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Aviation History
1937
1937 - 2371.PDF
AUGUST 26, 1937 n THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT vp, W„ =. '- cos <t> •no,' VP W, = '- sin 4> tra% Also tan ^ = tan 9 The resultant of W, and W, is given by W, = (W„2 + \W)> VP, (cos2<£ -f- sin2<£) W The inclination of W, to the x x axis is thus -1 W, * f ° + tan W = e + e = 2d The resultant Wr is therefore constant round the section its direction being inclined at 2 0 to the xx axis, (vi) End Load in Stringers. The longitudinal component F, of the diagonal tension fields is given by F, - q. The end load taken by any stringer plus adjacent skin is therefore P,t .q.dl dl aj Direct Shear. Applying this to elliptic rings subjected to a vertical shear V the end load in a stringer P is given by : P = V . P, e2 sin2<p cos * d<t> 1 — - e' 6 2 . V 64 1 — e 2 sin2<£ d<t> 9 fr'-l >-i* •~ e< —~1 Ti - -e2 -i^.-"_". 64 J L 4 64 It is found that for a range of e values, 0.6 — 1.0, the above function of e is to a reasonable degree of accuracy equal to unity. 2 . V . P, .-. P 77-"a In a similar way due to a horizontal shear load H the end load in the stringer is found to be 2 . H . P. P = ir2b b\ Torsion. The longitudinal component F, of the diagonal tension is in this case equally distributed round the section. ••• F, - -2- The end load in the stringer is thus O P P = F,* P 8 _ P 25 a . b Q P, 2 nab TECHNICAL LITERATURE SUMMARIES OF A.R.C. REPORTS REPORTS published by His Majesty's Stationery Office, London, which may be purchased directly from H.M. Stationery Office at the following addresses: Adastral House, Kingsway, W.C.2 ; 120, George Street, Edinburgh; York Street, Manchester, 1; St. Andrew's Crescent, Cardiff; 15, Donegall Square West, Belfast; or through booksellers. THE PRESSURE DISTRIBUTION AND FORCES ON THIN AEROFOIL SEC TIONS, HAVING SHARP LEAPING AND TRAILING EDGES AND MOVING WITH SPEEDS GREATER THAN THAT OF SOUND By S G Hooker, D.Phil., 1851 Senior Exhibitioner Brasenose College, Oxford Communicated by Professor R. V Southwell, F.R.S. R. & M No 1721 (i3 pages and 11 diagrams.) July, 1936 Price 2s 6d. net. When a body moves through the air at speeds greater than the velocity ot sound waves are set up and the flew pattern in the air is entireiv different from that accompanying the same body moving at sub-sonic speeds. Considering two- dimensional flow past a lenticular shaped aerofoil, having sharp leading and trailing edges, if the section is thin the amplitude ot the plane waves set up is very small, and they resemble sound waves, being propagated normal to their wave front at the speed of sound. Such waves, therefore, cut the field of flow obliquelv. making the " Mach " angle with the direction of motion of the aerofoil. The work of Taylor and Maccoll* on the disturbances at the nose oi projectiles with conical heads has shown that the Rankine-Hugomot relations give a remarkably accurate representation of the conditions pertaining to permanent shock waves. The pressure and condition of the air at a sharp leading edge can thus be determined with sufficient accuracy from the strength of the shock wave necessary to turn the air stream into a direction tangential to the surface. This has been done in the present paper and the results show good agreement with Stanton'st work on special aerofoil sections tested in the N.P.L. 3-inch High Speed Wind Tunnel. * G. I. Taylor and j. W. Maccoll, 1'roc. Hov. Soc.. t Sir T. E. Stanton R. & M. 1130. 1928 A, Vol. 139. pp BW-8H. TURBULENCE MEASUREMENTS IN FLIGHT, By J.'E. Serby, B.A., and M B Morgan, B.A Communicated by the Director of Scientific Research. Air Ministry R. & M No 1725. (7 pages and 1 dia grams.) March 27, 1936. Price is. 6d. The Reynolds num!