Part 4

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.