ordinated with the engine and the airplane. European engineers are also working on the development of a variable pitch propeller and a two-propeller arrangement, the first of the ordinary pitch and the second of an extraordinary, to be used at high altitudes.

An interesting development at McCook Field was the construction of a wind tunnel operated by a 24 blade suction fan. The tunnel has a minimum throat diameter of 9 inches, at which point a speed of over 350 miles an hour is attainable. In this connection, special reference should be made to the wind tunnel and other laboratory facilities developed by the Curtiss Company at Garden City.

The importance of the air-cooled aeronautical motor is fully realized in this country. While no substantial development has been formally noted, the Dayton-Wright Company have done some vital fundamental work and it is understood that similar study is being carried on by the Wright Aeronautical and L. W. F. companies.

Reports from England show very valuable progress. A nine cylinder ABC engine developed 340 horse-power with a weight complete of 600 pounds, of 134 pounds per horse-power. As the air-cooled engine carries neither water nor radiator, this shows remarkable progress over the old type. A Cosmos Jupiter engine, also a ninecylinder stationary air-cooled type, gave 450 horse-power for a weight of 662 pounds, an extraordinary figure.

One of the most interesting phases of aeronautical activity during the year, and one which is likely to have the greatest possible influence on the commercial growth of the industry is the construction and use of parachutes. The Army has developed completely successful parachutes which, strapped in a pack on the back of the aviator, acting at the same time as a cushion operated whether by a rip-cord attached to the plane or by the wearer himself, have enabled numerous perfectly safe descents to be made.

An experiment which may ultimately lead to very important results was the delivery of air mail to an ocean liner. C. J. Zimmerman piloting an Aeromarine flying boat, delivered mail to the White Star liner Adriatic. The plane was equipped with a specially devised weighted cable with shock absorbers, which when released caught and wrapped itself around a cable that ran from the masthead to the deck of the Adriatic.

CHAPTER VII

TECHNICAL DEVELOPMENT, BALLOONS AND

T

AIRSHIPS, 1914-1919

HE technical development of aerostats

larly called lighter-than-air craft has made enormous strides since the beginning of the World War.

Nonrigid Airships.— The German submarine warfare was more than any other single factor responsible for the development of new airship types in the Allied countries. The ability of airships to regulate their flying speed and to extend vision below the surface of the seas, made of these craft an extremely valuable auxiliary to the Allied naval forces engaged in fighting the submarine menace.

The first type of airship developed with this end in view was introduced by the British in March, 1915; it was designated as S.S. (Sea Scout) and soon nicknamed Blimp. These were small nonrigid airships with a capacity of 60,000 cubic feet, at first, which was gradually increased to 100,000 cubic feet, and were chiefly remarkable for the original manner in which the problem of a lightweight car and power plant was solved. The car was merely an airplane fuselage, complete with its engine and tractor screw, gas and oil tanks, and accommodations for a crew of two or three men. This arrangement had the further advantage of permitting to utilize the fuselage of many obsolete machines. A notable feature of these airships was that the customary ballonet blower was dispensed with; instead a blower pipe, or "air scoop," was arranged to collect air from the slipstream of the propeller and to discharge it into the distributing duct leading to the ballonet. Later on, to save head resistance, the blower pipe was hinged to the envelope so that it could be folded up when not in use.

The Blimp type of airship proved highly successful in coastal antisubmarine defense and about fifty ships were built for the British Navy with successive improvements. Toward the end of 1916, the French produced a similar type of airship, which was fitted with twin engines and twin propellers, an arrangement which increased security of operation and was subsequently adopted by the British.

When the United States declared war on Germany, the Navy Department ordered sixteen airships of a type similar to the original

British Blimp, but incorporating a number of refinements. Nine of these B-class ships were built by The Goodyear Tire & Rubber Company, five by The B. F. Goodrich Company and two by the Connecticut Aircraft Company. About 170 pilots were trained on the B-class ships and 400,000 miles flown on coast patrol prior to the Armistice.

The extension of submarine warfare and the change in the tactics of undersea boats prompted Great Britain to develop in 1917 larger types of nonrigid airships, capable of lifting a greater load and having a longer endurance. These were used with great success for coast. patrol and convoy work and for extended cruising.

At the same time the French Naval Air Service introduced a nonrigid which was chiefly remarkable for its armament; this consisted of a 37 milimeter aircraft gun, firing a 1-pound shell. These ships were the only ones built in any country during the war to carry artillery, though machine guns were used on both Allied and German airships.

