Kawasaki Ki-91

By 1943, the bombers then in service were not adequate to the task. For too long Japanese designers remained with twin engined bombers and these had reached a point where no more capability could be squeezed out of them, regardless of modifications tried. Service aircraft such as the Nakajima Ki-49 Donryu ( Storm Dragon ) and the older Mitsubishi Ki-21 "Sally" could not keep pace with and survive in the face of allied fighter power. The Mitsubishi Ki-67 Hiryu ( Flying Dragon ) proved better able to cope to a degree but it arrived in the war area much too late to make much of an impact. What was needed was something more capable with a greater range, heavier bomb load, and most importantly, something faster than those bombers in the field. And to do this required the use of more engines.

While the Navy struggled with the Nakajima G8M Renzan ( Mountain Range ) four engined bomber ( which was hampered by allied air attacks and material shortages ), Kawasaki undertook a four engined design for the Army and this was the Ki-91.

Kawasaki began investigating this design in May of 1943 but progress was slow. The Ki-91 featured a fully pressurized cabin and had a radius of action of 2,796 miles with a 8,818lb. bomb load. While this range was 436 miles more than the Ki-67 Hiryu, the bomb load able to be carried by the Ki-91 was 7,053lbs. more than the Ki-67, a substantial payload improvement. If the bomb load was less, a maximum range of 6,214 miles could have been reached. The estimated speed of 360mph for the Ki-91 was 26mph faster than the Ki-67. All around, the Ki-91 was proving to be a superior airplane to the best of the bombers then in service.

The defensive armaments for the Ki-91 were heavy, easily outgunning the weapon fits of the Ki-67. There were five power-operated turrets, all but one of them mounting two 20mm cannon. The remaining turret, mounted in the tail, was equipped with four 20mm cannon. There was a turret in the nose, one on the top of the fuselage, and two beneath the fuselage along with the tail position.

The engine array consisted of four Mitsubishi Ha-214 Ru engines, each developing 2,500hp which would drive the plane at its maximum speed of 360mph. Two engines were mounted in each wing in streamlined cowling/nacelles.

Overall, the Ki-91 would have been 108ft . and 3in. long, have a span of 157ft. and 5in., and have a loaded weight of 127,868lbs.

As mentioned, for one reason or another, progress on getting the Ki-91 from the drafting table to flying prototype lagged. The prototype was partially complete by 1945 but a bombing raid by U.S. B-29s in February of 1945 destroyed the tools and jigs needed to complete the Ki-91 and prepare the design for production. With the required materials gone, work on the Ki-91 ceased.