The Avro 555 Bison was a British single-engined fleet spotter/reconnaissance aircraft built by Avro.
The Bison was designed to meet British Specification 3/21 for a carrier-based fleet spotter and reconnaissance aircraft. An order for three prototypes was placed in October 1921, together with three of the competing design from Blackburn Aircraft, the Blackburn Blackburn. Avro's design, the Type 555 Bison, was a two-bay biplane, powered, like the Blackburn, by a Napier Lion engine. The deep slab-sided fuselage was constructed of steel tube, with the pilot sitting in an open cockpit forward of the wings, and the engine cowling sloping steeply down ahead of the pilot. An enclosed cabin with large rectangular windows on each side housed the navigator and radio operator and all their equipment, with sufficient headroom to stand upright, while a cockpit for a gunner armed with a Lewis gun on a Scarff ring was provided in the rear fuselage. The upper wings were mounted directly on the top of the fuselage.
The first prototype flew in 1921, with an order for 12 Bison Is following. The aircraft had handling problems, however, caused by interference of the pilots cockpit with the airflow over the upper wing. This was resolved by revising the wing design of the second prototype, raising the centre section of the upper wing by 2 ft (0.6 m) and removing dihedral from the upper wings, flying in this form in April 1923. Further production orders followed with these modifications incorporated as the Bison II, while some Bison Is were modified to a similar standard, sometimes known as the Bison IA. A Bison I was fitted with floats and retractable wheels but tests proved the design was not suitable for seaborne use.
Although designed for a naval requirement the first deliveries were to the Royal Air Force in 1922 to replace the Westland Walrus for coastal reconnaissance work with No. 3 Squadron RAF. In April 1923, 3 Squadron was broken up to form a number of Fleet Spotter Flights of the Fleet Air Arm. Naval aircraft served on, and and onshore at Gosport, England and Hal Far, Malta. The aircraft were retired in 1929 when they were replaced by the Fairey IIIF.
United Kingdom