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Nakajima Ha-5
Nakajima Ha-41
Nakajima Ha-109


The "Kotobuki" air-cooled aircraft engine was improved and developed into the "Hikari (light)" engine with the bore and stroke expanded to the limit of the cylinder (160 × 180 mm for a displacement of 32.6 L), with the power was increased to 720 PS. The "Hikari" was used in Type 95 carrier fighters and Type 96 Carrier Attack Plane.  

Nakajima knew that engines of higher power would be needed and began work on a new two-row, 14 cylinder design that was based on the 160 × 180 mm cylinder design of the Hikari. The Ha-5 prototype engine was completed in 1933, producing 1,000 PS, combining features of the Bristol Jupiter and Pratt & Whitney R-1340 Wasp designs. The Ha-5 had separate camshafts for the front and rear rows of cylinders like American designs, rather than using a single, front-mounted camshaft and long pushrods to operate both rows of cylinder valves. An improved Ha-5 was developed as a 1,500 PS engine. In all about 5,500 Ha-5 engines were produced for the military.

Later on, as the weights of aircraft rose and higher speeds were required, Nakajima continued to improve the Ha-5 design, creating the "Ha-41" and "Ha 109", which shared the same 146mm x 160mm bore and stroke as the Ha-5, but were increased from the 950 hp of the Ha-5 to 1,260 hp and 1,440 hp, respectively. The unified code for the Ha-41 was "Ha-34". Later the engine was developed into an 18 cylinder, twin-row engine called the "Ha-219", but this never got past the development phase. All these engines used essentially the same cylinder heads, the differences being in supercharging and engine revolutions per minute. The Ha-5 and Ha-41 shared the same weight of 630 kg, while the Ha-109 weighed 720 kg due to its larger, twin-stage supercharger system. The Ha-41 was the primary engine of early variants of the Nakajima Ki-49 "Helen" bomber, and the Nakajima Ki-44 "Tojo" fighter, later versions of both planes using the more powerful Ha-109 engine. Early versions of the Mitsubishi Ki-21 "Sally" used the Ha-5. The Ha-41 would have been an ideal powerplant in aircraft that used the Mitsubishi Kasei, being of smaller dimensions and displacement, yet making equivalent power levels.

About 7,000 civilian and 5,500 military Ha-5's were built during World War II.


Ha-5 634 kW (850 hp), Base design, (used on Mitsubishi Ki-21 Army Type 97 Heavy Bomber)
Ha-5 KAI 634 kW (850 hp), (used on Mitsubishi Ki-30)
Ha-5 660 kW (890 hp) (used on Nakajima Ki-19)
Ha-5 KAI 708 kW (950 hp), (used on Mitsubishi Ki-57 and Ki-57-I Army Type 100 Transport Model 1)
Ha-5-KAI 708 kW (950 hp) take-off, 805 kW (960 hp) at 3,000 m (11,810 ft), (used on Mitsubishi Ki-30 and on first prototype Nakajima Ki-49 Donryu)
Ha-5 KAI 708 kW (950 hp) take-off, 805 kW (1,080 hp) at 3334 m (13,125 ft), (used on Mitsubishi Ki-21-I Army Type 97 Heavy Bomber Model 1 and Ki-21-Ia, Army Type 97 Heavy Bomber Model 1A)
Ha-41 1,260 hp@2,500rpm takeoff, 1,260 hp@2,450rpm @ 3,700m
Ha-109 1,500 hp@2,650rpm takeoff, 1,440 hp@2,600rpm @ 5,200m


The Ha-5 engine was used to power:
Mitsubishi Ki-21 "Sally"
Mitsubishi Ki-30
Mitsubishi Ki-57

The Ha-41 engine was used to power:
Nakajima Ki-49-I 'Donryu' ("Helen")
Nakajima Ki-44-I 'Shoki' ("Tojo")

The Ha-109 engine was used to power:
Nakajima Ki-49-II
Nakajima Ki-44-II



Nakajima Ha-5
Type: 14-cylinder, air-cooled, two-row radial piston engine
Bore: 146 mm (5.75 in)
Stroke: 160 mm (6.3 in)
Displacement: 37.5 L (2,288
Diameter: 1,260 mm (49.6 in)
Dry weight: 625kg (1,378 lb) (720kg Ha-109)
Valvetrain: four-valve intake and exhaust pushrod-operated overhead valve system
Supercharger: Centrifugal, 280mm impeller at 8.39:1 reduction (Ha-5 and Ha-41), 6.55:1 and 8.55:1 for Ha-109 (twin stage supercharger)
Cooling system: Air-cooled
Reduction gear: 0.6875:1 (11/16)
Power output:
890hp (663.7 kW) at 2,200 rpm at 4700m (15,490 ft) with -50mm boost (Nominal Power)
950hp (708.4 kW) at 2,200 rpm with +50mm boost (Takeoff Power)
Specific power: ( to ) 0.58 hp/ to 1.02 hp/
Compression ratio: 6.7:1





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