Built in 1936, the S-125 was a two place, cabin monoplane. The single example, NX18300, was powered by a 115hp engine.

Built in 1935, the S-90 was a two place, cabin monoplane. The single example, N15175, was powered by a 100hp Cirrus Mk III.

A Navy scout and fighter of 1925.

A fighter/reconnaissance aircraft, this biplane was designed by Fre¬derik Koothoven in the early 1920s for the NV (Nationale Vliegtuigindustrie, national aircraft industry), a small number being pro¬duced in 1924 25. Powered by a 400 hp Bris¬tol 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)

On formation of the N.V. Koolhoven, Frits Koolhoven took with him the design of the FK-30 “Toerist” light sportsplane original designed for NVI, but not built.

Several “Toerists” were built in 1927, featuring a rotating wing for transport.