page_title: SPAD S.XIII
section_title: Design
hierarchical_section_title: SPAD S.XIII / Design
caption_attribution_description: English: SPAD S.XIII at Air Service Production Center No. 2, Romorantin Aerodrome, France, 1918
context_page_description: The SPAD S.XIII was a French biplane fighter aircraft of the First World War, developed by Société Pour L'Aviation et ses Dérivés from the earlier and highly successful SPAD S.VII.
  During early 1917, the French designer Louis Béchereau, spurred by the approaching obsolescence of the S.VII, decided to develop two new fighter aircraft, the S.XII and the S.XIII, both using a powerful new geared version of the successful Hispano-Suiza 8A engine. The cannon armament of the S.XII was unpopular with most pilots, but the S.XIII proved to be one of the most capable fighters of the war, as well as one of the most-produced, with 8,472 built and orders for around 10,000 more cancelled at the Armistice.
  By the end of the First World War, the S.XIII had equipped virtually every fighter squadron of the Aéronautique Militaire. In addition, the United States Army Air Service also procured the type in bulk during the conflict, and some replaced or supplemented S.VIIs in the Royal Flying Corps, pending the arrival of Sopwith Dolphins. It proved popular with its pilots; numerous aces from various nations flew the S.XIII during their flying careers.
context_section_description: The SPAD S.XIII was a single-engine biplane fighter aircraft. In terms of its construction, it shared a similar configuration and layout to the earlier S.VII, featuring a mainly wooden structure complete with a fabric covering; however, it was generally larger and heavier than its predecessor. Other changes included the tapered chord of its ailerons, the rounded tips of the tailplanes, bulkier cowling accommodating the gear-drive Hispano-Suiza 8B engine choice, and enlarged fin and rudder. The S.XIII was armed with a pair of forward-mounted Vickers machine guns with 400 rounds per gun, which took the place of the single gun that had been used on the earlier aircraft.
  The S.XIII featured relatively conventional construction, that being a wire-braced biplane with a box-shaped fuselage and a front-mounted engine, except for its interposed wing struts located half-way along the wing span, which gave the fighter the deceptive appearance of being a double-bay aircraft instead of a single bay. This change prevented the landing brace wires from whipping and chafing during flight, and was attributed by Andrews as a key factor for the aircraft's high rate of climb. Otherwise, it had an orthodox structure, comprising wooden members attached to metal joint fixtures. The fuselage consisted of four square-section longerons, complete with wooden struts and cross-members while braced with heavy-gauge piano wire; wire cable was instead used for the flying and landing wires.
  To facilitate its two-hour endurance, the S.XIII was furnished with an assortment of underbelly fuel tanks were held within the forward fuselage area; these were fed into the main service tank located in the center of the upper wing by an engine-driven pump. Similar pumps were used for supplying pressurised oil and water circulation between the engine's radiator and a header tank in housed within the upper wing. The circular nose radiator incorporated vertical Venetian-style blinds as a means of regulating the temperature of the engine.
  The upper wing was a single-piece structure, featuring hollow box-section short spars which connected with linen-bandaged scarf joints, Andrews claims that long runs of spruce were difficult to obtain. The ribs consisted of plywood webs and spruce capping strips, which were internally braced with piano wire. The upper wing was provisioned with ailerons, which were actuated by the pilot via a series of tubular pushrods which ran vertical directly beneath the ailerons, with external, 90º bellcranks exposed above the lower wing panels' top fabric covering. The lower wing consisted of spruce leading edges and wire-cable trailing edges, while the surfaces were fabric-covered and treated with aircraft dope to produce a scalloped effect, much as with the contemporary German Fokker D.VII that also used a wire trailing-edge component, along the trailing edges.
  While the forward Vickers machine guns were installed as standard, they were not always present upon all aircraft. As a result of fears of a shortage of Vickers guns during the last few months of the war, several American squadrons equipped with the S.XIII decided to replace their existing Vickers .303 machine guns with the lighter-weight (25 lbs/11.34 kg apiece) .30/06-calibre Marlin Rockwell M1917 and M1918 aircraft machine guns, saving some sixteen pounds (7.3 kg) in weight over the twin-mount Vickers' total weight of 66 lbs (29.94 kg) for the guns alone. Reportedly, by the end of the war, roughly one half of the aircraft in American service had been converted in this fashion.
  The powerplant of the S.XIII was a geared Hispano-Suiza engine, at first a 8Ba providing 200 hp (150 kW), but in later aircraft a high-compression 8Bc or 8Be delivering 220 hp (160 kW) was often used. The sum of these improvements was a notable improvement in flight and combat performance. It was faster than its main contemporaries, the British Sopwith Camel and the German Fokker D.VII and its relatively higher power-to-weight ratio gave it a good rate of climb. The SPAD was renowned for its speed and strength in
caption: A SPAD S.XIII at Air Service Production Center No. 2, Romorantin Aerodrome, France, 1918
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