Nationale Vliegtuigindustrie Industrie FK.31
A fighter/reconnaissance aircraft, this biplane was designed by Frederik Koothoven in the early 1920s for the NV (Nationale Vliegtuigindustrie, national aircraft industry), a small number being produced in 1924-25. Powered by a 400-hp Bristol Jupiter radial engine, it seated a pilot and observer/gunner in tandem open cockpits, operating respectively two fixed, forward -firing machine-guns and two ring-mounted.
Reconnaissance versions sometimes carried a fifth gun, firing downward through the floor of the rear cockpit. Performance was not up to LVA (Luchtvaartafdeling, army air service) requirements, but the F.K.31 was used until about 1930 by the Netherlands East Indies army air service as a fighter trainer.
The Finnish air force operated 12 over a similar period, four of them built in Finland under licence. Louis de Monge in France also built a few, with Gnome-Rhone (Bristol) Jupiter engines.
Gross weight: 1760 kg (3880 lb)
Maximum speed: 235 km/h (146 mph)