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Aviation History
1931
1931 - 0922.PDF
SUPPLEMENT TOFLIGHT AUGUST 28, 1981 THE AIRCRAFT "ENGINEER No. 1359 (Ae. 490). (8 pages and 2 diagrams.) October, 1930. Price 6d. net. All the experiment** were made with air preheated in a gas furnace andforced at high s >eedg through the experimental tube which was cooled by a water jacket. In order to compare the three-dimensional case with thetwo-dimensional one, the first series of observations was made in a pipe 1 In. in diameter. Subsequently, pipes of internal sections 1 in. by 0 125-in.and 2 in. by 0- 1-in., were tested. The results of the three-dimensional experiment were in fair agreement withprevious work on the subject, in showing an appreciably greater rate of heat transmission than that calculated from the Reynolds theory. Theresults obtained from the rectangular pipes show that as the flow becomes more two-dimensional in character the ratio of the observed heat trans-mission to the calculated transmission becomes progressively smaller and con- siderably less than unity. THE 5-PT. OPEN JET WIND TUNNEL, R.A.E. By F. B. Bradiield, Math, and Nat. Sci. Triposes. Communi- cated by the Director of Scientific Research, Air Minis- try. R. & M. No. 1364. (Ae. 492.) (11 pages and 11 diagrams.) November, 1930. Price Is. net. An open jet tunnel with enclosed return passage has been installed at theRoyal Aircraft Establishment in the building previously occupied by the 4-ft. closed tunnel. The design, which is largely due to Mr. It. McKinnonWood, has been based upon the Gottingen tunnel, but is more compactly arranged. The open jet is of#> ft. diameter, and is 9 ft. long. The maximum windspeed with a 60-h.p. motor overloaded 60 per cent, is 170 ft./sec, so that it is the highest speed tunnel at the R.A.E., the top speed hitherto available being140 ft./sec. The structure lias been designed to stand greater pressures, so that if a larger motor were substituted for the 50-h.p. motor, it might bepossible to use the tunnel up to 350 ft./sec. This tunnel thus forms a valuable extension to the plant. The power factor for the tunnel is exceptionally low the value of i^-yj being 0-38, with a fan efficiency of about 90 per cent. With a 50-h.p. motor overloaded 60 per cent., the wind speed is 170ft. /sec. The tunnel has been made very compact, so as to keep the building costs ofthe 24-ft. tunnel, of which it is a model, as low as possible; the expansion ratio of the tunnel is consequently only SiJ : 1. The velocity in the jet variesby ± 1J per cent, from the mean over the central 4 ft. diameter of the jet, without any honeycomb. If necessary this may be improved by using ascreen of wire gauze. THE LIMITS OF COMPRESSION RATIO IN DIESEL ENGINES. By D. It. Pye, M.A. Communicated by the Director of Scientific Research, Air Ministry. It. & M. No. 1365 (E. 45). (9 pages and 3 diagrams.) November, 1930. Price 9d. net. Although the place of compression ratio in the functioning of a petrolengine Is now well understood, there is no general concensus of opinion as to the limit to which compression ratio in the high compression injectedfuel engine can usefully In- raised, In the following report an endeavour is made to decide this question.ResuLs obtained in experimental compression ignition engines of 12 and 15 : 1 compression ratio arc given^ and these are compared with the calculatedefficiency of theoretical cycles of compression ratio between 10 and 20 : 1, In which a limit is placed upon the maximum pressure to be allowed in thecylinder. " It is concluded that there is experimental evidence that substantial gainsof economy may be achieved by a raising of the compression ratio to 15: 1 provided difficulties of design in regard to the shape of the combustion cham-ber can be got over ; but that an examination of the theoretical cycles makes It appear unlikely that any advantage would be obtained by raising thecompression ratio further, so long as maximum cylinder pressures are limited to about 1)00 1b. per sq. in. DRAG AND HEAT DISSIPATION OF THREE RADIATOR SYSTEMS. By E. T. Jonos, M.Eng. Communicated by the Director of Scientific Research, Air