Chapter II: Part 2

*The First Lebaudy.* The interest evidenced by the German War Department in Zeppelin’s airship was more than duplicated by that aroused in French military circles by the success of the Lebaudy Brothers. Since 1900 these two brothers had been experimenting with dirigible balloons. Their first dirigible—built by the engineer Juillot—made thirty flights, in all but two of which it succeeded in returning to its starting point. This machine was somewhat similar to the later types built by Santos-Dumont and carried a 40-horsepower Daimler motor. A speed of 36 feet per second, or about 25 miles per hour, was obtained. During tests in the summer of 1904, the balloon was dashed against a tree and almost entirely destroyed.

*Lebaudy 1904.* The next year the "Lebaudy 1904" appeared. This was 190 feet long and had a capacity of 94,000 cubic feet of gas. The air bag was divided into three parts and contained 17,600 cubic feet of air. It was supplied with air from a fan driven by the engine, and an auxiliary electric motor and storage battery were carried to drive the fan when the gas engine was not working. The storage battery was also used to furnish electric lights for the airship. A horizontal sail of silk was stretched between the car and the gas bag, which had an area of something over 1,000 square feet, and a sort of keel of silk was stretched below it. A horizontal rudder, shaped like a pigeon’s tail, was used at the rear, and immediately behind it were two V-shaped vertical rudders. A small vertical sail was carried, which could be used to assist in guiding the airship. The car was 16 feet long and was rigidly hung 10 feet below the bag. It was provided with an inverted pyramid of steel tubes meeting at an apex below the car to prevent injury in alighting. Sixty-three ascents were made in 1904 with this balloon, all of them comparatively successful, the longest being a journey of 60 miles in two hours and forty-five minutes.

The next year a new and larger balloon equipped with a more powerful motor was used. Many flights were made in tests for the French War Department.

*La Patrie.* La Patrie was then built for the French government by the Lebaudy Brothers and was of the same design as their earlier airships. In speed it was nearly equal to Zeppelin’s, and its dirigibility was nearly perfect. Fig. 9 shows a view of this airship in flight.

It was 200 feet long, and the 70-horsepower engine drove two propellers. It could carry seven people and one-half ton of ballast. It carried four people at a speed of 30 miles per hour. On its last trip it covered 175 miles in seven hours. A few days afterward, a heavy wind tore it away from its moorings and it was blown out to sea and lost.

*La Republique and Le Jaune.* Two more airships of the same type, La Republique and Le Jaune, followed this. These were tried by the French government, in 1908, and both proved successful. La Republique is illustrated in Fig. 10. The shape and equipment of the car are shown in Fig. 11. The automobile type of radiator may be seen attached to the side of the car. During a flight in the fall of 1909, a propeller blade broke and was thrown clear through the balloon envelope, causing the balloon to fall from a height of 500 feet. The four officers who formed the crew of the dirigible were killed instantly.

*Clement-Bayard II.* The numerous factors that must be considered in the design of a successful dirigible balloon as well as the many conflicting conditions that must be reconciled have already been referred to in detail. How these are carried out in practice may best be made clear by a description of what may be considered as an advanced type of dirigible, the Clement-Bayard II, Fig. 12, of French design, and the most successful of the French military air fleet. Its predecessor, the Clement-Bayard I, Fig. 13, made thirty voyages, some of them of considerable distances, without suffering any damage, but a study of its shortcomings led to their elimination in the following model.

The pisciform shape of the first Clement-Bayard was retained but given more taper, the dimensions being 248.6 feet overall by 42.9 greatest diameter, this being but a short distance back of the bow. This gives it a ratio of length to diameter of 5.76. The gas balloonet stabilizers were eliminated altogether, Fig. 12. The total gas capacity is approximately 80,000 cubic feet. Like all French dirigibles it is of the true flexible type, the only rigid construction being that of the framework of the car itself. To the latter are attached all rudders and stabilizing devices, instead of making them a part of the envelope as formerly. The latter is made of continental rubber cloth.

