Nakajima Homare

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Nakajima Homare engine

The Nakajima Homare (誉, "praise" or, more usually, "honour") was a Japanese aircraft engine manufactured during World War II. It was an air-cooled radial engine in the 2000-HP class, and was used widely by both the Imperial Japanese Army and the Imperial Japanese Navy. "Homare" was the navy service designation, and their experimental designation for it was NK9; the army called it the Ha-45 (ハ45) or, in service, the 1900hp Type 4. The manufacturer's designation was BA (or NBA).

Development of the 18 cylinder twin-row 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.