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Nakajima Ha-45 Homare
Nakajima NK9
Nakajima NBA
Nakajima Type 4



The Nakajima Homare (誉, "praise" or, more usually, "honour") was an air-cooled twin-row 18 cylinder radial Japanese aircraft engine. Given the Navy service designation NK9, the "Homare" was also given the company designation NBA, Army experimental designation Ha-45 (ハ45) or, Army long designation Nakajima Army Type 4 1,900 hp Air-Cooled Radial and, (coincidentally), unified designation code of Ha-45.

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

The design was compact, with an external diameter of 118 cm. 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)


Aichi B7A
Kawanishi N1K-J
Mitsubishi A7M
Nakajima C6N
Nakajima G8N
Nakajima Ki-84
Yokosuka P1Y1


Type: 18-cylinder air-cooled twin-row radial engine
Bore: 130 mm (5.12 in)
Stroke: 150 mm (5.91 in)
Displacement: 32 lt (1,940
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
Power output: 1,485 kW (1,990 hp) at altitude
Specific power: 46.4 kW/L (1.02 hp/
Compression ratio: 7.0
Power-to-weight ratio: 1.79 kW/kg (1.09 hp/lb)




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