FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 0104.PDF
SUPPLEMENT IO FLIGHT JANUARY 29, 1932 THE AIRCRAFT ENGINEER Certain other modifications had been introduced into the design of the -airship since the models used in the earlier work were constructed. These modifications will be discussed later, but it may be stated that the addition of the bay in itself was a sufficient justification for desiring further experi ments on a model of the airship as she was before starting on her last flight. The lift, drag and pitching moment were measured on a model at angles of pitch varying from + 20° to — 40° with the elevators set over a range of angles between ± 25°. M, was measured at various angles of pitch from 0° to — 40° approximately. Additional observations of cross-wind force, drag and yawing moment, with the control surfaces amidships, were taken at angles of yaw ranging from 0° to 20°. Data for examining the efficiency of the hull, fins and control surfaces were also obtained. The results have been applied to determine the conditions under which the ship would fly steadily along rectilinear paths inclined at angles ranging from 0° to — 30° to the horizontal, assuming the engines to develop a constant B.H.P. consistent with a speed of 55 knots in head-on flight. The effects of gas leakage from a forward gas-ba^, increased drag or decreased airscrew thrust have been considered. A brief discussion of the stability is also included. A comparison of the model results with those of earlier experiments before the extra bay was included show that the hull characteristics have under gone some change owing to the bay and also to the introduction of fifteen reefing girders. A modification in the design of the fins and control surfaces have given rise to appreciable changes in control efficiency. The equilibrium calculations show that the ship had ample control surfaces for keeping the axis of the ship pointing upwards at the nose even after (1) a considerable gas leakage forward, (2) a possible damage to the outer cover had caused an increase in the drag, or (3) a decrease in the thrust. The ship appears to have been provided with stabilising surfaces of sufficient area to satisfy the usual stability criterion. WIND TUNNEL TESTS ON HIGH TIP SPEED AIRSCREWS. FURTHER EXPERIMENTS ON SCALE EFFECT. By A. S. Hartshorn, B.Sc, and G. P. Douglas, D.Sc. Communi cated by the Director of Scientific Research, Air Ministry. R. & M. No. 1417 (Ae. 538). (17 pages and 9 diagrams.) May, 1931. Price Is. net. The present experiments continue the investigation into the effects of high tip speeds on airscrew performance and were designed to find if the Tesults which had been obtained for model airscrews were modified when the size of the airscrew was increased. An airscrew having blades geometrically similar but 50 per cent, larger than those of a model airscrew previously tested was made up. The blade .section was of conventional form 10 per cent, thick. Comparative measure ments of overall thrust and torque have been made and also of the thrust and torque grading. The results indicate that with this airscrew the compressibility stall is mainly dependent on radius rather than on the size of the airscrew. The effect "of the 50 per cent, increase in scale appears to delay the compres sibility stall about 0 02 of the speed of sound. THE USE OF MODELS FOR THE DETERMINATION OF CRITICAL FLUTTER SPEEDS. BV W. J. Duncan, D.Sc., A.M.I.Mech.E. R. & M. No. 1425 (Ae. 545). (5 pages.) July, 1931. Price 4d. net. The use of model tests in the prediction of full-scale critical flutter speeds is now well established, and the technique of such tests is therefore worthy of discussion. In order to obtain critical speeds for the model within the speed range of ordinary wind tunnels it is necessary that the model should differ in some respects from a mere small-scale replica of the full-scale aero plane. In the method originally suggested by JIcKinnon Wood the modi fication of the model consists in a reduction of its effective stiffness. This method has the defect (in most cases probably not serious) that the model experiment is conducted at a Reynolds' number much below that for full-scale. In the present paper it is pointed out that an alternative method of reducing the critical speed is to increase the mass loading of the model and to make the flutter tests in compressed air. It is then quite feasible to reach the full-scale Reynolds' number. This method of reducing the critical speeds Dy a proportionate increase of all effective densities may also be combined with a reduction of the elasticity of the model. The relation of model and full-scale stresses at the critical flutter speeds is considered. Where the reduction in critical speed is effected by increase of density only, the model and full-scale stresses are equal. In a model of reduced elasticity the stresses in the wires are the same as for full-scale, whereas, the stresses in the spars are less than for full-scale. This is in accord with the usual experience that the wires of such a model are the first parts of the structure to fail in a flutter. Lastly, the influence of gravity on flutter is considered. This is negligibly small for full-scale, but not necessarily so for the model. Gravitational -effects can sometimes be corrected by suitable orientation of the model. Density Wind Tunnel of the National Advisory Committee for Aeronautics. The tests were made to study certain discontinuities in the characteristic curves