Aviation of World War II
Takeo Doi began designing it in 1939, initially considering it a pure experiment in achieving high speeds. But the high design indicators (according to the creators, the aircraft could reach a speed of 700 km / h at an altitude of 5000 m) attracted the attention of the military, and already in October 1940 the project received the army designation Ki.64 and began to be considered as a heavy interceptor fighter.
High speeds were going to be achieved due to the high power of the engine and minimization of aerodynamic drag. Since motors with a power of about 2000 hp. then in Japan it was not yet, they decided to use a pair of Xa.40s installed in tandem in the fuselage. The second engine, located behind the cockpit, transmitted power to the front propeller through a long shaft passing under the pilot's feet. This arrangement of engines made it possible to significantly reduce the midsection of the aircraft, compared with the traditional arrangement of two engines on the wing. An additional effect was to be given by the use of a laminar wing profile and a steam cooling system.
Japanese engineers met the latter in Germany, where it was developed by Heinkel. The coolant mixture passed through the engine, boiled and evaporated, then flowing into the radiator-condensers under the wing skin. From there, it was pumped back to the reserve tank of the system. The absence of conventional honeycomb-type radiators protruding into the stream significantly improved the aerodynamics of the aircraft. In 1940, drawings and prototypes of the He 100 fighter and the He 119 high-speed reconnaissance aircraft were delivered from Germany. These aircraft were powered by DB601 engines (which were prototypes of Xa.40), with a steam cooling system.
Power point. At first, Doi wanted to place the engines one behind the other, as on the Italian racing seaplane Macchi MS.72 and the Soviet experienced bomber "C" designer VF Bolkhovitinov, taking the cockpit far back. Then he moved on to a very original scheme, dividing the motors with a pilot's cabin. The French did something similar a little earlier on Arsenal VG.10 and VG.20 aircraft.
A power plant that combined two Xa.40s (one of them with an extended shaft) with a steam cooling system and coaxial counter-rotation propellers was developed by the Kawasaki engine-building design bureau. She was designated as Xa.201. The screws were not synchronized with each other; each of them worked independently of the other. The front propeller was variable pitch, and the rear propeller was constant.
The cooling system was tested in October 1942 on a converted Ki.61. Until the end of 1943, he made 35 successful flights, overtaking serial fighters by 35-40 km / h. A considerable problem for the designers of Xa.201 was the shaking of the elongated shaft of the rear engine, but in the end they managed to get rid of it by introducing dampers into its supports. At the Xa.201 stand, it showed power up to 2350 hp.
The preliminary design of the Ki.64 was completed in January 1941, and on January 23, the Army Air Forces ordered one prototype aircraft from Kawasaki. However, further work was delayed due to the great complexity and novelty of the design, as well as due to the design bureau being overloaded with the design of the first Ki.60, and then Ki.61. Only at the end of 1943 was it possible to complete the first and only prototype machine. Radiators-condensers were placed in the wing consoles, since the inner sections were occupied by gas tanks and weapons (the aircraft carried two 20-mm Ho.5 cannons), left radiators for the front engine, right ones for the rear. It is interesting that the Japanese designers used shields as radiators and the movable part of the wing. The oil cooler was common, it stood asymmetrically, under the right half-wing. Since the Japanese failed to achieve good tightness of the cooling system, a large reserve tank was installed in the fuselage to compensate for the loss of coolant. The same tank was supposed to compensate for possible water losses from bullet holes in battle.
In December 1943, the Ki.64 took to the air for the first time. The flight data turned out to be high, although they did not reach the promised 700 km / h. Difficulties arose with the cooling system - water losses turned out to be significantly more than calculated. The plane took off, enveloped in a cloud of steam. A total of five flights were made. On the fifth, the rear engine jammed due to overheating. The tester made an emergency landing, severely damaging the machine.
In the series, it was supposed to produce an improved version, Ki.64-KAI with a more powerful motor unit based on a pair of Xa.140, which was supposed to develop up to 2800 hp. Another difference was the Sumitomo counter-rotation propeller, the production of which was established under license from the German company VDM. The front and rear propellers in this unit were not only adjustable in pitch, but also completely feathered - they were installed along the stream, reducing resistance when the propeller was idle. Such an innovation made it possible to turn off one engine in cruising flight. The armament of the Ki.64-KAI was supposed to be supplemented by a pair of Ho.5s above the front engine with a complex synchronization system - the movement of two sets of blades had to be taken into account. According to calculations, this fighter could reach a speed of 800 km / h.
In parallel with the Ki.64-KAI, in 1943 a simplified modification of the Ki.88, the Japanese Airacobra, was developed. She did not have a front motor, the only Xa.40 (or Xa.140) was behind the cockpit. The cooling system was returned to traditional honeycomb radiators. The armament of the Ki.88 consisted of one Xo.203 (37 mm), which fired through the propeller hub, and a pair of Xo.5s at the bottom of the forward fuselage. The data, of course, was much lower than that of the Ki.64: it was believed that the maximum speed would be of the order of 600 km / h. A wooden full-size layout of the Ki.88 was made, but that was it - in October 1943, work on it was stopped.
The design of the Ki.64-KAI continued until the middle of 1944, when the Koku Hombu decided that it would take too much time to fine-tune this machine. Specialists were switched to other projects that promised faster returns. The Xa.201 engine after the accident of the first prototype aircraft returned to the engine plant, and the disassembled Ki.64 airframe was stored in one of the hangars in Kagamigahara.
It was there that American intelligence officers found him in the autumn of 1945. The unfamiliar machine was given the code name "Rob". Soon they also found a motor installation, which was of greater interest than the aircraft. Both were sent to the USA. The fighter itself did not reach America - probably on the way it was washed away by a storm from the deck of an aircraft carrier. But Xa.201 was tested at the Wright Field Air Force Research Center, but the rapid development of jet aircraft quickly depreciated its merits. Ki.64 remained only a memory of the talent and originality of Japanese designers.