FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1925
1925 - 0710.PDF
OCTOBER 29, 1925> and positive angles it would, however, appear as if the section was not entirely symmetrical, since there is a slight difference in the curves at negative and positive angles. In the original work the lift and drag coefficients are, of course, given in German units, i.e., they are the absolute units employed in this country multiplied by 200. In the accompanying graph these have been converted to the usual " absolute " coefficients. Although not shown on the curves Senor de la Cierva was probably led to his choice of wing section by the very small travel of the centre of pressure of Gottingen Nr». 429. It will be seen that the maximum L/D is fairly high, i.e., nearly 20 at 5° incidence. The maximum lift coefficient is low, but owing to the fact that the windmill rotates at fairly high speed, presumably a low value of £L is not as great a drawback as it would be in a normal machine.—ED.] A series of cinematograph films were then shown illus- trating the flights of some of the earlier types of " Auto- giro," as well as recent flights by Capt. Courtney on the machine now at Farnborough. Finally, a " slow-motion " film was shown, which had been intended to illustrate the vertical movement of the windmill blades, but this it rather failed to do. The. films were marred to a great extent by bad projection, the operator failing to get his light centred, so that there was constantly a purplish cloud in the middle of the screen, and at times it was almost uncanny to watch the way in which the " Autogiro," looking for all the world like a spider, seemed to be making for the centre of this cloud, as if to hide itself therein. Although this was certainly rather amusing, it was scarcely the main object of the film, which was largely defeated by the very bad projection. The Discussion At first it had been intended that the discussion should take the form of questions put by those taking part, which would be translated by Capt. Square into Spanish, Senor de la Cierva making his replies in Spanish, and they would then be translated into English by Capt. Square, but it was soon found that this would have taken too long, and it was ultimately decided that the various questions raised should be dealt with by Senor de la Cierva later and replied to in writing for publication in the Society's journal. Mr. Locke wished to know whether it was possible under certain conditions for the windmill to stop in flight—for instance, at very high speed. He also desired to know which was the smallest angle of attack at which rotation was maintained, and he would also like to know whether it was possible to stop the windmill in flattening out after a dive. It had been stated that the machine could descend almost vertically. He would like to know if it would land vertically in still air, i.e., in the absence of wind. Senor de la Cierva replied to these questions, via Capt. Square, that it was quite impossible to stop the windmill in flight, since there was always a forward speed and, therefore, a relative wind. A great deal of amusement was caused by the statement that if forward speed was stopped the machine would sink, and then , there would be a vertical draft keeping the windmill rotating. Maj. F. M. Green referred to a paper read by him a couple of years ago before the Royal Aeronautical Society, in which he had stated as his conviction that the helicopter did not appear to offer good possibilities for improvement over existing types. He was, therefore, glad that Senor de la Cierva had not called his machine a helicopter. He referred to the very ingenious mounting of the wings, by which all bending stresses were taken care of by centrifugal force, which turned all the stresses into purely tensile ones. There were certain problems in connection with the machine which he would like elucidated. For instance, he would like to know what variation in windmill speed was possible, i.e., how fast and how slow it was possible to run them. Sir Sefton Brartcker said that, from a conversation he had had a day or two before with the inventor of the " Autogiro," he would be able to reply to some of the questions at once. For instance, the tip speed of the windmill blades was always the same, s:> that if one built a big commercial machine with windmill blades of larger span and retaining the same tip speed, this would necessarily mean that the number of revolutions per minute of the windmill would be lower. Mr. F. Handley Page said he first saw the " Autogiro " flying over Laffan's Plain. He was a passenger in the Handley Page " Hampstead," and his first view of the "Autogiro" in flight was from above. He was irresistibly reminded of the toys used by small boys, but, apparently, with the difference that this machine had a purpose in life. Before one could express an opinion of the " Autogiro," data were wanted concerning lift and resistance. He had seen the " Autogiro " referred to as a machine which landed on a roof. Presumably, that referred to flat roofs, since