have been of the two-bladed type.Control Surfaces.The numerous expedients formerly resorted to by various designers in providing for stabilizing, steering, and elevating surfaces have been abandoned for forms that are practically a duplication of aeroplane practice. Experience demonstrated that the different types of multiplane rudders, elevators, and stabilizing surfaces employed in earlier days not only offered no operating advantages but were actually detrimental, in that they increased the head resistance unnecessarily. Moreover, their complication meant increased weight and weaker construction. They have accordingly been displaced by monoplane surfaces which are of exactly the same type of construction as those used on the aeroplane and the location and proportions of which are very evidently based on aeroplane practice. Both the horizontal and vertical stabilizers are of approximately triangular form and have the steering and elevating surfaces hinged to them at their after ends, so that, except for the pointed extremity of the envelope which extends beyond them, the tail unit of the later Zeppelins is practically the same as the empennage of an aeroplane. The horizontal surfaces are apparently depended on entirely to effect the ascent and descent, there being no evidence of swiveling propellers by means of which the power of the engines could be employed to draw the airship up or down. The great weight of ballast carried is, of course, in the form of water, but this is discarded in order to ascend only when the power of the engines exerted against the elevating planes is no longer capable of keeping the airship at the altitude desired. In the low temperatures encountered in night flights, however, the contraction of the hydrogen gas is so great that the crew has found it necessary to reduce the weight by discarding not only every pound of ballast but, as far as possible, everything portable. Despite this, several airships have fallen when their fuel supply was exhausted, one coming to the ground in Scotland, two dropping into the North Sea, and three or four falling in France.Operating Controls.All the operating controls are centered at the navigating bridge, which is inclosed to form the commander’s cabin. By means of push buttons, switches, levers, and wheels every operating function required is set into motion from this central point. Whether auxiliary motors are carried for the purpose of pumping air into the balloonets or this is one of the duties of the main engine just back of the wireless room does not appear, but with the aid of a push button board the amount of air in any of the balloonets may be increased or decreased at will. There is a control button for each operation, or two for each balloonet, which fact necessitates a rather forbidding looking board, since the more recent Zeppelins have seventeen to nineteen gas bags within each of which is incorporated an air balloonet.The amount of fuel supplied to any one of the motor units can likewise be controlled from a central board, and this is also true of the ballast release apparatus, so that water can be emptied from any one of the ballast tanks at will, thus facilitating ascent or descent by lightening one end or the other. Elevating and steering surfaces are operated by small hand-steering wheels with cables passing around their drums, a member of the crew being stationed at each of these controlling wheels. Owing to the number of motors used, the instrument board is the most formidable appearing piece of apparatus on the bridge, since there is a revolution counter for each power unit in addition to the numerous other instruments required. Some of these instruments are the aneroid barometer for indicating the altitude, transverse and longitudinal clinometers to show the amount of heel and the angle at which the airship is traveling with relation to the horizontal, the anemometer, or air-speed indicator, manometers, or pressure gauges, for each one of the gas bags, fuel and ballast supply gauges, drift indicators, electric bomb releasers, mileage recorders, and the like. In addition to these, there are a large chart and a compass, so the navigating bridge of a Zeppelin combines in small space all the instruments to be found in the engine room and on the bridge of an ocean liner besides several which the latter does not require. That the proper coordination of all the functions mentioned is an exceedingly difficult task for one man seems evident from the numerous Zeppelins that have apparently wrecked themselves.Crew Carried.In the various Zeppelins that have been captured or shot down by the British or French, the personnel has varied from fifteen to thirty men but in the majority of instances has not exceeded twenty. The positions and duties are about as follows: The commander, lieutenant-commander, and chief engineer, and possibly a navigating officer are stationed at the bridge. Two or three of the crew are also stationed there to work the manually operated controls. In the cabin just back of the bridge are two wireless operators and one or two engine attendants for the motors in the engine room behind the wireless room. A similar number of engine attendants are stationed in the after engine room and there is at least one attendant for each of the other motor units. One man is stationed at each machine gun, of which there are three to five on the "roof" and two in each car, and at least as many bombers are needed to load the "droppers." As a reserve there are usually an additional gun pointer for each gun and an extra engine attendant, since to run continuously most of the crew would have to stand watch and watch as in marine practice. The sleeping accommodations consist of canvas hammocks slung in the gangway.Explosives Carried.In addition to a liberal supply of ammunition for the machine guns, a large weight of bombs is carried, though the quantity as well as the size of the bombs themselves has been exaggerated in the same or even greater ratio than that which has proved characteristic of the German military press-agency service. The bombs are carried suspended in racks amidships, and the bomb droppers are also located at that part of the ship so that the release of the bombs will not upset the longitudinal equilibrium of the craft. The bomb-dropping apparatus is controlled electrically from the navigating bridge but may also be operated by hand from the same point. It has been reported by the Germans that their latest types of Zeppelins are capable of dropping bombs weighing 1 ton each. In view of the effect that the sudden release of a weight of 1 ton would have on the airship itself, this is manifestly very much of an exaggeration. Zeppelin bombs that have failed to explode have never exceeded 200 to 300 pounds and many of those employed are doubtless still lighter. So far as the total amount carried is concerned, many of the later airships doubtless are capable of transporting 2 to 3 tons and still carrying sufficient fuel, though adverse conditions would prevent their return, as has frequently happened.
