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Aviation History
1932
1932 - 0283.PDF
MARCH 25. 1932 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT 2AWK8 0-7 X—D* 4 H.P, i.e. Hp=3^WK,.HPi (xvii) Equation (xvii) shows that the additional thrust horse power required on account of slipstream drag varies directly as the total thrust horsepower given by the airscrew and inversely as the square of the diameter of the airscrew. It is advantageous, therefore, to make the airscrew diameter as large as possible. For anv particular combination of machine and air- " ... 3.64 Aw K, . . screw the quantity —— in equation (xvii) is constant. Call this constant S. Net thrust horsepower available = H.P.T — H.P., = H.P.T (1 - s). But H.P.T = i) x B.H.P., where JJ = airscrew efficiency. Therefore the net thrust horsepower available = B.H.P. X »/(l — s), and »;(1 — s) is the net or propulsive efficiency of the airscrew. (To be continued) TECHNICAL LITERATURE PAPERS AT INSTITUTE OF METALS. A NUMBER of papers were presented at the 24th Annual General Meeting of the Institute of Metals held in London on March 9 and 10. Of these papers we have space to mention two only: " Intercrystalline Corrosion of Duralumin," by Sidery, Lewis and Sutton, and " Magnesium Alloy Protection by Selenium and other Coating Processes," by Bengough. " Intercrystalline Corrosion of Duralumin." By A. J. Sidery, Assoc.Met.Member, Scientific Officer, Royal Air craft Establishment, Farnborough; K. G. Lewis, M.Sc Assistant Lecturer in Metallurgy, The College of Tech nology, Manchester; and H. Sutton, M.Sc., Member, Senior Scientific Officer and Head of the Metallurgical Department, Royal Aircraft Establishment, Farn borough, was presented on Wednesday, March 9. Experiments were carried out to determine the influ ence of overstrain in tension or in compression and of certain modifications of heat-treatment on the tendency of Duralumin to develop intercrystalline corrosion. For the purpose of evolving a reliable test which would permit the relative susceptibility of various samples of Duralumin to this form of corrosion to be estimated in a reasonable space of time, several reagents were investigated. It was found that partial immersion in a N-l solution of sodium chloride to which 1 per cent, (by weight) of hydrogen chloride had been added was capable of producing intercrystalline corrosion consist ently in samples of Duralumin, where a propensity towards this type of corrosion existed. The effect of overstrain was examined by subjecting to this test a number of specimens of heat-treated Duralumin sheet, to which tensile test had been applied to produce various degrees of permanent elongation, and a number of longitudinal strips cut from samples of heat-treated Duralumin tube, which had been compressed to arbi trarily selected stresses above the elastic limit in com pression. The results of the experiments indicated that overstrain in tension increased slightly the tendency towards intercrystalline penetration, but no relation was observed between this tendency and the degree of elongation. There appeared, however, to be a critical range of stress in compression, viz., 14.0-16.9 tons/in.1, for the material employed in the experiments. Samples which had been compressed in this range of stress showed the greatest susceptibility. Corrosion tests were made on samples of the sheet and tube which had been heated at various temperatures in the range 470- 260 520 deg. C, quenched in cold or in boiling water and aged at room temperature with a view to ascertain the influence of such modification of heat-treatment and of quenching medium on the susceptibility of the material to intercrystalline attack. It was observed that, in general, the higher the quenching temperature the smaller was the tendency of the material to develop intercrystalline corrosion, but there was, however, an increased tendency towards the pitting form of super ficial corrosion under the conditions of test emploved. Material quenched in boiling water showed a very much greater propensity towards the intercrystalline form of corrosion than did material quenched in cold water or in cold oil. " Magnesium Alloy Protection by Selenium and Other Coating Processes." By G. D. Bengough, M.A., D.Sc, Member, and L. Whitby, M.Sc., Member, Chemical Research Laboratory, Department of Scientific and Industrial Research, Teddington, was presented on Thursday, March 10. A process has been developed for the production of films of selenium on several light magnesium alloys. These films confer considerable resistance to the corro sive action of sea-water spray. The firms are normallv produced by immersion for a few minutes in a bath containing selenious acid at laboratory temperature, but may also be produced by running the alloy with porous material dipped in the bath. The film has the property of self-healing to a limited extent, especially when im mersed in stagnant sea water. The film is only a few thousandths of a millimetre thick, and its production does not cause any appreciable dimensional change in the alloys treated. The film forms a satisfactory base for certain types of paint, and further work on this property is proceeding. 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. COLLECTED REPORTS ON BRITISH HIGH-SPEED AIRCRAFT FOH THE 1927 SCHNEIDER TROPHY CONTEST. With an introduction by W. L. Cowley, A.R.C.Sc. R. & M. No. 1300. (372 pages and numerous diagrams.) January, 1931. Price 20s. net. In this volume a comprehensive account is given of the large amount of work carried out on the British seaplanes designed for the Schneider Trophy Contest of 1927. held at Venice. The subject-matter is divided into four sections under the following headings:—(a) Research, (ft) Specifications, Desigi; and Construction, (c) Inspection and Test, (ii) Operational. It deals with three different types of machines, the S.5 constructed by the Super- marine Aviation Company, the Gloster IV by the Oloster Aircraft Company, and the Crusader by Messrs. Short Bros. The first of these, the winning type, was a monoplane with a water-cooled engine, the second a biplane with a water-cooled engine and the third a monoplane with a radial air-cooled engine. The research section of the publication describes work carried out. both before and after the Contest. The research prior to the race was for the purpose of developing the craft, and after the race mainly for investigating points of interest that arose subsequent to the construction of the machines. In the main, this research work consisted of wind-tunnel tests carried out at the Royal Aircraft Establishment and the National Physical Laboratory. The results show clearly the superiority for racing purposes of the water-cooled over the air-cooled engined type, although it was also found that the latter could be greatly improved by cowling the engine cylinders. Remarkable results were obtained in some of these cowling experiments. Considerable interference sometimes occurred on both lift and drag and the results were in many cases sensitive to small differences, such as sealing up the joints between the cowling and the fuselage. In striking contra t it. was found that comparatively little interference occurred at minimum drag between the main components of the S.5. The resistance of the complete model of this machine was found to be only 5 per cent, more than the sum of the resistances of the separate components, and the Gloster IV also showed little interference effect on minimum drag. Other features which formed the subject of tests were the projection of rivet heads on the floats and corrugations on the wings due to radiators. In addition, wind tunnel tests were carried out for the purposes of measuring the heat dissipation from the surface of the wing radiators and tests on floats for the machines were made in the N.P.L. Tank. Some of the floats were also tested in the wind tunnel, while full scale research on many of the airscrew problems that arose was carried out at the Marine Aircraft Experimental Establishment at Felixstowe. The section devoted to specifications, design and construction, deals mainly with the reports of the designers and constructors of the machines and engines. In addition a copy of the specification of the S.5 is given and reports are appended upon the engines used in the Contest. g
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