Koolhoven F.K.58

The Koolhoven F.K.58 was a single engine, interceptor-fighter aircraft designed by Koolhoven under contract by France. Intended for Armée de l'Air use, the F.K.58 saw limited service in the Battle of France.

In 1937 it became apparent to the French Air Council that domestic manufacturers could not equip the Armée de l'Air with enough fighters. The Dutch were contracted to produce a cheap, high performance fighter to supplement French needs. As produced, the F.K.58 was rather better than the M.S.406 and comparable to the Bloch MB.151 but inferior to the D.520 and most of the German aircraft it was to face. 

The FK.58 can be seen as a further development of the Fokker D.21 (also Erich Schatzki) with retractable undercarriage. It had the same composite structure: fuselage of steel tubing with a skin of metal plating and linen; the wing of wooden structure with plywood and linen skin.
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Specifications F.K.58
Crew: One
Length: 8.7 m (28 ft 6.75 in)
Wingspan: 11 m (36 ft 1.25 in)
Height: 3 m (9 ft 10 in)
Wing area: 17.3 m² (186.2 ft²)
Empty weight: 1,930 kg (4,255 lb)
Loaded weight: 2,750 kg (6,063 lb)
Powerplant: 1 × Gnome-Rhône 14N-16 radial engine, 768 kW (1,030 hp)
Maximum speed: 505 km/h (314 mph)
Cruise speed: 450 km/h (280 mph)
Range: 750 km (466 mi)
Service ceiling: 10,000 m (32,810 ft)
Rate of climb: 11.6 m/s (1,130 ft/min)
Wing loading: 159 kg/m² (32.6 lb/ft²)
Power/mass: 0.28kW/kg (0.17 hp/lb)
Armament: 4 x 7.5 mm FN-Browning machine guns in underwing fairings
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The prototype Model 1166 (later named F.K.58) first flew on 17 July 1938. The French placed an order in January 1939 for 50 F.K.58s Just 17 of the French order were completed at the Koolhoven works due to insufficient French-supplied engines and instruments, and they were subsequently sent to France fitted with Dutch equipment. Production was transferred to Nevèrs where just one more F.K.58 was produced. The completed fighters (7 F.K.58s, 11 F.K.58As) were fitted with French equipment and their loaner parts returned to the Netherlands. Even had the order of 50 aircraft been available for the Battle of France, it is unlikely that the small number of aircraft, outclassed as they were by German fighters, could have changed the outcome much. Had they been employed in their intended role as colonial fighters, they might have acquitted themselves well against the Italian aircraft in that theatre.

The Dutch placed an order in late 1939 for 36 fighters powered by Bristol Taurus engines. As the Taurus was no longer available due to British restrictions these engines were to be replaced by Mercury VIII , spares of the Dutch Fokker D.21 and G.1A The lower output of these engines would have reduced the top-speed to some 480 km/h

The F.K.58 was originally procured for use as colonial fighters. Instead, the 13 fighters operational by May 1940 were manned by expatriate Polish pilots of Captain Walerian Jasionkowski's improvised escadre, the patrouille DAT (Défense Aérienne du Territoire) based at Salon and Clermont-Aulnat. As delivered, the fighters were not armed and the Poles had to acquire machine guns and fit them. From 30 May 1940, they were used in the defence of French cities, patrolling in Avignon - Marseille area, then from Clermont-Ferrand, without any encounters with the enemy. The type's service life was short-lived with only 47 or so operational sorties recorded; the unit had no confirmed victories, but at least one F.K.58 was lost. After the fall of France, all surviving airframes were scrapped.

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 build.
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.
Operators
 France
Armee de l'Air
 Poland
Polish Air Forces in exile in France
Eskadra "Koolhoven" operated eight aircraft, probably all were FK.58A variant.