Japanese Aircraft of the Sino-Japanese and Pacific War

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ABOVE: The aircraft proposed by Tachikawa, which received the designation Ki-94 (later Ki-94-I), was of highly unconventional design.

Preliminary discussions regarding a heavily armed high-altitude fighter were held between the Koku Hombu and Tachikawa Hikoki KK in mid-1942. At that time the Japanese Army wanted to obtain a fighter fitted with a pressure cabin and capable of reaching a top speed of 800 km/h (497 mph) and having a maximum range of 3,000 km (1,864 miles). As these performance requirements were rather stringent, the Koku Hombu decided to instruct Tachikawa to proceed with the design of the aircraft while they placed a contract with Nakajima for another high-altitude fighter with a less stringent range requirement. The aircraft proposed by Tachikawa, which received the designation Ki-94 (later Ki-94-I), was of highly unconventional design. The aircraft was a large twin-boom monoplane powered by two 2,200 hp Mitsubishi Ha-211 Ru eighteen-cylinder air-cooled radials which were mounted fore and aft of the pilot's cockpit and drove four-blade tractor and pusher propellers. Proposed armament included two 37 mm (1.46 in) Ho-203 cannon and two 30 mm (1.18 in) Ho-105 cannon, and a maximum speed of 780 km/h (485 mph) at 10,000 m (32,810 ft) was anticipated. A full-size wooden mock-up was completed late in 1943, but development of the aircraft was discontinued as the Technical Department of the Koku Hombu judged the project too complex and its calculated performance unduly optimistic.

Soon after, Tachikawa submitted a new proposal designed to meet the same requirements as the competitive Nakajima Ki-87. The new aircraft was a single-engined single-seat high-altitude fighter of conventional design with laminar-flow wings and featuring a pressure cabin mounted in the fuselage behind the wing trailing edges. The aircraft was to be powered by a fan-cooled turbosupercharged 2,400 hp Nakajima [Ha-44] 12 eighteen-cylinder radial, rated at 2,450 hp for take-off, 2,350 hp at 1,100 m (3,610 ft), 2,200 hp at 4,400 m (14,453 ft) and 2,040 hp at 11,000 m (36,090 ft), and driving a six-blade propeller, and the wing-mounted armament was to include two 30 mm (1.18 in) Ho-105 cannon and two 20 mm (0.79 in) Ho-5 cannon. The proposal was accepted by the Koku Hombu which ordered one static test airframe, three prototypes and eighteen pre-production aircraft under the designation Ki-94-II. The first Ki-94-II was scheduled for completion on 20 July, 1945, but eventually was completed two weeks behind schedule. The six-blade propeller planned for the Ki-94-II was not ready in time, and it was decided to begin testing of the first prototype on 18 August, 1945, by temporarily fitting a four-blade airscrew. A second prototype, intended to be fitted with the six-blade propeller, was under construction, but the end of the war prevented it from being completed, while the first aircraft was still being readied for its intended maiden flight three days later.

Technical Data

Manufacturer: Tachikawa Hikoki KK (Tachikawa Aeroplane Co Ltd).

Type: Single-engined high-altitude fighter.

Crew (1): Pilot in pressurised cockpit.

Powerplant: One 2,400 hp Nakajima [Ha-44] 12 eighteen-cylinder air-cooled radial engine, driving a (1st prototype) four-blade or (planned production aircraft) six-blade constant-speed metal propeller.

Armament: two wing-mounted 30 mm (1.18 in) Ho-105 cannon and two wing-mounted 20 mm (0.79 in) Ho-5 cannon. External stores: one 500 kg (1,102 lb) bomb.

Dimensions: Span 14 m (45 ft 11 3/16 in); length 12 m (39 ft 4 7/16 in); height 4.65 m (15 ft 3 1/16 in); wing area 28 sq m (301.388 sq ft).

Weights: Empty 4,690 kg (10,340 lb); loaded 6,450 kg (14,220 lb); wing loading 230.4 kg/sq m (37.2 lb/sq ft); power loading 2.6 kg/hp (5.8 lb)/hp).

Performance: Maximum speed 712 km/h (442 mph) at 12,000 m (39,370 ft); cruising speed 440 km/h (273 mph) at 9,000 m (29,530 ft); climb to 10,000 m (32,810 ft) in 17 min 38 sec; service ceiling 14,680 m (48,170 ft); range 2,100 km (1,305 miles).

Production: One prototype competed by Tachikawa Hikoki KK in August 1945.

The Mitsubishi Ki-109 with nose-mounted 75 mm Type 88 cannon.

