Avro Bison

Avro

Industry	Aerospace
Founded	1910 in United Kingdom
Products	Aircraft

The Avro 555 Bison was a British single-engine aircraft developed by Avro for fleet spotting and reconnaissance missions.

Development and design

The Bison was created to satisfy the British Specification 3/21, which called for a carrier-capable fleet spotter and reconnaissance plane. In October 1921, an order was placed for three prototypes of the Bison, alongside three prototypes of a competing Blackburn design, the Blackburn Blackburn. Avro's Type 555 Bison featured a two-bay biplane configuration powered by a Napier Lion engine, similar to its Blackburn rival. The fuselage had deep, slab-sided construction made from steel tubing. The pilot's open cockpit was positioned ahead of the wings, beneath an engine cowling that sloped sharply forward. Behind the pilot, an enclosed cabin with large rectangular windows on each side accommodated the navigator and radio operator along with their equipment, offering enough headroom to stand upright. A rear fuselage cockpit housed a gunner armed with a Lewis gun mounted on a Scarff ring. The upper wings were attached directly atop the fuselage.

The initial prototype took to the skies in 1921, followed by an order for twelve Bison I aircraft. Early handling difficulties arose due to airflow disruption over the upper wing caused by the pilot's cockpit placement. To address this, the second prototype featured a redesigned wing configuration: the central section of the upper wing was elevated by 2 ft (0.6 m) and the dihedral angle was removed from the upper wings. This adjusted version first flew in April 1923. Subsequent production incorporated these changes as the Bison II model, while some Bison I units were retrofitted similarly and occasionally referred to as Bison IA. One Bison I was equipped with floats and retractable wheels for amphibious testing; however, evaluations demonstrated it was unsuitable for maritime operations.

Operational history

Though originally intended for naval use, initial deliveries in 1922 were made to the Royal Air Force, where they replaced the Westland Walrus in coastal reconnaissance roles with No. 3 Squadron RAF. In April 1923, No. 3 Squadron was disbanded to form several Fleet Spotter Flights within the Fleet Air Arm. These naval aircraft operated aboard HMS Argus, HMS Eagle, and Furious, as well as from shore bases at Gosport, England and Hal Far, Malta. The Bison remained in service until 1929 when it was superseded by the Fairey IIIF.

Operators

United Kingdom

• Royal Air Force
  • 421 Fleet Spotter Flight Fleet Air Arm
  • 423 Fleet Spotter Flight Fleet Air Arm

Variants

Avro 555 Bison

Constructed as three prototypes conforming to Air Ministry specification 3/21.

Avro 555 Bison I

Twelve production models powered by the Lion II engine; remaining units were later upgraded to IA standard.

Avro 555 Bison IA

Modifications included the addition of a biplane gap and an enlarged dorsal fin applied to the Bison I.

Avro 555A Bison II

Enhanced version featuring the biplane gap modification, with a total of 23 aircraft produced.

Avro 555B Bison I

A single Bison I was converted into an amphibious model to satisfy Air Ministry Specification 8/23 but did not proceed to mass production.