Ministry. R. # M. No. 1306 (Ae. 493). (14 pages and 12 dia- grams.) August, 1930. Price Is. net. The heat dissipation and the drag of unshuttered radiators and radiatorsfitted with flat and conical shutters have been measured In the wind tunnel. Borne uncertainty remains owing to the possibility of interference betweenradiators and the aeroplane, and experiments have now been made to deter- mine the change of performance of an aeroplane with a radiator fitted withdifferent fairings and shutters and operating at the same cooling capacity. The level speed and maximum rate of climb of a Fairey " Fox " aeroplanewere measured with three radiator systems adjusted to give, in turn, their maximum and minimum cooling. The cooling capacity of each radiatorsystem has also been determined, and the performance results interpolated at the same radiator and air temperatures.The drag of each radiator has been deduced from the performance results, and is compared qualitatively with the wind tunnel results.The top speed and maximum rate of climb of the aeroplane at an aneroid height of 5.000 ft. when fitted with the radiator systems adjusted to givethe same Inlet temperature (90° C.) when operating l"n the maximum English summer temperature (14-6° C.) are compared. An analysis of the windtunnel results places the radiators In the same order of merit as In the lull •cale tests; namely, without a radiator with a retractable radiator, with afaired umlcrsluiin radiator, anil with an unfalred underslung radiator. The virtual drag of the exposod radiator unshuttered ond unfalred is proportionalto the area exposed, and is approximately 15 per cent, greater than the tree drag measured in the wind tunnel. QUANTITATIVE MEASUREMENTS OF THE LONGITUDINAL CONTROL AND STABILITY OF THE BRISTOL FIGHTER WHBN STALLED, WITH REFERENCE TO STALLED LANSINGS. By E. T. Jones, M.Eng., and R. P. Alston, B.A. Com- municated by the Director of Scientific Research, Air Ministry. R. & M. No. 1367 (Ae. 494). (8 pages and 13 diagrams.) September, 1930. Price 9d. net. The possibility of utilising the stalled glide on to the ground for anemergency landing, where there may not be room to flatten out and a small horizontal velocity is essential, has long been mooted. The development ofthe slotted wing has made the idea more feasible in two ways:—(a) IUis possible by slotting a wing along its whole length to increase the maximumlift by at least 50 per cent, without altering the gliding angle much at the stall, so that the stalled horizontal and vertical velocities can be reduced by25 per cent. (6) Auto control slots at the wing tips, working in conjunctior with some form of spoiler device connected to the aileron, provide a sufficientamount of lateral stability and control. Quantitative experiments have accordingly been made on a Bristol Fighter aeroplane to determine thedegree of longitudinal control and stability at high incidence in order to obtain data relevant to landing from stalled glides.A unique trimming curve is obtained from a definite C.G. position up to the highest incidence that can be maintained, and there is no evidence offailure of the elevator control. The power of the longitudinal control up to the highest incidence is adequateto neutralise the maximum rate of pitch obtained during bumpy atmospheric conditions. Small incidence changes beyond stalling incidence can beeffected fairly quickly, but to change from a fully stalled^to a slightly unstalled glide (24° to 16-3°) takes about 30 sec, and the aircraft losesabout 600 ft. before the motion becomes steady at the new incidence. A visual elevator angle indicator is of considerable assistance to the pilotwhen flying stalled, and it is suggested that such an indicator graduated in ft./sec. would enable a pilot to fly steadily in the stalled state at a desiredrate of descent. A good degree of longitudinal stability is shown at all incidences beyondthe peak of the lift curve. Stalled glides could be made right down to the ground in fairly calm atmospheric conditions, and a safe landing made,provided the undercarriage and tail skid were sufficiently robust to withstand a vertical velocity of 10 per