The Koolhoven F.K.58 was a single engine, interceptor-fighter aircraft designed and mainly manufactured by N V Koolhoven in the Netherlands under contract by France.
Intended for Armée de l’Air use, the F.K.58 saw limited service in the Battle of France.
In 1938, the French Air Ministry noticed that domestic aircraft manufacturing capacity could not re-equip the Armée de l’Air with modern fighters quickly enough.
In order to win some contracts with the French, the Dutch manufacturer Koolhoven quickly designed a single-seat fighter that would use French-supplied engines and other components.
The Koolhoven fighter was intended primarily for fighter units based in the colony of French Indochina.
The prototype, designed by Erich Schatzki and powered by a Hispano-Suiza 14AA radial engine, flew for the first time on 17 July 1938.
The structure of the fuselage consisted of welded steel tubing covered with sheet metal (front part) and fabric (aft); the wing had 2 wooden box spar members and ribs, with a Bakelite stressed skin covering.
Aerodynamically balanced split flaps on the wing trailing edges ensure a lower landing speed.
The oleo-pneumatic undercarriage retracted inwards with the wheels housed in the lower fuselage faired into the lower engine cowling by small doors.
The empennage is built up from wood and control surfaces are metal framed with fabric covering.
In January 1939, the Armée de l’Air placed an order for 50 aircraft, to be powered by Gnome-Rhône 14N engines.
Due to the unavailability of Gnome-Rhône engines and French instruments, just 17 aircraft six F.K.58s and 11 F.K.58As were completed at the Koolhoven works, with Dutch-supplied engines and instruments and delivered to the Armée de l’Air.
The remaining 23 aircraft, which were at different stages of completion, were transferred to Nevers, where the aircraft were to be finished by personnel employed by Koolhoven.
However, only one F.K.58 was completed before the factory was captured by the Germans, together with the remaining airframes.
In July 1939, the Dutch government placed an order on behalf of the Luchtvaart Afdeling (Netherlands Army Aviation Corps) for 36 F.K.58s, powered by Bristol Taurus engines.
As the British government restricted exports of the Taurus, they were to be replaced by Dutch stocks of the Bristol Mercury VIII (as used by the Dutch Fokker D.21 and Fokker G.1).
The lower output of the Mercury, relative to the Taurus, would have reduced top speed to some 480 km/h (300 mph; 260 kn).
The F.K.58s comprising the Dutch order were in various stages of construction when they were destroyed by a German air raid on the Koolhoven factory in May 1940.
Had the Armée de l’Air received its full order of 50 aircraft, before for the Battle of France, it is unlikely that they would have changed the outcome.
Even though Koolhoven credited the F.K.58 prototype with high performance, French test centres recorded that the series aircraft were 120 km/h (75 mph; 65 kn) slower than what was claimed by the manufacturer.
Additionally, the manoeuvrability was found to be poor by the French pilots.
Variants
F.K.58 Prototype
Prototype powered by 1,080 hp Hispano-Suiza 14AA engine, 2 built.
FK-58
[Bristol Taurus]
Dutch version powered by Bristol Taurus engine, projected Dutch aircraft, none built.
F.K.58
First production variant powered by Hispano-Suiza 14AA radial engine, 7 built.
F.K.58A
Production version powered by Gnome-Rhône 14N-16 engine, 11 built.
Specifications
Crew
1
Length
8.69 m (28 ft 6 in)
Wingspan
9.96 m (32 ft 8 in)
Wing area
17.3 m2 (186 sq ft)
Empty weight
1,810 kg (3,990 lb)
Fuel capacity
505 l (133 US gal; 111 imp gal) in three wing tanks
Powerplant
1 × Hispano-Suiza 14AA-10,
14-cylinder air-cooled radial piston engine,
810 kW (1,080 hp) at 4,511 m (14,800 ft)
Alternative powerplants include
670 kW (900 hp) Bristol Taurus
&
770 kW (1,030 hp) Gnome-Rhône 14N-16
Propellers
3-bladed variable-pitch propeller
Performance
Maximum speed
483 km/h (300 mph, 261 kn) at 4,493 m (14,740 ft)
Cruise speed
431 km/h (268 mph, 233 kn)
Range
853 km (530 mi, 461 nmi)
Service ceiling
10,200 m (33,500 ft)
Rate of climb
16.3 m/s (3,210 ft/min) at 4,001 m (13,126 ft)
Time to altitude
6,998 m (22,960 ft) in 8 minutes 48 seconds
Wing loading
147 kg/m2 (30.2 lb/sq ft)
Power/mass
0.31 kW/kg (0.19 hp/lb)
Armament
Guns
4 × 7.5 mm FN-Browning machine guns in underwing fairings.
