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Aviation History
1937
1937 - 0516.PDF
SUPPLEMENT TO FLIGHT 198A 14 THE AIRCRAFT ENGINEER FEERU ARY 25. 1 937 Welcoming Major Mayo's remarks, Mr. Fedden said that the Bristol Company valued tremendously the information de rived from the use of their engines by Imperial Airways, and the development resulting therefrom. Imperial Airways were hard taskmasters, and the Bristol Company had to watch their step when they put on to an Imperial Airways' service an engine which had been developed for military purposes. Quite frankly, there were no civil engines, of the big type to-day. The big engines were always military engines, and when the Bristol Company had done the work they had to do for the Air Ministry and had obtained good results from their engines in military service, Major Mayo and his engineers usually found some trouble! Nevertheless, the use of the engines by Imperial Airways was of great value. Dealing with the question as to why he felt that the com pression-ignition engine had a better chance to compete with the petrol engine in the larger than in the smaller sizes, he said there were three main reasons. In the first place, the measurement of a very small quantity of fuel was a difficult problem, and, therefore, he would not like to have to think of getting reasonable combustion in cylinders of less than about 5 in. bore, judging by the Bristol Company's experience Secondly, it was more difficult to compete in respect of weight in the smaller sizes than in the larger sizes, because, owing to scantlings, more weight had to be used to deal with the higher explosion pressure of the compression-ignition engine. Thirdly, owing to the more severe torque of the compression-ignition engine for a given power, it was necessary to provide more cylinders. The Five-year Period Commenting on Mr. Chorlton's query as to why the period of prophecy covered by the paper was limited to five years, Mr. Fedden said that, as a matter of fact, he had been invited to visit a Russian aero-engine factory at which, he was told, one thousand draughtsmen were employed, and he was hoping to go. However, prophecy was frightfully rash, and probably he had chosen the period of five years because he might have made a bigger ass of himself by attempting to prophesy over a period of more than five years. Dealing with the question as to why the compression-igni tion engine had not come to the front before now, he said that so long as people persisted in the attitude that compression- ignition engines would be used as soon as they were equal to the petrol engine in respect of weight, we should never use them. He was not satisfied to hear designers say that they had no objec tion to the compression-ignition engine, but he wanted them to feel, as he did, that in certain categories of aircraft the ad vantages of the compression-ignition type of engine were so great that they were prepared to give away something in favour of it while it was feeling its feet. If they would be patient for a few years and give it a chance to feel its feet, he was cer tain they would be very surprised and pleased by some of its characteristics. Replying to Mr. Lipscomb, he said he was hoping to secure advice on the subject of the number of engines that could be used on the leading edge of a wing; it was desirable to reduce the size of the power unit as much as possible. In view of Mr. Lipscomb's remarks concerning the propeller problem it seemed that we must meet it by means such as a two-speed gear or concentric propellers. He felt that the assisted take type of aircraft offered the compression-ignition engine fh best chance of making good, because that engine was rath less sensitive to rich mixture and overboosting than \\ high-octane petrol engine, but, nevertheless, it cruised at nearer its normal output. could be When he had chosen the Potez engine for illustration one of the most interesting engines shown at the Paris S-l*8 he had no idea that M. Menetrier, the designer of it \Vn "lH have done the meeting the honour of attending. He aim ciated very much the fact that M. Menetrier had attended aiul the interesting information he had given. The question with regard to scaling-down had been put to him frequently by Major Carter, but he had always failed to answer it. All that he could tell Major Carter was that the tabulations he had made were honest and genuine, havin° been taken from all the data he could find. Further than that he must struggle out of the argument as best he could by point- ing out that it was not quite fair to scale down an engine in size and weight exactly, for the carburettors, magnetos and plugs, for example, weighed the same whatever the size of the engine. Mr. Fedden agreed with M. Pontremoli that progress had been made in increasing the power developed by engines of given size during the last few years, and that we should make more progress. He did not agree, however, that we should not use 100-octane or even 130-octane fuel, at airy rate for military machines, if the fuel suppliers provided such fuel. If we could obtain 1,000 h.p. from an engine of 3 ft. size fitted inside a wing, it would be worth doing for the super-military machine, no matter what it cost. With regard to Mr. Evans's remarks concerning propellers being located at 30 per cent, and 50 per cent, of the chord ahead of the leading edge of the wing, he believed that re search work at the Royal Aircraft Establishment had shown that 30 per cent, ahead was the most efficient position for a normal wing when using a radial engine. Nevertheless, long distances were used for the purposes of balance and for con venient housing of the undercarriage, and his Company had certain machines in course of construction, with their new en gines, in which they were going as far as 45, 47, aud even 48 per cent., in an endeavour to reduce the general overall drag of the radial nacelle. When he had referred to 10 per cent. | in the paper he had visualised using engines buried inside the wing. He had nothing up his sleeve about that, but he hoped . that somebody else had, because if the flat engine were as important as he believed it to be forthe fighter aircraft, much would depend upon whether or not the propeller could be located as near as 10-T5 per cent, of the chord in front of the wing without loss of efficiency and without giving rise, to trouble with the engine or the wing. Dealing with the comments on his statement about engines buried in the wing necessitating the use of propeller shafts, he said that in the design which he had suggested he would not propose using a separate shaft; but he did not think it was impossible to use propeller shafts successfully. Replying to the adverse comments made with regard to the double-row radial of 1931, Mr. Fedden said he had illustrated that engine in order to emphasise that we could not afford too many cylinders for a given volume. I.C.I. Alloys TO meet the increasing demand, particularly from aircraft manufacturers, I.C.I. Metals„ Ltd. (a subsidiary of Im perial Chemical Industries) are entering the aluminium alloy field. They are on the Air Ministry list, and their material- sheet and strip—complies with B.S.I, and D.T.D. specifications. Hiah-tensile Brasses " XJTGH-TENSILE brasses are of considerable engineering -£1 importance, and are widely employed in both cast and fabricated conditions. Although the use of fabricated high- tensile brasses in extruded or rolled rod aud section forms is very extensive, the high-tensile brass alloys are far more fre quently encountered in the form of castings, which may range iii size from quite small products up to marine propeller cast ings weighting go tons or more. The widespread adoption of high-tensile brasses for general casting purposes is largely due to the facility with which they may be cast into complex shapes coupled with the very satisfactory strengths which are obtainable ; indeed it is doubtful if such" consistently uniform results can be obtained with any other alloys, as the ratio or strength in the cast conditions compared with strength after forging or other working treatment is unusually high. By selec tion of suitable composition, tensile strengths slightly exceeding 50 tons/sq. in. in the cast condition can be obtained, althougi alloys giving a strength of about 40 tons/sq. in. are generally | preferred as they possess better ductility. Such brasses ar often referred to as manganese bronze, although this expres sion, like many others used in metallurgical parlance, is misnomer." This is an extract from "High-tensile-strength Brasses Metallurgical Review of their Properties and Uses,' a n informative booklet issued by the Copper D^^°PmeI!fil^ ciation. Copies are obtainable from the Association at 1M House, Millbank, London, S.W.i. Edgar Allen Laboratories Extended er the general laboratory of Edgar Allen and Co., 1 INCREASED pressure of work has necessitated extens •*• the general laboratory of Edgar Allen and Co. Sheffield steelmakers. These extensions include ai and beautifully tiled and equipped balance room. J™^"^j space for carrying out of analyses, and additional 0 cloakroom accommodation.
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