cent, above the mean fully stalled rate ofdescent. FURTHER EXPERIMENTS ON THE FLOW AROUND A CIR- CULAR CYLINDER. By A. Fage, A.R.C.Sc, and V. M. Falkner, B.Sc. R. & M. No. 1369 (Ae. 496). (13 pages and 11 diagrams.) February, 1931. Price Is. net. In an earlier paper, R. & M. 1179,* an examination of the airflow in.theboundary layer around a circular cylinder near the region where the separation from the surface took place was made from observations of total head takenwith a small exploring tube. The types of now considered were those associated with the large change of Ku which occurs at high values of Keynoldsnumber (V 0D,'v). An analysis of these experimental results showed thatthere was a critical point on the cylinder, just beyond the region of maximum negative pressure, where a transition from laminar to turbulent^now inthe boundary layer began, and that the position of this point on the cylinder was indicated by a pronounced inflexion in the curve of normal pressure.In a later paper, R. & M. 12Sl,t an attempt was made to determine from the experimental data given in the earlier paper, the intensity of frictionon a limited part of the surface of the cylinder anterior to the region of maximum negative pressure. Since the publication of these two papersan experimental method of measuring the friction on the surface of a body immersed in an air stream from observations of velocity taken with exceed-ingly small surface tubes has been developed and tested on a large metal aerofoil.% This method was found to be reliable. The character of the frictional distribution depends on the value of (VD,V).At a relatively low value of (VD/i/), the frictional intensity rises gradually to a maximum value and then rapidly falls to a zero value ; whereas at alarger value of (VD/..) within the sensitive range the frictional intensity after reaching its maximum value falls less abruptly to a minimum value, andthen rises to a second maximum before the zero value is reached. A transition from laminar to turbulent flow occurs in the boundary layer where thefrictional intensity is a minimum. The transition region is also clearly indicated by a marked inflexion in the curve of pressure distribution.The frictional distribution measured on the 5 • 89-in. cylinder is in reasonably close agreement with that predicted by modern boundary layer theory.-Experiments have also been made to determine the effect of disturbances In the general stream on the characteristics of the now. • R. & M. 1179. " The Airflow Around a. Circular Cylinder in the Regionwhere the Boundary Layer Separates from the Surface." A Fage. t R. & M. 1231. " The Skin Friction on a Circular Cylinder." A Fage.| K. i M. 1315. " An Experimental Determination of the Intensity of Friction on the Surface of an Aerofoil." Fage and Falkner. THE DEAG OF CIRCULAR CYLINDERS AND SPHERES AT HIGH VALUES OF REYNOLDS NUMBER. By A. Fage, A.R.C.Sc. R. & M. No. 1370 (Ae. 497). (6 pages and 2 diagrams.) May, 1930. Price 6d. net. The paper gives the results of experiments made recently to measurethe drag of a circular cylinder of large diameter (23 in.). The more important measurements made in this country and abroad* of the drags of circularcylinders and spheres at high values of Reynolds number are also included. An analysis of these measurements leads to the conclusion that the flow inan open jet tunnel of the Gottingen type, with a contracting mouth and with the honeycomb at the larger end," is steadier than that in an N.P.L.type of tunnel. The drag coefficients of a circular cylinder and of a sphere appear to beslowly increasing, at the highest values of Reynolds number attained. • See Prandtl, (iottingen, Nachrichten Math. Phys., 1914.R. & M. 190. Bacon and Reid, JX.A.C.A. Report 185. Jacobs, N.A.UA- Technical Note 812. Flachsbart, Phya. Zeit.. July, 1927. ITyden andKuethe, N.A.C.A. Report No. 342. THE VALIDITY OF DRAG TESTS ON A LARGE SCALE MODEL IN A SMALL CLOSED WIND TUNNEL. DRAG OF 1/5TH SCALE NACELLE INSTALLED ON THE UPPER SUB- FACE OF A MONOPLANE. By F. B. Bradfield, Math. & Nat. Sci. Triposes, and W. G. A. Perring, R.N.C. 862/
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