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Aviation History
1939
1939 - 0102.PDF
46 FLIGHT. JANUARY 12, 1939 much trouble in that direction, but suggested that the oscil lations of the model in the tunnel were due to the moment of inertia of the model not corresponding with that of the full scale. In one case of an American machine with three fins and rudders, he understood this was due to the fact that with a single tall fin the machine would not have been able to pass through the hangar door. MR. W. H. SAYERS said his experience was that one could get out of a 5ft. or even a 4ft. tunnel practically everything that one could get from a 10ft. tunnel, without applying an enormous amount of ingenuity. He had recently been engaged in making what was probably one of the biggest wind-tunnel models yet made in this country. Even on that he was doubtful whether the 24ft. tunnel would really tell him what he wanted to know, be cause certain items on the model were still in the transition region at the highest speed of the 24ft. tunnel. There was not anywhere in the world a tunnel in which representative- sized working models could be tested. His personal view was that we did not want a lot of 12ft. tunnels (though they would save a lot of trouble in model making), but that we ought to have a few 30ft. tunnels and at least two 60ft. by 30ft. tunnels. The D.CA's Rudders MR. F. RADCLIFFE was a little doubtful as to the meaning of the reference to fixing the transition point far forward. He asked whether the reference was to the transition from laminar to turbulent flow. He confirmed the statement that the three fins and rudders on the D.C.4 were selected mainly from considerations of hangar dimensions. Had it not been for that the machine would probably have had two fins and rudders. MR S. SCOTT-HALL said he had understood Mr. Ellis to say that the flight condition probably lay between the stick-fixed and stick-free conditions and asked for further explanation. MR. ELLIS said that in stating that the stick-free stability tended to become more important he had not meant with in crease of loading, but with increase of speed. If the speed of a given aeroplane were considerably increased the compromise in stability as between the stick-free and stick-fixed condi tions would become much nearer the stick-free condition. Taking the extreme case where the speed was very high, the hinge moment would be such that the pilot could not move trie stick. MR. L. W. BRYANT said that in the past satisfactory dynamic stability had been secured by providing a stable slope to the static moment curve. The low drag, high loading and high moment of inertia of the modern aeroplane had modified the conditions, and in the future it might be expected that unstable phugoid oscillations would be a less rare occurrence than formerly. He explained that at the N.P.L. they were going to try a new method of experiment which, it was hoped, would fulfil the same function as a free-flight model except so far as longi tudinal motion was concerned. The model would be given three degree's of freedom. Thus all the elements of the phugoid would be included as the models were to be dynamic ones. The tunnel speed would be so adjusted that the model and part of the supports floated when undisturbed. A similar technique for lateral stability tests was on trial. He thought the partially-constrained model would give results more easily interpreted than those obtained in the American free-flight tunnel, and hoped it would be possible to develop a type of test analogous to that of the spinning-tunnel. MR. E. OWER thought the authors had been rather pessimis tic on the problem of overall drag tests. In the duplex tunnel at the N.P.L., in which the models averaged about 8ft. span, the knowledge now available concerning transition point enabled a fairly good estimate to be made of the overall drag of the model. He agreed with Mr. Pierson that the models should be truly representative of full scale, and in addition it was im portant that they should be well made. The time spent in making a really first-class model was repaid many times by the time saved in the actual