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ZR-2 / R-38

In 1919, with the First World War behind it, the U.S. Navy began a rigid airship program, ordering the construction of two dirigibles, plus a very large hangar at Lakehurst, New Jersey. One of the new rigids was built in England as the British R-38, using what was presumed to be a tested and reasonably mature technology. Upon delivery, she was to become the American ZR-2. The other, ZR-1 (later USS Shenandoah), was assembled at Lakehurst, and her construction was delayed awaiting the completion of the new hangar. Thus R-38 was the first of the new ships to be completed, making her first trial flight in June 1921, nearly a year before ZR-1's first frame was erected.

Already wearing U.S. markings, R-38 made three more flights during the next two months, both for testing purposes and for the training of her American crew. Delivery was to take place soon thereafter, with the airship being flown across the Atlantic to begin operations from Lakehurst. Her fourth flight began on 23 August 1921, amid growing questions about her performance and structural strength. After an overnight flight out to sea, the next day R-38 undertook full power and maneuvering trials. These proved too much for her. She broke up in the air, some of her hydrogen lifting gas exploded, and the wreckage fell into the Humber River near Hull, England. Of the forty-nine men on board, there were only five survivors, including one American. Sixteen U.S. Navy officers and men were killed, essentially wiping out the Service's small cadre of experienced rigid airship personnel.

Germany launched her first "super-Zeppelin," a 2,000,000 cubic foot vessel, in 1916, after fifteen years' experience in this branch of engineering, in which period she built some sixty Zeppelins ranging all the way from 400,000 cubic feet to 1,250,000 cubic feet. In the fall of 1916 one such super-Zeppelin, the L-33, was brought down fairly intact in England and the British Admiralty instructed its airship designers to duplicate it. Up to that time British experience in rigid airship design and construction was limited to that obtained from a number of experimental ships that were being built after very incomplete drawings of pre-war Zeppelins.

The British copy of the L-33, called the R-33, was only finished after the armistice, her trials taking place in the spring of 1919. Although the vessel embodied some improvements found in another captured Zeppelin, the L-49, which had come down intact in France, it should be pointed out that while the latter ship had a useful load of 39 tons, and the L-33 one of 30 tons, the British copy of these 2,000,000 cubic feet dirigibles had only a useful load of 24 tons. All of which is merely mentioned to show that a painstaking copy of an engineering structure will not necessarily be identical in all respects with the prototype-although they may look alike.

But while the R-33 carried a smaller useful load than her German sisterships, she seemed to be in every way as strong as the latter. How strong the hull of these ships was. the R-34 (sistership of the R-33) demonstrated at Mineola, Long Island, where for four days she withstood buffeting by winds, although on one occasion the anchorage fitting of the main handling rope was pulled clean out of the framework.

The success of the R-33 class airships prompted the British Admiralty in 1918 to prepare drawings for a much larger class of airships which were to be superior to the German L-71 type. This was the ill-fated R-38 (the ZR-2, as she was called in the US) class, which incorporated numerous novel and original ideas. Now, it should be emphasized that when this class was laid down, all the experience the British had in rigid airship construction had been derived from copying German ships. The only firm which eventually was to produce a highly successful original design (Vickers. Ltd., with their R-80) had not by then emerged from the experimental period of their work; their experience was therefore unavailable.

As to the question "Was the purchase of the R-38 by the United States Navy justified?" - it would seem to the impartial observer that it was not. Indeed, why should the Government spend abroad $2,000,000 on a foreign-built, untried type of dirigible? The Navy was desirous of developing rigid airships in this country. This can be brought about only through experimentation, and it will be admitted that if the necessarily heavy financial outlay has to be faced it will better serve its purpose if the money is spent here rather than abroad. American inventive genius is second to none in the world and can be relied upon to solve the problems of rigid airship construction just as well as it has solved other engineering problems.

