Derived from a 1917 project designated LeO 3, the LeO 9 single-seat cantilever monoplane fighter was of metal construction and of advanced aerodynamic concept. Powered by a 300hp Hispano-Suiza 8Fb eight-cylinder water-cooled engine, the LeO 9 was exhibited, prior to first flight at the Paris Salon in 1921. Flight testing was initiated in the following year, but, on 24 September 1923, the wing folded during a very sharp turn and the aircraft crashed at Villacoublay with the death of the pilot, Gaston Martin. Further development of the LeO 9 was then discontinued.
Engine: 300hp Hispano-Suiza 8Fb
Empty weight: 1175 kg / 2590 lb
Wingspan: 10.94 m / 35 ft 11 in
Length: 6.59 m / 21 ft 7 in
Height: 2.18 m / 7 ft 2 in
Wing area: 17.20 sq.m / 185.14 sq ft