The Mercury N-1 of 1940 was a two place all-metal monoplane featuring a unique X-spar, slotted cantilever wing with interchangeable front and rear spars. Only the one was built, NX28646, and retractable landing gear was planned for production models, of which none were built. The N-2 designation was apparently for this one, and specs were the same except for higher speeds (projected: Maximum 155 mph / Cruise 138 mph / Stall 55mph).

Production was curtailed by the war but the design reappeared in 1947 as the Midwest Mercury.

N-1
Engine: Lycoming GO-145, 75hp
Wing span: 30’0″
Length: 20’6″
Useful load: 610 lb
Max speed: 142 mph
Cruise speed: 138 mph
Stall: 43 mph
Range: 450 mi
Seats: 2

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.

The 1929 Air Prince two-place cabin monoplane was designed to be marketed as an inexpensive trainer a $3250. Powered by a 90hp LeBlond engine, only one prototype was built (NX43N), which was still registered in 1936.

The 1928 Air King Mono-4 four-place, high wing, cabin monoplane, was powered by a 220hp Wright J-5 and only built in prototype form (N7610 c/n 101).