Light steel and aluminum tubing are employed in the construction of the frame supplemented by numerous piano-wire stays. This frame extends almost the entire length of the envelope and carries at its rear end a cellular, or box-kite, type of stabilizing rudder, instead of the former gas balloonets employed on the Clement-Bayard I, Fig. 13. This cellular rudder is in two parts, consisting of two units of four cells each, the two groups being joined at the top, with a space between them. In addition to acting as a stabilizer, this is also the direction rudder, its leverage being increased by making the end planes somewhat larger than the partitions of the cells. Between the cellular stabilizing rudder and the envelope is placed the horizontal rudder for ascending or descending. In the illustration this appears to be a flag, but it is in reality a long rectangular plane, which may be tilted on its longitudinal axis, the latter being at right angles to that of the balloon. There are two air balloonets of about one-third the total capacity of the balloon itself, and they are designed to be inflated by large aluminum centrifugal blowers driven from the main engines themselves.

There are two motors, each of 125 horsepower, both being of the same conventional design, _i.e._, four cylinder four cycle vertical water cooled. In fact, they are merely light automobile motors. The cylinders have separate copper water jackets and the motors themselves are muffled, which is a departure from the usual custom. Each drives a separate propeller carried on top of the main frame through bevel gearing.

The Clement-Bayard II made itself famous by its rapid and successful flight from the suburbs of Paris across the Channel to London, in October, 1910.

*Astra-Torres.* In reviewing the specifications of any of the big dirigibles, the observer cannot fail to be struck by the excessive amount of power necessary to drive them at speeds which are lower than the minimum, or landing speeds, of many aeroplanes. When a speed of 45 miles per hour was first reached by a dirigible, it was acclaimed as a great feat. But this comparatively moderate rate of travel was surpassed only by increasing the number of motors and their horsepower until the fuel consumption became exceedingly high. This necessitated the carrying of a great weight of fuel and cut down correspondingly the useful load that the dirigible was capable of lifting as well as restricted its radius of flight at full speed. Until aerodynamic research had demonstrated the contrary, the necessity for such a tremendous amount of power was considered necessary to overcome the head resistance of the balloon itself. Research brought out in a striking manner how great a proportion of the total head resistance of an aeroplane was due to the struts and bracing wires. In the construction of the different types of airships illustrated, it will be noted that the gear provided for suspending the car or cars below the balloon requires a great number of cables. Later developments showed that by eliminating the great amount of head resistance caused by these numerous surfaces, the speed of a dirigible could be increased by over 50 per cent with the same amount of power.

_Improved Suspension._ The shortcoming of the dirigible with reference to suspension was realized more than ten years previous by a Spaniard—Torres—but owing to lack of financial support, he was unable to put his idea into execution. The principle he evolved is made clear by Fig. 14, which gives a section of an Astra-Torres dirigible illustrating the method of suspension. Instead of the ropes _SR_ used to suspend the car being attached to bands passing around the envelope, these reinforcing bands _CB_ and also the ropes fastened to them are placed inside the envelope, thus eliminating head resistance from those sources.

_Performance._ Failing to obtain any encouragement in Spain, Torres finally succeeded in interesting the French Astra Company, which built a vedette, or scouting airship, of a little over 50,000 cubic feet capacity. It was pitted against the Colonel Renard, at that time the leading unit in the French aerial navy and the fastest airship in commission. The small Torres dirigible so completely outclassed its huge competitor that another of close to 300,000 cubic feet capacity was built and tried against the Parseval with similar results. An Astra-Torres dirigible built for the British government showed a speed in excess of 50 miles per hour. This particular dirigible has been at the front in France almost since the outbreak of hostilities and has rendered considerable valuable service. Its success led the French Government to order a huge replica of it, having a capacity of over 800,000 cubic feet and with motors developing 1,000 horsepower, which would give it an indicated speed of 60 miles per hour. So confident were its builders of attaining or even exceeding this, that an order for a second and even larger airship of the Astra-Torres design was placed before the first one was finished. This is also fitted with motors aggregating 1,000 horsepower and displaces 38 tons, making it larger than any Zeppelin that had been constructed up to the time it was built. As its construction and trials were undertaken during the war, no details have been published, but it is said on good authority that its speed exceeds 60 miles per hour, so that it is faster than any of the German dirigibles.

