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Aviation History
1932
1932 - 0190.PDF
SUPPLEMENT TO FLIGHT 16 THE AIRCRAFT ENGINEER FEBRUARY 26, 1932 TECHNICAL LITERATURE SUMMARIES OF AERONAUTICAL RESEARCH COMMITTEE REPORTS These Reports are published by His Majesty's Stationery Office, London, and may be purchased directly from H.M. Stationery Office at the following addresses : Adastral House, Kingsway, W.C.2; 120, George Street, Edinburgh; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff; 15, Donegall Square West, Belfast; or through any Bookseller. PRESSURE AND FORCE MEASUREMENTS ON AIRSCREW- BODT COMBINATIONS. By H. Bateman, B.Sc, D.I.C., and F. C. Johansen, M.Sc, A.M.I.Mech.E. R. & M. No. 1380 (Ae. 505). (62 pages and 16 diagrams.) December, 1930. Price 3s. net. Airscrew body research has, in the past, been confined mainly to work on tractor airscrews and only one research on pusher screws, relating to an airscrew behind a very bluff bodv, is included in the R. & M. Series. The results of these experiments, described in R. & M. 830,* lead to the conclusion that the net efficiency of the pusher combination is at least of the same order as that of the tractor, despite an unsuitable shape of pusher body. It may reasonably be supposed, therefore, that pusher airscrews in combination with suitably designed bodies, may yield efficiencies in excess of those occurring with tractor screws, especially in view of the high velocities to which the body is subject in the tractor position as a result of its situation in the slipstream. The present series of experiments has, therefore, been carried out with the object of making a detailed comparison between one tractor and two pusher airscrew combinations. For this purpose a short streamline body with rounded tail was chosen as being suitable for either a tractor or pusher body, and arrangements were made whereby a medium-pitched airscrew could be placed in the three positions to be tested. For each position a spinner was fitted to the airscrew so as to maintain unbroken the contour of the body. The experiments extend the work on tractor airscrew-body combinations described in K. & M. 1230t and 12844 The influence of the airscrew on the pressure distribution over the body is most marked in the neighbourhood of the screw, and generally more notice able In the case of the forward pusher position, where the screw is appreci ably distant from either extremity of the body, than in the tractor or after pusher positions. The variation of surface pressure with airscrew thrust follows an approximately linear relationship. With each combination tested, a region of high negative pressure was observed in the region of the tail at large airscrew thrusts, constituting a " spoiling effect," probably due to rotation of the slipstream. In combination with a low-resistance body, tractor and pusher screws with the same proportion of spinner shielded have equal overall maximum efficiency (64-8 per cent.). The forward pusher combination, with larger spinner, is least efficient. These may be contrasted with the maximum efficiency (72-0 per cent.) of the airscrew blades alone. With a high resistance body the pusher combinations are more efficient than the tractor (56-8 per cent.), and of the two pushers, that having the smaller spinner shielding is more efficient (61-6 per cent.). The presence of a rounded tail aft of the pusher screws has negligible effect on the net efficiency of the airscrew-body combination. * R. A M. 830. Experiments with a family of airscrews, including effect of tractor and pusher bodies. Part II—Fage, Lock, Bateman and Williams. B. A M. 1030. Experiments with a family of airscrews, including effect of tractor and pusher bodies. Part IV.—On the effect of placing the airscrew in various positions within the nose of a streamline body.—Bateman, Town-•nd and Kirkuy. t B. A M. 1230. Pressure plotting a streamline body with tractor air screw running—Lock and Johansen. t B. A M. 1284. Pressure plotting a streamline body with tractor air screw running. Part II. Airscrew in rear position.—Lock and Johansen. EXPERIMENTS ON THE GROWTH OF CIRCULATION ABOUT A WING WITH A DESCRIPTION OP AN APPARATUS FOR MEASURING FLUID MOTION. By P. B. Walker, M.A., Ph.D. From work done in the Aeronautical Laboratory of the University of Cambridge directed by Prof. B. M. Jones, A.F.C., M.A., F.R.Ae.S., and W. S. Farren, M.B.E., M.A., F.R.Ae.S. R. & M. No. 1402 (Ae. 523). (75 pages and 44 diagrams.) January, 1931. Price 4s. 6d. net. The apparatus consists of a water tank through which models are towed and the behaviour of the fluid photographed with the aid of oil particles in the water. It is intended for accurate quantitative investigation of the flow produced by wings and cylinders at a moderately high Beynolds number and appears to be the most suitable means of investigating such flow before the motion has reached a steady state. Experiments have been made with R. A.F. 30 wing section and the results compared with calculations made with the aid of a mathematical theory published by Wagner for the early unsteady flow about a wing. Similar work which has been done previously has usually given results of a qualitative nature, and for a low Beyno.ds number Such is the work of R. A M. 1065, but in this case the apparatus used gave promise of being developed into an instrument of precise measurement, with the possibility of a greatly increased Beynolds number. The author had the original water-tank in which the experiments of B. A M. 1065 WTe made, and Mr. W. S. Farren supplied to him complete designs for the mechanism which propels the model through the water. The early part of the first chapter gives a brief description of the driving machinery, and is followed by the developments and improvements which have been made during the course of my research. The remaining chapters of Part I de scribe the investigations which have been made, and the apparatus which has been constructed during the two years which were required to bring the new instrument reasonably near to perfection. The apparatus in its present form may become a standard instrument for certain classes of work, which cannot be done in the wind tunnel. In particular, it appears to provide the most suitable means of investigating the flow round a wing (or cylinder), before the motion has reached a steady state. When the apparatus had been proved consistent and reliable, and the technique of its operation thoroughly mastered, the work described in Part II was begun. A series of photographs of the flow round B.A.F.30 were taken at various distances from the starting position. The photo graphs reproduced here show the flow