Blériot-SPAD S.91

The Blériot-SPAD S.91 was a French light-weight fighter aircraft. It would be later developed into the Blériot-SPAD S.510, the last biplane produced by the French aeronautic industries.

Development
The S.91 was a single-seat single-bay biplane developed towards the end of the 1920s by Blériot in order to meet the requirements of a French government program for a light fighter plane type designated as "Jockey".

The first prototype was flown on 23 August 1927. It featured a wooden fuselage of monocoque construction and metal wings skinned in fabric. This prototype was destroyed in a crash and a second prototype followed. Even after the French government dropped interest in the program seeking a light fighter for the French Air Force, André Herbemont designed a further prototype with an inverted sesquiplane wing configuration.

Operational history
Despite flight demonstrations in Romania and Greece no orders followed. André Herbemont would use his experience with the S.91 prototypes in order to develop the S.510, another biplane fighter which would go into production and would be later used by the French Air Force.

In 1936 at least one of the surviving S.91 prototypes ended up in the Spanish Republican Air Force.

Variants

 * S.91 Leger:Powered by a 500 hp Hispano-Suiza 12Hb 12-cylinder water-cooled engine with twin-leg radiators mounted on the undercarriage.


 * S.91/1:The S.91 Leger fitted with a frontal radiator design.


 * S.91/2:The same S.91/1 prototype fitted with a 500 hp Hispano-Suiza 12Gb 12-cylinder water-cooled V-engine. It was displayed in Romania and Greece.


 * S.91/3:The S.91/2 was then fitted with a 420 hp Gnome-Rhône Jupiter 9As nine-cylinder air-cooled radial engine.


 * S.91/4:The S.91 Leger, fitted with a 500 hp Hispano-Suiza 12Mb, flew again on 4 July 1930 with some modifications, including radiators mounted on top of the upper wing.


 * S.91/5:The S.91/3 fitted with a similar but more powerful 480 hp Gnome-Rhône Jupiter 9Ae. This prototype then crashed.


 * S.91/6: This S.91/4 version flew in November 1930 and differed from the prototype in having rounded wingtips, a lengthened fuselage and a tailplane lowered to the fuselage base. Later the tailplane was restored to its former position.


 * S.91/7: A new prototype with inverted sesquiplane wing configuration in which only the lower wing had ailerons. It flew on 23 December 1931 and was fitted with a 500 hp Hispano-Suiza 12Mc engine. On 2 June 1932, in a 500 km closed-circuit, this plane established a record of 308.78 km/h.


 * S.91/8: The S.91/7 prototype fitted with a supercharged Hispano-Suiza 12X engine and a variable-pitch Ratier propeller made its maiden flight on 20 August 1932. This version is reported to have achieved a speed of 360 km/h.


 * S.91/9: The S.91/8 became a testbed for Hispano-Suiza's engine-mounted 20 mm cannon, after being leased to the company in December 1932. Besides the cannon it was also fitted with a large-diameter Levasseur fixed-pitch propeller.

Operators

 * 🇪🇸 Spain
 * Spanish Republican Air Force