Hermione Giffard's thesis

John Mortimer seems unduly critical, especially regarding Dr Arnold Griffith

John Mortimer seems unduly critical of Hermione Giffard's thesis, especially regarding Dr Arnold Griffith (Books, PE April).

In 1926, two years before Mortimer’s suggested starting point, following Griffith’s paper entitled “An aerodynamic theory of turbine design,” the Royal Aircraft Establishment (RAE) started research work on axial-flow gas turbines for aircraft propulsion.

Griffith’s papers were classified as secret for 50 years and only made available in 1976. Metropolitan Vickers collaborated with the RAE from 1937 and tested the first British axial-flow jet engine in 1941 (two were later installed in a Gloster Meteor) and the first ducted fan engine in 1943.

The radial or centrifugal compressor, used by Frank Whittle and Hans von Ohain, soon became obsolete. I understand that they were used initially by Whittle because of the expertise gained from their application in piston engine superchargers.

Axial-flow compressors are more efficient than radial-flow compressors and component efficiency is of prime importance. The Rolls-Royce Ghost was the last with the radial-flow compressor; the Rolls-Royce Avon had an axial-flow compressor. Metrovick produced the Beryl and the Sapphire, later manufactured by Armstrong Siddeley at Brockworth adjacent to Gloster at Hucclecote where the engine was installed in the Gloster Javelin.

BMW bled 10% of the air from the axial-flow compressor to cool the hollow, fabricated with air passages, mild steel turbine blades employed, due to the non-availability of exotic metals in Germany at that time.

Brian Cowell, Hucclecote, Gloucestershire

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