Royal Aircraft Factory S.E.5a
|FIGHTER||Virtual Aircraft Museum / United Kingdom / Royal Aircraft Factory|
The third prototype of the S.E.5 flew at Farnborough on 12 January 1917 powered by a 200hp geared Hispano- Suiza 8B water-cooled eight-cylinder V-type engine, but otherwise similar to the 150hp-engined earlier prototypes. While production deliveries of the 200hp engine were awaited, airframe modifications were introduced in the light of early experience with the first production batch of S.E.5s. In particular, the wing rear spars were shortened at the tips to provide greater strength, this serving to blunt the previously raked tips and reduce overall span by 39.4cm. At the same time, lateral control was improved by shortening the levers on the ailerons. With a small Avro-type windscreen in place of the S.E.5's voluminous structure, a small fabric-covered head fairing behind the cockpit, the blunt wings and the standard Vickers + Lewis gun armament, the version with 200hp engine became the subject of large-scale production as the S.E.5a, starting with part of the second batch S.E.5s already ordered from the RAF. Two hundred more were built at Farnborough itself and, in addition, by the time the war came to an end in November 1918, some 5125 S.E.5a's had been built by five companies in less than 18 months: Austin (1,550), Bleriot & Spad (560), Martinsyde (400), Vickers (2,215) and Wolseley (400). Production of the 200hp Hispano (in several sub-variants, and including licence-production by Wolseley as the W.4B Adder I, II and III) failed to keep pace with this prodigious output, and numerous operational difficulties with the engine enhanced the problem. Consequently, many S.E.5a's were fitted (without change of designation) with the 200hp direct-drive Wolseley W.4A Viper, a derivative of the French engine. At least six S.E.5a's were flown with the 200hp Sunbeam Arab I (geared) or Arab II (direct drive) water-cooled eight-cylinder engine in trials at Farnborough, and some production aircraft received high-compression versions of the French-built Hispano-Suiza engine, increasing maximum" output to 220hp. Twenty-two squadrons of the RFC and the US Air Service were flying the S.E.5a by the time of the Armistice, but this brought an end to planned largescale production by Curtiss in the US when only one of 1,000 on order had been completed (in addition to 56 assembled from British components). Service use continued on a small scale for only a short time after the end of the war, in Australia, Canada and South Africa as well as with the RAF.