Walkaround - Nakajima NK1F Sakae 21 engine

Walkaround - Nakajima NK1F Sakae 21 engine
RAF Cosford Museum
November, 9th, 2018.

The Nakajima Sakae (Prosperity) 21 engine was a 14 cylinders, double row air cooled engine used by a number of important combat aircraft of Imperial Japanese Navy and Army during World War II. The version 21 was probably the most used version of this engine, and it had variations in the Sakae (NK1) and Homare (Ha) family.

A small number of original Sakae power plants are on display in aviation museums, usually mounted into the airframes of restored Mitsubishi A6M Zeros. Only one airworthy Zero worldwide still flies with a restored Sakae power plant, the Planes of Fame Museum's A6M5 example (actually, the only fully authentic Zero example flying in the world), bearing tail number "61-120" [Wikipedia]. The importance of the Sakae 21 to Japan's war effort is better illustrated by the fact that several types of the most produced IJN/IJA aircraft during the war - the Mitsubishi A6M Zero, Nakajima Ki-43 Oscar, Nakajima N1K Irving, among others - were powered by it.

This example was photographed by your editor during a visit to the RAF Museum Cosford, November 2018. The Sakae 21 was displayed along with other historically important engines in the Hangar 1 - Transport & Training aircraft. It was virtually authentic, except for the colors.
The museum reference is 84/E/1098.

Much of the Sakae 21 success was due to the work of the Japanese aircraft/automotive engineer Ryoichi Nakagawa (中川 良一 Nakagawa Ryōichi, 1913–1998). He graduated from Tokyo Imperial University in 1936 and joined Nakajima Aircraft Company in the same year. Right after, he improved Nakajima Sakae engine for the Zero, Oscar and other planes. He was the chief designer of Nakajima Homare engine for Nakajima Ki-84, Nakajima C6N, Kawanishi N1K and others.


  Nakajima Aircraft Company
Type14-cylinder air-cooled two-row radial engine
Bore / Stroke / Displ.130 mm (5.1 in) / 150 mm (5.9 in) / 27.9 L (1,700 in³)
1,600 mm (63 in)
Diameter1,150 mm (45 in)
Dry weight590 kg (1,300 lb)
Valve trainOverhead valve
SuperchargerGear driven, two speed
Fuel system2 BBL D.D. Float Carb. automatic mixture and boost control
Fuel type92 Octane
Cooling systemAir-cooled
Power output842.64 kW (1130hp) at altitude
Specific power30.2 kW/L (0.66 hp/in³)
Compression ratio
Power-to-weight ration1.428 kW/kg (0.869 hp/lb)
Production total30,233 units (21,166 made by Nakajima / 9,067 by other firms)

* Data from Janes Fighting Aircraft of WWII and TAIC manual OPNAV-16

I don't have any intel on the records of this particular engine in the museum collection. It probably was part of a captured Japanese aircraft brought to UK after the war, but I may be wrong.

Regardless you are interested in this historic piece of aeronautics or want to build a scale model, I hope you find these photos useful somehow.

If you have any interesting information about the history of this artifact, please drop me a line.

Rato Marczak © 2019