Nakajima Homare

Nakajima Homare
Nakajima Homare engine
Type Piston aircraft engine
Manufacturer Nakajima Aircraft Company
Designed by Ryoichi Nakagawa
First run 1941
Major applications Nakajima Ki-84, Kawanishi N1K-J, Yokosuka P1Y, Nakajima C6N
Number built 9,089
Developed from Sakae

The Nakajima Homare (誉, "praise" or, more usually, "honour") was an air-cooled twin-row 18 cylinder radial Japanese aircraft engine manufactured during World War II. Producing almost 2,000 horsepower, it was used widely by both the Imperial Japanese Army and the Imperial Japanese Navy. NK9 "Homare" was the navy service designation, and their experimental designation for it was NBA; the army called it the Ha-45 (ハ45) or, in service, the Nakajima Army Type 4 1,900 hp Air-Cooled Radial. According to unified designation code it was also Ha-45.[1]


Design and development

Development of the Homare started in 1940, and certification was completed in 1941. It succeeded Nakajima's previous 14 cylinder Sakae (Ha-25) engine, with its forward nine cylinders staggered from the rear nine for efficient cooling.

The design was exceptionally compact, with an external diameter of 118 cm, a mere 3 cm larger than the Sakae. With a bore and stroke of 130 mm x 150 mm, it was classified as a short-stroke engine. It was designed to output around 1800 hp (1340 kW), or 100 hp (75 kW) per cylinder. However, the tight design of the engine made it difficult to maintain quality in manufacturing, and unreliability in the field was a significant problem; actual output of early models at altitude was in the range of 1300 hp (970 kW), far below the designed capability. Later models had improved performance, and it became one of the predominant powerplants of Japanese military aircraft in the latter part of the war. A total of 8,747 were produced.


  • Homare 11 - 1,650 hp (1,230 kW) , 1,820 hp (1,357 kW) , 1,900 hp (1,417 kW)
  • Homare 12 - 1,825 hp (1,361 kW)
  • Homare 21 - 1,990 hp (1,484 kW)



Data from Jane's[2]

General characteristics

  • Type: 18-cylinder air-cooled twin-row radial engine
  • Bore: 130 mm (5.12 in)
  • Stroke: 150 mm (5.91 in)
  • Displacement: 32 L (1,940 in³)
  • Length: 1,778 mm (70 in)
  • Diameter: 1,182 mm (46.5 in)
  • Dry weight: 830 kg (1,830 lb)


  • Valvetrain: push rod operated overhead-valve system with 2 valves per cylinder
  • Supercharger: Two-speed single stage centrifugal
  • Fuel system: Water-methanol injection
  • Cooling system: Air-cooled


See also

Comparable engines
Related lists



  1. ^ Gunston 1989, p.105.
  2. ^ Jane's 1989, p.298.


  • Jane's Fighting Aircraft of World War II. London. Studio Editions Ltd, 1998. ISBN 0-517-67964-7
  • Gunston, Bill. World Encyclopaedia of Aero Engines. Cambridge, England. Patrick Stephens Limited, 1989. ISBN 1-85260-163-9

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