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Aviation History
1929
1929 - 0644.PDF
SUPPLEMENT TO FLIGHT 24 THE AIRCRAFT ENGINEER MARCH 28, 1920 2° to 20°. and of rotational speed from 3 to 12 revolutions per second. It was found that the model would not rotate at all at a blade angle of 4°, while at 3° blade angle it would only rotate at angles of incidence above 12°. In order to supplement the measurement of forces and rotational speed at zero torque, observations of forces and angular accelerations were made over a more limited range at varying rotational speed, by means of a chronograph and stroboseope. These observations were interpreted as giving the forces and torque in steady motion when the torque was not zero. Observations were also made of the angular motion of the blades in napping about their hinges. The greatest value of lift/drag ratio was observed on the screw with blade angle 1-8° at an incidence of 3°: this value, subject to considerable uncer- tainty on account of the large correction for drag of the boss, was 7'5 for the four-blader and 8 0 for the two-bladrr at 4° incidence. The scale effect was appreciable on lift coefficient at all angles of incidence, but on other coefficients it was small except at the smallest incidence. The comparison between two- and four-blader was in good agreement with the simple Prandtl theory of interference given in B. & M. nil,* so that the results should apply to an autogyro of any intermediate solidity. The torque curves derived from the observations of angular acceleration confirm the remaining observations in showing that the results vary critically with change of blade angle. The observed flapping motion is in good qualitative agree- ment with theory, the second and higher harmonics being negligible on account of the high density of the model blades. • R. <fe St. 1111. " A General Theory of the Autogyro."—H. Glanert. ON THE CONVECTION OF HEAT PROM THE SURFACE OF AN AEROFOIL IN A WIND CURRENT. By L. W. Bryant, B.Sc, A.R.C.Sc. E. Ower, B.Sc., A.C.G.I.," A. S. Halliday, B.Sc., D.I.C., and V. M. Falkner, B.Sc. R. & M. No. 1163. (Ae. 327). May, 1928. (24 pages and 37 diagrams). Price Is. 3d. net. Although considerable construction difficulties are encountered in the installation of wing radiators, their attractiveness from the point of view of saving head resistance seems likely to render them an indispensable feature of the fasteft aeroplanes for some time to come. A research on the cooling of a wine surface in a wind tunnel was begun in 1925 with a view to providing information which would be of value to the designer of wing radiators. The results obtained are believed to be sufficient to form a reliable guide to the relative effectiveness as cooling agents of the different parts of the wing section at various incidences over the normal Hying range. Comparisons are made with results of tests made at the R.A.E. on the overall cooling of a B.A.F. 30 wing radiator, and of a new type of radiator which uses the front portion only of the wing surface. The agreement between the X.P.I. and R.A.E. results is considered to be reasonably good in view of the fact that the wing sections were not the same. A model of R.A.F. 26 spction was covered with platinum strips over a spaTi of 8 in., the strips being heated by passing a current through each until all strips were at a uniform temperature, as measured by their resistances. The input, measured electrically, gave the heat dissipated by the wind. Tests were made at incidences from — 2 • 5° to 12 • 6°, and at wind speeds from 32 to 75 ft. sec. Supplementary measurements were made on a suitable duplicate wing of pressure distribution around the section, and also of total head behind the model. The rate of cooling is a maximum at the leading edge : it then drops very rapidly on the upper surface to a minimum at incidences above 2°. rising to a second maximum which recedes towards the trailing edge as incidence increases, finally disappearing at the stall. The cooling of the lower surfaces does not appear to vary appreciably with change of incidence except below 0°. It would appear that the skin friction near the leading edge is greater than anywhere else on the surface, according to Prof. Bairstow's theoretical investigations, and this explains the intense cooling at the nose. It seems likely also that the skin friction along