GERMAN DIRIGIBLESEarly Zeppelin Airships.At the same time that Santos-Dumont was carrying on his hazardous experiments, the problem was being attacked along slightly different lines by Count Zeppelin.It will be remembered that Dumont experienced much trouble on account of the envelope of his balloon being too flexible, causing it to crumple in the middle and to become distorted in shape from the pressure of the air. His efforts to overcome this by the employment of air bags did not meet with great success, even in his later types.Fig. 15. Zeppelin Dirigible Rising from Lake ConstanceFig. 15. Zeppelin Dirigible Rising from Lake ConstanceConstruction.Zeppelin employed a very rigid construction. His first balloon, which was built in 1898, was the largest which had ever been made. It is illustrated in Fig. 15, which shows his first design slightly improved. It was about 40 feet in diameter and 420 feet long—an air craft as large as many an ocean vessel. The envelope consisted of two distinct bags, an outer and an inner one, with an air space between. The air space between the inner and outer envelopes acted as a heat insulator and prevented the gas within from being affected by rapid changes of temperature. The inner bag contained the gas, and the outer one served as a protective covering. In the construction of this outer bag lies the novelty of Zeppelin’s design. A rigid framework of strongly braced aluminum rings was provided and this was covered with linen and silk which had been specially treated to prevent leakage of gas. The inner envelope consisted of seventeen gas-tight compartments which could be filled or emptied separately. In the event of the puncture of one of them, the balloon would remain afloat. An aluminum keel was provided to further increase the rigidity. A sliding weight could be moved backward or forward along the keel and cause the nose of the airship to point upward or downward as desired. This would make the craft move upward or downward without throwing out ballast or losing gas. Lender each end of the balloon a light aluminum car was rigidly fastened and in each was a 16-horsepower Daimler gasoline engine. The two engines could be worked either independently of each other or together. Each engine drove a vertical and horizontal propeller. The propellers each had four aluminum blades. As will be seen from Fig. 15, the ears were too far apart for ordinary means of communication and so speaking tubes, electric bells, and an electric telegraph system were installed.First Trials.Very little was known as to the effects of alighting on the ground with such a rigid affair as this vessel, therefore the cars were made like boats so that the airship could alight and float on the water. The first trials were made over Lake Constance in July, 1900. The mammoth craft was housed in a huge floating shed, and the vessel emerged from it with the gas bag floating above and the two cars touching the water. She rose easily from the water, and then began a series of mishaps such as usually fall to the lot of experimenters. The upper cross stay proved too weak for the long body of the balloon and bent upward about 10 inches during the flight. This prevented the propeller shafts from working properly. Then the winch which worked the sliding weight was broken and, finally, the steering ropes to the rudders became entangled. In spite of all this, a speed of 13 feet per second, or about 9 miles per hour, was obtained. These breakages made it necessary to descend to the lake for repairs and in alighting the framework was further damaged by running into a pile in the lake. The airship was repaired and another flight was made later in the year, during which a speed of 30 feet per second, or 20 miles per hour, was obtained.Second Airship.Zeppelin had sunk his own private fortune and that of his supporters in his first venture, and it was not till five years later that he succeeded in raising enough money to construct a second airship. No radical changes in construction were made in the new model, but there were slight improvements made in all its details. The balloon was about 8 feet shorter than the original and the propellers were enlarged. Three vertical rudders were placed in front and three behind the balloon, and below the end of the craft horizontal rudders were installed to assist in steering upward or downward. The steering was taken care of from the front car.The most important change was made possible by the improvement in gasoline engines during the preceding five years. Where, in the earlier model, he had two 16-horsepower engines, he now used an 85-horsepower engine in each car, with practically the same weight. In fact, the total weight of the vessel was only 9 tons, while his first airship weighed 10 tons.His new craft made many successful flights. One was made at the rate of 38 miles per hour and continued for seven hours, covering a total distance of 266 miles.Later Zeppelins.The later Zeppelins embody no remarkable changes in design, the principal alteration being in size. One of these is illustrated in Fig. 16. In this the gas bag was increased to 446 feet in length and it held over 460,000 cubic feet of gas. This gave it a total lifting power of 16 tons. With this, Zeppelin made a voyage of over 375 miles. He was in the air for twenty hours on this trip and carried eleven passengers with him.Fig. 16. Zeppelin Airship in FlightFig. 