tunnel tests, and the gain in accuracy was unquestionable. MR. G. B. FENTON asked for information about interpre tation of pitching moment curves. When testing a model wing and fuselage without tail he had found that the lift curve was, of course, straight at first and then in the region of the stall had lost its linearity. There was a kink in the pitching moment curve at about the same angle. He assumed that this was due to a partial stall but asked how to interpret that char acteristic when the angles of attack were different. Concerning the use of wool tufts, he had used tufts on the surface and at the ends of pins away from the surface, and from the results had drawn pictures of the flow over the wing. He would like to know whether pictures of flow so drawn were likely to be correct. MR. ELLIS replied that the interpretation concerning the kink in the pitching moment curve must be an inspired guess. His own guess was that one would extend the pitching moment curve to correspond to the lift curve. He believed tufts were very useful and that Mr. Irving had used them extensively. Scale-effect Contrasts MR. H. B. IRVING drew contrasting lift curves of the R.A.F. 34 and Clark YH wings. On the former the top of the lift curve was rounded off at high Reynolds Number, whereas with the Clark YH the peak became sharper at high Reynolds Number. One could not help being rather pessimistic when confronted with two such completely different types of scale effect. It seemed to indicate that the process of stalling must be different in the two cases. With regard to wool tufts he had done a large amount of work but as results had not yet been published, he could not say very much about it. He thought on the whole the tufts were fairly reliable in giving a rough sort of indication of the flow. At the R.A.E. it had been found very important to use tufts not only on the surface but also on the ends of posts away from the surface. Mr. Irving concluded by suggesting that a more appropriate title for the paper might have been " The Use of Wind Tunnels in Aeroplane Design." Forthcoming Events JANUARY. Fri., 24th. R.Ae.S. Yeovil Branch Lecture : " Retractable Undercarriages," by R. H. Bound. Tues., 28th. R.Ae.S. Portsmouth Branch Lecture : " Recent Progress in German Aircraft," by B. S. Shenstone, A.F.R.Ae.S. Coventry R.A.F.V.R. Annual Supper Dance, Thurs., 2nd. Drill Hall, Coventry. Bristol and Wessex Club : Bristol Aviation Ball, Thurs., 16th. Victoria Rooms, Clifton. R.Ae.S. Lecture* : " Corrosion Problems," by A. J. Siderv, A.F.R.Ae.S., and J. W. W. Will-strop, B.Sc, A.I.C. Southend Flying Club: Supper Ball, Garon's T burs., 20th. Banqueting Hall, Southend. FEBRUARY. Wed.—Fri., 1st—3rd. Aerodrome Owners Association : Air- Thurs., 4th. ports Conference and Exhibition. R.Ae.S. Joint Lecture with I.A.E. and others : Thurs., 25th. " Sleeve-Valve Engines," bv A. H. R. Fedden, D.SC, M.B.E., M.I.A.E., M.S.A.E., F.R.Ae.S. Fri., 10th. Lancashire Aero Club : Annual Dance, Grand Hotel, Manchester. Sat., 24th. Thurs., 16th. R.Ae.S. Lecture* : " Ignition Problems," by Dr. G. E. Bairsto, M.I.E.E., F.Inst.P. Fri., 17th. Cinque Ports Flying Club : Annual Dinner and Sat,< 8th—Sun Dance, Majestic Garden Hotel, Folkestone. Sat., 15th. Thurs., 12th. Fri., 13th. Thurs., 19th. Fri., 20th. Tues., 7th. York and Leeming Flying Club : Annual Ball Harrogate. Hampshire Aeroplane Club : Annual Dinner and Dance, South Western Hotel, Southampton. MARCH. R.Ae.S. Lecture* : " Testing Stability and Control," by Dr. A. G. von Baumhauer. R.Ae.S. Lecture* : " Relative Merits of Car buretters and Direct Petrol Injection," by J. E. Ellor, F.R.Ae.S.,andF.M. Owner,F.R.Ae.S APRIL. R.Ae.S. Lecture * : " Possible Steel Develop ments," by Dr. T. Swinden, F.R.Ae.S. MAY. R.Ae.S. Lecture* : " Strength of Thin Metal Construction," by H. L. Cox. R.Ae.S. : Wilbur Wright Memorial Lecture, bv Dr. G. W. Lewis. JUNE. Royal Air Force Garden Party, Trent Park. JULY. , 23rd. Brussels Aero Show. Deauvllle Rally. * All these lectures take place at 6.30 p.m. at the Institution of Mechanical Engineers, Storey's Gate. London, S.W.I.
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