Nationale Vliegtuigindustrie Industrie

In 1921, a group of businessmen founded the N.V. Nationale Vliegtuig Industrie (National Aircraft Industry, Inc.), and hired Frederick Koolhoven as their chief designer. The company lasted only four years. N.V.I. turned out many technically advanced designs, which attracted attention from all over the world but virtually no orders.
In 1926 he became a consultant engineer at The Hague; then designed several aircraft, including the F.K.23A, a single-seat biplane fighter; F.K.29 three-seat commercial biplane; and F.K.31 two-seat high-wing monoplane which served in the pursuit, interception, and army observation roles, and F.K.41 three seat cabin monoplane.
At the demise of N.V.I., Koolhoven convinced several shareholders that the company would still have been viable if he had had complete control of the operations. So when N.V.I. was dissolved, its assets were taken over by a new company: N.V. Koolhoven Vliegtuigen (Koolhoven aircraft, Inc).

In 1934, when the NV Koolhoven Vlietuigen was formed, it was claimed that 51 F.K. types had been produced. More followed, including the F.K.52, an outstanding two-seat fighter biplane with cantilever undercarriage, and the F.K.58 single-seat fighter monoplane, ordered in quantity by France.

Apart from the Heidevogel of 1911, Koolhoven designed 59 aircraft, which he consecutively numbered FK-1 to FK-59. About half of this were design studies that were never built. Koolhoven designed projects FK-1 to FK-28 in England for Armstrong Whitworth and BAT, projects FK-29 to FK-34 for N.V.I. and projects FK-35 to FK-59 for his own company.