The Spad A.1 made its maiden flight on 21st May 19155. Its performance was notably better than contemporary pusher designs and the French Air Force duly placed an order for the aircraft. Serial-production Spad S.A1s featured additional, mesh-covered intakes, six being mounted on either side of the gunner/observer’s nacelle, in order to provide cooling air for the engine. A new tubular mounting for a flexible machine gun was devised. The upper support struts were detachable allowing the nacelle to be lowered for engine maintenance. The observer was protected from the propeller – spinning right behind his back – by a wire mesh guard. A transparent panel in the floor of the observer’s nacelle was provided. The tailfin was enlarged and tapered. A total of 11 Spad A.1s were manufactured for the Aviation Militaire6.
Serial-production Spad S.A2s featured a reduced wingspan and wing area, as well as a redesigned engine cooling system with additional air intakes on either side of the fuselage. A shield to deflect exhaust fumes was also installed. Of the 99 aircraft produced, 42 were delivered to the French Air Force, while 57 were exported to Russia. The Spad S.A4 was a development version, basically the S.A2 airframe coupled to a Le Rhône 9J rotary engine rated at 81 kW (110 hp)7. Ten aircraft were sold to Russia. The Spad S.A4 first flew in February 1916. The Spad S.A3 was a dual-controlled version with a gun fitted to both cockpits. Interestingly, the two crewmembers could switch roles and hence increase the field of fire. Only one prototype of the S.A3 version, designated S.40, was built. The Spad S.A5 was an S.A4 airframe powered by a 75 kW (100 hp) air-cooled, V-shaped Renault 8 engine.

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The S.A2 and A4 versions were not popular with French airmen. Pilots claimed that they were difficult to handle, while the observers had serious doubts about the front nacelle they were supposed to fly in, especially the reliability of the hinged mounting points. The unsatisfactory layout of the Spad S.A2 was best summarized by a British report dated to early 1916:

“In this machine the passenger is slung in a small fuselage in front of a tractor propeller. This arrangement is considered to be unnecessarily dangerous and the objects attained as regards arc of fire do not justify it. All the Spad machines are of similar type and are considered to be of no interest in their present form”.
The Spad A2s and A4s were popular in Russia though, where they remained in active service until 1921. One Russian crew – Ju.A. Bratolubov and A.A. Kazakov – even scored an aerial victory in one of them.
In early 1916 the Spad S.A2 was used as the basis of an experimental single-seater design armed with one, or alternatively four, fixed machine guns mounted in a cupola. In April 1916 an official British aircraft review mentioned a single-seat Spad armed with a single Hotchkiss mitrailleuse d’Infanterie machine gun with a belt of 1000 rounds mounted in a gondola in front of the propeller. This was the Spad S.G2, a prototype fighter. It was lighter, had a smaller wingspan, and a wing area of about 18.4 square meters. At 2000 meters it reached the speed of 161 kph and climbed to that altitude in seven minutes and 15 seconds. However, early 1916 saw the rise of the German Fokker Eindekker armed with a synchronized machine gun, while the very manoeuvrable and fast Nieuport 11C1 “Bébé” reigned in the French Air Force. Compared with these, the Spad S.G2 seemed a dead end in the evolution of combat aircraft designs.
Louis Béchereau strove to construct a similar aircraft, a single-seat fighter armed with a single machine gun firing through the propeller arc. Power was to be provided by a 96 kW (130 hp) rotary engine. Three variants8 , the SL and SK biplanes and the SJ monoplane, were envisaged and respective prototypes were built, but none was actually flown. They all used a revolutionary method of constructing fuselages, first used in the Deperdussin Monocoque, a record-breaking racing aircraft – the light and strong ‘monocoque’ fuselage. Still, it took more than a well-constructed airframe to make a successful aircraft design. What Louis Béchereau needed was a new powerplant for his aircraft.

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