The Armstrong Whitworth Siskin was a biplane single-seat fighter aircraft developed and produced by the British aircraft manufacturer Armstrong Whitworth Aircraft. It was also the first all-metal fighter to be operated by the Royal Air Force (RAF), as well as being one of the first new fighters to enter service following the end of the First World War. The Armstrong Whitworth Siskin was a development of the Siddeley-Deasy S.R.2 Siskin designed by Major F. M. Green (formerly chief engineer of the Royal Aircraft Factory) of the Siddeley-Deasy Motor Car Company. A major impetus for the aircraft's development was the Air Ministry's issuing of RAF Specification Type I, which called for a single-seat fighter that was powered by the ABC Dragonfly radial engine. The Dragonfly would prove to be a disappointment as it failed to meet its anticipated performance. The SR.2 Siskin was a single-bay biplane of wood and fabric construction. It angular in form, with little attention paid to obvious avenues for drag reduction. Perhaps its most distinctive feature was its fixed conventional landing gear, which had relatively lengthy oleo strut shock absorbers carrying the axle, which was in turn connected by radius rods to a pair of V-struts situated behind the axle. Its wings were of unequal span. It was powered by a single ABC Dragonfly radial engine, which was installed on the nose in a streamlined cowling. To regulate the engine's temperature, each individual cylinder had its own cooling channel. Armament consisted of a pair of Vickers machine guns mounted directly in front of the pilot. The Siskin made its first flight in May 1919. While the initial aircraft was powered by the intended Dragonfly engine, it would only deliver 270 hp (200 kW) rather than the expected 320 hp(230 kW). Despite early promise, the Dragonfly was disastrous, being less powerful, unreliable, and prone to overheating while excessive vibration resulted in crankshaft failures after only a few hours of use. Despite the engine, the Siskin displayed generally good properties, possessing favourable stability and handling characteristics, along with performance that could outmatch its direct rivals for RAF orders. In 1919, Siddeley-Deasy merged with Armstrong Whitworth, with the aviation interests becoming Armstrong Whitworth Aircraft. Siddeley-Deasy had inherited the design of the RAF 8 fourteen-cylinder radial engine and its designer Sam D. Heron. By 1920, this engine, as the Jaguar, had been developed sufficiently to replace the Dragonfly. A prototype Siskin fitted with a Jaguar flew on 20 March 1921. Air Ministry officials were impressed but urged Armstrong Whitworth to continue developing the aircraft as only an all-metal design would be acceptable to the Royal Air Force (RAF). During 1922, Air Ministry Specification 14/22 was issued for an all-metal single-seat high performance landplane. The Siskin was submitted leading to an order for a single Jaguar-powered prototype. Aside from the engine change, Major Green redesigned it with an all-metal structure, as the Siskin III. The all-metal Siskin was the start of the British transition to metal for military aircraft. For details of operational history and variants, click here. A total of 485 Siskins were built. These photos clearly show that the Siskin was a prime example of a sesquiplane.
