Jn the RRHT book '
The Rolls-Royce Crecy' there's a photo of one of those 'inducers' (rotating guide vanes) for a Crecy engine, and the caption describes it as 'conically turned'. ?
From the RRHT book ‘
Rolls-Royce Piston Aero Engines – a designer remembers’ by A. A. Rubbra:-
The The Merlin’s predecessor, the Kestrel, didn’t have the 'inducer' (rotating guide vanes). Rolls-Royce had started using superchargers on the V-12 Eagle in the 1920s, but they were very inefficient. Arthur Rubbra was packed off with a supercharger to RAE Farnborough, who had the brains and the apparatus to investigate. Long-short, efficiency improved from 37% to ~70% under the guidance of James Ellor of the RAE (Royal Aircraft Establishment).
Attempts were made to lure Ellor to America, with the offer of considerably more money than the RAE could pay him (they were a government department with fixed salary scales). The Govt dept, anxious to retain his skills, suggested that Rolls-Royce make him an offer, and there he went, in 1927. During WW2 he was one of three leading R-R engineers sent to the USA for the unenviable task of liaising with Packard on production of the Merlin. He was there from 1940 to 1944.
Now, to Bristol:-
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These photos show stages of production of a Bristol Mercury supercharger impeller, which starts as a nickel steel forging. It seems that the main product of radial engine makers would have swarf.
Photos from ‘
Aero Engines’ published by Newnes in 1937. The Mercury went into production in 1927, and it looks as though the profiling machine might have already been an antique then!
Bristol were already using the curved guide vane supplement in 1927 on their Jupiter engine superchargers, but strangely it doesn’t seem to have been used on the later Mercury (ref photos in aviation adverts link below).
From having partially free-standing vanes, Bristol went to fully shrouded impellers. Advert No. 13 at the top of the link below shows a ‘Forged light alloy impellor machined all over, dynamically balanced’.
Classic British Aviation Industry Advertisements 1909 - 1990