Koolhoven F.K.51 "1935"

Koolhoven F.K.51 "1935"



Koolhoven F.K.51 "1935"

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Koolhoven F.K.51

The Koolhoven F.K.51 was a 1930s Dutch two-seat basic training biplane built by the Koolhoven Company The Koolhoven F.K.51 was the winning design in a 1935 Dutch government contest for a new trainer. Designed by Frederick Koolhoven the prototype biplane trainer first flew on 25 May 1935. The aircraft was an equal-span biplane designed to use a variety of engines of 186 to 373 kW (249 to 500 hp). It was a two-seater and had a fixed tailwheel undercarriage. The Royal Netherlands Air Force (LVA) ordered 25 aircraft in 1936 and 1937, powered by a 201 kW (270 hp) Armstrong Siddeley Cheetah V radial engine. A further 29 aircraft were later ordered with 261 kW (350 hp) Armstrong Siddeley Cheetah IX engine. The Dutch Naval Aviation Service ordered 29 aircraft each powered by a 335 kW (449 hp) Pratt & Whitney radials. The Royal Dutch East Indies Army bought 38 aircraft between 1936 and 1938 each powered by a 313 kW (420 hp) Wright Whirlwind


While the majority of F.K.51s were employed as elementary trainers within the Netherlands or in reconnaissance roles by the Royal Netherlands Air Force in the Dutch East Indies, twenty-eight were clandestinely sold to the Republican government during the Spanish Civil War, all despite a Dutch embargo on the sale of arms to either side of that conflict. Some of those arriving in Spain were used as light bombers by the Republicans in the Cantabrian region of Spain.[2]

The F.K.51s were in active use in Royal Dutch Flight Schools during 1939–1940 in the training of young Dutch pilots. The majority of F.K.51s were destroyed in May 1940 on the ground by attacking Luftwaffe aircraft.



Role Trainer, Reconnaissance Aircraft
Manufacturer Koolhoven
First flight 1935
Primary users
Royal Netherlands Air Force
Spanish Republican Air Force
Number built 142

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Koolhoven Fk.51 "1935"

Door dit vliegtuig werd Koolhoven een fabriek die flinke aantallen vliegtuigen in produktie had. De latere Koolhoven FK-56 laagdekker maakte gebruik van de ervaringen van de FK-51. In totaal werden zo’n 160 stuks FK-51 geproduceerd.

Koolhoven Fk.51 Specifications

  • Crew: 2 (one observer or student, one pilot)
  • Length: 7.85 m (25 ft 9 in)
  • Wingspan: 9 m (29 ft 6 in)
  • Height: 2.8 m (9 ft 2 in)
  • Empty weight: 990 kg (2,183 lb)
  • Max takeoff weight: 1,600 kg (3,527 lb)
  • Powerplant: 1 × Armstrong Siddeley Cheetah IX 7-cylinder, air-cooled radial piston engine, 261 kW (350 hp)
  • Maximum speed: 253 km/h (157 mph, 137 kn) at 2,200 m (7,218 ft)232 km/h (144 mph; 125 kn) at sea level
  • Cruise speed: 229 km/h (142 mph, 124 kn) at 2,200 m (7,218 ft)206 km/h (128 mph; 111 kn) at sea level
  • Landing speed: 84 km/h (52 mph; 45 kn)
  • Range: 775 km (482 mi, 418 nmi)
  • Service ceiling: 6,300 m (20,700 ft)
  • Time to altitude:
  • Guns:
    #1 to #10: no armament
    #11 to #25: one or two 7.7 mm (0.303 in) Lewis gun(s) in the wing
    #400 to #428: two 7.7 or 7.9 mm (0.303 or 0.311 in) machine guns, 1 in the wing and 1 for the observer.



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Varianten F.K. 51 LVA eerste serie, lesvliegtuig: geen bewapening. F.K. 51 LVA tweede serie, verkenner: uitgerust met één 7,7mm Lewis mitrailleur in de bovenvleugel. F.K. 51 LVA derde serie: uitgerust met één 7,7mm Lewis mitrailleur in de bovenvleugel én eenzelfde mitrailleur bij de achterste cockpit. F.K. 51 MLD: uitgerust met een Wright "Whirlwind" R-975-E1. Zes exemplaren bewapend als de LVA eerste serie en negen exemplaren bewapend als de LVA derde serie. F.K. 51 LA: uitgerust met een Pratt & Whitney "Wasp Junior". F.K. 51 "Spaanse versie": uitgerust met een Armstrong Siddeley "Jaguar" of een Wright "Whirlwind" R-975-E3 stermotor.

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