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Aviation History
1931
1931 - 0923.PDF
AUGUST 28, 1931 63 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT Communicated by the Director of Scientific Research, Air Ministry. II. & M. No. 1371 (Ae. 498). (11 pages and 10 diagrams.) November, 1930. Price 9d. net. The purpose of the investigation was to find whether the drag of a 10-in.diameter nacelle, mounted on a wing of 2 14 ft. chord, can be correctly measured in a 4-ft. tunnel to check a test by Messrs. Boulton and Paul ina 4-ft. tunnel of a ith scale nacelle housing a Jupiter XF engine on a wing of 2-14 ft. chord and 3-5 ft. span by tests in a 7-ft. tunnel at the B.A.E. Lift and drag have been measured on :—(1) Aerofoil alone. (2) Nacellealone, with and without a Townend ring. (3) Nacelle on aerofoil, with and without Townend ring. Two series of tests were made, with a 5-ft. lengthof wing, and with a wing of infinite aspect ratio. This latter case was repre- sented by filling the gap between the aerofoil and the wall by lengths of aero-foil carried from the wall and separated from the central aerofoil by a very small gap.The measured drag results are applicable to the complete aeroplane when the " local " lift coefficient of the wing adjacent to the nacelle is the samein the two cases. It is preferable to carry the model wing right across the tunnel, so that the flow is two dimensional and no doubt as to the lift coeffi-cient at the centre of the wing is introduced by the tunnel constraint. The same value of nacelle drag against local lift coefficient is obtained with theinfinite wing and with No. 5 ft. wing in the 7 ft. tunnel, but the agreement is less good with the 3i-ft. wing in the 4 ft. tunnel, indicating that the modeltunnel size ratio is getting too large to calculate the relevant tunnel correc- tions.The effect of the Townend ring is large, the nacelle drag being reduced from 82 to 22 II). full scale at 100 ft./sec. when*,. = 0-1. The drag of the uncowlednacelle seems high. THE STRENGTH AND POSITION OF THE EDDIES BEHIND A CIRCULAR CYLINDER. By A. Thorn, D.Sc, Ph.D., A.R.T.C., Carnegie Teaching Fellow, University of Glas- gow. Presented by Professor J. D. Cormack. R. & M. No. 1373 (Ae. 500). (8 pages and 10 diagrams.) De- cember, 1930. Price 6d. A cylinder suspended transversely in a moving fluid can be made to oscillatecontinuously if the natural frequency of the suspended cylinder is the same as that of the eddies which are known to be given off by a cylinder at nearlyall values of Reynolds number. This phenomenon provides a method of measuring the frequency of these eddies and of estimating the strength ofthe impulse given to the cylinder. The present paper deals with measurements carried down to the lowestvalue of Reynolds number at which eddies exist. It is shown that the impulse decreases with decreasing speed until It becomes zero at the Reynolds numberwhere eddying stops. AN INVESTIGATION OF A POSSIBLE CAUSE OF AIRCRAFT FIRES ON CRASH. By W. G. Glendinning, B.A., B.Sc with an Appendix by Staff of the Engine and Electrical Department, R.A.E. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1375 (E. 47). (19 pages and 8 diagrams.) January, 1930. Price Is. net. One of the possible causes of aircraft flres on crash is the ignition of petrolor lubricating oil by contact with hot exhaust pipes. Various observers have carried out determinations of the minimumtemperature of an exhaust pipe, which will cause ignition of petrol or oil in contact with the outer surface of the pipe under conditions likely to occuron crash, and it has been stated that to obtain complete immunity from a hot exhaust pipe, it is necessary Upkeep the temperature of the pipe down to350c C. (R. & M. 795.*) It was thought probable, however, that conditions more favourable to theignition of petrol or oil might exist in the interior of an exhaust pipe, and it was decided to carry out tests to find the minimum temperatures at whichpetrol oil willlignite inside exhaust pipes and to study the action of the various factors which affect the minimum temperatures of ignition.It was found that petrol wouldfexplode after a lag period of about 10 minutes, when introduced into a steel vessel filled with air and kept at 235° C.In an exhaust pipe, into which petrol was introduced while the pipe was cooling, the lowest temperature (measured at the time of introduction)which caused ignition to occur was 280° C, the lag period at this temperature being about 10-20 seconds. With higher temperatures the lag period wasshorter, and at 360°^explosion followed the introduction of the petrol almost instantaneously.The risk is less from lubricating oil, as its minimum igniting temperature is about 50° higher than that of petrol. • R. & M. 795.—The prevention of fire in single-engined aeroplanes. SOME CASES OF FLOW OF COMPRESSIBLE FLUIDS. By Professor G. I. Taylor, F.R.S. R, & M. No. 1382 (Ae. 507). (16 pages and 5 diagrams.) February, 1930. Price Is. net. In previous reports I have shown that w7hen a body moves through the airat a speed less than, but comparable with, that of sound, irrotational motion ceases to be possible as soon as the speed of the body relative to still airattains some definite value which is always less than that of sound, but depends on the shape of the body. The greatest speed at which irrotational motionIs possible seems in the cases so far examined to be determined by the rule that the greatest speed at the surface of the body is equal to, or slightlygreater than, that of sound ; but the mechanical mpthod in one case and the approximate method in another which were used in obtaining the solutionsare not capable of determining accurately whether or not the real criterion Is the first attainment of the velocity of sound at some point in the field.