Ki.78
The Aeronautical Research Institute of the University of Tokyo (Koken) was working since 1938 on the design of an experimental aircraft capable of flying at 850 kph powered by a DB 601 German engine. The project was known as Ken-3, for Kensan (Research), the airframe had been carefully designed with laminar flow wings and one streamlined fuselage made as narrow as possible. One 60 hp auxiliary engine, driving a cooling fan would be installed behind the cockpit to improve the performance of the two ‘P-38 style’ radiators located inside the fuselage.
Following the presentation of the wooden mock-up to the IJA in May 1941, the Ken-3 received the Kitai number Ki.78 and the construction of the prototype began four months later. The Ki.78 was flown on December 1942 powered by one DB 601A-Kai Methanol-water boosted to 1,550 hp, for short periods.
On April 1943, at the same time when the Ki.61-I entered combat over New Guinea, the Ken-3 experimented tailplane flutter at the relatively low speed of 635 kph. The problem was cured fitting a horn-balance to the elevator. Early 1944, the prototype reached a top speed de 704 kph, but the IJA considered that the foreseen 850 kph in the initial design could only be reached with more powerful engines. The construction of the 2nd prototype was cancelled on 11 January 1944.
The high-speed research programme was dropped on 1 February 1945 when Kawasaki stopped the manufacturing of the Ha-140 V-12 engine.
Ki.78 technical data
Wingspan: 8.00 m, length: 8.10 m, height: 3.07 m, wing area: 11.00 sqm, max speed: 704 kph, max weight: 2,300 kg, ceiling: 8,000 m.