>er at which the well-known sharp tail in the drag coefhcien". of a sphere occurs is dependent on the degree of turbulence in the air stream, and the critical Reynolds number (R0) for a sphere is defined as the value of Vd/f for which the drag coefficient C„ of the sphere is 0.3. The " sphere turbulence indicator " used in the experiments described in this report, was devised to measure Rc in wind tunnels and in free flight. The principle of the indicator is that a sphere and a disc (set normal to the air stream) are carried on spindles fixed at either side of a balance arm (Fig. 1) so that when the apparatus is set up in an air stream the drags of the sphere and the disc are opposed. The aiea oi the disc is chosen so that its drag balances the drag of the sphere when the latter has a drag coefficient of 0.3, i.e. at the critical Reynolds number as defined above. A 6-in, diameter sphere gave a convenient speed for flight tests, and wind tunnel tests showed that a 3.2-in. diameter disc was needed to balance the sphere when the drag coefficient of the latter was 0.3. In gliding flight R0 the critical Reynolds number at which the sphere drag coefficient CD is 0.3 was found to be 3.51 x 105. This agreed (within the order of accuracy of the experiments) with the Reynolds number at which the static pressure immediately behind the sphere equalled the static pressure in the undisturbed stream. The value of Rc was decreased by vibration when the engine throttle was opened, the biggest reduction being about 10 per cent, at full throttle on the climb. This effect of vibration may have a bearing on all measurements in flight or in tunnels where the flow is critical. U may be important in wiad tunnel work to ensure that the model is held steady to avoid false values of drag and max. C^ The value of Rc agrees closely with that fouud in free flight tests in America AN ANALYTICAL COMPARISON OF MODEL AND FULL SCALE SPINNING EXPERIMENTS ON A BRISTOL FIGHTER. By R P Alston, B A., and I Cohen B Sc. Communicated by the Director of Scientific Research, Air Ministry R. & V! No 1726 (14 pages and 13 diagrams.) March 3, 193b Price 2s net The R.A.fc. Free Spinnmg Tuunei was brought into use in 1032 to examine the spinning properties of various existing and projected designs of aeroplanes as well as to assist in a general programme of spinning research, and it was desirable to make some comparison with full scale results. At that time detailed measurements of full scale spins had been made on a Bristol Fighter only, though there was a certain amount of less detailed information on a few other types-: it was therefore decided to make tests on a Bristol Fighter model tor comparison. These tests would really be an extension of the dropping tests already made in the balloon shed,1 which had indicated that two types of equilibrium spin were possible on the model. It was therefore anticipated that the results of further tests might not be conclusive. The free model tests described in this report were made in the summer of 1933, but the results of rolling balance tests at the N\P.L. were not immediatelv available. Full scale tests had been going on for a number of years before L932 on the Bristol Fighter, the time being mostly spent in the development ot instruments suitable for the work. The first report on this work in which measurements ot incidence, rates of roll, pitch and yaw, sideslip and rate of descent were quoted, was R & M. 1281 by Wright.1 The chief feature of the results quoted in that report was the vagueness of equilibrium incidence even after several turns; the incidence ranged from 29° to 53". In later experiments' by Stephens on the same aeroplaue this vagueness of equilibrium was not found and it was suggested that all the spins of R. & M. 1261 would have settled down to one at about 50" incidence if prolonged in duration. The latter experiments were, however, made alter a number of small modifications to the aeroplane, and there appears to be no reason tor neglecting the earlier results in considering possible, though not necessarily final, incidences ot equilibrium. The results ot the rolling balance tests were tound to be invaluable as affording a connecting link between the model and full scale tree spinning results. In the case of the Bristol Fighter considered, a number of peculiar features was found ; in the model and some of the full scale tests the incidence tor spinning equilibrium was not unique, and the desijn appeared extremely sensitive to yawing moment variations. 1
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