Many civilians have been mystified to discover, while watching the U.S.S. Macon soar through the air, that the group of tiny planes they saw flying around the ship only a short time before had disappeared. Even in the fleet their disappearance is novel and many of the Navy personnel are apt to think that the launching and retrieving of heavier-than-air craft from lighter-than-air craft is being done for the first time. This is not the case. Rather, the operation sustains the accuracy of the old observation that “there is nothing new under the sun.”
The Macon and Akron have been very successful in launching and retrieving airplanes while in flight, although it was the Los Angeles which carried the brunt of the early work. Hook-ons are now made in daylight or in darkness, in smooth air or in bumpy air.
This operation is carried on only by the United States Navy at present, although it is undoubtedly true that had other countries not restricted the use of lighter-than-air craft they too would have attempted to fly airplanes from airships.
Nevertheless, it is our Navy which has brought this operation to its present high stage of development. Few of the early attempts were any more than experiments which were quickly discarded when the real difficulties became apparent. As a matter of fact, the initial efforts were concerned only with the release of airplanes and it was not until 1924 that efforts were made to secure a plane onto a flying airship. The steps in combining heavier and lighter-than-air craft, however, extend back many years and, no matter what the individual ideas were which lay behind these efforts, they all form an interesting path leading to the daily operations aboard the U.S.S. Macon.
As early as 1912, Count Zeppelin is said to have discussed at great length the feasibility of using airplanes in conjunction with his giants of the air. At that time some of his airships were being put to use on commercial air lines throughout Germany and he foresaw the ease with which passengers could be transported to and from aerial liners. War soon put a stop to any such novel ideas and it was not until 1915 that the discussion again came up, this time in connection with carrying fighting airplanes aboard the Zeppelin raiders. Actually, it was 1917 before the experiment was made when the L-35, an experimental ship, carried a plane aloft and launched it in the vicinity of Berlin. Captain Strasser, the chief of the Naval Airship Service, was enthusiastic over the operation of airplanes from airships but he met his death in the L-70 and further developments ceased.
A plan worked on for some time by the German airship personnel was the launching of torpedo gliders. Carried beneath the hull of the Zeppelins, the torpedoes were fitted with biplane wings. The after end of the missile was to carry control surfaces which could be set before launching efforts were made to control the weapon in flight, but the problem was so difficult that the entire experiment was laid aside in favor of bombs.
By 1915, the Zeppelin raids on London and the industrial areas of England became extremely aggravating to the English. True, the defenses had gradually driven the airships up to nearly 15,000 feet, but they still were a weapon which required much attention. Not much actual damage was being done, but many anti-aircraft forces were kept home when they were urgently needed overseas. Many airdromes and aviators had to be maintained in England when there was a crying need for them in France.
Balloons with nets were suspended in the sky in the hopes of entangling the airships; patrol boats were stationed in the North Sea to notify London of the approach of raiding Zeppelins; the antiaircraft defense was kept in trim only to spray London with their spent shells, for they had little effect upon the raiders; airplanes were kept aloft at all hours of night in an effort to intercept the giant lighter-than-air craft. Of all these defense weapons the one with the greatest potential power was the airplane firing incendiary bullets. Unfortunately, the low-powered engines of the day emasculated the potentialities of the defense airplanes, for the Zeppelins could easily out climb them.
Squadron Commander Ireland, of the Yarmouth Naval Air Station, had often been thwarted in his efforts to reach the enemy airships. After a long, slow climb his craft might finally attain the original altitude of the raiders only to find that they had quickly gone higher and were then en route to their home bases in Germany.
In the latter part of 1915, after a particularly disappointing episode, from his point of view, he conceived the idea of attaching a fighting plane to a nonrigid envelope. Upon receiving warning of an impending raid he proposed to send this novel craft to the height of the approaching Zeppelins. The lighter-than-air feature would permit a rapid ascent and, moreover the airplane need not release itself from the envelope until the Zeppelin came within striking distance, thus conserving fuel and permitting a longer period of attack.
