|Manufacturer||N.V. Koolhoven Vliegtugen|
|First flight||20 June 1938|
Design on a Koolhoven high-performance aircraft first started late in 1937. The result, finished in early 1938 was the F.K.55, a single-seat fighter of radical design with contra-rotating propellers and an engine housed behind the pilot. It had initially been proposed to do away with ailerons on the wings, and replace them with "slot-spoilers" for lateral control, however this idea was abandoned early in the project.
Of mixed metal and wood construction with wooden wings, the F.K.55's front fuselage was made of steel tube while wood formed the tail and rear fuselage. Its 640 kW (860 hp)Lorraine Pétrel engine afforded only just enough power to take off and to stay in flight. The production version would have used the more powerful (900 kW (1,200 hp)) Lorraine 12R Sterna engine but this never happened.
The aircraft flew for the first time on 30 June 1938. It flew for two minutes then landed. Underpowered, the FK.55 was cancelled in the same year.
Data from 
- Crew: 1
- Length: 9.25 m (30 ft 4 in)
- Wingspan: 9.60 m (31 ft 6 in)
- Height: 2.60 m (8 ft 6 in)
- Wing area: 16.00 m2 (172.23 ft2)
- Empty weight: 1600 kg (3527 lb)
- Gross weight: 2208 kg (5026 lb)
- Powerplant: 1 × Lorraine 12Hrs Pétrel V-12, 640 kW (860 hp)
- Maximum speed: 510 km/h (317 mph)
- Cruising speed: 450 km/h (280 mph)
- Range: 850 km (528 miles)
- Rate of climb: 13.1 m/s (2580 ft/min)
- 1 x 20 mm cannon firing through the propellor
- 4 x wing-mounted .303 machine guns
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- Green & Swanborough, pg 323
- Green, William; Gordon Swanborough. The Complete Book of Fighters. Godalming, UK: Salamander Books. p. 415.