Koolhoven FK.56

History

The Koolhoven Fk.56 was developed in response to the needs of the LVA new training aircraft for the advanced training.

For the construction of the prototype, construction number 5601 and (later) civil registration PH-ASB, the hull of a FK.51 was used.

The centre section was removed and replaced with a new part, with two cockpits with one canopy and a gull wing (Frits Koolhoven had an unjustified dislike of low-deckers, the gull wing was a kind of compromise). On June 30, 1938 the first flight was made and in the autumn the Fk.56 was offered to the LVA for testing.

The type was compared with the Focke-Wulf FW.56 Stösser.

The Koolhoven was chosen and a first order for ten aircraft placed.

A second prototype, construction number 5602 and civil registration PH-ATE, was built with some adjustments, e.g. a retractable undercarriage, a Amrstrong-Siddeley Cheetah engine, a modified fuselage, enlarged rear cockpit with possibility for applying a machine gun and a adjustable canopy, now more in line with that of the Koolhoven Fk.58.

Also a third prototype was built, a pre production version for the LVA, with construction number 5603.

Led by ir Schatzki, who had worked for Fokker, a number of changes have been made; the engine became a Wright Whirlwind of 420 hp, the tail was modified and became identical to that of the Fk.58 and the gull wing was replaced by a straight wing, which was quite high joined to the fuselage and the retractable undercarriage was further improved and customized.

On January 4, 1940 was a last test flight was made. Because of flutter the wing broke off and the aircraft crashed.

The cause proofed to be lack of using diagonal laminated plywood. The wings were also modified and built with diagonal plywood.

A new copy with construction number 5613 was built. Before the crashed device

Meanwhile Koolhoven had received an order for twenty aircraft from Belgium. The LVA also placed  a follow-up order for another ten examples.

Because of the war not all aircraft were delivered.