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Aviation History
1921
1921 - 0136.PDF
lift/drag ratio is not less than 16 and perhaps as high as 21 or 22, a great economy will be effected in the horse-power that is required. Economy does not, however, rest with the planes alone, for if the planes are more efficient it will pay to sacrifice a little weight to diminish the body resistances of the aeroplane. It would appear from our recent experiments that a total lift/drag ratio on a complete aeroplane can be obtained of not less than r to 15 at the top speed. With this value and a propeller efficiency of 70 per cent., a speed of 120 m.p.h. can be obtained with 33 lbs. per horse-power. It is evident that results such as these will emphasise the importance of improved methods of propulsion at slow speeds, so that the problem of arising with such heavy loads per horse-power is made easier than it would be at the present time. The experimental results which have been given above , have been confirmed by full-size tests on a D.H. 9, the front edge of which was altered so that its section included a slot in front of the front spar. The increase in lift coefficient measured from the decrease in stalling speed showed that the full-scale results followed closely the laboratory experiments. Mechanical Devices Necessary The operation of the auxiliary plane or planes to effect the . transformation from slot closed to slot open does not present very great difficulties, nor does their addition to the structure lead to very much increase in weight. One of the simplest methods is by the simple swivelling of the front auxiliary portion, but in this device and in the actual methods of control, many solutions are possible, and only experience in manufacture and operation can indicate which is the best. It is to be hoped that the results which have been given above and the investigation which has been conducted will lead to further experiments being carried on elsewhere, so that improved results may be obtained to the benefit of aircraft and aviation generally. The writer's thanks are due to Mr. R. O. Boswall, now lecturer on mechanical engineering at Manchester University, and who, until the beginning of last year, was in charge of our wind tunnel and carried through all the original experiments, as well as to his successor, Capt. G. T. R. Hill, and Miss Chandler and Messrs. Reynolds, Pirrie, Hall, Miles, Campbell and Fossett, assistants in our Research Department, for their able assistance. The Discussion After the lecture, the Chairman (Sir Joseph Petavel, K.B.E., F.R.S., F.R.Ae.S.) stated that he would like to ask one of the pioneers of flying to open the discussion, and called upon Col. ALEC OGILVIE, who congratulated Mr. Handley Page on his discovery and on the most interesting paper which he had just read. He said that he was very impressed by the figures which the lecturer had given, and that, accepting them, the possibility of carrying 33 lbs./h.p. at a speed of 120 m.p.h. was a very great improvement, as the present-day machine could only carry 12 to 15 Ibs./h.p. at that speed. A rough estimate indicated that with the H .P. wing it would be possible to carry a paying load two to three times as great, which would help materially to make aviation a commercial proposition. Col. Ogilvie then pointed out what appeared to him to be the main advantage of the new wing : that it would lower the landing speed of machines. He said he thought that the present maximum speed of machines (about 125 m.p.h.) was adequate for the present requirements,but that the landing speed was, in the majority of cases, too high. If the new wing would reduce landing speed to a considerable extent, this would help greatly towards safety, and would also have the effect of lowering the insurance rates. The extra lift of the wings would leave more weight available, and consequently engines could be built more heavily and with greater reliability. Also it might be possible to fit a retractable undercarriage. He then referred to his own early Wright machine, which was loaded at the rate of 33 lbs./h.p., the same figure as that a given by Mr. Handley Page. His engine, he said, weighed something like 11 lbs./h.p., so that if it were possible to fly and get off in the early days with such a load, it should be possible in these more enlightened times. With regard to the mechanical problems connected with the H.P. wing, he was not going to say anything except that he was somewhat doubtful on that point. Professor L. BAIRSTOW said he would like to join in congratu- lations to Mr Handley Page. The manner of presenting the paper, showing the various steps in the evolution of the wing, was extremely good, and gave a much better idea of the amount of work that had been done before the most favourable results were obtained. In the main, he agreed with the lecturer, and also with Col. Ogilvie on the point of the advantage of low landing speed. On the question of stability he would point out that the travel of the c.p. was not quite the same FEBRUARY 24, 1921- problem in this wing as it is in the ordinary wing. For instance, suppose the machine to be flying with slot closed near its stalling speed, and with the tail trimmed for that attitude and speed. If the slot is then" opened the first effect is to shift the c.p. back. But there is another consideration, that of downwash on the tail. Now the angle of downwash is approximately proportional to the lift coefficient, and there fore as the lift increased so would the angle of downwash on the tail. It might be, he said, that things would balance themselves out, but he was not sure that this would necessarily follow. Another thing connected with stability was the ques- tion of spinning. At the large angles of incidence correspond- ing to the high lift coefficients the rate of spinning would probably be great, and we were, he said, only just beginning to understand the nature of the spin. Before one could be quite certain on these points, further research would probably have to be made. Capt. W. H. SAVERS called attention to a triplane built at Brooklands in the old days, in which the system of slots was incorporated. Unfortunately for the inventor, the small aerofoils were arranged the wrong way, and so the machine was not much of a success. Major F .,M. GREEN also congratulated thelecturer, and pointed . out that it had become almost a generally accepted opinion that we were not likely to make much more progress with regard to wing sections. Mr. Handley Page had altered that opinion, and, really for the first time in the history of flying, a startling change had been made in wing design. He called attention to the question of scale effect, and stated that cases were on record of the scale eilect having " gone the wrong way," that is to say instead of the lift increasing with scale it had decreased, while the drag had not become proportionately smaller, as is usually the case. He would particularly like to hear more about the results of full-scale tests, and hoped that the lecturer would give fuller particulars of these than he had done in the THE GERMAN LACHMANN WING : A model of this was tested in the Handley Page wind tunnel, but gave a maximum lift coefficient of 0*5 (absolute) only. paper. With regard to the figure of L/D for the complete machine of 15/1, this might be theoretically possible at one particular speed, but seemed rather high for maximum speed. He then pointed out that although the lecturer had said that there should be no particular difficulties in carrying out the construction of the wing, he (Major Green) was not quite so sure on that point. It was always a matter of difficulty to arrange for any sort of articulated wing, and he thought that very considerable difficulties were to be anticipated. He mentioned that the hinged trailing flap had not been found of any great use on military machines, since the lift was deter- mined more by questions of ceiling and climb than by considera- tions of landing speed. Mr. GNOSPELIUS said his experience had been that the ques- tion of L/D ratio was the bad feature of the high-lift wing, and that one must have the auxiliary portions of the wing movable. Dr. A. J. S. PIPPARD was pleased with the way the lecture had been arranged, showing the successive stages in the development of the wing. He thought, however, that there was a gap in the lecture, as there seemed no logical explanation of the change from longitudinal to lateral slots. He rather thought this must have been a stroke of genius on the part of the lecturer. He would like to hear more of the reasons for this change. From a constructional point of view he thought there would be considerable difficulty in making the separate planes. Another point which he would like to see further elucidated was the arrangement of the planes in relation to the fuselage. The very high lift of the multiple slot section occurred at angles somewhere near 45 degrees, and it would be necessary to make provision for altering the angle between the planes and the fuselage. He agreed that the advantage of reduced landing speed would be very considerable. Dr. A. P. THURSTON pointed out that we had been accus-
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