SPAD S.XII

SPAD S.XII
Role	biplane cannon-armed fighter
National origin	France
Manufacturer	SPAD
Designer	Louis Béchereau
First flight	5 July 1917
Primary users	Aéronautique Militaire Red Army
Number built	unknown, 300 ordered
Developed from	Spad S.VII

The SPAD S.XII or SPAD 12 was a French single-seat biplane fighter aircraft of the First World War developed from the successful SPAD 7 by Louis Béchereau, chief designer of the Société Pour L'Aviation et ses Dérivés (SPAD).

The SPAD XII was inspired by the ideas of French flying ace Georges Guynemer, who proposed that a manoeuvrable single-seat aircraft be designed to carry a 37 mm cannon, a weapon which had previously been mounted only in large two-seat "pusher" aircraft such as the Voisin III. Béchereau took his own SPAD 7 design as the starting point, but the many major and minor changes incorporated into the SPAD 12 made it a quite different aircraft.

The gun chosen for the SPAD XII was not the old Hotchkiss cannon but a new 37 mm Semi Automatique Moteur Canon (SAMC), built by Puteaux, for which 12 shots were carried. The Hispano-Suiza aviation engine had to be geared to allow the gun to fire through the propeller shaft. The SPAD XII also carried a single 0.303 inch synchronized (7.7 mm) Vickers machine gun mounted on the starboard side of the nose. In order to carry the heavy cannon the airframe was lengthened and the wingspan and wing area increased. The wingtips were rounded rather than squared off and the wings given a slight forward stagger. To accommodate the required geared output propshaft engine, which easily allowed for the hollow propeller shaft for the cannon to fire through, and power the resultingly heavier airframe, 587 kg compared to the 500 kg of the SPAD 7, the 180 bhp Hispano-Suiza 8 direct-drive Ab engine was replaced by the geared 220 bhp model 8Cb, and gave the SPAD XII a clockwise rotating propeller, as seen from a "nose-on" view.

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