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Aviation History
1924
1924 - 0686.PDF
OCTOBER 23, 1924 LARGE ALL-METAL SEAPLANES A PAPER under above title was read by Dr. Rohrbach before the Royal Aeronautical Society on Thursday of last week, October 16. It was unfortunately not possible for the Society to send out advance proofs of the paper, so that the discussion was perhaps rather less interesting than it might have been. The paper itself suffered somewhat from being partly technical and partly popular, the author stating just enough to arouse the interest, or even to invite challenge on certain points, without advancing the proofs or giving the steps in his reasoning which had led him to the conclusions at which he arrived. To add to the difficulties, Dr. Rohrbach, although speaking English extraordinarily well, was obviously not always able to express himself with the clearness and conciseness with which he would have addressed an audience in his native language, and thus any shortcomings that might be apparent may very well have been, and probably were, due to this handicap rather than to any unwillingness on the part of the lecturer to disclose any real information. Col. Alec Ogilvie was in the chair in the absence of Col. Tizard, who was suffering from a very bad cold and was unable to preside. In introducing the lecturer Col. Ogilvie recalled briefly the long experience which Dr. Rohrbach had had in all-metal construction, both on airship work and on heavier-than-air craft. Dr. Rohrbach, who was greeted with hearty applause by The lecturer also stated that with heavy wing loading the loss in manoeuvrability with size became less. Referring to the very large dihedral angle at which the wings of the Rohrbach monoplane were set, Dr. Rohrbach said that this had been found to result in making the machine quicker on the turns. A very minute change in dihedral had a very considerable effect on the rate of turning, and he thought the difference in the behaviour of machines of the same type might in some cases be due to some such small variation in dihedral. He had found out that an increase in dihedral of one-fifth degree was sufficient to counteract a very large increase in the moment of inertia of the machine. Concerning the construction of the Rohrbach monoplane (photographs and a description of which were published in FLIGHT of July 17, 1924), the lecturer had very little to say, but a series of lantern slides were shown, which illustrated some of the constructional features. One slide which caused much merriment was a view of the Rohrbach with both its Rolb-Royce engines stopped, but rigged up with two small lugsails and proceeding on its way undismayed. Jt should, the lecturer thought, be quite possible for a large seaplane forced down by total engine failure to rig up a couple of sails and so to work slowly towards some point where there was more likelihood of being picked up. He referred to the use of a drogue, which kept the nose of the machine head to the THE ROHRBACH RO. II ALL-METAL FLYING BOAT : Two Rolls-Royce " Eagle " Engines. The men standing on the wings give a good idea of the size of the machine. a numerous audience, recounted briefly the advantages which all-metal construction had been found to possess as compared with wood construction. Among these were increased seaworthiness, less effect on the structure of sea-water, and a saving in structure weight of 15 to 20 per cent. If the question of absorption of water by wooden hulls was taken into consideration this saving was even greater. He asked to be forgiven if he devoted himself to the machines of which he had personal experience, and said that he knevv very little about the machines designed and built by others. For very large machines the lecturer thought the seaplane was the type most easily developed, questions of space for taking off and alighting being less serious than in the case of land aeroplanes. He showed a series of slides intended to demonstrate how the problem of increased structure weight with increase in size became much less serious if heavy wing loading was employed, using as a basis the transporta tion of a certain load over a given distance, at the same time indicating that the more heavily-loaded machine covering the distance in a shorter time made up for the larger amount of fuel consumed. Dr. Rohrbach also outlined the reasons which had led him to adopt the monoplane type, and showed genera! arrange ment drawings of a design for the biplane with which the comparison was made. This part of the lecture was some what unintelligible, the lecturer stating that the biplane structure would have given a saving in weight of approxi mately 300 kgs., but that its performance would have been inferior. Thus the ceiling for the biplane (estimated pre sumably) would have been 1,300 m., while that of the monoplane was 3,000 m. seas, but thought sails gave some advantage in that they enabled the machine to be taken along a course not neces sarily down wind. In other words, they left the crew a certain choice of direction. A most interesting film was then shown, illustrating the method adopted for transporting the Rohrbach over the ground on two large-diameter Duralumin wheels attached in the place normally occupied by the side-floats. Then came a section illustrating " business with engine," as Little Tich would say, and an examination of the wing structure by opening the hinged leading and trailing edge flaps. What particularly impressed the audience was the fact that, judging from the film, the most popular tool in use by the mechanics who looked after the machine was a hammer. Finally the machine was shown taxying, turning right and left in the most amazing manner by the use of a water rudder, and ir1 full flight, the latter picture being taken from another aeroplane. The Discussion Mr. W. O. Manning said he would like to ask the lecturer his reasons for adopting the rectangular plan form of wing, as it was fairly generally admitted that the tapered wing was slightly better, affording a certain saving in structure weight, and being better able to withstand torsional stresses. He also wished to know what Dr. Rohrbach's experience had been with Duralumin, particularly as regards the effect on it of sea-water, and whether any trouble had been ex perienced with corrosion. With regard to the Rohrbach monoplane flying boat, he pointed out that it would appear that there might be a danger of the machine being blown over when moored in a tide running against the wind, thus 686
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