the- majority of roofs in this country were rather too sharp to permit of landing on them with any machine. However, even assuming flat roofs, he would also like to know if it were possibfr^for the machine to ascend vertically from such a roof by speeding up the windmill. He would like also to know what was the loading of the windmill blades, as this appeared to be somewhat high. It had been stated that the machine landed at very low horizontal speed. In normal types of aeroplanes one could also descend at \'ery low landing speed, but this was obtained at the expense of top speed, and he would like to know if the same applied to the " Auto- giro." In other words, for the same landing speed, what would be the top speed of the " Autogiro " ; or, conversely, for the same top speed, what would be the landing speed ? Again, Sir Sefton Brancker came to the rescue with a certain number of replies, although further details would be given by the inventor himself in the written replies which he will prepare. For instance, concerning the question of taking off, he was told that if the windmill was initially speeded up to about 120 r.p.m., the machine need only attain a forward speed of 20 m.p.h., before sufficient lift was attained for the machine to leave the ground. This, of course, would mean a very short run. He would also remind them of the fact that the machine tested at Farnborough was something like 600 lbs. heavier than the standard Avro, and with about one-half the wing area. Even so, the top speed was 68 m.p.h. As many of the parts employed in this experimental machine were needlessly heavy, he felt sure that much better results would be attained. Prof. L. Bairstow said that much had been made of the very short landing run of the " Autogiro," and he thought that probably this particular feature of the machine was its greatest merit. At first, it seemed extraordinary that the machine was able to fly at a speed of some 15 or 20 m.p.h., but, when one began to examine the problem and found that the tips were travelling at somewhere between 150 and 200 m.p.h., one began to realise the possibilities of obtaining high unit lift. The future of the " Autogiro " would, of course, depend upon the load the machine would carry per h.p. developed, and the speed at which it could transport that load. In a inormal aeroplane the work done could be represented by the drag of the machine, multiplied by the straight line distance between the starting and finishing point. In the " Autogiro " one would have to take the drag, multiplied, not by the straight line distance, but by the spiral distance through which the wings travelled, and it would therefore seem that the " Auto- giro " must be less efficient than the normal type of aeroplane. He greatly admired the extreme mechanical simplicity of the machine, and the rotating windmill with hinged blades was an admirable device for reducing stresses. This seemed to be one of those very rare cases where nature presented her gifts to the inventor. This was obviously so in the manner in which centrifugal force reduced the wing stresses, or rather converted them into purely tensile stresses. The flapping up and down movement of the wings was necessary to the reduc- tion of the stresses. If, as the inventor appeared to claim, this flapping was also beneficial from an aerodynamic point of view, this would appear to be another gift of nature. Mr. \V. O. Manning said that before one could express an opinion of the value of the Autogiro, it would be necessary to have L/D curves, so that one could ascertain the efficiency of the machine. He referred to the fact that the machine appeared to have a speed range of 4§ to 1, which he thought was the highest so far attained by any heavier-than-air craft. Mr. Harris Booth said that he had been present at some of the test flights in Spain, and he had then asked all the questions he could think of, and all had been satisfactorily answered by the inventor. Before getting the machine to this country for testing they had stipulated certain con- ditions which had to be fulfilled Not only were all these conditions fulfilled but, actually, also a number of others which it had not occurred to them to stipulate. He thought there remained nothing more for him to do than to thank the lecturer for a most interesting paper. Capt. W. H. Sayers referred to the enormous speed range of the " Autogiro," Mr. Manning had referred to a range of 4J to 1. Actually, as the machine flew at 68 m.p.h. top speed, and at probably 10 m.p.h. low speed, the speed range was nearer 7 to 1. Nothing of the sort had, of course, ever been attained before, and it remained to be seen whether that speed range could be " stepped up." In other words, could one assume that if a landing speed of 50 m.p.h. was designed for, top speed would be 340 m.p.h., and so forth. He said there were a number of questions he would like to ask, some of which had already been asked by others, and a considerable number he would like to give careful consideration before 710
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
