Frederick (Frits) Koolhoven (11 January 1886 – 1 July 1946) was an aircraft designer in Britain and his native Netherlands. Koolhoven was born in Bloemendaal, Netherlands. After training as an engineer in Liège and Antwerp, he worked from 1907 as a mechanical engineer for Minerva in Antwerp, and also drove in races and rallies for them. He became interested in aviation. In 1910 he acquiried his own Hanriot aircraft, and was involved in the construction of the first Dutch plane the “Heidevogel”.
He designed many aircraft, initially in England from 1912 for British Deperdussin, then from 1914 for Armstrong Whitworth Aircraft, then from 1917 as chief designer for the British Aerial Transport Company which went bankrupt in 1919.
He returned to the Netherlands, but there the market was dominated by Fokker, so he returned to his old job as an automobile engineer for the Spyker automobile factory.
In 1921, a group of businessmen founded the N.V. Nationale Vliegtuig Industrie (National Aircraft Industry, Inc.), and hired him as their chief designer. The company lasted only four years. As with BAT, N.V.I. turned out many technically advanced designs, which attracted attention from all over the world but virtually no orders.
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, by which time 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.
By 1933 however the military market picked up and Koolhoven increasingly built trainers and observation aircraft for the Dutch air force as well as for various other countries. By 1938, with a new war looming, its order books continued to fill as air forces from all over Europe were virtually fighting over each plane that rolled off the production line. Even France found itself buying Koolhoven FK-58 fighters as its own aircraft industry was unable to keep up with the demand from the Armée de l’Air.
In 1938, the Koolhoven factory at Waalhaven covered 8000 square meters and boasted 1200 employees. While still no match for Fokker, Koolhoven had established itself firmly as the number 2 manufacturer in the Netherlands.
The factory at Waalhaven was destroyed by German bombing in the Blitzkrieg on 10 May 1940 at the outbreak of World War II. More important, with the factory also disappeared all drawings, models, documents of Koolhoven’s projects. Even today, the only photographs remaining of Koolhoven’s planes are newspaper clippings and private snapshots.
Frederick Koolhoven was convinced that the bombing had everything to do with his contribution as an aircraft designer in England during World War I. For unknown reasons he became a very inactive member of the NSB. After the war he was captured by the Dutch police because of this membership but he was released several days later. Frederick Koolhoven died of a stroke at Haarlem in 1946.
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.
His company, although without means of production, continued to exist as a holding. Over the next 10 years various attempts were made to start up new projects, but apart of the construction of two prototype sailplanes nothing happened and in 1956 N.V. Koolhoven Aeroplanes was finally closed and liquidated.
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. The first ‘true’ Koolhoven airplane therefore would have been the FK-35. However 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” built by the new FK Koolhoven therefore constitute the earliest airplanes of that company, if not by production date, then at least by numbering.
The Koolhoven foundation lists 26 Koolhoven designs, starting with the F.K.30 and then going from F.K.35 to F.K.59. It however also notes that the designs F.K.37, 38, 39 and 59 were never built, while only giving pictures of wooden models for the designs F.K.35 and F.K.36. Jane’s Encyclopedia of Aviation only lists the Koolhoven designs F.K.40, 41, 42, 43, 46, 48, 49, 51, 52, 53 and 58 but mentions a F.K.50-b bomber project, which the Koolhoven foundation site doesn’t.
The best-known amongst those designs are the F.K.41 high-wing monoplane, which was built in license as the Desoutter Mk.II and the F.K.50 twin engine transport monoplane, two of which were used by the Swiss aircraft company alpar. Amongst the military designs, the most successful were the Koolhoven F.K.51 biplane reconnaissance aircraft, which saw service in extensive numbers in the Dutch air force from the mid-Thirties until the Second World War, the Koolhoven F.K.52 biplane which was used by the Finnish Air Force and the Koolhoven F.K.58 single-seat monoplane fighter. The latter was the plane ordered by France and flew in the Armée de l’Air during the Battle of France
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