The Bleriot SPAD 81 paradoxically preceded the Types
51 and 61, the first prototype having flown at Buc on 13
March 1923. A single-bay staggered biplane of mixed
construction with fabric-covered metal wings and a
wooden monocoque fuselage, the Type 81 was
powered by a 300hp Hispano-Suiza HS 8Fb watercooled
engine and carried an armament of two 7.7mm
MAC (Vickers) machine guns. A production batch of 80
was ordered for France's on 28 March
1924. The Types 81-2 and 81-3, built in prototype form
only and flown on 20 May and 18 August 1924 respectively,
differed primarily in the types of radiator fitted,
and a further prototype, the Type 81-4 flown on 11 September
1924, differed in having wings of wooden construction.
W.Green, D.Swanborough "The Complete Book of Fighters", 2000