when the wing has travelled one chord, and intermediate distances up to six chords. These have been analysed with a measuring microscope designed for the purpose, with the object of extracting the most useful information for a given expenditure of time, and in particular the value of the circulation. Observations have been reduced to the form of curves, a large number of which have been reproduced here ; the most important being the curve which gives circulation against length of run. Recently Wagner published a mathematical theory for the early unsteady flow about a wing. This, if correct, is of great importance, since its applica tions to aerodynamical problems appear to be unlimited: but it has not hitherto received experimental confirmation. I have, therefore, applied Wagner's theory to the flow which is here investigated experimentally and made a comparison. The conclusion reached is that Wagner's theory can be used to predict the unsteady flow about a symmetrical wing, with a fair degree of accuracy. THE EFFECT OF VARIOUS TYPES OF LATERAL STABI LISERS ON THE TAKE-OFF OF A FLYING-BOAT. By L. P. Coombes, B.Sc, and R. H. Read, B.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1411 (Ae. 532). (5 pages and 6 diagrams.) October, 1930. Price 6d. net.* Large seaplanes are usually constructed with a single hull, and owing to the fact that with this type of construction the metacentre is below the centre of gravity of the aircraft, the hull alone is unstable laterally. Some means of securing lateral stability must, therefore, be employed, and three methods are commonly used. These are:—(a) hull with wing tip floats, (6) hull with inboard floats, (c) hull with stubs. The question as to which of these arrangements is the best is to some extent a matter of opinion, and the view commonly held in this country Is that though a hull fitted with stubs is the most satisfactory for seaworthiness, the loss of efficiency during take-off due to the extra resistance and weight introduced by the stubs is too great a price to be paid. The effect of the additional resistance due to any particular arrangement could be deduced from the results of systematic tank tests, provided these were available. Unfortunately, no systematic tests with various types of stabilisers have been done, and the resistance of any arrangement must be estimated from scattered testa on different hulls. In spite of this difficulty, it has been thought worth while to calculate the effect of different types of lateral stabi lisers on the take-off of a flying boat, and for this purpose the Short " Singa pore 1 " has been taken as typical. The data on which the calculations were based were deduced partly from model results and partly from full scale tests. Calculations for the time to take-off over a range of weights was done. Further, the suitability of throttled take-off tests for predicting the limiting weight at which a seaplane can take-off was investigated. The loss of efficiency due to fitting either inboard floats or stubs in lieu of wing tip floats is very great, amounting to a reduction in service load of 9 per cent, and 17 per cent, respectively for a take-off of 60 seconds in calm conditions. Throttled take-offs at normal load, while they are convenient, may give rise to errors of the order of 2 per cent, if used for predicting the maximum weight at which a seaplane can be taken off in a reasonable time. THE ADHESION AND FATIGUE OF THIN COATINGS OF WHITE METAL DEPOSITED ON MILD STEEL SURFACES. BY T. E. Stanton. R. & M. No. 1424 (M. 74). (8 pages and 2 diagrams.) December, 1930. Price 6d. net. The cracking of white metalled bearings under service conditions and the possibility of improving the fatigue strength of the white metal, has been investigated at the National Physical Laboratory to find the effect of com position and method of application on the adhesion and fatigue of such coatings. Rings of S.14 mild steel 3 in. in external diameter, 1 -5 in. long and 0 15 in. thick, were lined with white metal to a thickness of 0-02 in by various makers and were subjected to a predetermined cycle of bending stress at a frequency of 3,000 per minute. No attempt was made to introduce a frictional resist ance at the surface of the white metal, but to imitate the conditions of practice the tests were made at a temperature of approximately 120° C, and the surface of the white metal was covered with oil. Tests were also made on steel rings lined with lead bronze and supplied by the Allison Company of U.S.A. Finally, one of the lead bronze lined rings and a ring lined with Richards A.C.E. white metal were tested for coefficient of friction at various pressures and temperatures in the N.P.L. .Journal bearing testing machine. At various stages of the test the liner was examined and the progress of the cracks noted. The initial adhesion of the white metal to the steel was also measured by a method specially devised for the purpose. Comparison of the behaviour of white metal liners (1) cast and (2) centrifuged, was also made and the distribution of the constituents of the white metal due to centrifuging was investigated. The tests of the strength of the static adhesion of the white metal to the steel indicated that in the best practice the adhesion was fully equal to the ultimate shear stress of the white metal. Under long continued alteration of stress within the fatigue limit of the steel to which the white metal was attached, the surface of the latter rapidly became covered with a network of cracks, and in all the methods and materials tested, with the exception of the lead bronze, its adhesion to the steel was ultimately destroyed. In the best practice it was found that the complete destruction of the adhesion was only effected when the stress was a large fraction of the limiting fatigue stress of the steel and the number of repetitions of the order of 15 millions. In the case of the steel rings lined with lead bronze supplied by the Allison Company, no apparent deterioration in adhesion and comparatively insigni ficant fatigue cracking of the liner was apparent after 15 million cycles of stress at a range of 18-9 tons per sq. in. It was clear that in both respects the merits of this alloy were of an entirely different order from those of the other so-called white metals. A very complete series of comparative tests in the N.P.L. Journal friction testing machine at high loads (up to 2,500 lb./sq. in.) and with various lubricants indicated a performance of the lead bronze under forced lubrication and continuous rotation which was fully equal to that obtained from one of the best tin base alloys. \74h
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