And what was particularly odd, the Admiralty gave the contract for the construction of the R-38 (or ZR-2) to Short Bros., of Bedford-a firm that had never before built a Zeppelin type airship and whose entire experience with rigids was obtained from the building of R-31 and R-32, which were patterned after the plywood-framed SchuetteLanz type.

Here then is, in part at least, the answer to the question which heads this article: What was the matter with the ZR-2? The ship was built in a factory that had no previous experience with duralumin airship construction, and to plans which were not based on practical experience. To cite but one instance, the well-proven radial truss of the transverse frames was replaced on the ZR-2 by a tangential truss system, the merit of which had yet to be demonstrated. In this connection one cannot do less but pay a respectful homage to the memory of the late Colonel Campbell, chief airship designer of the Admiralty, who had sufficient faith in his ideas to go up on the ZR-2 during her several trial trips and who lost his life with the ship.

Knowing the circumstances which surrounded the construction of the ZR-2 begins to explain why, as one report has it, "several girders were strained in the factory when as many as thirty fitters crowded on them in the course of assembly work." It is quite conceivable that workmen accustomed to the resiliency of plywood girders would do just such a thing and that their foremen, not knowing any better, would not wam them. And a 700-foot airship is such a gigantic structure that the engineers familiar with the vagaries of duralumin-whom the Admiralty had detailed to the Short Works-could not personally supervise every detail.

For the sake of completeness it may be added that when Messrs. Short Bros, closed down their airship department, the Admiralty took over their factory and completed the ZR-2, whereupon she was handed over to the British Air Ministry.

That the hull of the ZR-2 was structurally weak was first demonstrated on the inflation of the ship when, due to unequal load distribution, several girders buckled. The failing members were repaired, but during the first trial flight trouble was again experienced from several intermediate longitudinals and transverse frames, so that it became necessary to reinforce certain portions of the framework. Details are not available as to the exact nature of this stiffening work, but one might suggest that by reinforcing certain girders others may have been further weakened. Of course, this is merely a guess.

Judging, however, from all that has been said before it appears beyond a doubt that the ZR-2 was structurally weak - a condition brought about by the desire to carry the greatest possible useful load. This, as originally designed, was to be in excess of 50 tons, but it was subsequently reduced by the fitting of a bow mooring gear, not to speak of the reinforcement of the hull.

It is not difficult to visualize what went wrong with the ZR-2. Statements by survivors seem to establish pretty definitely that the big airship broke in two not under the strain of full speed trials, as had first been assumed, but that the longitudinals snapped when the helm was put hard over. The commander of the dirigible, who was rescued, has declared that at the time of the accident the ship was making 50 knots-as against 65 knots "all out." On the other hand, another survivor, Lieutenant Bateman, states that just prior to the accident the ship had made turning tests, and that two turns had been managed without difficulty, but that on the third the vessel broke her back. His statement is particularly significant in view of the fact that he was able to observe the working of the rudders as he was seated in the stern cockpit, which is aft of the rudders.

So it becomes rather obvious that the ship was turned too suddenly for the speed at which she was flying, although this maneuver might have been totally harmless at a lesser speed.

There is still a further point to be considered: information reaching this country from men who were in close contact with the development and trials of the ZR-2 shows that her control surfaces were overbalanced. That is to say, the balanced portion of the rudders was so large that they were extremely sensitive to air pressure, so that when the ship was under way a slight turn of the steering wheel would suffice to whip about the rudders. At high speed this would naturally cause a tremendous strain on the TOO-feet-long framework.

It would therefore seem that the design of the ZR-2's rudders was faulty. This defect, which might have been easily remedied, would not have been a serious matter on a stronger ship. But the ZR-2, far from being a strong ship, was what one may call an " extra-light" vessel-a feature which borders on structural weakness. To understand the why and wherefore of the situation wc must look at the history of rigid airship development, which takes us back to Count Zeppelin.

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Page last modified: 07-07-2011 02:39:59 ZULU