The Kawasaki Ki-66 was a twin-engined dive bomber designed after the German successes in Poland and France in 1939-40, but that never entered production.
The Kawasaki Ki-66 was very similar to the more successful Kawasaki Ki-45 Toryu heavy fighter and Kawasaki Ki-48 light bomber. All three aircraft were mid-wing twin-engined monoplanes, with a single vertical tail. All three had long cockpits, with glazed sections at the front and rear. The Ki-66 fell between the older aircraft in size, being larger than the Ki-45 but smaller than the Ki-48. The fuselage was less angular than that of the K-45, and less bulky than the Ki-48. The glazed nose of the Ki-48 was replaced with a solid nose carrying the fixed forward firing guns.
The Ki-66 was designed to satisfy a Japanese Army specification issued after the successes of the German Stukas over Poland and France. The specification was issued in September 1941, and called for a twin engined aircraft, armed with two fixed forward firing 12.7mm machine guns and one flexibly mounted rear firing 7.7mm machine gun. It was to be capable of carrying 661lb of bombs normally or 1,102lb at overload.
Kawasaki's designer Takeo Doi began work on the new aircraft in October. The aircraft used two 1,130hp Nakajima Ha-115 engines, and carried one extra gun - a flexibly mounted ventral gun. It was a two-seater, with a pilot and radio-operator/ gunner, so only one of the two rear firing guns could be used at any one time.
The first of six prototypes was completed in October 1942, and the last in April 1943. In trials the aircraft proved a disappointment. Its top speed was only slightly higher than that of the Ki-48-II (314mph on the Ki-48, 332mph on the Ki-66), and so it wasn't placed into production.
The dive-brakes were used on the Ki-48-IIb and a number of alternative configurations were suggested in an attempt to save the project. One prototype of the Ki-66-Ib, powered by two 1,360hp Nakajima Ha-315-I radials was completed by modifying one of the existing prototypes. Two more dive-bomber versions with more powerful engines, the 2,100hp Nakajima Ha-39 powered Ki-66-Ic and 1,900hp Nakajima Ha-45 powered Ki-66-Id, were proposed but not built. A heavy fighter version, the Ki-66-II, was also designed, but never built.
Engine: Two Army Type 1 (Nakajima Ha-115) 14 cylinder air cooled radials
Power: 1,130 at take off, 1,100hp at 9,350ft, 940hp at 18,370ft
Wing span: 50ft 10 ¼ in
Length: 36ft 8 15/16in
Height: 12ft 1 21/32in
Empty Weight: 9,039lb
Loaded Weight: 12,677lb
Max Speed: 332mph at 18,370ft
Service Ceiling: 32,810ft
Range: 1,243 miles
Armament: Two fixed forward firing 12.7mm machine guns, two flexibly mounted rear firing 7.7mm machine guns, one dorsal and one ventral
Bomb-load: 661lb normal, 1,102lb maximum