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.
Design and development
In 1937, the French Conseil Supérieur de l'Air decided that domestic aircraft manufacturing capacity could not, in the event of war, equip the Armée de l'Air with fighters quickly enough. The Dutch manufacturer Koolhoven was contracted to design a cheap, easily built, high-performance fighter, that could be built and serviced with French-supplied engines and other components. According to some sources, the Koolhoven fighter was intended primarily for fighter units based in French colonies. The prototype Koolhoven Model 1166, designed by Erich Schatzki, flew for the first time on 17 July 1938. The structure of the fuselage consisted of welded steel tubing covered with sheet metal and fabric ; the wing had 2 wooden box spar members and ribs, with a bakelite stressed skin covering. Aerodynamically balanced split flapson 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. Production was transferred to Nevers, where the aircraft were re-built with French components and the extraneous parts were returned to the Netherlands. However, only one more F.K.58 was produced from scratch at Nevèrs. In July 1939, the Dutch government placed an order on behalf of the Luchtvaart Afdeling for 36 F.K.58 variants, 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. The lower output of the Mercury, relative to the Taurus, would have reduced top speed to some. 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. The F.K.58s that became operational were regarded as superior to the Morane-Saulnier M.S.406, comparable to the Bloch MB.151,, but inferior to the Dewoitine D.520 and the latest German fighters.
Operational history
The F.K.58 was originally ordered to serve with AdA units based in French overseas territories. Following the outbreak of war with Germany, however, the type was assigned to an ad hoc, Free Polish air force unit commanded by Captain Walerian Jasionowski. Roughly equivalent to a French escadrille, or Polish eskadra, it was often known by the unofficial name "Eskadra Koolhoven". The unit's official role was patrouille – as the AdA designated units that defended rear areas against long-range bombers and other enemy aircraft, as part of the Défense Aérienne du Territoire. The unit operated from the Salon and Clermont-Aulnat air bases. By May 1940, 13 aircraft were operational with Eskadra Koolhoven. As delivered, however, the fighters were unarmed and the Poles had to acquire machine guns and fit them. From 30 May 1940, they were in service, patrolling firstly in the Avignon-Marseille area, and then over Clermont-Ferrand. At least 47 operational sorties were recorded, but the Escadron did not encounter enemy aircraft. The type's service life was short-lived, with ; 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.
