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Aviation History
1928
1928 - 0811.PDF
AUGUST 30, 1928 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT slot. Choice of hinge position so as to bring the flap to the best position whenset down is important. Distribution of pressure over the leading auxiliary aerofoil on R.A.F. SI isto be measured particularly in connection with the development of the automatic front slot. AN ANALYSIS OF SOME CAUSES OF DISCREPANCY BETWEEN THE CALCULATED FAILING LOAD OF THE STRUCTURE OF AN AIRCRAFT AND THE LOAD AT WHICH FAILURE OCCURS ON STRENGTH TEST.—By H. B. Howard. B.A., B.Sc, and K. T. Spencer, B.Sc., A.M.I.C.E. of the Airworthiness Department, Royal Aircraft Establishment. Presented by the Director of Scientific Research. Air Ministry. R. & M. No. 1125. (Ae. 298). (9 pages and 5 diagrams). August. 1927. Price 6d. net. It is well known that the load at which an aircraft structure fails is seldomexactly the same as the maximum load which calculations show the structure to be capable of carrying. The present Report deals with some of the moreusual causes of this discrepancy, and records some values for th^ratio between the calculated and test failing loads for some typical structures and com-ponents. Records of mechanical tests on complete structures, components andmaterials have been analysed and compared with calculations on the structure and the strength values for the material assumed in calculations.No reliable conversion factors for relating the strength as calculated with that obtained on test can be established without considerably more testdata than are at present available. Records of strength test as they become available will be examined andcompared with calculations on the structure tested. In this way it is hoped to collect sufficient information to justify a statistical treatment of the sub-ject. MOTORING LOSSES IN INTERNAL COMBUSTION ENGINES.— By H. Moss, D.Sc, A.R.C.S., D.I.C., of the Air Ministry Laboratory. Communicated by the Director of Scientific Research/ R. & M. No. 1128 (E. 27). (7 pages and 2 dia- grams.) July, 1927. Price 6d. net. Experiments which have been made on internal-combustion engines at theAir Ministry Laboratory and elsewhere (see The Automobile Engineer, March, 1925),* have led to the conclusion that the frictional losses whenrunning under power may be considerably different from the losses when the engine is motored round at the same speed and wall temperature : thededuction of the indicated horse-power from the brake horse-power and the motoring losses is consequently in error. In the case of an aero-engine ofnormal design, a large increase of sliding friction has been found. Part of the increase can be attributed to carbonisation of the oil and part to increase ofthe normal forces at the rubbing surfaces. An investigation into the magni- tude of the latter effect has been made. The total frictional losses of a Benz single-cylinder engine were found whenmotored at speeds of 1,200 r.p.m. and 900 r.p.m. with air at densities ranging from normal to twice normal. The pumping losses, measured by an R.A.E.electrical indicator, were deducted, the remainder being the sliding friction of engine and accessories.The sliding friction under power may be greater than that when motoring by the equivalent of 3-5 lb. per sq. in. M.E.P. due to this cause. With anincrease of 3-5 lb./sq. in. in M.E.P. found by Kicardo due to carbonisation, the magnitude of the effect when running under power with a normal sparksetting is fully explained. * See also Ricardo " Internal-Combustion Engines," II, 217. A HIGH SPEED WIND CHANNEL FOR TESTS ON AEROFOILS. —By T. E. STANTON. R. & M. No. 1130 (Ae. 300). (9 pages and 6 diagrams.) January. 1928. Price 9d. net. A number of experiments have been made on high tip speed airscrews atthe Royal Aircraft Establishment, and it was desired to obtain, if possible, a check on the performance of the blade sections at the high wind speeds atwhich they work. The Airscrew Panel of the Aeronautical Research Com- mittee accordingly requested that some tests might be made of small aerofoilsections in an existing high-speed wind tunnel at the National Physical Laboratory.The National Physical Laboratory 3-in. high-speed wind channel has been modified for the purpose of the tests," and an aerodynamic balance constructedfor tests on aerofoils. Tests under conditions of infinite aspect ratio and at speeds ranging from 0 -25 to 1 -7 times the velocity of sound have been madeon scale models of R.A.F. 31a and a circular arc section, whose maximum ordinates were respectively 7 per cent, and 3 per cent, of the chord (Fig. 4).Two models of each section were tested—R.A.F 31a with chords of 0-5 and 0-25 in. circular arc with chords of 0-r> and 0-3 in. The same sectionshave been tested in airscrews at the Royal Aircraft Establishment.* The increase in the slope of the lift curve without appreciable change inthe angle of no lift, as the speed increases Tip to 0-6 of the velocity of sound, predicted in 11. & M. 1135.1 has been verified. The limiting speed at whichthis effect ceases appears to be considerably higher for the circular arc aerofoil than for B.A.F. 31a, but in both cases, when the limit is reached, the liftfalls rapidly for higher speeds, and the angle of no lift tends to zero value. At speeds considerably above the velocity of sound (1 -7a). the angle of no lifthas a negative value for R.A.F. 31a and a positive value for the circular arc aerofoil. * R. & M. 1086. Wind tunnel tests with high speed airscrews. The characteristics of the aerofoil section R.A.F. 31a at high speeds.—G. P. Douglas and W. G. A. Perring. t Wind tunnel tests with high tip speed airscrews.—G. P. Douglas and W. G. A. Perring. R. & M. 1091. . . t R & M. 1123. Wind tunnel tests with high tip speed airscrews.—Thecharacteristics of bi-convex No. 2 aerofoil section at high speeds.—G. P. Douglas and W. G. A. Pen-ins:. f R. & M. 1135. The effect of compressibility on the lift of an aerofoil.— H. Glauert. FULL-SCALE AND MODEL MEASUREMENTS OF THE LlFT AND DRAG OF THE BRISTOL FIGHTER WITH M.2 SECTION WINGS.