Metro-Vick played an important role

Ministry of Aircraft Production ordered a back-up design, similar to the Avon, and this engine - the Saffire - proved to be highly successful

The letter from Brian Cowell refers to the early development of axial flow aero engines and the contributions from Dr Griffith and the Royal Aircraft Establishment (RAE) as well as the involvement of Metro-Vick. 

Crucially when Rolls-Royce reached the limit capability of radial compressors and an axial design was required for the Avon, this was duly produced by the RAE under Dr Griffith. Unfortunately this design proved to be a failure due to it`s tendency to go into stall and I understand that when installed in early versions of the Hunter, would be provoked into this condition if the aircraft`s guns were fired! Because of the known difficulties in designing axial compressors the Ministry of Aircraft Production (MAP) had ordered from Metro-Vick a back-up design similar to the Avon and this engine called the Saffire, proved to be highly successful. Rolls-Royce revised the Avon compressor design to incorporate Sapphire features, and with MAP agreement handed over the complete design to Armstrong-Siddeley at Coventry for further development and production, and it was used in a range of aircraft. In addition Armstrong-Siddeley licensed the Sapphire to Curtis-Wright of America who produced them in very large numbers for use in various US warplanes.

I am sure Brian Cowell will agree that Metro-Vick played a much more important role than is suggested by the final paragraph of his letter, and that due recognition should be made, of the man responsible for the Sapphire design - Dr D M Smith Dsc.

To anyone interested in this fascinating period of gas-turbine development the story is told in great detail in two publications:

• “Engineering Progress Through Development” edited by R.R.Whyte, pub by MEP but out of print.
• “Parkside, Armstrong Siddeley to Rolls-Royce”, by Roy Lawton and available from the Rolls-Royce Heritage Trust: heritage.trust@rolls-royce.com

Don Nicholas, Rugby

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