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Aviation History
1941
1941 - 1843.PDF
AUGUST I4TH, I94I. FLIGHT great promise held out of maximum engine power in everycondition of flight. Tentative designs were drawn up. At that time wood was the only available blade material,and the difficulty presenting itself was'in making a satis- factory attachment between the blade and the hub. Noreal solution of the problem had been evolved before the advent of the metal blade (which, of course, did not presentthe same difficulties), and later, the compressed wood blade which is now used on some airscrews. It was from a consideration of the forces acting upon arotating airscrew that Mr. Milner discovered the important principle of what has since become known as the centrifugaltwisting moment in virtue of which an airscrew blade tends to assume a fine pitch position, which tendency must beovercome in order to increase the pitch of the blade. It was failure to recognise this principle that foredoomedmany early designs of V.P. airscrews. Meanwhile Dr. Hele-Shaw and Mr. Beacham had con-ceived the idea of the hydraulically operated V.P. air- screw, the provisional patent for which was lodged onDecember 3rd, 1924 (No. 29015/24), and the complete patent accepted in April, 1926 (No. 250292). Little did theordinary public realise that in this patent for '' feathering screw propellers'' was an invention which would ultimatelyrevolutionise flying and affect materially the whole future of aviation. Air Ministry Encouragement During the year 1924 the Air Ministry had become veryinterested in the subject of V.P. airscrews owing to the development of the supercharged engine, which was thentaking place. It was recognised that, save in conjunction with a V.P. screw, the advantages of the superchargedengine could not be thoroughly utilised. Accordingly in February, 1925, the Director of Contracts, Air Ministry,invited a number of firms to tender for an all-metal V.P. airscrew. For factual material in the following observa-tion I must acknowledge the assistance of records preserved by the Royal Aeronautical Society and the testimony ofMr. Beacham and Mr. Milner. At this period Dr. Hele-Shaw and Mr. Beacham wereassociated in the development of the Hele-Shaw-Beacham variable stroke pump and hydraulic transmission gear, andthey had been previously associated with the development of the original Hele-Shaw hydraulic transmission. Theyconsidered that an hydraulic mechanism similar to the type which they had developed would best meet aircraft require-ments. Working models of the mechanism were pro- duced, and officials of the Air Ministry who investigatedthe designs were convinced the proposal was a sound one, the main reason for their decision being the widespreaduse at that time of the original Hele-Shaw pump in con- Mr. T. E. Beacham, B.Sc, A.C.G.I., A.M.Inst.C.E.,A.M.I.Mech.E. nection with ships' steering gear, an auxiliary where reliability was a sine qua non. The estimate, which was for ^1,500, was forwarded onMarch 6th, 1925, and accepted in a letter by the Director of Contracts on May 1st. The outcome was the productionof a steel-bladed constant-speed airscrew for the Rolls- Royce Condor III engine, the blades being made by MetalPropellers, of Croydon, and the hub by Harper Sons and Bean, of Dudley. In August, 1925, spinning trials wereheld at Farnborough, together with bench tests on an engine, and subsequently flight tests on a Service aircraft.Incidentally the experimental airscrew was fitted with Leitner-Watts hollow steel blades. As a result of these tests and other tests which had in Diagrammatic layout of the first Hele-Shaw-Beacham variable pitch airscrew
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