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Aviation History
1931
1931 - 0602.PDF
SUPPLEMENT TO FLIGHT JUNE 19, 1931THE AIRCRAFT ENGINEER The full-scale experiments made at the Royal Aircraft Establishmentshowed that these modifications hnd considerable effects on the spinning of the machine, but, although no actual difficulty in recovery was found,recovery was slow, 3—4 turns. Previous experiments at Martlesham with a slightly smaller fin and rudder had shown that danger had not been entirelyeliminated ; so that even with the larger fin and rudder, the machine could not bo regarded as having been far removed from the danger point. If such a hot wire is placed normally to a current of air, it is found that thethin band of heated air in its wake persists coherently for some distance down- stream and that, due to its reduced density it will cast, a shadow on a screenif suitably illuminated. Some experiments have been made to explore the possibilities of this as amethod of observing air flow, and a few photographic reproductions show the kind of results obtainable. A SYSTEM FOR THE AUTOMATIC TIMING OF AIRCRAFT OVER A SPEED COURSE. By ,T. K. Hardy, B.A., and K. V. Wright, B.A., with an appendix by S. B. dates, M.A. Com- municated by the Director of Scientific Research, Air Ministry. R." & M. No. 1343 (Ae. 475). (9 pages and 9 diagrams). February, 1930. Price Is. net. Accurate timing of an aircraft over a speed course with watches, by observersstationed at either end of the course, has been found unsatisfactory even when the most elaborate precautions have been taken. A system has beendevised which eliminates the errors, both human and instrumental, that were associated with the older system. In this, the timing counting mechan-isms at cither end of the course arc controlled by a single instrument. A detailed account Is given of the apparatus for this system, which wasdeveloped for measuring the speeds of racing seaplanes over the 3 kilometre course at Calshot during 1021). Two cinema cameras were used and these,in addition to recording the passage of the aircraft at either end of the course, by a scries of photographs, recorded tho time at which each exposure wasmade in terms of vibrations of a tuning fork, which was in electrical connection with counters in both cameras.The apparatus, which is built up from commercially produced components. has proved very reliable in service. Tho, accuracy with which the time of anyone transit of the aircraft can be determined is not less than 1/20 second, so that speeds of about 350 m.p.h. over 3 kilometres may be measured to thenearest i-m.p.h. This is sufficient for experimental work, but it could be considerably Improved by a modification to the design of the apparatus ifoccasion demanded. The necessary modifications are briefly discussed, and two alternative schemes outlined. A theory of time determination for anapparatus functioning Ideally on the principle of the present design is given In an Appendix. THE APPLICATION OF THE METHOD OF OPERATORS TO THE CALCULATION OF THE DISTURBED MOTION OF AN AERO- PLANE. By L. W. Bryant, A.R.C.Sc, and D. H. Wil- liams, B.Sc. R. & M. No. 1346. (Ae. 478.) (13 pages.) July, 1930. In the theoretical Investigations of low speed control and spinning theproblem arises of how best to compute rapidly the motion due to applied forcM Hnd eoupleg. The method of operators has been found of great utility in dealing with thisproblem. The method appears to be due. to HeaviRide in the first instance* and Bromwleh established its validity. In the present note a treatment ofsimultaneous linear differential equations of the first order is given, following a presentation given by Jeffreys in a recent mathematical tract. The eightsimultaneous equations defining the general motion of an aeroplane in three dimanslons are taken as an example in dismissing the method, and the types ofsolution corresponding to real, complex, and repeated real roots of the stability equation are indicated. The cases of lateral and longitudinal disturbances from steady straightflight are considered In detail, and the operational forms In terms of the derivatives are given expanded ready for computation. • "On Operators In Physical Mathematics." Proc. Roy. Boc. A.52, 1893,and 54, 1894. ON THE VALIDITY OF LARGE SCALE TESTS IN AN OPEN JET WIND TTJSHEL. TESTS ON ONE-FIFTH SCALE BRISTOL FIGHTER IN 5 FT. OPEN JET TUNNEL. By W. G. A. Perring, R.N.C., and C. Callen. Communicated by the Director of Soientific Research, Air Ministry. R. & M. No. 1348 (Ae. 480). (12 pages and 9 diagrams.) July, 1930. Price 9d. net. The testa were undertaken to investigate the possibilities of experimentsIn an open jet tunnel upon aeroplanes of wing span greater than the jet diameter. Interest In the tests was chiefly concerned with the measurementof changes In the force along wind, due to changes in the parts of the aero- plane situated near the centre of the jet. The tests were carried out In a 5 ft. open Jet tunnel* on a one-fifth scale modelBristol Fighter. Lift and drag without airscrew, and with stopped airscrew, •ml the lift and nett thrust with airscrew running have been measured atangles of Incidence varying from —4° to 8°. From the results the pitching moments have been calculated, the additional drag due to a stopped airscrewhas been deduced and the effective thrust of the airscrew has been determined. The results are compared with those for similar tests carried out on the samemodel in the Duplex tunnel at the National Physical Laboratory, Teddington. In addition, some exploration of the jet was made with the model inposition. The tests have demonstrated the possibility of measuring in an open jetwind tunnel, the changes of drag or thrust resulting from modifications to parts of the aeroplane situated near the axis of the jet, even when the aero-plane span greatly exceeds the jet diameter. * R. & M. 1364. The !> ft. open jet wind tunnel, R.A.E.