Nakajima Ha5

Ha-5
Type	14-cylinder, air-cooled, two-row radial piston engine
National origin	Japan
Manufacturer	Nakajima Aircraft Company
Major applications	Mitsubishi Ki-21 Mitsubishi Ki-30 Mitsubishi Ki-57 Nakajima Ki-49 (Ha-41/Ha-109) Nakajima Ki-44 (Ha-41/Ha109)
Developed into	Nakajima Sakae

Nakajima Ki-44 (Ha-41/Ha109)

The Nakajima Ha-5 is a twin row, 14 cylinder air-cooled radial aircraft engine built by the Japanese Nakajima Aircraft Company. The engine was a development of earlier single-row Japanese engines, the Kotobuki and Hikari, which had combined features of the Bristol Jupiter and Pratt & Whitney R-1340 Wasp designs. First introduced in a 1,000 PS prototype in 1933, about 7,000 civilian and 5,500 military Ha-5's were built during World War II. The Ha-5 had separate cam-discs for the front and rear rows of cylinders like American designs, rather than using a single, front-mounted cam-disc with long and short pushrods to operate both rows of cylinder valves. The Ha-5 was a twin-row development of the Nakajima Hikari, which was itself a development of the Nakajima Kotobuki. It spawned several improved variants, namely the Ha-41, with a single stage supercharger, and the Ha-109, which featured a two-speed, single stage supercharger. The later Ha-219 was based on the same cylinder design, but was increased in size to 18 cylinders.

In 1917, Chikuhei Nakajima set up the "Airplane Institute" at Ojima Town in Gunma Prefecture. In 1918 they built their first airplane; the "Nakajima Type 1" with a U.S.A. made engine. In 1920 the company sent Kimihei Nakajima to France to study European advances, and in 1922 started their own engine factory in Tokyo. This led to production of engines based on the Lawrance A-3 two-cylinder air-cooled horizontally opposed engine.

At the time the Lawrance was an oddity. Most air-cooled engines at that time were rotary engines, using cylinders that rotated together with the propeller with a fixed crankshaft, in order to improve cooling but Kimihei overheard that an engine with good cooling capability with stationary cylinders was being developed in England: a radial engine. He observed the English Gloster Gamecock fighter with its Bristol Jupiter engine, which was an advanced design for the era with an automatic adjustment device for tappet clearance, spiral intake piping for even charge air distribution, and a four-valve intake and exhaust system. He acquired a manufacturing license for the Jupiter in 1925. In 1927, after inviting two production engineer instructors from the Bristol company, the Jupiter Type 6 of 420 PS and Type 7 of 450 PS with a supercharger were put into production at the Nakajima factory.

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