Blériot-SPAD S.51

The Blériot‑SPAD S.51 was a French single‑seat fighter biplane developed in the early 1920s by the Blériot‑SPAD company, a merger of Louis Blériot’s aircraft works and the former SPAD factory. Conceived to replace the aging Nieuport‑Delage and SPAD fighters that served after World War I, the S.51 first flew in 1922 and was evaluated by the French Army Aviation Service. Its structure combined a wooden box‑spar wing with a fabric‑covered fuselage and a conventional fixed‑gear undercarriage. Powered by a 450 hp Hispano‑Suiza 12Hb V‑12 engine, the aircraft could reach 260 km/h and climb to 5 000 m in seven minutes. Armament consisted of two synchronized Vickers .303 machine guns mounted on the forward fuselage. Although the S.51 demonstrated good maneuverability and a robust climb rate, it suffered from structural vibration at high speed and was outperformed by newer monoplanes such as the Dewoitine D.1. Consequently, only a handful of prototypes were built and the type never entered mass production. Nevertheless, the S.51 provided valuable data on high‑power inline engines and biplane aerodynamics, influencing later French fighter development throughout the interwar period and contributed to the evolution of French air power.