The Aichi Kokuki KK AE1A Atsuta (Japanese:アツタ or 熱田) was a Japanese licensed version of the German Daimler-Benz DB 601A 12-cylinder liquid-cooled inverted-vee aircraft engine. The Atsuta (first rn in 1942) powered only two models of Imperial Japanese Navy Air Service (IJNAS) aircraft aircraft in World War II. The Imperial Japanese Army Air Service (IJAAS) used the same engine (manufactured by Kawasaki as the Ha-40) to power its Kawasaki Ki-61 Hien (Allied reporting name "Tony") fighter. Contents
Daimler-Benz granted Aichi Kokuki KK, a part of the Aichi Clock and Electric Co. (Aichi Tokei Denki KK), a license to manufacture the DB 600A through D models in November, 1936. At that time the Aichi Aircraft Company was building only the Nakajima Kotobuki 9-cylinder air-cooled radial engine at its Atsuta Engine Plant, located in south central Nagoya. It was necessary to re-tool the factory for the production of the new Daimler-Benz engine. Two DB-600 series engines were imported that year and three the next, all to be used as production patterns.
It was the Imperial Japanese Navy's common practice to use a coded designation while an engine was in experimental or pre-production status. This engine was coded "AE1A", which decodes as: A=Aichi Tokei Denki KK, E=Liquid-cooled, 1=Aichi's first liquid-cooled engine model, and A=first version of that engine model. It was the Imperial Japanese Navy's common practice to refer to its engines by name, while the Imperial Japanese Army referred to its engines by their engine (Japanese: Hatsudoki abbreviated Ha) model number. Ha numbers were assigned in sequence as the engine design was accepted.
The Japanese method of identifying model numbers of aircraft engines is unique in that the model number always has two digits and may be followed by one or more letters. The first digit represents the major version of the engine and the second number represents the minor version of that model engine. The model number follows the name (IJNAS engines) or the Ha number (IJAAF engines).
The first model number assigned to an engine is always 11, meaning the first major design and first minor version of that design. A major change to the design increments the first number and resets the second number to one. A minor change to the engine model increments the second number by one. If a very minor change is made, suffix letters are added after the model number.
When the AE1A engine was accepted by the IJNAS, its coded designation was dropped and a name was chosen. It is from the Atsuta factory that the engine name was derived.
The first production engine was the Atsuta 12 rated at 1200 hp. The model number 12 indicates this was the first model with one minor change.
By early 1938 the Japanese Navy had also acquired the German He 118 V4 two-seat dive bomber aircraft, along with its production rights. This aircraft was powered by the DB 601A. By 1939, eleven of the more advanced model DB 601A engines were imported. Manufacturing rights were updated for Aichi and granted to Kawasaki to build this model. The new engine received AE1P as its experimental designation.
When the AE1P design was accepted, Aichi's version became the Atsuta 32 and Kawasaki's version became the Ha-40.
The Atsuta 12 rated at 1200 hp was chosen to power the Yokosuka D4Y1 when it went into production. The D4Y2 was powered by the 1400 hp Atsuta 32 when it became available. The success of both airplanes was attributed to the slender lines of the high powered liquid-cooled engine.
A new top-secret aircraft that was to be transported and launched from a large submarine was ordered by the IJN in the spring of 1942 as the 17-Shi Special Attack Bomber. That aircraft became the Aichi M6A Serian (Shisei-Seiran), along with its M6A1-K Ninzan (Shisei-Seiran Kai) land-based trainer version.
Four preproduction M6A aircraft were completed, a firsthand account stating that one had a 1,200 hp Atsuta 12 engine, while the others three had Atsuta 32's. The first aircraft's engine was later changed to an Atsuta 32.
Eighteen M6A1 Special Attack Bomber versions followed, and these had the Atsuta 32 engine as well. Lastly, two of the original M6A1 prototypes were converted into M6A1-K Nanzan land-based training aircraft.
Aichi manufactured 873 Atsuta series engines during World War II. These were shared between the twenty-two M6A1/M6A1-K and all D4Y1/2 aircraft. Peak production of the Atsuta 32 engine was in May, 1944, when 107 engines were produced.
A serious problem with the Aichi and Kawasaki version of the Dailmer-Benz engine was that that of holding a close tolerance fit between the crankshaft and its bearings on this fairly long engine. The result was that the engine proved to be prone to crankshaft failure. Additionally, there was often great difficulties obtaining engine components which, along with repeated air attacks on the Atsuta engine plant, eventually brought engine production to a standstill.
Maintenance difficulties with the Atsuta and Ha-40 engines eventually led to the installation of the more reliable Mitsubishi Kinsei 62 radial engine for the D4Y3 model 33, and the Mitsubishi Ha-112 radial air-cooled engine for the Army's Kawasaki Ki-61, which then became known as the Ki-100 Type 5 Fighter. Such a modification was not possible for the M6A1 as it could only use the liquid-cooled inverted-vee type engine, as it had to fit the submarine's confined hangar. The M6A1 Seiran then became the only Japanese airplane that retained the inverted-vee engine installation throughout the war.
Postwar evaluation by the Air Technical Service Command's Foreign Aircraft Evaluation Center for the Air Force (located at Wright Field and Freeman Army Airfield) found the Atsuta engine's standard of workmanship was not as good as that of the Army's Kawasaki Ha-40, and far worse than Mitsubishi and Nakajima.
Type: Twelve-cylinder liquid-cooled supercharged 60° inverted Vee aircraft piston engine
Bore: 150 millimetres (5.91 in)
Stroke: 160 millimetres (6.30 in)
Displacement: 33.93 L (2,071 cu in)
Length: 215 cm (84.65 in)
Width: 71.2 cm (28.03 in)
Height: 106 cm (41.73 in)
Dry weight: 715 kg (1,576 lb)
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
Fuel system: Direct fuel injection
Oil system: Dry sump with one pressure and two scavenge pumps
Cooling system: Liquid-cooled
Reduction gear: 0.532:1 (AE1A); 0.4:1 (AE1P)
Takeoff: At sea level: 1,400 hp (1,419 PS) at 2,800 rpm
Cruise: At 1,700 m (5,600 feet): 930 kW (1,250 hp) at 2,600 rpm (AE1A)
Cruise: At 1,000 kW (1,340 hp) at 2,600 rpm (AE1P)
Cruise: At 5,000 m (16,000 feet): 960 kW (1,290 hp) at 2,600 rpm (AE1A)
Compression ratio: 7.2:1 (AE1A); 7.5:1 (AE1P)