In 1918 an excellent type of coast patrol airship was produced in the United States to the designs of the Navy Department. Owing to careful design, the ships attain a speed of 60 miles per hour with only 250 horse-power, furnished by two Hispano-Suiza or two Union engines a higher efficiency ratio than has hitherto been obtained anywhere. Another factor which greatly contributed to this result was the use of the "finger patch" rigging, a type independently developed by The Goodyear Tire & Rubber Company, although it bears a certain resemblance to the Eta Patch. In this system, which permits to eliminate the heavy suspension girdle of German origin, the suspension wires are attached to patches of fabric strips, in the form of a hand, which are cemented and sown to the envelope. The finger patch rigging insures a very wide distribution of the load and thus reduces the number of suspension wires. Hence, the great reduction in head resistance.

These "C-class" airships have a length of 192 feet, a diameter of 4134 feet, a capacity of 180,000 cubic feet, and a useful load of 4,760 pounds. They carry four 260-pound bombs, a radio set and a crew of six men. The endurance at 45 miles per hour is 47 hours, or 2,150 statute miles.

An interesting innovation is found on the British N.S. airships in the manner in which the fuel supply, amounting at times to three tons, is distributed. This is carried in 80-gallon tanks, made of

fabric lined with a gasoline resisting dope, which are trussed to the inside of the envelope. The tanks are controlled from the car by means of wires and access to them is obtained from a tube which leads through the center of the ship to a gun platform fitted on the top.

Among the principal developments produced in Italy is an ingenious arrangement for compensating a contraction of gas in Forlanini airships. These have a double envelope, the inner one containing the gas, while the space between the inner and outer envelopes acts as a ballonet. Pressure in this space is derived from the air stream which strikes the nose of the airship in flight; this is admitted by means of a valve fitted in the bow, and is operated from the control car. An outlet valve of the spring-loaded type is fitted on the stern and automatically relieves the pressure in the air space whenever the latter reaches the designed limit.

Rigid Airships.- Real advance in rigid airship design and performance since 1914 has been, with few exceptions, limited to Germany, which entered the war with an efficient Zeppelin fleet and fifteen years' experience. The history of German Zeppelin development during the war is one of continuous increase in size and horsepower, resulting in greatly improved carrying efficiency (ratio of useful load to gross lift), speed and endurance, although a great deal of detail refinement work was also carried out. The evolution of the Zeppelin airship during the last twenty years is shown in the following table:

DEVELOPMENT OF THE ZEPPELIN AIRSHIP, 1900-1919

The most striking departure noticeable on the Zeppelins produced since the war is the suppression of the external keel, for which an internal was substituted, and the discarding of the shaft drive for

propellers, instead of which engines and propellers are mounted in streamline cars along the sides of the hull.

With the knowledge gathered from Zeppelins brought down in the Allied lines, Great Britain succeeded in producing in 1918 some very serviceable rigids, among which the R-34 type of transatlantic fame. The development of an original British rigid design just started when the Armistice intervened and ultimately caused the virtual scrapping of the British airship program. As a result, the largest British airship laid down the R-38 was sold to the United States Navy. This vessel, which is still in course of construction, has a capacity of 2,700,000 cubic feet, and is driven by six engines totaling 1,900 horse-power. The useful load will be in the neighborhood of 50 tons.

This purchase marks the first step of the United States toward the building up of a rigid airship fleet for naval use. An airship hangar 800 feet in length is being constructed with this end in view at Lakehurst, New Jersey, and a great amount of research work has been conducted by various government agencies for developing materials of construction suitable for rigids. The problems of duplicating the aluminum alloy of which Zeppelin girders are built and of developing a satisfactory fabric for the internal gas bags have in particular been investigated. With respect to the former, American ingenuity succeeded in producing an alloy which is slightly better than the German product; it has the strength of mild steel, although it weighs only half as much. As to the development of a suitable fabric for internal gas bags, this has not yet been achieved, but the Bureau of Construction and Repair of the Navy Department has succeeded in producing a compound, or "dope," which approximates the impermeability of goldbeaters' skin and is but slightly heavier.

Minor Developments. In the field of nonrigid airships, the development of internally trussed, streamline fins was a most original and successful American innovation, alongside of which should be mentioned the Gammeter valve, produced by the Goodyear Company. The development of this valve represents a great achievement in that a gas tightness hitherto unachieved is secured thereby.

An important contribution to the science of aerostatics has undoubtedly been the discovery, in the United States, of a process whereby helium can be produced at comparatively low cost.

Helium has a lifting power of 92.6 per cent. as compared to hydrogen and is absolutely non-inflammable. Although its production