the under surface i? independent of incidence since the velocity along it is always approximately that of the free stream. A test of the heat communicated to the air in the wake gave good agreement with the heat lost by the strips, and it was concluded that all the heat was confined to the air which had lost energy as measured by total head. THE EFFECT OF WIND, WEIGHT AND ATMOSPHERIC CON- DITIONS (INCLUDING SEMI-TROPICAL CONDITIONS) ON THE DISTANCE TO TAKE-OFF AND LAND AN AIRCRAFT. By Flight- Sergt. B. H. Rolles and H. L. Stevens, B.A. Presented by the Director of Scientific Research, Air Ministry. R. & M. No. 1172. (Ae. 336). (14 pages and 7 diagrams).* May, 1928. Price 9d. net. The distance to take-off of an aircraft has been previously examined* and in the present report, the effect of atmospheric changes on the take-off run, as in India and the Middle East, consistent with aerodromes of high altitude or under semi-tropical conditions has been calculated. ^t In Part I, atmospheric effects are calculated for a troop carrier and a high performance two-seater, the altitude ranging from 0 to 6,000 ft. and tempera- ture variation from 0° C. to -j- 45° C. The wind effect has also been taken into consideration and a semi-graphical method evolved for correcting measured take-off runs to the condition of " no wind." In Part II, simplified correction factors are obtained for gmali changes In weight, "wind and atmospheric conditions, and the calculations have been extended to include landing runs. In Part III. full scale, test* with weight variations up to 62 per cent, and in winds up to 17 per cent, of the take-off speed in a calm have been com- pared with theoretical predictions using the simple formula' of Part II. At a given altitude the take-off run is directly proportional to the absolute temperature, that is an increase in temperature from - 15- C. to -4-45° C. increases the run by 10-5 per cent. If, however, the engine power under hot renditions were a function of density instead of pressure only, this figure would br- increased to 30 per cent. An increase in altitude from 0 to 5,000 ft. at a temperature of 15' C. increases the run approximately 60 per cent. A loperm* °f "' m'I>-h" Wlth normal loa(Ungs> reduces the nm by abont Unless the aeroplane is fairly near the limit for a reasonable take-off, •p *i?V* M- 6?i0-' A T1'f distance required to take-off an aeroplane," by Sent Bradfleld, of the Royal Aircraft Kstablish- the correction factors are not appreciably affected by aeroplane character- istics. Comparison of the full scale and theoretically predicted results over the ranges of weight and wind variation experienced in the practical tests shows good agreement. Further, a comparison is made with somejull scale tests contained in American N.A.C.A Technical Note 257.t t Technical Preparation of the Aeroplane " Spirit of St. Louis." PHOTOGRAPHS OF STREAMERS ILLUSTRATING THE FLOW AROUND AN AIRSCREW IN THE VORTEX RLNG STATE. BY C. N. H. Lock, M.A. R. & M. No. 1167 (Ae. 331). (4 pages and 13 diagrams). April, 1928. Price Is. net. The work described in this report is at present mainly of a theoretical interest, as it is unlikely that airscrews will be designed which will be working under conditions of a negative thrust (except perhapR for airships). The work may, however, have application later to the Vortex Theory of Airscrews, and so help in the prediction of result*? under more normal conditions. A previous attempt to photograph the flow around a model screw of 1-in. diameter in a water channel is described in R. & M. 1043.* From the result of these experiments, it was anticipated that the flow in the wind tunnel under these conditions would prove highly turbulent, and a preliminary exploration was accordingly made by means of streamers. A 3-ft. airscrew was set to run at a constant speed of 18 revolutions per second, and pieces of cotton wool on the end of threads were used to indicate the direction of the flow. The photographs illustrating the report, show the flow past the airscrew when in the normal state of running, the flow when running under static conditions, and the flow when in the windmill brake vortex state. * R. & M. 1043. Photographs of the Flow round a model Screw working in water, especially in the " Vortex Ring State."