_Construction._ Unlike the German dirigibles, the larger types of which have been characterized by a rigid frame, the Astra-Torres is a flexible airship and, owing to its method of suspension, its external appearance is decidedly unconventional, since the envelope instead of being of the usual cigar shape is more like a triangular bundle of three cigars with the third one on top. At the point where the three envelopes join, as shown in section, Fig. 14, heavy cloth bands _CB_ are stretched across the arcs, forming a chord across each arc, the three chords comprising an inverted triangle. The suspension ropes _SR_ are attached to the opposite ends of the base of this inverted triangle and converge in straight lines downward through the gas space, so that the air resistance offered by the ropes is practically eliminated since only a very small part of the suspension system appears outside the envelope. This external part consists of vertical cables _A_ attached to the collecting rings of the bracing system and extending downward through special accordion sleeves _S_ which permit the free play necessary at the points where they pass through the outer wall of the envelope. These sleeves also have another function—that of permitting the escape of gas under the pressure of expansion. A short distance below the envelope _E_ each of these cables splits into two parts _C_ and _C’_ attached to opposite sides of the car.

The British airship mentioned is provided with but one car, but the larger French ships have two placed tandem, each of which carries a 500-horsepower motor driving two two-bladed propellers of large diameter. While the form of envelope made necessary by this construction increases the frictional resistance, this is negligible in comparison with the great saving in power effected by the method of suspension, not to mention the greater simplicity of construction.

GERMAN DIRIGIBLES

*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.

_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.

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 term _stream-line_ has 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.

_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.

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.

BRITISH WAR DIRIGIBLES

*Adoption of Small Type.* German designers have continued to pin their faith blindly to the huge rigid type, despite the fact that prior to the war almost a dozen of these costly machines met with disaster as fast as they could be turned out. Since the war started, their destruction has kept pace pretty closely with their building without their accomplishing anything of military value. The British naval aeronautic service, on the other hand, appreciated the futility of such tremendous and unwieldy construction and, after a single demonstration of its uselessness, abandoned it altogether. This single attempt was the ill-fated Mayfly, which was most appropriately named, since its performance resolved into a certainty the doubt expressed by its title. In being taken out of its shed, the framing of the airship was damaged, and it collapsed a few minutes later so that it never did fly. One of the early types of small British dirigibles is shown in Fig. 20.

Attention has since been concentrated in most part on the construction of aeroplanes in constantly increasing numbers, although the dirigible has not been given up altogether. However, its restricted usefulness as well as the necessary limitations of its effective size has been recognized. Early in the war Great Britain planned the construction of fifty small dirigibles, of both the rigid and nonrigid types, all of which have undoubtedly since been completed. They are small airships designed chiefly for scouting and short-range bombing raids over camps when in army service and for coast patrol and submarine hunting as an aid to the naval forces. While no specifications are available, the cubic capacity of these patrol airships probably does not exceed 50,000 to 75,000 cubic feet, their over-all length being approximately 100 to 125 feet.

*Aeroplane Features.* To simplify the construction and at the same time minimize the amount of head resistance, the car consists of an aeroplane fuselage of the tractor type, fitted with a comparatively small motor—under 100 horsepower—and having accommodations for a pilot and an observer in two cockpits, placed tandem. The control surfaces are also similar to those used in aeroplane construction. Despite their low power, these dirigibles can make 40 miles an hour, owing to their greatly reduced head resistance. Instead of employing either an auxiliary blowing motor or a blower driven by the motor itself, the supply duct to the air balloonet is made rigid and is sloped forward so that its open end comes directly in the slip stream of the propeller; thus the latter serves to inflate the balloonet as well as to drive the dirigible. The desired amount of inflation is controlled by a valve.

*Use in Locating Submarines.* Many of these small scouting and naval-patrol dirigibles have given a good account of themselves and comparatively few have met with accident or have been destroyed by the enemy. On frequent occasions they have been very successful in locating submarines below the surface, since the body of the under-water boat is readily detected from an altitude of a thousand feet or more, even though submerged to a great depth and despite a heavy ripple on the surface that makes the water absolutely opaque when viewed from the deck of a ship. Doubtless they will be employed to an increasing extent as the hunt for the submarine becomes more and more intensive, though their use is very much restricted during the winter months, owing to the frequent and severe storms encountered.