that have been obtained from previous tests of these aerofoils, and to compare the characteristics of the different sections at values of the Reynolds number comparable with those attained in flight. The discon tinuities ware found to disappear as the Reynolds number was increased. The results obtained from the large-scale tests in this series indicate that the N.A.C.A. 0J21 aerofoil, a symmetrical aerofoil having a thickness ratio of 21 per cent., has the best general characteristics. No. 400. THE AERODYNAMIC CHARACTERISTICS OF A SLOTTED CLARK Y WING AS AFFECTED BY THE AUXILIARY AIRFOIL POSITION. By Carl J. Wenzinger and Joseph A. Shortal. Price 15 cents. Aerodynamic force tests on a slotted Clark Y wing were conducted in the vertical wind tunnel of the National Advisory Committee for Aeronautics to determine the best position for a given auxiliary aerofoil with respect to the main wing. A systematic series of 100 changes in location of the auxiliary aerofoil were male to cover all the probable useful ranges of slot gap, slot width, and slot depth. The results of the investigation may be applied to the design of automatic or controlled slots on wings with geometric charac teristics similar to the wing tested. An increase of 41-5 per cent, in the maximum lift above that of the plain wing was obtained for the slotted Clark Y wing. At the same time, the angle of afctaex for maximum lift was increased 13°. It was found that a miximim inereaje of about 30J was possible in the highest stalling angle, bat at a maximum lift coefficient slightly less than that of the plain wing. However, with one slot position, an increase of 25°. together with an increase in the maximum lift coefficient of 23-3 per cent, was obtained. The best positions of the auxiliary aerofoil were covered by the range of the tests, and the position for desired aerodynamic characteristics may easily be obtained from charts prepared especially for the purpose. SUMMARIES OF N.A.C.A. TECHNICAL REPORTS The National Advisory Committee for Aeronautics is the American equivalent of our Aeronautical Research Committee, with headquarters at Washington, D.C. The Technical Reports issued by the N.A.C.A. are obtainable from the Superintendent of Documents, Washington, D.C., U.S.A. In the summaries printed below the prices of Reports are given. These prices are net, and a small amount should be added to cover postage. For the guidance of potential purchasers it may be pointed out that the Reports rarely exceed 5 oz. in weight. No. 391. THE AERODYNAMIC CHARACTERISTICS OF EIGHT VERY TnicK AIRFOILS FROM TESTS IN THE VARIABLE DENSITY WIND TUNNEL. By Eastman N. Jacobs. Price 10 cents. A group of eight Tery thick aerofoils having sections of the same thickness JUS those used near the rcots of tapered aerofoils were tested in the VariabVs MECHANICAL PROPERTIES OF NICKEL ALLOY STEELS. THIS is the title of an extremely useful booklet issued by the Mond Nickel Co., Ltd. The compilers have endeavoured to present in a convenient form a summary of the mechanical properties obtainable from various nickel alloy steels. Many steels containing from 1 to 5 per cent, of nickel are now available, and in each of these a variety of properties may be obtained by suit able heat-treatment. A limited number of well-known and widely accepted official specifications have been taken as a basis. Some of these are for aircraft and automobiles issued by the B.E.S.A., and reference is made also to others published by the Directorate of Technical Development, Air Ministry. Details of the chemical composition, heat-treatment and mechanical tests are tabulated, as are also such typical properties of the core as chemical composition, refining and hardening quenching temperatures, results of mechanical tests such as yield point, maximum stress, elongation, reduction of areas, and Izod impact figures. The first part of the booklet deals with nickel and nickel-chromium case-hardening steels, while in the latter part tempering curves for a number of steels are given. These curves, it is stated, are based upon figures which represent the averages of a large number of test results. The choice of a suitable steel for any particular pur pose depends, of course, on a number of factors, and these have to be taken into account in using the curves. In the curves the figures are based on test pieces machined from 1^-in. bars, and, strictly speaking, the curves apply only to parts of approximately this section. To give an idea of the range covered by the booklet it may be of assistance if we give a list of the steels included : —3 per cent, nickel case-hardening steel; 5 per cent, nickel case-hardening steel; nickel-chromium case- hardening steel (3J per cent, nickel); nickel-chromium case-hardening steel (4\ per cent, nickel); 1 per cent, nickel steel (a) oil hardened and tempered; (b) water hardened and tempered; 3 per cent, nickel steel, oil hardened and tempered; 3£ per cent, nickel steel, oil hardened and tempered; 55 ton nickel-chromium steel. oil hardened and tempered (a) without molybdenum; (6) with molybdenum; 65 ton nickel-chromium steel, oi! hardened and tempered; air-hardening nickel-chromiuii' steel, air hardened and tempered. Readers interested in the subject would be well advised to obtain a copy of the booklet, which can be had on application to the Bureau of Information on Nickel, The Mond Nickel Co., Ltd., Imperial Chemie;i; House, Millbank, London, S.W.I. 93 h
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