—('. N. H. Lock and H. C. H. Townend. THE BOUNDARY LAYER OF THE FRONT PORTION OF A CYLINDER. By A. Thom. B.Sc., Ph.D. Communicated by Professor J. D. Cormack. R. & M. No. 1176 (Ae. 340) (20 pages and 7 diagrams). July, 1928. Price Is. net. A large amount of information is now available regarding the flow of water or air past a cylinder placed across the stream, so far as the behaviour of the main body of the fluid is concerned ; but the conditions in the layer close to the surface of the cylinder seem to be largely unknown. Accordingly it seemed advisable to explore the velocity, etc., close to the surface. This paper consists of two parts, first, a description of experiments on the boundary layer carried out in the summer of 1927 in the James Watt Engineering Laboratories, University of Glasgow, and, secondly, a theory of the boundary layer over the front portion of the cylinder based on Prandtl's simplified boundary layer equations. *^ The experiments were made on a brags cylinder 4 • 5 in. in diameter, which extended across the 2-ft. square tunnel, at speeds of 12-3 and 36 ft./seo. Good agreement was obtained between the calculated and measured distri- bution of velocity, and with some N.P.L. experiments (K. <t M. 1179— T 2644). THE INCLUSION OF PARTIAL GLIDES IN ROUTINE PERFORM- ANCE TESTS. By A. E. Woodward Nutt, B.A. Presented by the Director of Scientific Research, Air Ministry. R. & M. No. 1180 (Ae. 344). (3 pages and 2 diagrams.)' May, 1928. Price 4d. net. A request was received to investigate the desirability of carrying out partial glides in addition to partial climbs on aircraft submitted for type trials at Martlesham Heath, in order to obtain information at values of V'uT) higher than those given by the partial climbs, and with a view to the possible deter- mination of the best gliding angle of the aircraft. Sets of partial glides with the engine shut off or throttled down have been carried out on a number of aircraft over K wide range of speed, and the results plotted in conjunction with those of the partial climbs carried out on these aircraft during their type trials. Valuable additional information at high values of V/nD U given by these tests, and a check provided on the theoretical extrapolation of the curves of Vc V " against V/nD for level flight. An indication of the best gliding angle of an aircraft can be obtained if require 1 A? a result of this and other work, partial glides are now carried out as a routine test on all aircraft sent to Martlestiam Heath for complete type trials. ON THE USE OF A FOLLOW-UF MECHANISM IN AERO- DYNAMIC SERVO-CONTROL SYSTEMS H. M. Garner. M.A., and K. V. Wright, B.A. Presented by the Director of Scientific Research, Air Ministry. R. & M. No. 1187. (Ae. 349) (8 pages and 2 diagrams). May, 1928. Price 6d. net. Up to the present servo rudders have been fitted with an arbitrary amount of " follow-up " and it appeared desirable to investigate the properties of servo control systems fitted with different amounts of follow-up. Some wind tunnel testa of "these controls have, been described in R. & M. 1180.* The analysis applies to the flap type servo control whose aerodynamic properties were investigated in R. A M. llOS.t The effects of follow-up on the " efficiency " of Itus system (as aeflned In that report) and on tli« stability of the aeroplane are determined (1) when no additional force is applied to the servo control, (2) when a spring force proportional to its angular displacement is applied. The effect of follow-up is to increase the " efficiency " of the system, because the pilot does part of the work of moving over the. control and so less power is lost by the servo, but the analysis indicates that larger amounts of follow-up than those in use at present would require to be provided. The stability with no follow-up, when the control is fixed by the pilot, is the same as the stability with ordinary controls free. The introduction of follow-up bring? the stability nearer to that with controls fixed, and is therefore advantageous It is suggested in the report that full scale experiments on a twin-engined aeroplane fitted with gervo rudders be made to test the effect of ./various amounts of follow-up. • K & M. 1186. Wind tunnel test* of various servo rudder systems.— K. V. Wright, B.A. t E. & M. 1105. The aerodynamics of a simple gervo rudder system. H. M Garner, M.A. and 0. E. W. Lockyer, B. A. 258*
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