*British Astra-Torres.* A number of comparatively small Astra-Torres dirigibles have also been built in Great Britain for coast patrol and anti-submarine work. The line drawing at the left of Fig. 21 illustrates the general design and construction of these small airships, while the various letters indicate the different parts of the gas container, air balloonets, suspension and car, and the end view at the right of the figure shows the small amount of head resistance offered by the suspension of this type as compared with that of the usual form of nonrigid dirigible. _A_ is the balloon itself, or main gas container, the pressure relief valve for which is located at _M_. _BB_ are the air balloonets connected with the blower _H_ in the car. In the illustration these balloonets are shown fully inflated as they would be after the gas bag had lost a considerable proportion of its original contents through leakage or expansion. At the beginning of a flight, when the gas bag is fully inflated with hydrogen, they lie perfectly flat along the lower side of the envelope, being brought into service only as they are needed to keep the envelope distended to its full volume.

The novel method of suspension to which this type of dirigible owes its greater speed and fuel economy, because of the reduction of the head resistance, is shown by the numerous supporting ropes _O-O-O_, which terminate in a comparatively few cables attached to the car. In the small British airships referred to here, there is but one small car designed to carry a crew of two men and the engine is of comparatively low power, driving a propeller at either end of the car, but in the large French dirigibles of the same type, two large cars are placed tandem some distance apart and are fitted with 500-horsepower motors. The various parts indicated by the letters are: _CC_ propellers, _D_ motor, _F_ space for pilot and crew, _G_ fuel and oil tanks, _J_ guide rope, _K_ gas valve, _LL_ air valves, _NN_ balloonet cable, _P_ rudder, _Q_ stabilizer, _RR_ bracing cables, and _S_ the car itself.

MILITARY USES OF ZEPPELINS

*Limitations of Use.* Nothing excites the Teutonic imagination so strongly as things military to which the characteristic German adjective _kolossal_ can be enthusiastically applied. It was for this reason that, despite its uniform record of tragic disaster for years before the war, the Germans pinned their faith to the Zeppelin as a weapon that could not fail to strike terror to the hearts of the British and French and make them hasten "to sue for peace." However, apart from its reputed employment on the single occasion that the German grand fleet left the security of the Kiel Canal, it is not known to have been used in any purely military operation. The aeroplane has been developed to a point that, in spite of the ability of the Zeppelin to ascend rapidly when hard pressed, would make it suicidal for one of the huge gas bags to sally forth in daylight, unless attended by a large number of battle planes to prevent enemy flying machines from attacking it. No such use of the Zeppelin has been recorded thus far. Consequently, it has been used only in nocturnal bomb-dropping expeditions, chiefly directed against London and only undertaken when weather conditions made detection difficult. In order to carry these out, it has been necessary to establish stations in Belgium, since the fuel consumption of the Zeppelin is so great that, even with its tremendous fuel supply of 3 to 5 tons, a flight to London and return to points well within the German border is impracticable. The first raids of this character were carried out successfully, but subsequent attempts were marked by the loss of one or two airships on each occasion, so that the practice was abandoned as being too expensive for the results attained and aeroplanes were substituted.

*Number Built.* Taking it for granted that the numbering of the German airships has been consecutive, the total number built during the first three and one-half years of the war by the Germans would be between eighty and one hundred. All large German airships have come to be commonly termed Zeppelins, but a number of them were of the Schutte-Lanz type, almost equally large and also characterized by rigid construction, which, however, was of wood with aluminum fittings instead of being all metal, as it was found that the huge metal frame accumulated a static charge of high potential that was responsible for igniting the gas in one or two instances.

*Weakness of Type.* The L-I (_Luftschiff_, or airship), the first of the German airships designed for purely military purposes, was a Zeppelin 525 feet long by 50 feet in diameter, of 777,000 cubic feet capacity, and 22 tons displacement. Its three sets of motors developed 500 horsepower and it had a speed of 52 miles per hour. It was launched at Friedrichshafen in 1912, and after a number of successful cross-country trips, it was tried in connection with naval maneuvers off Heligoland. Before the trial had proceeded very far, a sudden squall broke the backbone of the huge gas bag and hurled it into the sea, drowning fifteen out of the crew of twenty-two. It is a striking commentary on the frailness of these aerial monsters that every one of the big airships built up to that time had met disaster in an equally sudden manner but from a totally different cause in each instance. The L-II was slightly shorter but had 5 feet longer beam and displaced 27 tons. She was designed particularly for naval use, had four sets of motors developing 900 horsepower, and was fitted with a navigating bridge like that of a ship. It was confidently thought that all possible shortcomings had been remedied and success finally achieved in the L-II, but before there was any opportunity to demonstrate its efficiency, the airship exploded in mid-air, killing its entire crew.

