NASM Japanese Engine Research
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by Robert Mawhinney
Published 11 Jan 2007; Revised 26 Aug 2026
| Smithsonian National Air and Space Museum (NASM) Japanese engine researcher and restoration specialist Robert Mawhinney kindly provided a collection of "working" images he used in his research before his untimely death on 3 November 2021. Regarding the images, Rob said, "These are not all the greatest photos. They are used to avoid climbing the racks at Garber, pencil/paper in hand, to translate data plates and take notes on details. They also help save time by not moving engines here and there. They are a good peek into the Japanese engine collection at NASM though, and for that alone they are worth it." |
Japanese Aircraft Engines - The Book
Nakajima J1N1-S Gekko
Rob's Japanese engine research work fitted nicely into a project where he was part of a three-man crew disassembling NASM's Nakajima J1N1-S Gekko (Code name: "Irving"). NASM restored the Gekko years ago but never put it on display. It was being moved and reassembled at the Udar-Hazy center. This was a good chance to have a look at complete power plant installations.
The engines are Nakajima Sakae Model 21's. It is interesting to note the differences between the two engines. The right engine's nose case has "Sakae" cast into it in Hiragana. Hiragana is a phonetic way of "spelling out" Japanese words. The left engine has a "data tag" that uses the Kanji symbol for Sakae and states the model number. The quality of the casting on the right engine nose case is not as good as that of the left engine. Other differences are; No carb data plate on the right engine, rocker box oil sumps are not the same and many other minor details.
The carburetors are Nakajima two-venturi Model 100 "Ko" units on both engines. Of note in the carburetor close up from the rear are the two large hoses running to it. These are engine oil lines feeding hot oil through the carb for anti-icing protection.
Right Engine (Nakajima)
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| Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 |
Left Engine (Nakajima)
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| Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 | Sakae Model 21 |
Sakae Model 21 Specifications
Displacement = 27.9 liters
Bore = 130 mm, Stroke = 150 mm
Compression Ratio = 7.0:1
Takeoff Rating = 1,130 hp @ 2,750rpm
Low Blower Rating = 1,070 hp at 2,700rpm and 2,850 meters
High Blower Rating = 940 hp at 2,700 rpm and 6,000 meters
Propeller Reduction Gear Ratio = 0.5833:1, planetary spur
More Japanese Engines
Nakajima Homare 21
Hitachi "Hatsukaze Model 11"
Another Hatsukaze -- but with a twist
Tsu 11 on Ohka 22
Hitachi Amakaze 31 (Also known as Tempu 31)
Tentative Identification: Army Type 98 450Hp Radial (Army Ha13 "Ko")
Ha 31-21 Zuisei 21, Army Type 1 1050 hp Radial, Army Ha 102)
Ha32-21 Mitsubishi Kasei Model 21 (MK4P)
Ha32-22 Mitsubishi Kasei Model 22 (MK4Q)
Army Type 1 1,050 hp Radial Army Ha102, Mitsubishi Zuisei 21)
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