Early in the war when Japanese fighter pilots were in control of the skies, the few Boeing B-17 Flying Fortresses available in the Southwest Pacific area were the only Allied aircraft to challenge their superiority effectively. As the war developed in favour of the Allies, the longer-ranging Consolidated B-24 Liberators, better suited to the island-hopping war, replaced the B-17s. But for the Japanese the problem of attempting to destroy high flying, well protected and formidably armed bombers remained the same. The Koku Hombu were also aware of the US development of a still more formidable four-engined bomber, the Boeing B-29 Superfortress, and by 1943 they were feverishly studying every means of defence against this feared enemy aircraft.

In early 1943 the Mitsubishi Ki-67 heavy bomber then undergoing flight trials had proved that despite its size and weight it was fast and remarkably manoeuvrable. Consequently in November 1943, officers of the Rikugun Kokugijutsu Kenkyujo (Army Aerotechnical Research Institute) at Tachikawa suggested that the Ki-67 be used as the basis for a hunter-killer aircraft. The project received the designation Ki-109 and two versions were to be built: the Ki-109a, the killer was to mount in the rear fuselage two obliquely-firing 37 mm (1.46 in) Ho-203 cannon while the Ki-109b, the hunter, was to be equipped with radar and a 400 mm searchlight. However, soon thereafter, the project was re-directed at the instigation of Maj Sakamoto who suggested that a standard 75 mm (2.95 in) Type 88 anti-aircraft cannon be mounted in the nose of a standard Ki-67. It was hoped that with this large cannon the aircraft would be able to fire on the B-29s while staying well out of range of their defensive armament. As the Koku Hombu anticipated that, initially at least, B-29s would have to operated without fighter escort, the project was found sound and feasible and, accordingly, Mitsubishi were instructed in January 1944 to begin designing the aircraft, which retained the Ki-109 designation.

Modification of the Ki-67 to mount a 75 mm (2.95 in) Type 88 (Ho-401) cannon in the nose was entrusted to a team led by Engineer Ozawa and the first prototype was completed in August 1944, two months after the B-29s had made their first bombing raid over Japan. Except for its nose, in the lower part of which was mounted the Type 88 (Ho-401) cannon, the Ki-109 prototype was identical to the Ki-67 and retained the waist gun positions and dorsal and tail turrets of the bomber. Ground and inflight test firings of the heavy gun were affected by Maj Makiura of the Rikugun Kokugijutsu Kenkyujo and was sufficiently successful to warrant the placing of an initial order for 44 aircraft. The first twenty-four were each to be powered by two Mitsubishi Ha-104 radials rated at 1,900 hp for take-off, 1,810 hp at 2,200 m (7,220 ft) and 1,610 hp at 6,00 m (20,015 ft) but subsequent aircraft were to receive a pair of Mitsubishi Ha-104 Ru radials fitted with Ru-3 exhaust-driven turbosuperchargers and rated at 1,900 hp for take-off and 1,810 hp at 7,360 m (24,150 ft) to improve performance at the cruising altitude of the B-29s. These engines were actually tested on the second Ki-109 prototype, but no production aircraft were powered by Ha-104 Ru engines. Another attempt to im prove climbing speed was made when a solid propellent rocket battery was installed in the rear bomb-bay of the first prototype but this scheme was abandoned.

Starting with the third Ki-109, the dorsal turret and lateral blisters were dispensed with and no bomb-bay fitted. Fifteen shells were carried for the 75 mm (2.95 in) Type 88 cannon which was hand-loaded by the co-pilot, and the sole defensive armament consisted of a flexible 12.7 mm (0.5 in) Type 1 machine-gun in the tail turret. The rest of the airframe and the powerplant were identical to those of the Ki-67. Despite the lack of high-altitude performance the Ki-109 was pressed into service with the 107th Sentai but, by the time enough aircraft were on hand, the B-29s had switched to low-altitude night operations.

Unit Allocated

107th Sentai.

Technical Data

Manufacturer: Mitsubishi Jukogyo KK (Mitsubishi Heavy Industries Co Ltd).

Type: Twin-engined heavy interceptor.

Crew (4): Pilot, co-pilot and radio-operator in forward cabin and gunner in rear turret.

Powerplant: Two Army Type 4 (Mitsubishi Ha-104) eighteen-cylinder air-cooled radial engines. driving four-blade constant-speed metal propellers.

Armament: One forward-firing 75 mm (2.95 in) Type 88 cannon and flexible one 12.7 mm (0.5 in) Type 1 machine-gun in the tail turret.

Dimensions: Span 22.5 m (73 ft 9 13/16 in); length 17.95 m ( 58 ft 10 11/16 in); height 5.8 m (19 ft 1 1/32 in); wing area 63.85 sq m (708.801 sq ft).