16. Zeppelin Airship in FlightIn August, 1908, the Zeppelin left its great iron house at Friedrichshafen and sailed in a great circle over Lake Constance. The day after it started, however, it was destroyed by a storm, and sudden destruction from one cause or another has ended the existence of practically every one of the Zeppelins built since, usually after a very brief period of service.Shape and Framing.In the early days of dirigible design the data upon which the shape and proportions of the envelope were based were purely empirical. Schwartz, Germany’s pioneer in this field, adopted the projectile as representing the form offering the least air resistance and accordingly designed his envelope with a sharply pointed bow and a rounded-off stern, giving it a length four times its diameter. Zeppelin did not agree with these conclusions and adopted a pencil form, rounded at the nose and tapering to a sharp point at the stern, making the length nine to ten times the diameter. Subsequent research work in the aerodynamic laboratory has demonstrated that the most efficient form for air penetration is one having a length six times its maximum diameter with the latter situated at a point four-tenths of the total length from the bow. It has likewise been proved that an ellipse is more efficient than either the projectile or pencil form and that tapering to a sharp point at the stern offers no particular advantage. As a result, the most approved form resembles the shape of a perfecto cigar, the nose being somewhat blunter than the after end. This form is likewise that of the swiftest-swimming fishes and has been shown to have the least head resistance as well as the minimum skin friction; it results in a section to which the termstream-linehas been applied, and it is now employed on all exposed non-supporting surfaces on aeroplanes, such as the struts and even the bracing cables. Laboratory research has demonstrated that it is worth while to reduce the head resistance of even such apparently negligible surfaces as those presented by these wires and cables and, therefore, they are stream-lined by attaching recessed triangular strips of wood to their forward sides.Framing Details.Despite this, the builders of the Zeppelins have adhered to the original pencil shape with but slight modifications at the bow and stern, probably because that shape is much easier to build and assemble from standard girders. The form of girder employed is shown in Fig. 17, while the complete assembly of the frame is illustrated in Fig. 18. The girders form the longerons, or longitudinal beams, running the entire length of the rigid frame and supported at equidistant points by ring members built of similar girder sections. The fourth ring from the nose and each alternate ring after that are further braced by being trussed to the longitudinal beams around their entire circumferences, as shown in Fig. 18. The larger V-shaped truss at the bottom forms the gangway, which is now placed inside the envelope instead of being suspended beneath it, as formerly. This is done to eliminate the head resistance set up by the additional surface thus exposed. In the first instance in which this gangway was incorporated in the envelope, no provision was made for ventilation, and the ship was wrecked by a gas explosion. Regardless of how tight the fabric is made, gas is always oozing out through it to a greater or less extent. This fact is now met by providing ventilating shafts leading from the gangway to the upper surface of the envelope. Additional shafts through the envelope lead to gun platforms, forward, amidships, and aft, and are reached by aluminum ladders.Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 18. Aluminum Frame Construction of Zeppelin HullFig. 18. Aluminum Frame Construction of Zeppelin HullFraming of Schutte-Lanz Type.It has become customary to refer to all large German airships as Zeppelins, but many of those used during the past three years have been of the Schutte-Lanz build, which is also a rigid frame type of dirigible but has been designed with a view of overcoming some of the disadvantages of the aluminum frame construction encountered in the use of the Zeppelin. The length and diameter of the latter airships are such that, no matter how rigidly the framing is assembled, there is more or less sag. When the sag exceeds a certain amount, the frame is apt to buckle at the point where it occurs, involving expensive repairs or wrecking the airship altogether. To overcome this difficulty, the Schutte-Lanz type employs a rigid frame of flexible material, namely, laminated wood in strip form, held together at joints and crossings by aluminum fittings and braced inside by cables. As shown by Fig. 19, no rigid longitudinal beams are employed, the only girders used being rings, to which a network built of the wood strips is attached. Starting at the nose, each continuous strip follows an open spiral path such as would be traced in the air by a screw of very large pitch, in fact, approximating the rifling of a gun barrel. It will also be noted from the illustration that the form of the Schutte-Lanz airship is the cigar-shape, which laboratory research has shown to be the most efficient.Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsFig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsThe use of wood in conjunction with the spiral construction of the supporting members of the framing affords the maximum degree of flexibility, since the displacement of any of these members under stresses of either tension or compression would have to be very great to cause damage to the frame as a whole. The frame not being rigid, strictly speaking, either as units or as a complete assembly, stress at any particular point would simply cause all the members near that point to give in the direction of the strain, and the rest of the frame would accommodate itself to their change of position by either elongating or shortening slightly. In addition to these advantages, the Schutte-Lanz type of construction is said to be lighter than the Zeppelin for an airship of the same load-carrying capacity.Power Plant.Compared with their successors of war times, the early Zeppelins were mere pigmies where power is concerned. Many of these pioneers were driven by less than 100 horsepower all told, whereas in the later types no single motor unit as small as this total has been employed. The motors used most largely have been the 160-horsepower Mercedes and the 200-horsepower Maybach, both of which are described in detail under the title "Aviation Motors." From five to ten of these units have been used on a single ship, giving an aggregate in some of the latest types of close to 2,000 horsepower. Power has been applied through five or six propellers to limit their diameter and to guard against the breakdown of any one of the units putting the power plant out of commission as a whole. To distribute the weight of the engines equally and to insure each propeller a position in which it can work in undisturbed air, the engines have been placed at widely separated points on the airship and in different planes so that no two are coaxial. The main engine room is usually located in a cabin just back of the operating bridge and wireless room, while the remaining motors are suspended in independent gondolas at different points along the sides. Where more than 1,000 horsepower has been used, each of these gondolas' has been fitted with two motors placed side by side and so coupled that either one or both may be employed to drive the single propeller carried by the propelling car. All the more recent propellers have been of the two-bladed type.Control Surfaces.The numerous expedients formerly resorted to by various designers in providing for stabilizing, steering, and elevating surfaces have been abandoned for forms that are practically a duplication of aeroplane practice. Experience demonstrated that the different types of multiplane rudders, elevators, and stabilizing surfaces employed in earlier days not only offered no operating advantages but were actually detrimental, in that they increased the head resistance unnecessarily. Moreover, their complication meant increased weight and weaker construction. They have accordingly been displaced by monoplane surfaces which are of exactly the same type of construction as those used on the aeroplane and the location and proportions of which are very evidently based on aeroplane practice. Both the horizontal and vertical stabilizers are of approximately triangular form and have the steering and elevating surfaces hinged to them at their after ends, so that, except for the pointed extremity of the envelope which extends beyond them, the tail unit of the later Zeppelins is practically the same as the empennage of an aeroplane. The horizontal surfaces are apparently depended on entirely to effect the ascent and descent, there being no evidence of swiveling propellers by means of which the power of the engines could be employed to draw the airship up or down. The great weight of ballast carried is, of course, in the form of water, but this is discarded in order to ascend only when the power of the engines exerted against the elevating planes is no longer capable of keeping the airship at the altitude desired. In the low temperatures encountered in night flights, however, the contraction of the hydrogen gas is so great that the crew has found it necessary to reduce the weight by discarding not only every pound of ballast but, as far as possible, everything portable. Despite this, several airships have fallen when their fuel supply was exhausted, one coming to the ground in Scotland, two dropping into the North Sea, and three or four falling in France.Operating Controls.All the operating controls are centered at the navigating bridge, which is inclosed to form the commander’s cabin. By means of push buttons, switches, levers, and wheels every operating function required is set into motion from this central point. Whether auxiliary motors are carried for the purpose of pumping air into the balloonets or this is one of the duties of the main engine just back of the wireless room does not appear, but with the aid of a push button board the amount of air in any of the balloonets may be increased or decreased at will. There is a control button for each operation, or two for each balloonet, which fact necessitates a rather forbidding looking board, since the more recent Zeppelins have seventeen to nineteen gas bags within each of which is incorporated an air balloonet.The amount of fuel supplied to any one of the motor units can likewise be controlled from a central board, and this is also true of the ballast release apparatus, so that water can be emptied from any one of the ballast tanks at will, thus facilitating ascent or descent by lightening one end or the other. Elevating and steering surfaces are operated by small hand-steering wheels with cables passing around their drums, a member of the crew being stationed at each of these controlling wheels. Owing to the number of motors used, the instrument board is the most formidable appearing piece of apparatus on the bridge, since there is a revolution counter for each power unit in addition to the numerous other instruments required. Some of these instruments are the aneroid barometer for indicating the altitude, transverse and longitudinal clinometers to show the amount of heel and the angle at which the airship is traveling with relation to the horizontal, the anemometer, or air-speed indicator, manometers, or pressure gauges, for