It was February, 1916, before the experiment could be carried out, with Wing Commander Osborne, commandant of the airship station at Kingsnorth, acting as observer and Squadron Commander Ireland piloting the odd craft. Reaching their ceiling, the pilot pulled the releasing mechanism. The three suspension cables failed to release evenly and the resulting jerk threw the pilot out of the plane to fall to his death. Wing Commander Osborne, a pilot of lighter-than-air craft only, now found himself aloft in a strange machine. The plane finally found its way into a spin from which it never recovered. The experiment was promptly discarded.
The British immediately set to upon another scheme for intercepting the Zeppelins far at sea before darkness set in. Improvements upon the Curtiss flying boats which the English had imported early in the World War had resulted in the “Big-America” type of Felixstowe patrol plane, a forerunner of the famous F5L (Felixstowe, Fifth model, Liberty engine). Mounting two Rolls-Royce Eagle engines, the “Big-America” type had fairly good performance for that period. It was proposed that these patrol planes cruise far out into the North Sea, each carrying a small fighting landplane upon its upper wing. When a Zeppelin was sighted the landplane was to be flown off to attack the invader with excellent prospects for success due to its fine performance as well as the advantage of a surprise attack.
The first launching of the Bristol Bullet landplane in flight was successfully carried out by an R.A.F. pilot, Day, who returned and landed ashore. It was found that the difficulties involved were not worth the results to be obtained and this idea was abandoned in favor of launching fighting planes from a small platform towed at high speed by a destroyer. This latter method proved its worth when Flight Lieutenant S. D. Culley was awarded the D.S.O. for shooting down the L-53 commanded by Captain Proelss.
As soon as rigid airships became available in England plans for airplane-carrying experiments were put forward, and in 1917-18 the schemes bore fruit. A Camel fighting plane with locked controls was carried aloft by the R-23. When released without a pilot it assumed a normal glide and made a good landing. Later on another Camel with F. O. Keys as pilot was safely launched from the same airship, but no efforts were made to attach the airplane to the airship while in flight. These experiments were eagerly received throughout England and it was immediately suggested that the mission of airships should be that of a fast airplane carrier patrolling routes to over-sea bases. In May, 1920, further tests were ordered to be made, but about this time Great Britain temporarily ceased her development of lighter-than-air craft and the plane-launching project, of necessity, stopped.
Interest in this project was not restricted to Europe, for in the latter part of 1918 a small airplane was carried aloft in the United States in a C-class nonrigid airship and successfully dropped. It was clearly recognized that the offensive and defensive qualities of the airship would be enhanced if they could be made to carry scouting and fighting planes.
Up to this time all experiments dwelt solely with the release of airplanes from airships. The more difficult task of landing airplanes upon an aerial mothership had not been attempted. During the summer of 1924, the United States Army Air Corps devoted much thought to this problem which culminated in actual tests later in the year. The original thought was to release radio-controlled airplanes carrying a war load of bombs. However, this early idea was gradually discarded as First Lieutenant Clyde V. Finter, A. C., was ordered to proceed to Scott Field, Belleville, Illinois, for the purpose of “testing apparatus for hooking Messenger airplane to airship.” Mr. Lawrence Sperry also was closely connected with the design and testing of the hook-on and release apparatus, mounted on a nonrigid Army airship of approximately 200,000 cubic feet capacity.
The airplane used for the experiments was a Sperry Messenger having a gross weight of nearly 1,000 pounds. On the center section of the upper wing was mounted a pyramidal structure having a longitudinal, horizontal guide bar which served the purpose of a propeller guard as well as a guide to slide the trapeze bar into the hook mounted at the rear of the guide bar. The aperture of the hook was only about one-fourth inch larger than the trapeze bar thus adding to the difficulty of hooking-on. The hook was designed to automatically open in case the relative difference in speed between the plane and the airship exceeded 2 miles per hour, for it was calculated that a greater shock would carry away some part of the apparatus.
The trapeze bar was mounted on the airship by means of two rigidly secured uprights joined at the lower ends by a crossbar. Just below this, the trapeze bar, a straight bar 3 feet in length, was secured by means of a shock absorber cord which was designed to permit a fore and off movement of about 4 inches to absorb the shock of landing. However, this flexibility was not attained in the tests.
