Imperial Japanese Army

Kawasaki Ki-64

Designers at times relish the freedom to let their visions develop and flow from the drafting board to the tarmac, ready to take to the skies. Takeo Doi, working for Kawasaki, was just such a designer. Despite the very real work developing, testing and producing combat air­craft for the IJA, Doi had a concept that he, on his own, brought to the fore. Initially, the IJA would not hear of the design but later, when the Ki-64 took shape, their mind would change.

In 1939, Doi was involved with two Kawasaki programs: the Ki-45 Toryu and the

КІ-60/КІ-61 Hein. The Ki-45 was proving to be a horribly troublesome aircraft. Problems with the landing gear, concerns with drag, engine difficulties and more were proving a thorn in Kawasaki’s side. It was Doi who stepped in to solve the issues plaguing the initial Ki-45 design. In addition to working to fix the floundering Ki-45, by 1940, Doi was involved with the preliminary develop­ment of the Ki-60 heavy fighter and the Ki-61 Hein.

Even with such responsibilities, Doi had a design of his own for a high-speed fighter. His concept incorporated a number of novel fea­
tures which were perceived as rather unorthodox in comparison to other more conventional types. Since Koi’s aircraft was purely his own and not created to meet any sort of specification, Koi would be disap­pointed when the IJA forbade Kawasaki giv­ing any further time to the design.

Doi’s disappointment then turned to joy when, in October 1940, the IJA authorised Kawasaki to proceed with developing the Ki-64 to meet a requirement for a fighter capable of a maximum speed of 700km/h at 5,000m (435mph at 16,405ft) and a 5 minute climb to that height.

To power the Ki-64, Doi would enlist the help of fellow engineers employed by the Akashi engine plant. The decision was made to use the Kawasaki Ha-201 ([Ha-72] 11) engine. This was actually a combination of two Ha-40 engines, the Ha-40 being the licence-built version of the Daimler-Benz DB601A. Each Ha-40 was a 12-cylinder, liq­uid-cooled powerplant and the Ha-201 was formed through having one engine in front of the cockpit and the second behind it. The rear engine drove the first of the contra-rotating propellers and it had a variable pitch. The front engine drove the second propeller, which was of a fixed pitch. Both propellers were three-bladed. All told, the Ha-201 was expected to produce 2,350hp.

The use of the Ha-201 was not the most novel feature of the Ki-64. It was the means of cooling the engine that was notable. The Ha-201 was to be cooled by a steam con­densing system. A tank of 15.4 gallons of water was fitted into each wing and the outer wings and flaps served as the cooling surface, totalling 23.99m2 (258.3ft2). The port wing ser­viced the front engine while the starboard wing provided coolant to the rear engine. As the water coolant turned to steam, it was pumped out into the wings where the steam would condense back into water which in turn was pumped back into the engine. The main benefit of this system was lower drag on the airframe as the need for air inlets was removed or minimised. Each laminar flow wing housed the fuel tanks and one 20mm Ho-5 cannon while two more were fitted in the fuselage deck. One drawback to the wings being packed with the cooling system apparatus was that it left little room for the fuel tanks and consequently the Ki-64’s oper­ational range suffered. The majority of the fuel was carried in the fuselage, the tanks being placed in and around the space left available by the Ha-201 engine. The main fuel tank was situated in front of the cockpit, hold­ing 306.7 litres (81 gallons). Under it was the oil reservoir, holding 79.5 litres (21 gallons) of oil for the engines. Behind the cockpit were
two coolant tanks holding 83.3 litres (22 gal­lons) and 117.4 litres (31 gallons) respec­tively. The smaller serviced the front engine, the larger the rear engine.

Doi tested the Ha-201 and the cooling sys­tem to a considerable degree. In 1942, one of the Ki-61 Hein fighters was specially modified to test the cooling method and its trial flights began in October 1942 and ran through to the end of 1943. Because of this thorough testing, the construction of the Ki-64 was delayed and so did not reach completion until December

1943. Nevertheless, Doi was satisfied that the cooling system would grant an additional 41 km/h (25mph) to the Ki-64 and battle dam­age would not significantly reduce the effec­tiveness of it and as such the exhaustive testing was worth the effort.

With the Ki-64 complete, flight testing com­menced in December 1943. Four test flights were successfully made without mishap. However, on the fifth, the rear engine caught fire. The test pilot was able to land the aircraft and the fire was quenched. Mechanics stripped the engine out of the Ki-64 and returned it to the Akashi plant for a full repair. The Ki-64 itself was returned to the city of Gifu which, at the time of World War 2, was a major industrial centre.

Plans were made to improve the Ki-64 by replacing the 2,350hp Ha-201 with an enhanced model that could generate up to 2,800hp. The propellers would be replaced with two, constant-speed contra-rotating pro­pellers that were electrically operated. It was envisioned that with these modifications, the Ki-64 Kai would be able to attain a top speed of 800km/h (497mph).

Unfortunately for the Ki-64, repair work lan­guished, especially in the face of more press­ing needs for the Japanese arms industry and the production of more conventional aircraft. As a result, both the Ki-64 and the Ki-64 Kai were cancelled. After Japan’s surrender, the Ha-201 was still at Akashi, its repairs incom­plete. When US forces arrived in Gifu, the Ki-64 was found and technical teams gutted the airplane of its cooling system. The system
was then crated and shipped to the United States for study at Wright Field in Dayton, Ohio.

Given the relatively long development time of the Ki-64, US intelligence had already become aware of the design. Thus, expecting the Ki-64 would see service, the airplane was assigned the codename Rob.