__NOTOC__ The Blériot-SPAD S.91 was a French light-weight fighter aircraft. It would be later developed into the

Blériot-SPAD S.510 The Blériot SPAD S.510 was a French single-seat, single-engined biplane fighter aircraft. First flying in 1933, 60 were built for the ''Armée de l'Air'' (French Air Force), entering service in 1936. The type remained in service as a fighter-t ...

, the last biplane produced by the French aeronautic industries.

Development

The S.91 was a single-seat

single-bay A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a ...

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 The fuselage (; from the French ''fuselé'' "spindle-shaped") is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraf ...

monocoque Monocoque ( ), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French term for "single shell". First used for boats, ...

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. SPAD 91 C

Operational history

Despite flight demonstrations in

Romania Romania ( ; ro, România ) is a country located at the crossroads of Central, Eastern, and Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, Serbia to the southwest, Moldova to the east, and ...

and

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders ...

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

Hispano-Suiza 12Hb Hispano-Suiza piston aero-engines were predominantly piston engines produced by Hispano-Suiza in France, Spain, and under licence in the United Kingdom, the United States and Russia from the First World War through to the 1950s. Development of these ...

V-12 water-cooled engine with twin-leg radiators mounted on the undercarriage, (1 built). ;S.91/1:The S.91 ''Leger'' fitted with a frontal radiator design. ;S.91/2:The S.91/1 prototype fitted with a Hispano-Suiza 12Gb W-12 water-cooled engine. It was displayed in

and

. ;S.91/3:The S.91/2 was fitted with a

Gnome-Rhône 9A Jupiter The Bristol Jupiter was a British nine-cylinder single-row piston radial engine built by the Bristol Aeroplane Company. Originally designed late in World War I and known as the Cosmos Jupiter, a lengthy series of upgrades and developments turn ...

nine-cylinder air-cooled radial engine, (1 built). ;S.91/4:The S.91 ''Leger'', fitted with a Hispano-Suiza 12Mb V-12 engine, flew again on 4 July 1930 with some modifications, including radiators mounted on top of the upper wing. ;S.91/5:The sole S.91/3, fitted with a Gnome-Rhône 9Ae Jupiter, which crashed on the day of its first flight killing the pilot. ;S.91/6:This S.91/4 conversion 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

Hispano-Suiza 12Mc The Hispano-Suiza 12M was one of two new V-12 engine designs first run in 1927–1928. It produced about 375 kW (500 hp), was the first to use gas nitride hardening and introduced wet cylinder liners into Hispano-Suiza's aircraft engi ...

V-12 engine. On 2 June 1932 this plane established a record of in a closed-circuit. ;S.91/8:The S.91/7 prototype fitted with a supercharged

Hispano-Suiza 12X The Hispano-Suiza 12X was an aircraft piston engine designed in France by Hispano-Suiza during the early 1930s. A 12-cylinder Vee, liquid-cooled design, the 12X was used on several aircraft types, some of them being used in limited numbers durin ...

brs engine and a variable-pitch

Ratier Ratier-Figeac is an aircraft components manufacturer in Figeac, France. From 1926 until 1930 it also built a car with a 746 cc overhead camshaft engine. From 1959 until 1962 Ratier made motorcycles, having taken over the motorcycle business of ...

propeller made its maiden flight on 20 August 1932. This version is reported to have achieved a speed of . ;S.91/9:The S.91/8 became a

testbed A testbed (also spelled test bed) is a platform for conducting rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies. The term is used across many disciplines to describe experimental rese ...

for Hispano-Suiza's engine-mounted 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

; * Spanish Republican Air Force

Specifications (S.91 ''Leger'')

References

Bibliography

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