The first use of this gear was at the air races in Dayton, October, 1924. The plane was carried aloft by the TC-3 and released from an altitude of 1,500 feet after the engine had been started. It was not until December of that year that actual tempts to hook-on in flight were made.
The first series of hook-on tests should have been sufficient to satisfy the most adventuresome souls. A small nonrigid airship has never been noted for its smooth flying characteristics. Besides, the air the day selected for the tests was extremely bumpy. To add to the difficulty of the pilot, the trapeze hung but 12 feet below the control car and the slip stream of the airship’s propellers was soon found to affect the control of the plane. Yet another problem offered difficulties. In order to carry the load of the plane, the airship was flown 1,000 pounds light. To compensate for this increased lift the ship could not be flown on an even keel without gaining altitude. When nosed down to counter the tendency to rise, the ship proceeded to alternately rise and fall.
Nevertheless, Lieutenant Finter began his approach upon the narrow bar suspended from the bobbing nonrigid which was flying at 55 miles per hour. He approached from the rear and below his objective. When close to the bar, a disturbed condition of air was encountered which threw his plane upward. The guide bar on his craft struck the trapeze violently throwing the plane downward. Swinging around the pilot made a second approach only to find himself once again bounced off the trapeze. During a third attempt an air current again took charge of the airplane and forced it upward, but this time the propeller was broken by striking the trapeze and the pilot was forced to land in a pasture.
Fortunately, during the second series of tests the air was smoother and the airship was flown only 250 pounds light, thus permitting it to fly more nearly on a level keel. On the very first attempt, Lieutenant Finter had no difficulty in engaging his hook around the trapeze bar, but the automatic device operated perfectly due to excessive speed and the plane flew right through without stopping. The second approach resulted in another flying contact which failed to stop the plane. On the third attempt the pilot slowed his plane down close to the stall and, barely overtaking the nonrigid, engaged the trapeze with his hook—and stopped. Here was the first actual landing of one aircraft upon another! Dumping out ballast, the TC-3 returned to the vicinity of Scott Field where the plane was released to fly to the landing field.
The Army discontinued their efforts along this line upon the successful culmination of these tests for they considered their particular project ended. Besides, the Navy had been assigned the task of developing the rigid type of airship and, obviously, only on this type of aircraft could the airplane be useful. Further, they concluded that an average pilot could make a successful contact using similar gear, providing his overtaking speed did not exceed 5 miles per hour. In the light of the great amount of development that has since taken place, and in view of present-day operations, the report might well have been a prediction.
In the meantime, lighter-than-air operations had again been undertaken by the Royal Air Force and the autumn of 1925 saw hooking-on experiments once again under way. In general, the airplane gear was similar to that used by the United States Army, except that the hook did not possess the automatic releasing feature. The trapeze was about 3 feet in width and was swung 30 feet below the hull of the airship. It was pivoted at the upper end and could be swung up by hand winches close to the skin of the ship in order that the plane pilot could disembark or enter his craft.
The first tests were made at Pulham on October 15, 1925, with an 800-pound D.H.53 piloted by Squadron Leader R. A. de Haga Haig. In these experiments the rigid airship R-33 carried the airplane powered with a Bristol Cherub 2-cylinder engine from the ground. The tiny plane was released at 3,000 feet when the ship was flying at 20 knots. By the time the trapeze was ready to accommodate the plane, the airship was flying at 38 knots at an altitude of 2,100 feet. The approach, however, was much too fast and as the hook engaged the trapeze the plane tended to pivot upward and swing around the bar with the result that the propeller fouled a brace wire of the trapeze. Both the wire and the propeller were broken and the pilot cut his ignition. Rather than trust the weakened structure, he released his craft and glided to the ground.tc
Haig made the second attempt from the same station on October 28. Again the plane was released in the air and approached the trapeze when the airship was flying at 42 knots. Again there was no difficulty in engaging the bar. The actual landing was made, but just as the pilot was relaxing the plane slipped violently to one side of the trapeze causing a strap to break and permitting the plane to fall off its precarious perch.
