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Aviation History
1932
1932 - 1088.PDF
so bUPPLEMENT TO FLIGHT OCTOBER 27, 1932 THE AIRCRAFT ENGINEER TECHNICAL LITERATURE SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS These Reports are published by His Majesty's Stationery Office, London, and 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 any Bookseller. THEORY OF AIRSCREW BODY INTERFERENCE. APPLICA TION TO EXPERIMENTS ON A EODY OF FINENESS RATIO 3: 0 WITH TRACTOR AIRSCREW. By C. N. H. Lock, M.A. R. & M. No. 1378. (23 pages and 10 diagrams.) May, 1931. Price Is. 3d. net. In R. & M. 1120,* 1238,t and 12391 a method was developed of calculating the effect on performance of housing a tractor airscrew in the nose of a body whose shape is an exact spheroid. The first part of the experiments described in R. & M. 13805 relates to a tractor airscrew and a body (fineness ratio 3'0), of which the forward half is an exact spheroid; calculations of per formance based on the above method were therefore made and compared with these experimental results. The present report includes a complete account of the theoretical method employed. A comparison of thrust grading curves at radius x = 0-3 suggests that this section in the airscrew has a maximum fej, of at least 1-2. as compared with the value 0-55 observed on the aerofoil. After allowance has been made for this, the agreement between theory and observation is, in general. satisfactory. Analysis of the drag observations in conjunction with those on a body of fineness ratio 5-45 (R. & M. 1030,it 12301J) indicates a "spoiling effect " (additional to the expected effect of slipstream velocity) amounting to about 4 per cent, of the thrust near maximum efficiency, but at larger thrusts this is partly offset by an increase in the effective efficiency of the airscrew. This spoiling effect is very roughly the same for both bodies, and also when the drag of the bodies is artificially increased by adding excrescences. The observations at static' on the short body with annulus indicate a spoiling effect rather smaller than would be predicted from the observations over the, normal working range, but this discrepancy amounts to only 2 per cent, of the thrust. The method of drag analysis used here has since been partly superseded by the simplified method of R. & M. 1445**, which is also applicable to pusher airscrews, and does not require observations of pressure over the nose or strip theory calculations of airscrew performance. * R. & M. 1120.—Analysis of experiments on an airscrew in various positions within the nose of a tractor body.—Lock. t R. &M. 1238.—Note on the effect of body interference on the efficiency of an airscrew.—Lock. t R. & M. 1239.—The application of the theoretical velocity field round a spheroid to calculate the performance of an airscrew near the nose of a streamline body.—Lock. § R. & M. 1380.—Pressure and force measurements on airscrew-body com binations.—Bateman and Johansen. || R. & M. 1030.—Experiments with a family of airscrews, including effect of tractor and pusher bodies. Part IV. On the effect of placing an airscrew in various positions within the nose of a streamline body.—Bateman. Townend, and Kirkup. «[ R. & M. 1230.—Pressure plotting a streamline body with tractor air screw running.—Lock and Johansen. ** R. <fc M. 1445.—Analysis of experiments on the interference between bodies and tractor and pusher airscrews.—Lock and Bateman. EFFECT OF SIDESLIP ON THE PERFORMANCE OF A MULTI ENGINED AIRCRAFT. By E. T. Jones, M.Eng. Com municated by the Director of Scientific Research, Air Ministry. R. <& M. No. 1455. (6 pages and 4 diagrams.) January, 1932. Price 6d. net. The performance of a nmlti-engined aircraft with one engine fully throttled has been measured with and without bank to determine the order of the loss of performance which may result from flying with sideslip when an out board engine has failed. The rate of climb of a three engine-in-line and a twin-enginel flying boat has been measured at the best climbing speed for angles of bank from — 10 deg. to + 10 0 deg. with an outboard engine fully throttled. The corresponding angles of sideslip have been calculated. The optimum rate of climb which should be obtained when the sideslip is zero is only slightly diminished within the limits ± 4 deg. of sideslip; outside these limits the loss of performance increases rapidly as the amount of sideslip increases. The amount of sideslip with ailerons neutral which is required to balance the side force on the rudders when an outboard engine is fully throttled is of the order of 5 • 5 deg. for the particular three-engined aircraft tested. A MEMORANDUM GIVING A SUMMARY OP PRESENT KNOWLEDGE ON THE RELATION BETWEEN GROUND CON TOURS, ATMOSPHERIC TURBULENCE, WIND SPEED AND DIRECTION. By W. R. Morgans, M.Sc. Communicated by the Director, Meteorological Office. R. & M. No. 1456. (39 pages and 28 diagrams.) December, 1931. Price 2s. 3d. net. The author has collected information published by a large number of workers, especially from Germany, where considerable attention has been paid to the subject He discusses separately the height and horizontal distance of influence of obstacles, a theoretical treatment of the flow of air over a mountain, a comparison of this theory with experimental results, • eddies in the neighbourhood of obstacles, the effect of coasts, vertical veloci ties and the lapse rate of temperature and some general problems arising from the memorandum. The evidence drawn from a comparison of experimental with theoretka] work shows that:— (a) Although the maximum velocity of the wind may occur at the summit it is not entirely horizontal. In the work of Koschmieder vertical velocities appear above the summit. (b) The vertical velocity is a maximum above the middle of the slope and is given, in the