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The Lion, in modified form, had powered several of the Supermarine competitors in the Schneider Trophy air races and several land speed record cars. However, by the late 1920s, work had started on replacements.
Two H-block designs, the H-16 Rapier and the H-24 Dagger, were produced. The H-block consisted of two horizontally opposed engines, lying one atop or beside another.
In 1927, Harry Ricardo published a study on the concept of the sleeve-valve engine. He argued that traditional poppet-valve engines would be unlikely to produce much more than 1,500hp; to pass this limit, a sleeve valve would have to be used, to increase volumetric efficiency. Ricardo started work with Bristol Engines on sleeve-valve designs and Major Frank Halford began work with Napier.
They used the opposed H layout of the Dagger but the new design positioned the cylinder blocks horizontally so as to use sleeve valves. All of the accessories were grouped above and below the cylinder blocks, rather than being at the front and rear of the engine as in most contemporary designs.
The first Napier Sabre engines were ready for testing in January 1938, limited to 1,350hp. By March, they were passing tests at 2,050hp and by June 1940, when the Sabre passed the Air Ministry’s 100-hour test, the first production versions were delivering 2,200hp. By the end of that year, they were producing 2,400hp. By comparison, the 1940 Rolls-Royce Merlin II was generating just over 1,000hp.
The first operational aircraft to be powered by Sabre were the Hawker Typhoon and Hawker Tempest. Other aircraft using the Sabre were early prototype and production variants of the Blackburn Firebrand, the Martin-Baker MB3 and a Hawker Fury. But the introduction of jet engines after World War Two led to the demise of the Sabre – there was less need for high-power military piston aero-engines. Napier turned to turboprop engines instead.
Napier’s archive is at the IMechE. For information, email archive@imeche.org.