_Effectiveness Grossly Overrated._ Despite this unbroken chain of disasters, the German official press bureau spread broadcast the prowess of the Zeppelin, its magnificent ability, and its remarkable achievements as an engine of war—in theory, since this was a year or two prior to the outbreak of hostilities. Had it not been for the forced descent of the Zeppelin IV at Luneville, where it was taken possession of by the French, these tales might have been accepted at their face value. But the log of the commander of this airship showed that its maximum speed was but 45 miles per hour, the load 10,560 pounds, and the ascensional effort 45,100 pounds. The fuel consumption averaged 297 pounds per hour while the fuel capacity was only sufficient for a flight of seven hours. During its flight, it had reached an altitude of only 6,250 feet, to accomplish which over 3 tons of ballast had to be dropped. It was also shown that the critical flying height of these huge airships is between 3,500 and 4,000 feet, Zeppelin himself declaring that his machines were useless above 5,000 feet. This probably accounts for the fact that the early raids on English towns were carried out at a height but slightly in excess of 2,000 feet. Later types, however, are said to have reached high altitudes.

Shortly before the outbreak of the war the L-5 was completed. This had a capacity of about 1,000,000 cubic feet, motors aggregating 1,000 horsepower or over, and a reputed speed of 65 miles per hour. Just what was the fate of this particular ship did not become known, since information of a military character has not been permitted to leak out of Germany from that time on. But capture or destruction has accounted for many of the intermediate numbers of the series; big German airships have been brought down in England, in the North Sea, in France, and at Saloniki, their loss culminating in the disaster to four out of the fleet of five that attempted a raid over London but were caught by adverse winds which exhausted their fuel supply so that they were blown out of control, toward the south of France. French anti-aircraft batteries or aeroplanes accounted for three of these, while the fourth, the L-49, was captured intact.

*L-49.* An essential part of the equipment of every form of German military apparatus is a means of destroying it in case of capture. In the case of the big airships, the officers are provided with revolvers loaded with incendiary bullets, which are fired into the gas bag, so that until the L-49 was forced to descend in the south of France by the activities of a battle plane, plus a lack of fuel, no airship of a recent type had ever been captured intact. In this case, the commander fired his pistol at the balloon but missed and was prevented from firing again by a French peasant who "covered" him with a shotgun. The wireless operator succeeded in using a sledge hammer on some of the apparatus of the very completely equipped wireless cabin before he was captured but did not do sufficient damage to prevent reassembly of the parts with little trouble. With the exception of the earlier type of Zeppelin that was forced to descend at Luneville prior to the war, the L-49 was the first that was ever known to have landed undamaged in hostile territory, as practically all the others were destroyed in the air, most of them having been wrecked either by aeroplane or anti-aircraft fire. Fig. 22 shows the L-49 as it rested on a hillside at Bourbon-les-Baines, France, and Fig. 23 shows a close view of the nose of the monster.

_Standardized Parts._ Comparing the L-49 with many of its predecessors led to the conclusion that it was one of the latest types, but an inspection of its construction revealed the use of many parts produced in quantities from standard patterns as well as a lack of the finish that has always characterized airship construction. Appearance and comfort had both been sacrificed with a view to saving the last ounce of superfluous weight in order to carry more fuel and ammunition. Evidently the production of these large airships has been reduced to a manufacturing basis and they are constructed in series in much the same manner as motor cars, though on a reduced scale.

_General Design._ In its general construction the L-49 was along the same lines that have characterized the Zeppelin since its inception, the outer envelope being stretched over a rigid frame of aluminum girders, inclosing a large number of independent balloons inflated with the usual hydrogen gas, no trace being discovered of the non-inflammable gas, the discovery of which had been hailed by the German press. The commander’s cabin was suspended well forward with the wireless room directly behind it, while a V-shaped gangway, recessed in the envelope proper so as to present no additional head resistance, ran back from the latter the whole length of the ship. This and the gun platform on top, mounting two machine guns and reached by a ladder suspended in a well amidships, have been familiar features of all the recent Zeppelins. The main envelope contained nineteen independent gas bags, each of which was made integral with an air balloonet to take care of the expansion and contraction of the hydrogen with varying altitudes and temperatures. Distributed along the lower part of the frame inside the envelope were a series of 50-gallon water-ballast tanks.

