Kawasaki Ki-64

The sole prototype Ki-64 experimental fighter taking-off on its initial flight in December 1943.

Despite active efforts to cure the early difficulties of the Ki-45 and to commence preliminary design studies for what were to become the Ki-60 and Ki-61, Takeo Doi found time in 1939 to conceive a highly unorthodox high-speed fighter. However, as a pressing need existed for the more conventional aircraft, the Japanese Army did not authorise Kawasaki to proceed with the design until October 1940 when the project was revived under the Ki-64 designation to meet a specially drafted specification calling for a maximum speed of 700 km/h (435 mph) at 5,000 m (16,405 ft) and a climb to 5,000 m (16,405 ft) in 5 min.

Takeo Doi, co-operating with his colleagues of the Akashi engine plant, decided to use the Kawasaki Ha-201, rated at 2,350 hp for take-off and 2,200 hp at 3,900 m (12,795 ft). The Ha-201 which actually comprised two Ha-40 twelve-cylinder liquid-cooled engines mounted in tandem fore and aft of the pilot's cockpit and drove two three-blade contra-rotating propellers. The forward propeller, driven by the rear engine, was of the controllable-pitch type and the rear propeller, driven by the front engine, was of fixed-pitch. Perhaps the most unusual feature of the powerplant was the steam vapour cooling system which utilised the wing and flap surfaces for cooling area. The coolant used was water, carried in a 70 litre (15.4 Imp gal) tank in each wing, and the total cooling area was 24 sq m (258.333 sq ft). The front engine used the cooling elements in the port wing while the rear engine used those in the starboard wing. The wings themselves were of modified laminar flow section and contained the fuel tanks and two 20 mm (0.79 in) Ho-5 cannon. The entire powerplant installation was tested during extensive wind-tunnel experiments and a Ki-61 was specially modified to test the surface evaporation cooling system. These various tests, although delaying completion of the prototype until December 1943, proved conclusively that the cooling system performed satisfactorily. It permitted an increase in speed of some 40.2 km/h (25 mph) and combat damage to it was not believed to create special problems, but it had the disadvantage of limiting the space available for fuel tanks thus reducing range.

The prototype was completed in December 1943, and flight trials began at the end of the month. Although the first four flights were relatively successful, during the fifth flight a fire started in the rear engine as the result of an oil lead fracturing, necessitating a forced landing. The only serious damage was suffered by the undercarriage. The engine was sent to Akashi for repair and the airframe to Gifu. The engine repair was not competed, and the airframe was captured at the end of the war and elements of the cooling system sent to Wright Field for evaluation.

The initial flight trials had indicated the need for modifications to the contra-rotating propellers. It was then decided to replace the original propellers with electrically-operated constant-speed contra-rotating propellers with which the fighter prototype was to have been redesignated Ki-64 KAI. The Ki-64 KAI was a proposed production version with a more powerful Ha-201 engine, rated at 2,800 hp at altitude. A maximum speed of 800 km/h (497 mph) was anticipated.

The development of a suitable contra-prop took appreciably longer than had been anticipated, however, and as by this time the war situation had become extremely critical for Japan, it was decided to suspend further work on the Ki-64 KAI in favour of research offering the prospect of more immediate results.

Technical Data
Manufacturer: Kawasaki Kokuki Kogyo KK (Kawasaki Aircraft Engineering Co Ltd).
Type: Single-seat fighter with tandem-mounted engines.
Crew (1): Pilot in enclosed cockpit.
Powerplant: One Kawasaki [Ha-72] 11 (Ha-201) twenty-four cylinder inverted-vee liquid-cooled engine, driving a three-blade contra-rotating propellers.
Armament: Two 20 mm (0.79) Ho-5 cannon in the fuselage decking and two 20 mm (0.79 in) Ho-5 cannon in the wings.
Dimensiosn: Span 13.5 m (44 ft 3 1/2 in); length 11.03 m (36 ft 2 1/4 in); height 4.25 m (13 ft 11 5/16 in); wing area 28 sq m (310.388 sq ft).
Weights: Empty 4,050 kg (8,929 lb); loaded 5.100 kg (11,244 lb); wing loading 182.1 kg/sq m (37.3 lb/sq ft); power loading 2.17 kg/hp (4.78 lb/hp).
Performance: Maximum speed 690 km/h (429 mph) at 5,000 m (16,405 ft); climb to 5,000 m (16,405 ft) in 5 min 30 sec; service ceiling 12,000 m (39,370 ft); range 1,000 km (621 miles).
Production: One Ki-64 prototype completed in December 1943.