—F. B. Bradflekl. ON RENDERING AIRFLOW VISIBLE BY MEANS OF HOT WIRES. By H. C. H. Townend, B.Sc. R. & M. No. 1349. (Ae. 481.) (5 pages and 5 diagrams.) October, 1930. Price 9d. net. This papar describes a method ot delineating the flow pattern round bodiesmounted In an airstream by means of fine wires electrically heated, similar to thi wall-known hot wire anemometers. REPORTS AND MEMORANDA PUBLISHED BETWEEN SEPTEM- BER, 1929, AND DECEMBER 31. 1930. R. & M. No. 1350. (8 pages.) January, 1931. Price 6c/. net. This is a list of all the Reports and Memoranda published by the Aero-nautical Research Committee between September 1, 1929, and December 31 1930. Previous lists of the Committee's published papers are Report* anilMemoranda 650, 750, 850, 950, 1050, 1150 and 1250. For a classified list of reports on sale as separate issues, with prices, see List B, for which applicationshould be made to H.M. Stationery Office. Most of the Memoranda have been or will be published in the annualtechnical volumes. The remainder are published in special monographs. THR AIK FLOW AROUND A SYMMETRICAL AEROFOIL. BV T. Tanner, A.C.G.I., D.I.C. Communicated by Profes- sor L. Bairstow, C.B.E., F.R.S. R. & M. No. 1353. (Ae. 484.) (11 pages, and 58 diagrams.) July, 1930. Price Is. net. The object of this investigation, which was undertaken at the Eoy«lCollege of Science at the suggestion of Mr. W. 8. Farren, was to determine the velocity of the air, both in magnitude and direction at all points in thefield around an aerofoil and to find from this, according to the circulation theory, the value of the lift coefficient, with a view to forming a basis forthe comparison of work being carried out In the watertank at Cambridge University. The aerofoil used was the one of symmetrical section known as R.A.F.SO,and the chord and wind speed were chosen so as to give the same Reynolds number 1-24 y 105 and the same tunnel constriction as the apparatus atCambridge. The circulation has been determined around a contour enclosing thraerofoil and for the purpose of checking the result, the pressure distribution around the median section of the model was determined by the usual methodof Inserting a piece of soft metal tubing in the Burface of the aerofoil and taking readings on a tilting manometer of the pressures at a number ofholes pierced through It. The lift coefficient was then determined by the integration of the pressure distribution diagram, giving a value of 0-868, or about 2 per cent, more than that determined by the circulation. VARIABLE DENSITY WIND TUNNEL TEST DATA ON MODELS OF THE HAWKER HORNBILL AEROPLANE AND THE AD-1 AEROFOIL SECTION. By W. S. Diehl and R, F. Anderson. Copy of a Report communicated by the National Advisory Committee for Aeronautics. R. & M. No. 1357. (Ae. 488.) (9 pages and 11 diagrams.) June, 1930. Price Is. net, At the request of the British Aeronautical Research Committee, theNational Advisory Committee for Aeronautics, U.S.A., agreed to conduct, routine tests In the variable Density Tunnel on a model of the HawkerHornbill aeroplane and a model of the AD-1 wing section used on the Hornbill. The purpose of these tests was to supply data for use in the study of theunusual high angle stability and control observed in flight tests of this aero- plane. The flight tests were made with and without, slots and their effect onthe control was found to be extremely small. It was observed that the stability at the stall, without slots, was similar to many aeroplanes withautomatic slots. This stability was attributed to the AD-1 aerofoil and further investigation of Its properties was suggested. The Variable Density Wind Tunnel tests show that the AD-1 lies in theclass of aerofoils having a low maximum lift coefficient and a flattened lift curve peak. Scale effect on the AD-1 and Hornbill models was similar andwas favourable for both lift and drag. The wind tunnel results for lift coefficients near the stall were found to be in good agreement with the flighttest data. CARBUBBTTOR FUHL MBTKRING CHARACTERISTICS. By W. C. Clothier, M.Sc, Wh.Sch. Communicated by the Director of Scientific Research, Air Ministry. R- & "'• No. 1361 (E. 43). (12 pages and 37 diagrams ) December, 1930. Price 9d. net. It has been suggested that the variation in mixture strength caused bychange of fuel temperature may be reduced by fitting sharp edged f.-nure edged) fuel metering orifices to carburettors. In the absence of infoni^nonas to the magnitude of the change of mixture strength to be expected wit tne range of temperatures likely to occur in flight, tests on a standard ty.n1 nicarburettor were made to obtain data. A carburettor (Claudel Hobson type A.V. 48.C) suitable for an 80-h.p- «;>r™ewas calibrated using 80/20 petrol Benzol mixture at various tempera'. ..re?. kerosene and white spirit, A constant inlet air temperature was maint nethroughout the test to reduce variation due to change of air density. -« coefficients of discharge for the various orifices were determined over a . ••«<of conditions from flow tests apart from the carburettor. „/ At full throttle the carburettor as supplied showed very little cnaif vmixture strength with fuel temperature from + 20° C. to - 30° t. oi "^ air flow range such as is likely to occur in service. At part throttle -*_was considerable weakening with decreased temperature. Over a•;•_*.•. temperature range + 20° C. to - 50° C. weakening of the mixture «•'-«£with temperature occurred, especially at the low air flows and at par t tni >^^j When fitted with sharp-edged orifices the mixture became rich mtnoK' < ^temperature, the increased mixture strength being greater than the var- given by the original jet at full throttle, but less at part throttle. ,fl Flow tests of jets (not fitted to the carburettor) withTariouB shapea c. ^ ^showed that sharp edged orifices have constant discharge <xx&fl large temperature range, and consequently give rich mixture* at lowturee due to the Increased density. 556 A
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