_Power Plant._ No less than nine large motors were employed to drive the huge gas bag, the maximum horsepower probably aggregating 1,600 to 2,000. The motors were distributed in five different locations, the largest being suspended just abaft the wireless room. The remainder were placed in self-contained units in the form of gondolas suspended from the sides of the frame, as shown in Fig. 24, the outline being that of a blunt-nosed fish. Each of these gondolas carried two motors placed side by side and coupled up so that either one or both could be employed to drive the single propeller. For cruising speeds one motor in each gondola supplied sufficient power or in some gondolas both motors could remain idle. No accommodation was provided for attendants in the gondolas, any of which could easily be reached by light ladders from the inclosed gangway.

To insure greater safety, the fuel supply was divided among sixteen tanks, all of which were interconnected with each other and the engines so that gasoline from any tank or tanks could be diverted to any particular engine. The supply of lubricating oil for each engine was carried in a tank in the gondola itself.

_Control._ Vertical and horizontal stabilizing surfaces of conventional form were built on the sharply tapering rear end of the frame, the elevator and rudder being similar to those used in aeroplane construction, except that the rudder was in two sections, the larger of which was placed on top of the envelope. The control of these surfaces, the operation of all the engines, the control of the water ballast, the air supply to the balloonets, and the fuel supply to the motors were all concentrated at a panel board in the commander’s cabin, the forward end of which bore a close resemblance to the bridge of a man-of-war. By means of thirty-eight push buttons, half red and half white, air could be released from or pumped into the balloonets, while in a similar manner the contents of any one of the water-ballast tanks could be emptied. Elaborate controls were provided for the power plant, it being possible to vary the speed or stop any one or more of the motors from the bridge. The rudder and elevators were operated by means of small hand wheels, similar to a marine steering wheel. One of the most prominent features of the operating cabin was a huge chart frame, capable of carrying a large scale map covering a considerable area, as well as an ample supply of maps. Few instruments were found in the captured ship and it is thought highly probable that everything not fastened in place had been dumped overboard at the last to increase its lifting power.

Apart from the use of standardized fittings and parts and the employment of a great deal more power in a slightly different manner than had characterized the earlier types of Zeppelins, the L-49 revealed nothing of unusual importance in airship design and certainly none of the world-beating features that German propaganda had been heralding for some time previous.

*Destruction of Zeppelins.* Mention has already been made of the fact that practically the only use made by Germany of her huge airships has been the bombardment of open cities, and that always at night. From the first of September, 1914, up to the end of 1917, between thirty and forty had met disaster, but only two were captured intact. The first of these was discovered by a Russian cavalry patrol while at anchor and its crew of thirty men were made prisoners. This was at an early period in the war, while the second one to be captured was the L-49, already referred to, which formed one of a squadron of five evidently sent out on a bombing expedition against London. Owing to adverse winds, they never reached their destination and four of them were known to have been put out of action, all except the L-49 being destroyed in the air. Not a few of these big airships have fallen victims to their own weakness and succumbed to the elements, in one instance a high wind tearing the airship loose from its moorings while the crew was not aboard. This was at Kiel, and after traveling a number of miles unguided, the big bag fell into the North Sea. In quite a number of other cases head winds have prevented the return of the raiders to their base and they have either been destroyed by their crews or wrecked at sea in attempting to return. In still other instances the unwieldy monsters have been wrecked by high winds when attempting to land, as was so frequently the case prior to the war.

_Aeroplane and Anti-Aircraft Fire Effective._ Before the war broke out the ability of either the aeroplane or the anti-aircraft gun to overcome the Zeppelin was purely theoretical, but actual experience has demonstrated that much of the theory was well founded. At least three Zeppelins have been destroyed by British aviators in mid-air, all or most of the crews being killed, while probably an equal number have been accounted for by French aviators in open battle. The war had not been under way a month before French anti-aircraft gunners showed their skill by bringing down-a "Zep," while only a week later a Russian battery accomplished the same feat, in this instance killing the entire crew. In 1916, British and French gunners succeeded in either "winging" or setting on fire three or four, while two dropped into the North Sea and one was blown up by its crew, having run out of fuel while raiding Scotch towns.