Nakajima Ki-27 Nate

Both competing machines began flight tests in mid-1935. The trials were carried out by military test pilots of Rikugun Kokugijutsu Kenkyusho (Army Technical Air Research Institute, contracted as Kogiken or Giken) at Tachikawa near Tokyo. They revealed that although the Ki‑10 biplane was faster than the Kawasaki Ki-5 monoplane, it was still inferior in terms of speed to the Nakajima Ki-11 monoplane. As to the rate of climb, the Ki-10 considerably ­outperformed the Ki-11. Combat simulations showed that the former design had superior agility, thus easily outperforming its rival in the type of dogfighting favored by Japanese pilots. This feature was the decisive factor, and in September 1935 Koku Hombu chose Kawasaki’s Ki‑10 for production, giving it the official designation Kyugo-Shiki Sentoki, Army Type 95 Fighter. As the result of the contracts that were signed over the following three years, from December 1935 until December 1938 Kawasaki assembled 300 production Ki-10-Is (Army Type 95 Model 1 Fighter) and 280 production Ki‑10‑IIs (Type 95 Model 2).

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Kogiken experts drew attention in their test report to the fact that the Ki-11’s Kotobuki engine was of a simpler construction, easier to handle, and less susceptible to failure and combat damage than the liquid-cooled Ha-9 of the Ki-10. The high speed of the monoplane could also be seen as an advantage, even at the cost of a loss of agility, provided that different fighter combat tactics were employed. These essentially comprised a fast diving or climbing attack and an equally fast exit avoiding a close-in dogfight (the so-called “hit-and-run” attack). However, these qualities were only recognized by Koku Hombu and later exploited in the next generation of army fighters, whereas the unsuccessful Ki-11 was to be the spur for a later Nakajima fighter that would enjoy some success. On the other hand, the operational employment of the Ki-10 biplane was undoubtedly a retrograde step in Imperial Army fighter development.
In 1935 another fighter type underwent trials with the IJAAF. Impressed by the performance of the prototypes of Mitsubishi’s Ka-14 fighter, intended as a new shipboard fighter for the IJNAF (9-Shi, later known as the A5M), Koku Hombu ordered one prototype designated Ki-18. It was a cantilever low-wing monoplane of all-metal construction with an open cockpit and fixed landing gear (and tail wheel). Built in August 1935, the Ki-18 was basically similar to the second Ka-14 prototype construction-wise, but its power plant was the Nakajima Kotobuki 5 rated at 600 hp with reduction gear. The engine cowling was wider, and the rudder and wheels were larger. The aircraft was armed with two 7.7-mm machine guns.
“Advanced fighter” competition
During the fall and winter of 1935 the Ki-18 underwent exhaustive trials at Rikugun Kokugijutsu Kenkyusho, Tachikawa, and at the research facility of Rikugun Hiko Gakko (Army School of Aviation) at Akeno in the Mie prefecture. As was to be expected, the Ki-18 – a fast monoplane lacking in agility compared with biplanes – failed to convince conservative Army pilots although Koku Hombu could not have overlooked the growing trend in the aircraft industries of the world to design fast cantilever monoplane fighters of metal construction, featuring retractable landing gear and an enclosed cockpit. With this in mind, no later than mid-1935 Koku Hombu drafted guidelines for a new, “advanced” (or simply monoplane) fighter aircraft boasting high performance (better than the monoplanes tested thus far), while at the same time retaining the requirement for outstanding agility (or at least only slightly worse than the biplanes in service at the time). These specifications were supplied in early 1936 (some sources say about April) to the three biggest Japanese aircraft manufacturers – Mitsubishi, Nakajima and Kawasaki – the factories being expected to each provide two prototypes. The three companies were soon ready with designs, presenting them as prototypes delivered for comparison testing.
First to respond to the new request was Mitsubishi, which in August 1936 built the first of the two Ki-33 prototypes (designated accordingly Ki-33.01). It was designed by Jiro Horikoshi and was a direct modification of the earlier Ka-14 and Ki-18. The reason for this was that Mitsubishi was at the time busy with production for Kaigun Koku Hombu (IJNAF Headquarters) of the A5M fighter and the G3M bomber, and the company’s managers decided that they could not afford to develop an entirely new construction. The Ki-33 differed from the Ki-18 mainly in that it had a new, air-cooled nine-cylinder Nakajima Ha-1a radial (an elaborated Kotobuki) of 620/745 hp, a different engine cowling, slightly redesigned fin and rear fuselage, and a half-enclosed cockpit with a backwards sliding canopy consisting of one top and two side glass panels. It was a cantilever low-wing monoplane of all-metal construction, with fabric control surfaces and fixed three wheel landing gear ­featuring a tail wheel. The main wheels were protected by fairings. The aircraft’s armament consisted of two 7.7-mm machine guns. The second prototype, Ki-33.02, was completed in late 1936.
The new Kawasaki fighter, designated Ki‑28, was designed by Eng. Takeo Doi. Overall, the idea of this machine resembled the factory’s earlier type, the Ki-5. It was an elegant cantilever low-wing monoplane of all-metal construction and partial fabric covering. The cockpit was half-enclosed by a rearwards sliding canopy. The landing gear was fixed and featured two main wheels with fairings and a tail skid. The aircraft offered a few novel solutions such as manual operation of landing flaps (used for the first time on this company’s fighter) and a manually operated radiator located under the fuselage. Armament consisted of two 7.7-mm fuselage-mounted machine guns. Unlike the other contestants, and typically for Kawasaki, the Ki‑28 was powered by the liquid-cooled twelve-cylinder V-type Kawasaki Ha-9-IIa of 720/850 hp, the same as used with the Ki-10. The two prototypes, Ki-28.01 and Ki-28.02, were built in November and December 1936 respectively.

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