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Aviation History
1927
1927 - 0056.PDF
10 SUPPLEMENT TO FLIGHT JANUARY 27, 1927THE AIRCRAFT ENGINEER National Physical Laboratory type having a straight tube. For testing airscrews, the last, namely, the closed N.P.L. type, is hot so suitable as the open jet wind tunnel of the Eiffel or Gottingen type on account of the larger correction for tunnel interference. The evidence for the preference to the open jet type is as follows :— (a) Theoretical.—A formula due to Mr. R. McKinnon Wood* is available, which gives a small but definite correction to be applied to a 3-ft. diameter airscrew working in a 7-ft. square closed tunnel. By the same argument the correction for an open jet tunnel is zero. An independent argument j based on considerations of vorticity leads to the same conclusion. (b) Experimental.—In the course of experiments on the American family of airscrews Dr. Durand tested a set of four similar airscrews of diameters. 2 ft. to 4 ft., in an open jet tunnel of diameter 5| ft., and obtained agreement between the performance of the extreme screws. The evidence for the closed type of tunnel is less definite but points to the accuracy of the theoretical formula. (c) Extreme Working Conditions.—Under extreme working conditions; : it is probable that the correction becomes large for a screw in a closed tunnel, and there is some evidence that the open jet tunnel retains its advantage in this case. * 11. * M. 66"2. Some Notes on the Theory of an Airscrew "Working in n"Wind Channel. E. McKinuon Wood and K. <;. Harris. t N.A.C.A. Report >*o. ;4. Experimental Research oil Air I ropellers.t See ii. <-V M. 1014. REPORT ON THE "BURNING" OF ALUMINIUM. By J. I). GKOGAN, B.A. Work performed for the Engineering Research Board of the Department of Scientific and Industrial Research. R, & M. No. 1035 (M. 44). (12 pages, 5 figs.) February. 1926. Price ]«. net, This research is a continuation of other work described previously in R. & M. 783, " Report of the Effects of Over-heating and Repeated Melting on Aluminium." Other work on the same subject has been reported in Light Alloys Sub-Committee Report 14 published in the special volume of Reports of the Light Alloys Sub-Committee (1921). The object of the present investigation was to find methods of treatment of aluminium which might lead to deterioration in the quality of the metal approximating to the condition generally described as " burnt." The influence of gases on aluminium has been investigated both by bubbling gas through the molten metal and by melting in a controlled atmosphere. It has been found that tensile tests on material rolled and annealed after treatment with gas did not show that any harm had been done to the metal. Charpy impact tests on chill cast material showed reduced values as the result of overheating in an atmosphere of nitrogen and carbon monoxide, and further reduction by passing gas through the metal while still over- heated, the reduction being substantially independent of the gas used. The notched bar impact test figure is partially restored by re melting the gassed material in air and still more in vacuo. Hydrogen passed through molten aluminium at normal casting temperatures lowers the test figure very appreciably ; carbon dioxide is less harmful. Nitrogen appears to be beneficial, though the evidence of this is somewhat contradictory. Repeated melting and rolling of high-grade material does not lessen the impact figure. The solubility of carbon in aluminium does not exceed 0 06 per cent., and carbon does not produce brittleness in that metal. THE CONSTITUTION AND AGE-HARDENING OF SOME TERNARY AND QUATERNARY ALLOYS OF ALU- MINIUM CONTAINING NICKEL. By KATHLEEN E. BINGHAM, M.SC. Work performed for the Engineering Research Board of the Department of Scientific and Industrial Research. R. & M. No. 1036 (M. 45). (13 pages, 16 diagrams.) April, 1926. Price Is. net. This investigation deals with (1) the age-hardening of some of the ternary alloys of copper, nickel and aluminium, the constitution of which has been investigated by the present author jointly with Dr. J. L. Haughton (J. Inst. Met., Vol. XXIX, No. 1, 1923); and (2) the constitution and age- hardening of similar alloys with the addition of small per- centages of magnesium. Three series of copper nickel aluminium alloys have been investigated, containing respectively 2 per cent., 4 per cent., and 6 per cent, of copper, while the nickel in each series was varied from 0 -2 to 2 per cent. Hardness measurements have been carried out during the ageing of the alloys for three weeks. Only very slight age-hardening has been observed, the maxi- mum increase in hardness, 16 per cent., occurred in the 4 per cent, copper series and appears to be due to the separation of CuAl,. The observations suggest that the slight increase in hardness may not be permanent, as after the alloys have attained their maximum hardness, on further ageing, the value falls back to that obtained in the quenched condition before ageing. The constitution of the alloys containing 1 per cent, mag- nesium has been investigated (see page 2), at 500° C. and 200° ('. The nickel content has been varied up to 2 per cent, and the copper up to 6 per cent. On comparing the constitu- tion of these alloys with that of the ternary alloys of copper, nickel and aluminium, to which reference has been made, this investigation has shown that the addition of 1 per cent, magnesium has caused a decrease of solubility of CuAl2 and the ternarj- constituent at 500° C. but no new constituent has appeared. On slowly cooling these alloys to 200° C. it has been shown that an additional constituent, the com- pound Mg,Si, has separated as well as NiAl:i, which now takes the form of fine needles, while at higher temperatures it occurs only in rounded pieces. The hardening of the alloys containing 4 per cent, copper, 1J per cent, magnesium and nickel varying from 0-2 to 2 per cent., has been investigated (see page 10), on ageing at room temperature for different periods up to a year after quenching from 500° C, and also after tempering at different temperatures. A marked increase in hardness has been found throughout the series on the first day after quenching from 500° C. followed by a more gradual rise up to the 15th day and succeeded by a fall on the 43rd day : a further marked increase in the hardness has been noted at the end of a year. In most cases, the best of the tempering results have been obtained after eight days at 150° C. The greatest increase of hardness after ageing at room temperature took place in the alloy containing 2 per cent, nickel, while the hardest alloy of the series is the one con- taining 0-2 per cent*nickel. It is suggested by this investi- gation that the marked age-hardening which takes place in this series of alloys is due chiefly to the precipitation of magnesium silicide (Mg:iSi), very little being due to the separa- tion of CuAl2. MECHANICAL PROPERTIES OF PURE MAGNESIUM AND CERTAIN MAGNESIUM ALLOYS IN THE WROUGHT CONDITION. By S. L. AECHBDTT, F.I.C., and J. W. JENKIN, B.SC, Ph.D. Work performed for the Engineering Research Board of the Department of Scientific and Industrial Research. R. & M. No. 1037 (M. 46). (13 pages and 8 figs.) February, 1926. Price, 9d. net. The use of magnesium and its alloys is of considerable importance where the saving of weight is a first consideration, as this metal is much lighter than aluminium. Cast magnesium alloys have already been used in aeroplane engines and research is needed on the wrought alloys. The present work com- mences a research to fill this gap in knowledge and the materials chosen for study include pure magnesium, 3 per cent, and 13 per cent, copper alloys, 6 per cent, aluminium alloy and the proprietary alloy, Electron, in the form of 1 in. diameter rod. The properties of these materials were determined : (1) at atmospheric temperatures both in the condition as rolled or supplied, and after exposure to elevated temperatures, and (2) at elevated temperatures after both short and pro- longed exposure. The microstructure has also been studied in so far as it bears upon the work. 46/
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