The Bleriot SPAD 91 was originally designed to the requirements
of the 1926 lightweight fighter specification
which called for an armament of two machine guns and
a range of 400km. An all-metal fabric-covered
single-seat single-bay biplane with wings of
equal span and chord, the first prototype, referred to as
the Type 91 Leger (Light), was powered by a 500hp
Hispano-Suiza HS 12Hb 12-cylinder water-cooled
engine with radiators mounted on the main undercarriage
legs. Flown for the first time on 23 August 1927,
the Type 91 Leger was followed by a second prototype,
the Type 91-1, which differed primarily in having a frontal
radiator in place of the twin leg-mounted radiators.
This second prototype was subsequently fitted with a
500hp HS 12Gb 12-cylinder engine of W configuration
as the Type 91-2, flying in this form on 31 August 1928.
After demonstrations in Romania and Greece, it was
again re-engined as the Type 91-3 with a 420hp
Gnome-Rhone Jupiter 9As nine-cylinder air-cooled radial. Early in 1931 it received a 480hp Gnome-Rhone
Jupiter 9Ae as the Type 91-5, but was destroyed on 10
May after six hours flying in the latter form. The original
Type 91 Leger had meanwhile been fitted with a 500hp
HS 12Mb engine and, with various minor modifications,
became the Type 91-4, which first flew on 4 July 1930.
Rounded wingtips were then applied, the fuselage was
lengthened and the tailplane was lowered to the base
of the fuselage, flight testing being resumed on 10 November 1931 as the Type 91-6. The tailplane was
later restored to its original position, but both the 1926
and subsequent lightweight, or "Jockey", fighter programmes
had meanwhile been abandoned and none of
the competing designs had been ordered into production.
W.Green, D.Swanborough "The Complete Book of Fighters", 2000