Weights: Empty 7,424 kg (16,367 lb); loaded 10,800 kg (23,810 lb); wing loading 164 kg/sq m (33.6 lb/sq ft); power loading 2.8 kg/hp (6.3 lb/hp).

Performance: Maximum speed 550 km/h (342 mph) at 6,090 m (19,980 ft); range 2,200 km (1,367 miles).

Production: A total of 22 Ki-109s were built by Mitsubishi Jukogyo KK between August 1944 and March 1945.

Begun in 1938 as a civil project for use in a high-speed research programme and for a contemplated attempt on to break the world air speed record, the KEN III (indicating Kensan III or Research III) project was taken over by the Imperial Japanese Army under the Ki-78 designation upon Japan's entry into the war.

Designed by a team from the Aeronautical Research Institute of the University of Tokyo, led by Shoroku Wada and comprising Mineo Yamamoto (fuselage design), Eichiro Tani (wing design) and Seichi Kurino and Shojiro Nomura (engine installation), the Ki-78 introduced several advanced design features not previously used by the Japanese aircraft industry. To minimize drag a fuselage of minimum cross section was designed and a laminar flow section was adopted for the wings. As the wing area was remarkably small, 11 sq m (118.404 sq ft), a combination of Fowler and split flaps and drooping ailerons was selected to reduce landing speed. An imported 1,175 hp Daimler-Benz DB 601A twelve-cylinder inverted-vee liquid-cooled engine was selected to power the aircraft and was modified to incorporate a system of water-methanol injection - the first such device used in Japan - to momentarily boost its power to 1,550 hp. Radiators of small frontal area were mounted on each side of the rear fuselage, and a fan, driven by a 60 hp turbine, was used to improve cooling.

A wooden mock-up of the KEN III was completed in May 1944 and production of two prototypes was entrusted to Kawasaki, where Isamu Imashi took charge of the project. Eventually only the first prototype, construction of which had begun at Gifu in September 1941, was completed and this aircraft first flew on 26 December, 1942. It was found extremely difficult to fly at low speeds, and take-off and landing speeds were respectively 205 km/h (127 mph) and 170 km/h (106 mph). Furthermore, loaded weight and wing loading exceeded calculated values and elevator flutter was experienced at 635 km/h (395 mph). On 27 December, 1943, during its 31st flight, the Ki-78 reached a maximum speed of 699.6 km/h (434.9 mph) at 3,527 m (11,539 ft). This was considerably less than the speed of 850 km/h (528 mph) which had been set as the ultimate goal for the programme. To achieve the calculated performance too many airframe and engine modifications were required and the flight trials of the Ki-78 were suspended after the 32nd flight, on 11 January, 1944.

Technical Data

Manufacturer: Kawasaki Kokuki Kogyo KK (Kawasaki Aircraft Engineering Co Ltd).

Type: Single-engined high-speed research aircraft.

Crew (1): Pilot in enclosed cockpit.

Powerplant: One Daimler-Benz DB 601A twelve-cylinder inverted-vee liquid-cooled inline engine, driving a three-blade metal propeller.

Dimensions: Span 8 m (26 ft 2 31/32 in); length 8.1 m (26 ft 6 29/32 in); height 3.07 m (10 ft 0 7/8 in); wing area 11 sq m (118.403 sq ft).

Weights: Empty 1,930 kg (4,255 lb); loaded 2,300 kg (5,071 lb); wing loading 209 kg/sq m (42.8 lb/sq ft); power loading 2 kg/hp (4.4 lb/hp).

Performance: Maximum speed 700 km/h (435 mph) at 3,500 m (11,485 ft); ceiling 8,000 m (26,245 ft); range 600 km (373 miles).

Production: One Ki-78 was completed by Kawasaki Kokuki Kogyo KK, at the Gifu plant in December 1942.

With its 1,500 hp Kawasaki Ha-140 liquid-cooled engine mounted behind the cockpit and driving a tractor propeller via an extension shaft, the Kawasaki Ki-88 was inspired by the Bell P-39 Airacobra of the US Army Air Forces. Proposed armament comprised a 37 mm (1.46 in) cannon in the propeller shaft and two 20 mm (0.79 in) cannon in the lower section of the nose. Design of the Ki-88 was undertaken in August 1942 but, following the inspection of a full-scale mock-up, development was discontinued within a year as its calculated maximum speed of 600 km/h (373 mph) at 6,000 m (19,685 ft) was only slightly higher than that of the Ki-61 already in production. Span 12.4 m (40 ft 8 3/16 in); length 10.2 m (33 ft 5 9/16 in). Loaded weight 3,900 kg (8,598 lb).