steady state, by « = V„ tan n. (c) The vertical velocity does not decrease with height everywhere, but in all the experiments shows, at some points, first a gradual increase with height and then a gradual decrease. (rf) The curves of equal ascending and descending velocities are not symmetrical with respect to the vertical through the summit, but that to leeward a region of turbulence occurs. The field to leeward differs essenti ally from that to windward. (e) The height of influence for extended dunes, which correspond to an infinitely extended obstacle transverse to the wind, give much higher heights of influence than isolated obstacles. But these experiments when compared aTong themselves point to the important conclusion that with wind velocities below a critical velocity of approximately 10 m/s. a comparatively steady state is obtained to wind ward, but that with wind velocities above the critical value, space time changes in the velocity field occur indicative of turbulence and of which little appears to be known. The author also remarks that if. with wind velocities below 10 m/s., stationary eddies exist, and with velocities above 10 m/s., turbulence, then any theory depending on streamline flow can have no application to the flow of air over obstacles. THE INTERFERENCE ON THE CHARACTERISTICS OF AN AEROFOIL IN A WIND TUNNEL OF RECTANGULAR SECTION. BY H. Glauert. F.R.S. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1459. (7 pages and 1 diagram.) February, 1932. Price 6d. net. Formulae for the interference on the characteristics of an aerofoil in a wind tunnel of rectangular section, based on the author's approximate theory (Ref. 1), have been known and used for several years. More recently, attempts have been made to increase the accuracy of these formulae by a closer analysis of the problem. Terazawa (Ref. 2) has developed the analysis rigorously for an aerofoil with constant circulation across its span, and has determined the mean value of the induced velocity experienced by the a?rofoil. Rosenhead (Ref. 3) has repeated Terazawa's analysis for uniform loading, obtaining the same result but in a very different mathematical form, and he has also developed the corresponding analysis for an aerofoil with elliptic distribution of lift across the span. These authors have not deduced general numerical values from their formulae, and indeed Rosenhead's formulae are not suitable for numerical computation unless the span of the aerofoil is only a small fraction of the width of the tunnel. In this paper the formulae given by Terazawa and Rosenhead are examined, then recast into a form suitable for direct numerical computation, and the numerical results are derived for the two shapes of practical interest, the square and the rectangle, whose width is double its height. The correction to the approximate formula is comparatively unimportant for a square tunnel, but important for a duplex tunnel. THE INDUCED FLOW THROUGH A PARTIALLY CHOKED PIPE WITH AXIS ALONG THE . WIND STREAM. By H. Glauert, F.R.S., D. M. Hirst, M.A., and A. S. Harts horn, B.Sc. Communicated by the Director of Scien tific Research, Air Ministry. R. & M. No. 1469. (15 pages and 5 diagrams.) March, 1932. Price Is. net. In connection with cooling problems, it was desired to know the flow which would be Induced through a duct lying in a stream of air, and the relation ship between this flow and the pressure difference between the two ends of the duct. Since no information on this subject was available, a few simple experiments have been made with some smooth straight pipes of external diameter of 1-5 in., containing various gauze obstructions at their mid sections. The induced flow can be derived from a theoretical formula, if allowance is made for the small suction at the outlet, which depends mainly on the length of the pipe. For a given pressure difference between inlet and outlet the induced flow decreases as the pipe is lengthened. The drag coefficient of a gauze disc depends not only on the blocked area, but also to a lesser extent on the diameter of the wires forming the gauze. SOME GENERAL THEOREMS CONCERNING WIND TUNNEL INTERFERENCE ON AEROFOILS. By H. Glauert, F.R.S. Communicated by ths Director of Scientific Research, Air Ministry. R. & M. No. 1470. (11 pages and 6 diagrams.) April, 1932. Price 9d. net. When an aerofoil is tested in a wind tunnel the finite extent of the stream modifies the whole nature of the flow, and it is necessary to apply certain corrections to the observed forces in order to derive those which would be experienced in an unlimited stream. The general basis of these corrections has been laid down by Prandtl.* In a closed tunnel with rigid walls, the necessary boundary condition is that, the component of the velocity normal to the walk shall be zero, and in an open tunnel or free jet the condition is that the pressure shall be uniform over the boundary. In the present paper two general theorems are proved :—(1) The inter ference on a very small aerofoil in an open tunnel of any shape is of the same magnitude, but opposite sign as that on the same aerofoil, rotated through a right angle, in a closed tunnel of the same shape. (2) The interference velocity, is uniform across the span of an aerofoil in any elliptic tunnel having the tips of the aerofoil as foci. The following general conclusion is of importance :—For tests of large aerofoils, it is desirable that the interference shall be constant along the span in order to avoid any distortion of the distribution of lift. This condi tion is satisfied by a confocal elliptic tunnel, whether closed or open, but as the magnitude of the interference is less in a closed tunnel, this type is to be preferred for tests of large aerofoils. * Tragfliigeltheorie II, G6tt. Nach (1919). 1008/t
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