Aichi Ha-70

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

The Aichi 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.^[1]

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^[2]

• Type: Two coupled twelve-cylinder liquid-cooled supercharged 60° inverted Vee aircraft piston engines
• Bore: 150 mm (5.91 in)
• Stroke: 160 mm (6.30 in)
• Displacement: 33.93 L (2,070.5 in³) each, 67.86 L (4141 in³) total

• Valvetrain: Two intake and two sodium-cooled exhaust valves per cylinder actuated via a single overhead camshaft per cylinder block.
• Supercharger: Gear-driven single-speed centrifugal type supercharger^[3]
• Fuel system: Direct fuel injection
• Oil system: Dry sump with one pressure and two scavenge pumps
• Cooling system: Liquid-cooled

• Power output: Takeoff: 2,500 kW (3,350 horsepower)

Comparable engines

• Allison V-3420
• Daimler-Benz DB 610

Related lists

• List of aircraft engines
• List of aircraft engines in use by Japan during World War II
• List of Aircraft engines used by Japanese Navy Air Service

• Monogram Close-Up 13 ISBN 0-914144-13-8
• R. J. Francillon, Japanese Aircraft of the Pacific War (1970 Putnam & Company) SBN 370 00033 1

• Wilkinson, Stephan (Jan 2003) 'With the Noise of a Stone Crusher', Popular Science
• NASM 'Aichi M6A1'