—By E. T. JONES, M.Eng.. and A. S. HARTSHORN B.Sc. Presented by the Director of Scientific Research, Air Ministry. R. &' M. No. 1133 (Ae. 303). (8 pages and 8 diagrams.) November, 1927. Price M. net. Full-scale and model measurements of the lift and drasi of the BristolFighter with M.2 section wings have been made to provide data on the Bcale effect of the thin symmetrical wing. The lift and drag of the BristolFighter, fitted with wings of R.A.F. 15. R.A.F. lit and R.A.F. 30 section have been measured both full-scale and in the National Advisory Committeefor Aeronautics variable density wind tunnel.' The lull-scale measurements with M.2 section wings extend the comparison between the results obtainedin the variable density tunnel and free fliuht tests. The lift and drag coefficients have been determined full-scale over as widea range of incidence as possible (2° to 20°). Wind tunnel experiments on a l/10th scale model have been made over ft slightly larger incidence range atwind speeds of 40. 00 and 80 ft./sec. The maximum lift coefficients i'or full-scale and model are. 0-432 and 0-38respectively. The minimum drag coefficient decreases as the Reynold* number increases, being 0-0315 at 40 ft./sec. on the model and 0-028 fullscale. The results are in quite good agreement with those of the N.A.C.A. variable-density tunnel.-f * R <6M. 1122. Lift and drag of ithree model aeroplanes. Comparativetests in atmosuherie and variable density wind tunnels at the same Reynolds number.—H. C. H. Townend. (N. A. C. A. Report No. 279).t N.A.C.A. Report No. 221. Model tests with a systematic series of 27 wing sections at full Rcvnolds number.—Max M. Munk and KIton W.Miller. THE THEORY OF PRESSURE CAPSULES. PART 1.—GENERAL DISCUSSION. PART II.—THE COMPLETE FLAT DISC WITHOUT CONTROL SPRING.—By A. A. GRIFFITH, D.Eng. Presented by the Director of Scientific Research. Air Ministry. R. & M. No. 1136 (Ae. 306). (14 pages and 1 diagram.) August, 1927. Price M. net. Hitherto no adequate theory of the action of pressure capsules has beenavailable. It has, therefore, not been possible either to predict the per- formance of capsules or to correlate the performance with the knownmechanical properties of the material. Consequently design and develop- ment have in the past been almost entirely empirical In the present series-of reports, the general principles governing the action of pressure capsules will be discussed, and the detailed theory of such action will be given in anumber of cases. The finite deformation of any capsule necessarily involves the occurrenceof extensional as wrell as inextensional strains. The principal condition for optimum performance is that the effects of the extensiona) strains shall bereduced to a minimum. Two general methods of attaining this end are described in the present report.References are made in the report to the work of J. H. Jellett (Dublin Trans. It. Irish Aead.. Vol. 22 (1855)) and Prescott (The Equations of Equili-brium of an Elastic Plate under Normal Pressure, Phil. Mag., Jan., 1922, p. 97). NOTES ON PERFORMANCE TESTING.—By H. L. STEVENS, B.A., and A. E. WOODWARD NUTT, B.A., of The Aeroplane and Armament Experimental Establishment, Martlesham Heath. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1140 (Ae. 309). (8 pages and 0 diagrams.) February, 1928. Price dd. net. In June, 1925, a report *was presented to the Aeronautical Research Com-mittee by Mr. Capon describing a method of performance testing which has since come, to be known as the " Research Method." and which was recom-mended for adoption by Martlesham Heath on selected aircraft. The object of the present note is to put on record the method of performance testing atpresent in force at Martlesham partly as a result of this recommendation. The present method is a combination of this research method with thestraightforward method of direct measurements of climbs and speeds. It is considered that the above method of performance testing provides both thedata required by the Service and that required for analysis by the designer and research worker with the minimum of flying time. The analysis allowsthe consistency of the figures to be checked and separates engine effects from aerodynamic effects. The effect of changes of weight can be readilycalculated taking into account the variation with height of the power of the actual engine employed. The effect of throttling the engine to predeterminedr.p.m. can be quickly found. Finally, the total flying time is very little in excess of that required for the straight tests, bearing in mind the number ofrepeat tests necessary, and the gain in accuracy is very great. • R.. <fe M. 985. " The Reduction of Aircraft Performance Tests." By R. 8.Capon, B.A. WIND TUNNEL TESTS ON A R.A.F. 15 AEROFOIL WITH PILOT PLANES.—By F. B. BRADFIELD, Math, and Nat. Sci. Triposes and K. W. CLARK. B.SC., D.I.C. Presented by the Director of Scientific Research, Air Ministry. R. & M. No. 1145 (Ae. 313). (17 pages and 15 diagrams.) October, 1927. Price Is. net. A " pilot plane " is an auxiliary aerofo 1 pivoted ahead of a wing so as to"provide automatically a slotted wing at high incidence without much increase of drag at fine angles. This forms part of an investigation into the use ofpilot planes with wings of various sections. The maximum lift region was investigated with pilot planes of chord7J per cent., 10 per cent., and 12J per cent, of the main chord, trying different hinge positions relative to the main wing in each case. The drag of the bestlift arrangement for each pilot plane was measured, and the angle at which the pilot plane floated freely was recorded. In the case of the 10 per cent,pilot plane, the drag and free settings were repeated with the pilot plane hinged ahead of its leading edge : and hinge moments were measured with thehinge both at, and ahead of, the leading edge. The tests were extended to cover the use of the pilot plane as a control, and rolling and yawing momentshave been measured with the pilot planes in front of the ailerons only, using Frise balanced ailerons.
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