each one of the gas bags, fuel and ballast supply gauges, drift indicators, electric bomb releasers, mileage recorders, and the like. In addition to these, there are a large chart and a compass, so the navigating bridge of a Zeppelin combines in small space all the instruments to be found in the engine room and on the bridge of an ocean liner besides several which the latter does not require. That the proper coordination of all the functions mentioned is an exceedingly difficult task for one man seems evident from the numerous Zeppelins that have apparently wrecked themselves.Crew Carried.In the various Zeppelins that have been captured or shot down by the British or French, the personnel has varied from fifteen to thirty men but in the majority of instances has not exceeded twenty. The positions and duties are about as follows: The commander, lieutenant-commander, and chief engineer, and possibly a navigating officer are stationed at the bridge. Two or three of the crew are also stationed there to work the manually operated controls. In the cabin just back of the bridge are two wireless operators and one or two engine attendants for the motors in the engine room behind the wireless room. A similar number of engine attendants are stationed in the after engine room and there is at least one attendant for each of the other motor units. One man is stationed at each machine gun, of which there are three to five on the "roof" and two in each car, and at least as many bombers are needed to load the "droppers." As a reserve there are usually an additional gun pointer for each gun and an extra engine attendant, since to run continuously most of the crew would have to stand watch and watch as in marine practice. The sleeping accommodations consist of canvas hammocks slung in the gangway.Explosives Carried.In addition to a liberal supply of ammunition for the machine guns, a large weight of bombs is carried, though the quantity as well as the size of the bombs themselves has been exaggerated in the same or even greater ratio than that which has proved characteristic of the German military press-agency service. The bombs are carried suspended in racks amidships, and the bomb droppers are also located at that part of the ship so that the release of the bombs will not upset the longitudinal equilibrium of the craft. The bomb-dropping apparatus is controlled electrically from the navigating bridge but may also be operated by hand from the same point. It has been reported by the Germans that their latest types of Zeppelins are capable of dropping bombs weighing 1 ton each. In view of the effect that the sudden release of a weight of 1 ton would have on the airship itself, this is manifestly very much of an exaggeration. Zeppelin bombs that have failed to explode have never exceeded 200 to 300 pounds and many of those employed are doubtless still lighter. So far as the total amount carried is concerned, many of the later airships doubtless are capable of transporting 2 to 3 tons and still carrying sufficient fuel, though adverse conditions would prevent their return, as has frequently happened.
Early Zeppelin Airships.At the same time that Santos-Dumont was carrying on his hazardous experiments, the problem was being attacked along slightly different lines by Count Zeppelin.
It will be remembered that Dumont experienced much trouble on account of the envelope of his balloon being too flexible, causing it to crumple in the middle and to become distorted in shape from the pressure of the air. His efforts to overcome this by the employment of air bags did not meet with great success, even in his later types.
Fig. 15. Zeppelin Dirigible Rising from Lake ConstanceFig. 15. Zeppelin Dirigible Rising from Lake Constance
Fig. 15. Zeppelin Dirigible Rising from Lake Constance
Construction.Zeppelin employed a very rigid construction. His first balloon, which was built in 1898, was the largest which had ever been made. It is illustrated in Fig. 15, which shows his first design slightly improved. It was about 40 feet in diameter and 420 feet long—an air craft as large as many an ocean vessel. The envelope consisted of two distinct bags, an outer and an inner one, with an air space between. The air space between the inner and outer envelopes acted as a heat insulator and prevented the gas within from being affected by rapid changes of temperature. The inner bag contained the gas, and the outer one served as a protective covering. In the construction of this outer bag lies the novelty of Zeppelin’s design. A rigid framework of strongly braced aluminum rings was provided and this was covered with linen and silk which had been specially treated to prevent leakage of gas. The inner envelope consisted of seventeen gas-tight compartments which could be filled or emptied separately. In the event of the puncture of one of them, the balloon would remain afloat. An aluminum keel was provided to further increase the rigidity. A sliding weight could be moved backward or forward along the keel and cause the nose of the airship to point upward or downward as desired. This would make the craft move upward or downward without throwing out ballast or losing gas. Lender each end of the balloon a light aluminum car was rigidly fastened and in each was a 16-horsepower Daimler gasoline engine. The two engines could be worked either independently of each other or together. Each engine drove a vertical and horizontal propeller. The propellers each had four aluminum blades. As will be seen from Fig. 15, the ears were too far apart for ordinary means of communication and so speaking tubes, electric bells, and an electric telegraph system were installed.
