Armstrong Whitworth Siskin - Design and Development

Design and Development

The design was a development of the Siddeley-Deasy S.R.2 Siskin, which was designed by Major F.M. Green (formerly chief engineer of the Royal Aircraft Factory) of the Siddeley-Deasy Motor Car Company, to meet the requirements of RAF Specification Type 1 for a single-seat fighter powered by the promising ABC Dragonfly radial engine.

The SR.2 Siskin was a single-bay biplane of wood and fabric construction. Its wings were of unequal span and the aircraft was fitted with a distinctive fixed conventional landing gear with long oleo strut shock absorbers carrying the axle, which was connected by radius rods to a pair of V-struts situated behind the axle. The Dragonfly engine was fitted in a streamlined cowling to reduce drag, with individual cooling channels for each engine cylinder. Two Vickers machine guns were mounted in the nose decking in front of the pilot.

The Siskin first flew in May 1919, powered by a Dragonfly engine delivering 270 hp (200 kW), rather than the promised 320 hp (240 kW). Despite the expectations piled on it, the Dragonfly proved to be a disaster, far less powerful than expected and very unreliable, being prone to overheating and catastrophic vibration, that would normally cause crankshaft failure within a few hours. Despite the engine problems, the Siskin displayed good performance and handling, outmatching its Dragonfly-powered contemporaries.

In 1919, Siddeley-Deasy merged with Armstrong Whitworth, with the aviation interests becoming Armstrong Whitworth Aircraft. Siddeley-Deasly had inherited the design of the RAF.8 fourteen cylinder radial engine and its designer Sam D Heron, and by 1920 this engine, now known as the Jaguar, had been developed sufficiently to be a possible replacement for the Dragonfly. One of the prototype Siskins was fitted with a Jaguar, flying in this form on 20 March 1921.

In 1922 Air Ministry Specification 14/22 was issued for an all-metal single-seat high performance landplane and one Jaguar-powered prototype was ordered from Armstrong Whitworth. As well as re-engining with the Jaguar, Major Green redesigned the Siskin with an all-steel structure, as the Siskin III. A contract for three production aircraft was placed on 13 October 1922 with a further six ordered on 26 January 1923 including one as a prototype of a two-seat variant. The Siskin III first flew on 7 May 1923, with first deliveries to the RAF (six for evaluation) taking place in January 1924. The fighter was the first all-metal fighter in the British Royal Air Force.

Following the order from the RAF, Romania ordered 65 aircraft but they were cancelled following a crash on takeoff at Whitley Abbey, Coventry, on 18 February 1925 during acceptance tests; the Romanian pilot being killed.

The main production version was the Siskin IIIA ordered in 1926, which originally was powered with a Jaguar IV engine, but was later re-engined with the supercharged Jaguar IVA engine. The supercharger, a novel idea at the time, had little effect on performance below 10,000 ft (3,050 m), but it greatly improved speed and climb above that height. Following an evaluation of two Siskin IIIs the Royal Canadian Air Force ordered 12 IIIAs which were delivered between 1926 and 1931.

With Armstrong-Whitworth busy building the Armstrong Whitworth Atlas some of the later Siskin IIIA production was sub-contracted out to Blackburn, Bristol, Gloster and Vickers.