On 8 September 1943, instructions were issued to redesign the Nakajima Ki-84 Hayate all-metal single-seat fighter for wooden construction because of the increasingly critical light alloy supply situation. The task of redesigning the airframe was assigned to the Tachikawa Hikoki which was to collaborate with the Army Aerotechnical Research Institute at Tachikawa.
Assigned the designation Ki-106, the wooden fighter was intended to utilise a high proportion of semi-skilled labour in its construction and to be broken down into components to be built by small wood-working shops grouped around designated assembly points.
Prototype construction was sub-contracted to Ohjo Koku, but the first of three prototypes was not flown until July 1945. The external characteristics of the Ki-84 were faithfully retained by the Ki-106, apart from some minor revision of the vertical tail, the first prototype being powered by the 2,000 hp Nakajima Ha-45-21 engine and carrying an armament of four 20-mm cannon. Appreciably heavier than the standard Ki-84, the Ki-106 was subjected to various weight saving measures, one of these being a reduction in the armament to two 20-mm cannon, and the second prototype flew with this armament during the last week of the war.
Engine: 2,000 hp Nakajima Ha-45-21
Length 32 ft 7 in (9.92 m)
Wing span: 36.8 ft (11.21 m)
Height: 3.59 m / 11 ft 9 in
Wing area: 21 sq.m / 226.04 sq ft
Max take-off weight: 3900 kg / 8598 lb
Empty weight: 2948 kg / 6499 lb
Max. speed: 620 km/h / 385 mph at 21,325ft (6 500m)
Range (+1.5 hr res): 800 km / 497 miles
Time to 16,405ft (5 000m): 7.85min