First Trials.Very little was known as to the effects of alighting on the ground with such a rigid affair as this vessel, therefore the cars were made like boats so that the airship could alight and float on the water. The first trials were made over Lake Constance in July, 1900. The mammoth craft was housed in a huge floating shed, and the vessel emerged from it with the gas bag floating above and the two cars touching the water. She rose easily from the water, and then began a series of mishaps such as usually fall to the lot of experimenters. The upper cross stay proved too weak for the long body of the balloon and bent upward about 10 inches during the flight. This prevented the propeller shafts from working properly. Then the winch which worked the sliding weight was broken and, finally, the steering ropes to the rudders became entangled. In spite of all this, a speed of 13 feet per second, or about 9 miles per hour, was obtained. These breakages made it necessary to descend to the lake for repairs and in alighting the framework was further damaged by running into a pile in the lake. The airship was repaired and another flight was made later in the year, during which a speed of 30 feet per second, or 20 miles per hour, was obtained.
Second Airship.Zeppelin had sunk his own private fortune and that of his supporters in his first venture, and it was not till five years later that he succeeded in raising enough money to construct a second airship. No radical changes in construction were made in the new model, but there were slight improvements made in all its details. The balloon was about 8 feet shorter than the original and the propellers were enlarged. Three vertical rudders were placed in front and three behind the balloon, and below the end of the craft horizontal rudders were installed to assist in steering upward or downward. The steering was taken care of from the front car.
The most important change was made possible by the improvement in gasoline engines during the preceding five years. Where, in the earlier model, he had two 16-horsepower engines, he now used an 85-horsepower engine in each car, with practically the same weight. In fact, the total weight of the vessel was only 9 tons, while his first airship weighed 10 tons.
His new craft made many successful flights. One was made at the rate of 38 miles per hour and continued for seven hours, covering a total distance of 266 miles.
Later Zeppelins.The later Zeppelins embody no remarkable changes in design, the principal alteration being in size. One of these is illustrated in Fig. 16. In this the gas bag was increased to 446 feet in length and it held over 460,000 cubic feet of gas. This gave it a total lifting power of 16 tons. With this, Zeppelin made a voyage of over 375 miles. He was in the air for twenty hours on this trip and carried eleven passengers with him.
Fig. 16. Zeppelin Airship in FlightFig. 16. Zeppelin Airship in Flight
Fig. 16. Zeppelin Airship in Flight
In August, 1908, the Zeppelin left its great iron house at Friedrichshafen and sailed in a great circle over Lake Constance. The day after it started, however, it was destroyed by a storm, and sudden destruction from one cause or another has ended the existence of practically every one of the Zeppelins built since, usually after a very brief period of service.
Shape and Framing.In the early days of dirigible design the data upon which the shape and proportions of the envelope were based were purely empirical. Schwartz, Germany’s pioneer in this field, adopted the projectile as representing the form offering the least air resistance and accordingly designed his envelope with a sharply pointed bow and a rounded-off stern, giving it a length four times its diameter. Zeppelin did not agree with these conclusions and adopted a pencil form, rounded at the nose and tapering to a sharp point at the stern, making the length nine to ten times the diameter. Subsequent research work in the aerodynamic laboratory has demonstrated that the most efficient form for air penetration is one having a length six times its maximum diameter with the latter situated at a point four-tenths of the total length from the bow. It has likewise been proved that an ellipse is more efficient than either the projectile or pencil form and that tapering to a sharp point at the stern offers no particular advantage. As a result, the most approved form resembles the shape of a perfecto cigar, the nose being somewhat blunter than the after end. This form is likewise that of the swiftest-swimming fishes and has been shown to have the least head resistance as well as the minimum skin friction; it results in a section to which the termstream-linehas been applied, and it is now employed on all exposed non-supporting surfaces on aeroplanes, such as the struts and even the bracing cables. Laboratory research has demonstrated that it is worth while to reduce the head resistance of even such apparently negligible surfaces as those presented by these wires and cables and, therefore, they are stream-lined by attaching recessed triangular strips of wood to their forward sides.
Framing Details.Despite this, the builders of the Zeppelins have adhered to the original pencil shape with but slight modifications at the bow and stern, probably because that shape is much easier to build and assemble from standard girders. The form of girder employed is shown in Fig. 17, while the complete assembly of the frame is illustrated in Fig. 18. The girders form the longerons, or longitudinal beams, running the entire length of the rigid frame and supported at equidistant points by ring members built of similar girder sections. The fourth ring from the nose and each alternate ring after that are further braced by being trussed to the longitudinal beams around their entire circumferences, as shown in Fig. 18. The larger V-shaped truss at the bottom forms the gangway, which is now placed inside the envelope instead of being suspended beneath it, as formerly. This is done to eliminate the head resistance set up by the additional surface thus exposed. In the first instance in which this gangway was incorporated in the envelope, no provision was made for ventilation, and the ship was wrecked by a gas explosion. Regardless of how tight the fabric is made, gas is always oozing out through it to a greater or less extent. This fact is now met by providing ventilating shafts leading from the gangway to the upper surface of the envelope. Additional shafts through the envelope lead to gun platforms, forward, amidships, and aft, and are reached by aluminum ladders.
Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin FrameFig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin Frame
Fig. 17. Trellis Type of Aluminum Girder used in Longitudinals of Zeppelin Frame
Fig. 18. Aluminum Frame Construction of Zeppelin HullFig. 18. Aluminum Frame Construction of Zeppelin Hull
Fig. 18. Aluminum Frame Construction of Zeppelin Hull
Framing of Schutte-Lanz Type.It has become customary to refer to all large German airships as Zeppelins, but many of those used during the past three years have been of the Schutte-Lanz build, which is also a rigid frame type of dirigible but has been designed with a view of overcoming some of the disadvantages of the aluminum frame construction encountered in the use of the Zeppelin. The length and diameter of the latter airships are such that, no matter how rigidly the framing is assembled, there is more or less sag. When the sag exceeds a certain amount, the frame is apt to buckle at the point where it occurs, involving expensive repairs or wrecking the airship altogether. To overcome this difficulty, the Schutte-Lanz type employs a rigid frame of flexible material, namely, laminated wood in strip form, held together at joints and crossings by aluminum fittings and braced inside by cables. As shown by Fig. 19, no rigid longitudinal beams are employed, the only girders used being rings, to which a network built of the wood strips is attached. Starting at the nose, each continuous strip follows an open spiral path such as would be traced in the air by a screw of very large pitch, in fact, approximating the rifling of a gun barrel. It will also be noted from the illustration that the form of the Schutte-Lanz airship is the cigar-shape, which laboratory research has shown to be the most efficient.
Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum FittingsFig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum Fittings
Fig. 19. Schutte-Lanz Type of Frame Construction of Laminated Wood with Aluminum Fittings
The use of wood in conjunction with the spiral construction of the supporting members of the framing affords the maximum degree of flexibility, since the displacement of any of these members under stresses of either tension or compression would have to be very great to cause damage to the frame as a whole. The frame not being rigid, strictly speaking, either as units or as a complete assembly, stress at any particular point would simply cause all the members near that point to give in the direction of the strain, and the rest of the frame would accommodate itself to their change of position by either elongating or shortening slightly. In addition to these advantages, the Schutte-Lanz type of construction is said to be lighter than the Zeppelin for an airship of the same load-carrying capacity.
Power Plant.Compared with their successors of war times, the early Zeppelins were mere pigmies where power is concerned. Many of these pioneers were driven by less than 100 horsepower all told, whereas in the later types no single motor unit as small as this total has been employed. The motors used most largely have been the 160-horsepower Mercedes and the 200-horsepower Maybach, both of which are described in detail under the title "Aviation Motors." From five to ten of these units have been used on a single ship, giving an aggregate in some of the latest types of close to 2,000 horsepower. Power has been applied through five or six propellers to limit their diameter and to guard against the breakdown of any one of the units putting the power plant out of commission as a whole. To distribute the weight of the engines equally and to insure each propeller a position in which it can work in undisturbed air, the engines have been placed at widely separated points on the airship and in different planes so that no two are coaxial. The main engine room is usually located in a cabin just back of the operating bridge and wireless room, while the remaining motors are suspended in independent gondolas at different points along the sides. Where more than 1,000 horsepower has been used, each of these gondolas' has been fitted with two motors placed side by side and so coupled that either one or both may be employed to drive the single propeller carried by the propelling car. All the more recent propellers have been of the two-bladed type.
