Aichi Ha-70

Aichi Ha-70
DB 610 gearbox end, showing same two-engine arrangement
Type	Piston X 2 inverted V12 aircraft engines
National origin	Japan
Manufacturer	Aichi
First run	1945
Major applications	Yokosuka R2Y
Developed from	Aichi Atsuta

The Aichi Kokuki KK Ha-70 was a compound engine composed of two 1,700 hp 12-cylinder liquid-cooled inverted V-12 Aichi Atsuta aircraft engines mounted to a common gearbox. The only aircraft powered by the Ha-70 was the Yokosuka R2Y, an Imperial Japanese Navy Air Service (IJNAS) prototype reconnaissance aircraft that was designed and built near the end of World War II.

In common with Daimler-Benz, Aichi Kokuki KK joined two Aichi Atsuta engines to drive a single propeller through a combining gearbox in very similar fashion to the Daimler Benz DB 606 (two Daimler-Benz DB 601 engines coupled to a gearbox),

The Yokosuka R2Y prototype reconnaissance aircraft required a new engine of 3,400 hp (2,535 kW) and after studying the Daimler-Benz DB 606A-2 engine that powered the Heinkel He 119 single-engine reconnaissance bomber, Aichi determined that the required horsepower could be attained by coupling two Atsuta engines with a common gearbox. To obtain the required power the Atsuta would require up-rating by at least 300 hp (224 kW) horsepower; Aichi continued to improve the Atsuta 32, eventually extracting the required 1,700 hp (1,268 kW)

The two inverted Vee Atsuta engines were mounted side-by-side, each rotated outboard from the centre-line so that the inner banks were upright, with sufficient room between them for the exhaust manifolds. The engines were attached to a gearbox that combined the two separate engine drives into a single output shaft.

Fitted to the R2Y the Ha-70 was mounted behind the pilot, requiring a long drive shaft to drive the nose-mounted gear box that mounted the six-bladed propeller.

Data from The First Naval Technical Arsenal, August 22, 1945

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