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Hirth HM 504
Hitachi Hatsukaze Model 11 / GK4 / Ha-47



The Hirth HM 504 is a four-cylinder air-cooled inverted inline engine. The 504 was a popular engine for light aircraft of the 1930-40s and it was used to power a number of Germany's trainer aircraft of WWII. The engine featured a cast magnesium alloy crankcase. The Hitachi Hatsukaze Model 11 was a Japanese licensed version.


The Hitachi Hatsukaze also known as the Hitachi model GK4, was Hitachi's fourth design in a series of aircraft engines built in Japan prior to and during World War II. The original Hatsukaze was a license-built Hirth HM 504. Hatsukazi engines were air-cooled, four-cylinder, inverted inline engines developing around 82 kW (110 hp).

Hatsukaze engines were produced in very large numbers, as the powerplant for the license-built Bücker Bü 131 Jungmann variants that were the standard primary trainers for the Imperial Japanese Navy and Imperial Japanese Army.

The naval version of the engine was designated GK4, the army version as Ha-47. 1,376 were built.

The Hatsukaze Model 12 was the power section linked to a compressor to create a primitive jet engine called a motorjet, the resulting Tsu-11 was intended to power Yokosuka MXY7 Ohka 22 flying bombs. The standard Hatsukaze 11 engine was modified at a Navy arsenal by replacing the propeller drive shaft and engine front crankcase cover with a step-up gearbox. The gearbox increased engine output shaft RPM at a 1:3 ratio. At engine speed of 3,000 RPM, the compressor section was operating at 9,000 RPM. The compressed air was then ducted into a combustion chamber where a liquid fuel was sprayed. The heated compressed air then exits through the tailpipe providing static thrust of 180 kg (396 lb). It is likely that about 1/3 of the total thrust was contributed by adding the combustion chamber aft of the compressor.

The Tsu-11 was also selected to power the Yokosuka MXY-9 Shuka ("Autumn Fire"), a trainer intended to prepare pilots for the Mitsubishi J8M rocket-powered interceptor. Neither of these aircraft entered service, however, as their development took place too late in the war.


GK4 Hatsukaze
license-built Hirth HM 504 inverted inline four-cylinder aviation engine.

GK4A Hatsukaze 11
82 kW (110 hp) IJN version, 339 built

GK4A Ha-47 11
82 kW (110 hp) IJA version, 1,037 built

Hatsukaze Toku ("Toku" translates as "special") Model 13
power section for the Ishikawajima Tsu 11 Motorjet engine


Bücker Bü 131
Bücker Bü 181
Klemm Kl 35
Morane-Saulnier MS.603
Repulogpegyar Levente II
BŻ-1 GIL (helicopter)
Kyushu K9W1 Type 2 Momiji ("Cypress") license built Bücker Bü 131s.
Kokusai Ki-86 Type 4 ("Cypress") license built Bücker Bü 131s.
Yokosuka MXY7 Ohka 22 (Tsu-11)
Yokosuka MXY-9 Shuka (Tsu-11)



HM 504
Type: 4-cylinder air-cooled inverted inline
Bore: 105 mm (4.13 in)
Stroke: 115 mm (4.53 in)
Displacement: 3998 cm3 (244 cu in)
Length: 957 mm (37.70 in)
Width: 505 mm (19.90 in)
Height: 726 mm (28.60 in)
Dry weight: 104 kg (230 lbs)
Valvetrain: 1 inlet and 1 exhaust valve per cylinder
Fuel type: 77 octane
Cooling system: air
Power output: 105 hp at 2500 RPM
Compression ratio: 6.00:1


Hatsukaze GK4A
Type: 4-cylinder air-cooled inline piston engine
Bore: 110 mm (4.13 in)
Stroke: 125 mm (4.53 in)
Displacement: 3,998 cm3 (244 in3)
Length: 1,070 mm
Width: 200 mm
Dry weight: 115 kg
Cooling system: Air-cooled
Power output: 82 kW (110 hp)
Compression ratio: 5.8:1


Power-to-weight ratio: 2.87 lb/hp at cruise speed



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