Control Surfaces.The numerous expedients formerly resorted to by various designers in providing for stabilizing, steering, and elevating surfaces have been abandoned for forms that are practically a duplication of aeroplane practice. Experience demonstrated that the different types of multiplane rudders, elevators, and stabilizing surfaces employed in earlier days not only offered no operating advantages but were actually detrimental, in that they increased the head resistance unnecessarily. Moreover, their complication meant increased weight and weaker construction. They have accordingly been displaced by monoplane surfaces which are of exactly the same type of construction as those used on the aeroplane and the location and proportions of which are very evidently based on aeroplane practice. Both the horizontal and vertical stabilizers are of approximately triangular form and have the steering and elevating surfaces hinged to them at their after ends, so that, except for the pointed extremity of the envelope which extends beyond them, the tail unit of the later Zeppelins is practically the same as the empennage of an aeroplane. The horizontal surfaces are apparently depended on entirely to effect the ascent and descent, there being no evidence of swiveling propellers by means of which the power of the engines could be employed to draw the airship up or down. The great weight of ballast carried is, of course, in the form of water, but this is discarded in order to ascend only when the power of the engines exerted against the elevating planes is no longer capable of keeping the airship at the altitude desired. In the low temperatures encountered in night flights, however, the contraction of the hydrogen gas is so great that the crew has found it necessary to reduce the weight by discarding not only every pound of ballast but, as far as possible, everything portable. Despite this, several airships have fallen when their fuel supply was exhausted, one coming to the ground in Scotland, two dropping into the North Sea, and three or four falling in France.
Operating Controls.All the operating controls are centered at the navigating bridge, which is inclosed to form the commander’s cabin. By means of push buttons, switches, levers, and wheels every operating function required is set into motion from this central point. Whether auxiliary motors are carried for the purpose of pumping air into the balloonets or this is one of the duties of the main engine just back of the wireless room does not appear, but with the aid of a push button board the amount of air in any of the balloonets may be increased or decreased at will. There is a control button for each operation, or two for each balloonet, which fact necessitates a rather forbidding looking board, since the more recent Zeppelins have seventeen to nineteen gas bags within each of which is incorporated an air balloonet.
The amount of fuel supplied to any one of the motor units can likewise be controlled from a central board, and this is also true of the ballast release apparatus, so that water can be emptied from any one of the ballast tanks at will, thus facilitating ascent or descent by lightening one end or the other. Elevating and steering surfaces are operated by small hand-steering wheels with cables passing around their drums, a member of the crew being stationed at each of these controlling wheels. Owing to the number of motors used, the instrument board is the most formidable appearing piece of apparatus on the bridge, since there is a revolution counter for each power unit in addition to the numerous other instruments required. Some of these instruments are the aneroid barometer for indicating the altitude, transverse and longitudinal clinometers to show the amount of heel and the angle at which the airship is traveling with relation to the horizontal, the anemometer, or air-speed indicator, manometers, or pressure gauges, for each one of the gas bags, fuel and ballast supply gauges, drift indicators, electric bomb releasers, mileage recorders, and the like. In addition to these, there are a large chart and a compass, so the navigating bridge of a Zeppelin combines in small space all the instruments to be found in the engine room and on the bridge of an ocean liner besides several which the latter does not require. That the proper coordination of all the functions mentioned is an exceedingly difficult task for one man seems evident from the numerous Zeppelins that have apparently wrecked themselves.
Crew Carried.In the various Zeppelins that have been captured or shot down by the British or French, the personnel has varied from fifteen to thirty men but in the majority of instances has not exceeded twenty. The positions and duties are about as follows: The commander, lieutenant-commander, and chief engineer, and possibly a navigating officer are stationed at the bridge. Two or three of the crew are also stationed there to work the manually operated controls. In the cabin just back of the bridge are two wireless operators and one or two engine attendants for the motors in the engine room behind the wireless room. A similar number of engine attendants are stationed in the after engine room and there is at least one attendant for each of the other motor units. One man is stationed at each machine gun, of which there are three to five on the "roof" and two in each car, and at least as many bombers are needed to load the "droppers." As a reserve there are usually an additional gun pointer for each gun and an extra engine attendant, since to run continuously most of the crew would have to stand watch and watch as in marine practice. The sleeping accommodations consist of canvas hammocks slung in the gangway.
Explosives Carried.In addition to a liberal supply of ammunition for the machine guns, a large weight of bombs is carried, though the quantity as well as the size of the bombs themselves has been exaggerated in the same or even greater ratio than that which has proved characteristic of the German military press-agency service. The bombs are carried suspended in racks amidships, and the bomb droppers are also located at that part of the ship so that the release of the bombs will not upset the longitudinal equilibrium of the craft. The bomb-dropping apparatus is controlled electrically from the navigating bridge but may also be operated by hand from the same point. It has been reported by the Germans that their latest types of Zeppelins are capable of dropping bombs weighing 1 ton each. In view of the effect that the sudden release of a weight of 1 ton would have on the airship itself, this is manifestly very much of an exaggeration. Zeppelin bombs that have failed to explode have never exceeded 200 to 300 pounds and many of those employed are doubtless still lighter. So far as the total amount carried is concerned, many of the later airships doubtless are capable of transporting 2 to 3 tons and still carrying sufficient fuel, though adverse conditions would prevent their return, as has frequently happened.