Steps were now taken to re-enforce and improve the entire gear. Additional brace wires were provided and better shock-absorbing devices were installed. The third attempt at hooking-on was not made until December 4, when the same flyer succeeded in attaching his craft to the suspended bar at a height of 2,500 feet and an airship speed of 45 knots. The trapeze was swung up close to the hull and the pilot disembarked into the airship.
Squadron Leader de Haga Haig’s conclusions resulting from these experiments are exceedingly interesting:
From the experience gained there is no doubt that, given an airship suitably designed, airplanes can be released and hooked on and housed again with ease. We have proved that it can be done and that very little more experiment is needed to make it a very straightforward job which can be carried out by any pilot who has had experience in close formation flying. For training purposes it would not even be necessary to use an airship. Any big airplane could have a suitable trapeze hung from it for other airplanes to practice on with dummy hooks.
The British realized that to be useful a military plane must be applied to the airship. Thus, the D.H.53 was discarded in the following year when the work was continued. Even then no more attempts were made to hook-on, due mainly to the slow top speed of the airship and higher landing speeds of the military planes. On October 21, 1926, the R-33 took the air carrying two Gloucester Grebe fighting airplanes each weighing 2,500 pounds. One plane was carried well aft and the other was slightly abaft the control car. Flown by Flight Officers Rogg and McKenzie Richards, these machines were successfully launched into flight from a height of 2,000 feet and a speed of less than 40 knots.
On November 3, 1926, trial landings were made by the R-33 at a new mooring mast at Cardington. During these tests two Grebes were carried although they were not launched. On the 17th, the airship attempted to demonstrate this experimental work before the Dominion Premiers but low clouds thwarted the efforts to launch the fighting planes. On the succeeding flight the two Grebes piloted by Squadron Leader B. S. Baker and Flight Leader F. H. Shales were dropped while the airship was in flight. The word "dropped" is used advisedly because in all of these tests the airplanes were released at well below their stalling speed. The R-33 was deflated on the following day and British attempts to combine the advantages of lighter anti heavier-than-air craft ceased.
In the meantime the ZR-3, added to the Navy Lists as the U.S.S. Los Angeles, was flown from Friedrichshafen to Lakehurst. Interest in the possibility of practical hooking-on was once more aroused in the United States and the problem was seriously considered by the Navy Department. Obviously, the releasing of airplanes presented no great difficulty. The earlier experiments by the U. S. Army and the Royal Air Force indicated that a hook mounted on the airplane combined with the trapeze suspended below the airship was probably the best means of solving the problem of hooking-on. The alternative was to use a bight of cable suspended from the ship rather than a rigid trapeze. Thus, more clearance between airplane and airship could be provided, reducing the danger of collision as well as keeping the bobbing plane in a smooth air flow. On the other hand, such a device would provide a most unstable target to steer for it would unquestionably add to the difficulties of housing the airplane within the ship.
After much thought, it was decided that the Navy would follow the trail blazed earlier by the U. S. Army. This included the rigid trapeze and the hook with the automatic releasing device. Advancing progress decreed that the apparatus be capable of handling a modern military plane weighing as much as 3,000 pounds, with an overtaking speed up to 10 miles per hour. Moreover, it was desired to draw the aircraft close up to the airship as a step towards housing them within the hull of future aerial giants.
Because of the familiarity of Goodyear-Zeppelin Corporation with airship construction it was felt that this organization was best fitted to build the trapeze gear and the contract was let as early as June, 1927. After much experimental work a trapeze was finally produced which combined all the good old ideas and many entirely new ones.
The hook was quite similar to the Army’s and an extension, or tube, led forward over the propeller. At this end a steel spider covered its whirling arc in order that it would not be fouled on the trapeze. The guard tube was also expected to provide a contact for sliding the plane forward until the hook closed securely around the bar.
Mounted on the plane’s upper wings were two smaller fittings known as auxiliary hooks. Arms in the trapeze were to be lowered into these fittings thus providing a 3-point suspension for the airplane during the process of housing. The plane was to be hoisted by an elaborate hydraulic-pneumatic apparatus which also served as a brake or decelerator for the trapeze during the landing of a plane.