• -The essential difference between two cases previously treated by the same author is that In the first the velocity has a maximum value in the constriction,BO that the pressure gradient is at right angles to the surface at the point of minimum pressure, whereas hi the second the speed increases and the pressuredecreases continuously along all stream lines. At first sight, one might suppose therefore that this is the condition whichdifferentiates between cases where the speed of sound may be attained and exceeded in a tegular manner and cages where the speed of sound is the maximum which can be attained in irrotational motion (if, indeed, thereare such cases). In the work which follows this hypothesis is tested and proved to lie untrue by finding cases in which the speed of sound is attainedand exceeded in a regular manner in the region where the velocity of flow is a maximum.The analysis leads to the prediction that a rapid thickening of the boundary layer might occur when the speed of sound is attained, and this hypothesisis shown to fit in with the existing experimental knowledge of the subject. TESTS OF VARIOUS LATERAL CONTROLS KITTED TO A SISKIN AIRCRAFT. By W. 0. .Jennings, B.Sc. Com- municated by the Director of Scientific Research, Air Ministry. R. & M. No. 1384 (Ae. 509). (10 pages and 43 diagrams.) December, 1930. Price 9d. net. Wing-tip automatic slots have proved an effective device for providingincreased lateral stability at the stall, and many service aircraft of the two- seater and larger types'have been fitted with this device. In the case ofsingle-seater fighter aircraft, where mandr-vrability is of primary importance, it is desirable that adequate control at-the stall should also be provided,and the plain automatic slot does not. in general, supply this need. Certain aircraft fitted with the interconnected slot and aileron-type control haveshown satisfactory control characteristics at the stall but little or no increase in stability.A proposal to combine the automatic slot with a device connected to the aileron for spoiling the slot in front of the raised aileron appeared to providea promising method for giving both stability and control at the stall. A method due to Mr. McKinnon Wood, for spoiling the action of the slot,is described in R. & M. 1260.* This device is hereiiffcr referred to as the " spoiled autoslot." Another method, due to Messrs. Handley Page, Ltd.,consists of a plate projecting from the main wing behind the slat and connected to the ailerons in such a manner that it comes into operation only as theaileron is raised. This device is known as the " interceptor autoslot," and is described in greater detail later.In normal flight none of the various controls which were tried differed appreciably from that of the standard aircraft. In all cases the side-slippingqualities were poor, and the interceptor autoslot was worst in this respect. At the stall the interceptor autoslot was distinctly superior to all theother types. With the control column central the aircraft was very stable, and when disturbed a dropped wing could be raised with ease, even againstthe rudder. When fitted with the plain autoslot, " spoiled " aiitosint ami interceptorautoslot, the aircraft could not be made to spin. * R. & M. 1260. Flight tests on an Atlas fitted witli automatic Blotsconnected with the ailerons.—E. T. Jones. THE MODE OF DEFORMATION OF A SINGLE CRYSTAL OF SILVER. By H. .). Gough, D.Sc., and H. L. Cox, B.A. R. & M. No. 1385 (M. 70). (13 pages and 14 diagrams.) June, 1930. Price Is. net. During a series of experiments on the behaviour of single crystals of zincand antimony under alternating torsional stresses*^ some information was obtained as to the mode of formation of mechanical twins. From the resultsof the work on zine.,*t it appeared that the formation of twins depended to a large extent on the slip system, and the actual planes on which twins wereformed at any point were found to depend simply upon the direction of slip at that point. The present experiment on a single crystal of silver was undertaken withthe object of investigating the twinning characteristics of the metal. A secondary object of the work was to investigate the slip phenomena. The observed slip phenomena were found to be in close accordance withthe distribution anticipated on the basis of the maximum resolved shear- stress law. In addition, the slip-band spacing (number of bands per unitdistance transverse to their length) was examined, and it was concluded that this spacing varies systematically with the intensity of resolved shear stress. No definite twins were observed, and it is concluded that twinning didnot occur under the conditions of the tests. Failure in torsional fatigue occurred by the formation of a crack after2-i x 10" reversals of ± 2-0 tons/in.2 nominal maximum shear stress, following a small number of cycles of smaller stress ranges. The crack as awhole tended to follow the direction of maximum resolved shear stress (i.e., the circumferential direction); but small portions of the crack tended tofollow the edges of the slip planes, especially in those regions where the operative slip plane changed.Since no twins were observed, the experiment must be regarded as having failed in its main object. That definite twins were not produced was sur-prising, and a second single crystal of silver is in hand, and this will be tested under alternating direct stresses. • R. <fc M. 1183. The behaviour of a single crystal of zinc subjected toalternating torsional stresses.—Gough and Cox. t R. & M. 1322. Further experiments on the behaviour of single crystalsof zinc subjected to alternating torsional stresses.—Gough and Cox. X R, & II. 1323. The behaviour of a single crystal of antimony subjectedto alternating torsional stresses.—Gough and Cox. THE INFLUENCE OF TITANIUM TETRACHLORIDE ON THE GAS CONTENT AND GRAIN SIZE OF ALUMINIUM AND SOME ALLOYS. By Dr. W. Rosenhain, F.R.S., J. D. Grogan, B.A., and T. H. Schofield, M.Sc. Work performed for the Department of Scientific and Industrial Research. R. & M. No. 1386 (M. 71). (10 pages and 10 diagrams.) November, 1929. Price Is. net. It has recently been shown by D. J. Tullis* that dissolved gas may beremoved rapidly and very completely from some of the alloys of aluminium by passing chlorine gas through the molten metal. Castings made frommetal so treated arc surprisingly free from gas cavities, but arc very coarse in grain size. If the treated metal, while still molten, is further treated witha mixture of chlorine and boron trichloride, the castings obtained are very sound and also very fine in structure. This refinement of grain size is saidto persist after repeated remelting. • J. Inst. Met. XL., 1928 (2), pp. 56-61. 862 g
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