The SPAD S.XIII is a French biplane fighter aircraft of the First World War, developed by Société Pour L'Aviation et ses Dérivés (SPAD) 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 (RFC), 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. Following the signing of the Armistice of 11 November 1918, which effectively marked the end of the First World War, surplus S.XIIIs were sold in great numbers to both civil and military operators throughout the world.
Development
Background
The origins of the SPAD S.XIII lies in the performance of its predecessor, the SPAD S.VII, a single-seat fighter aircraft powered by a direct drive Hispano-Suiza 8A water-cooled V-8 engine and armed with a single synchronised Vickers machine gun. The type demonstrated excellent performance for the time, entering operational service with the French Aéronautique Militaire during August 1916. By early 1917, however, the S.VII had been surpassed by the latest German fighters such as the Albatros D.I.
The emergence of increasingly capable German fighters, which soon resulted in a shift in aerial supremacy towards the Central Powers, led to calls for superior aircraft to be developed and procured. French flying ace Georges Guynemer personally lobbied for an improved version of the S.VII, telling the SPAD designer Louis Béchereau that "The 150 hp SPAD is not a match for the Halberstadt ... More speed is needed." An initial and quick solution to the problem was to increase the compression ratio of the Hispano-Suiza engine, which increased its power to to provide for significantly improved performance, allowing the SPAD S.VII to remain competitive for the time being.
Spanish manufacturer Hispano-Suiza were already in the process of developing a more powerful geared version of the 8A engine, and this engine was unsurprisingly chosen by Béchereau to power two developed versions of the S.VII. The British S.E.5a and Sopwith Dolphin fighters would also be powered by the same engine.
Intro flight
The first of Béchereau's designs to fly with the new, gear-reduction HS.8B engine design series was the S.XII in its HS.8BeC (or "HS-38") version, which was armed with an unusual cannon that fired through the propeller shaft. However, this aircraft only saw limited use, having been rapidly followed into production by the more conventionally armed S.XIII, which was deemed to be a preferable configuration by several French pilots and officials. Aviation author C.F. Andrews has claimed that a large portion of the credit for the S.XIII lies with Marc Birkigt, the designer of the engine, who had chosen to introduce various innovative features upon it, such as monobloc aluminium cylinders, which were furnished with screwed-in steel liners, which improved its performance.
On 4 April 1917, the SPAD S.XIII performed its maiden flight. An early distinguishing feature of the S.XIII - as with the SPAD S.XII - was that its similarly-geared HS.8Be V8 engine mandated a left-handed propeller rotating in the opposite rotation to the earlier, direct-drive HS.8A-powered S.VII. Early on, similarly to the British Sopwith Dolphin also powered with HS.8B-series geared V8s, problems were encountered with the HS.8B engine's gearing; however, Béchereau opted to persist with the engine, which was soon refined and became fairly reliable. Efforts to ramp up production of the type commenced almost immediately after the first flight was conducted. Within months of its first flight, the S.XIII had not only entered service with the Aéronautique Militaire but had quickly proven itself to be a successful fighter.