At dawn on the morning of July 3, 1929, a UO-1 airplane piloted by Lieutenant A. W. Gorton approached the Los Angeles for the first Navy attempt at a hook-on. Several approaches were finally made during which the plane appeared to nibble at the trapeze bar. Twice during the attempts the hook engaged the bar but the impact was too great and the automatic release functioned permitting the plane to fly through. Difficulty was experienced when the guard tube struck the trapeze, for this threw the airplane down several feet in a manner reminiscent of the Army experiments. One perfect landing was made and the plane remained on the trapeze for a moment before a hook failure allowed it to fall off.
The indefinite results of this first day’s work caused much concern and many other ideas for hooking-on were immediately advanced. Again it was thought that use might be made of the bight of a loose cable suspended from the airship. Another plan was to carry a suspended hook cm the ship into which the pilot would place, by hand, the ring of the plane’s hoisting sling. A quick attempt to simulate this idea with a sandbag quickly showed its futility.
Thus, it was concluded to continue the experiments with the original equipment, except that modifications were made to correct the early difficulties. Among other things the automatic releasing feature of the hook was eliminated as it was judged safe to trust the pilot’s estimate of overtaking speed. On August 20 Lieutenant Gorton succeeded in making three landings with little or no difficulty. On the following day he repeated his effort and Lieutenant Commander C. A. Nicholson (C.C.), U. S. Navy, also made two landings followed up by one landing by Lieutenant Commander L. C. Stevens (C.C.), U. S. Navy.
The first transfer of a passenger from a rigid airship in flight occurred during the National Air Races on August 28, 1929. Lieutenant Gorton made contact with the Los Angeles over the field, and Lieutenant C. M. Bolster (C.C.), U. S. Navy, climbed into the plane and was flown to the ground. It was fitting that Lieutenant Bolster should be the first passenger, for a considerable number of the refinements making this device a success were a result of his arduous work.
During the following year landings aboard were made by C. A. P. O’Brien and Lieutenant Commander Nicholson as well as by Lieutenant Gorton. The technic of the operation improved considerably and improvements on the gear were constantly being made. During this period a glider was launched twice from the Los Angeles, on the first occasion piloted by Lieutenant Commander Barnaby (C.C.), U. S. Navy, and the second by Lieutenant Commander Settle, U. S. Navy.
Up to the spring of 1930 a total of about 20 successful landings had been made aboard the Los Angeles and it was still considered experimental. However, the results had been such as to warrant the incorporation of a hangar space into the design of the Akron and the Macon which were in process of construction.
In February, 1931, Lieutenant D. W. Harrigan was ordered for duty in connection with lighter-than-air activities. Moreover, N2Y-1 training airplanes were provided for hooking-on. Their lower landing speed made the work more feasible and developments began to go along at a rapid rate. A second pilot, Lieutenant H. L. Young, was then ordered to this duty and the operation of hooking-on began in earnest.
The commissioning of the U.S.S. Akron provided a faster airship for this work and about this time a high-speed fighting plane, the F9C-2, was produced for use aboard airships and for the first time a really serviceable airplane was used aboard a lighter-than-air craft.
In June, 1932, steps were taken to organize a heavier-than-air unit for the two Navy airships when four more pilots were ordered to this duty. This made a total of six and it was the intention to eventually add two more thus making it possible to form two groups of four pilots each, one unit for each airship. The loss of the Akron prevented this and all six pilots were ordered to the Macon. By the winter of 1933, several hundred landings had been made and it is now a routine operation.
The lighter-than-air branch of naval aviation will forge ahead only by constant use of airplanes which will extend its scouting range manifold and will provide protection by intercepting an enemy air force far distant. The airship, thus informed of the presence of an enemy body, will be enabled to take every possible step to avoid it. The greater the number of airplanes carried the more effective will be the airship.
Nor is the use of the hooking-on operation restricted to military or naval airships. Huge passenger airship liners on extensive tours will make use of this device. It will become unnecessary for the tremendous ship to land for a few passengers or mail. Instead, the cargo will be flown up to the airship without loss of time and with practically no ground force. Again, our Navy will have paved the way.