Nakajima Ki-27 Nate

In total, Kawasaki built five KDA-5 prototypes in 1930-1931, 180 production Type 92s in 1932 (the designation Type 92-1 can also be found in the literature but the IJAAF did not officially recognize such a version), and a further 200 in 1933. The aircraft from this latter batch, sometimes distinguished from the former by the designation Type 92-2, were powered by the higher-rated Kawasaki-BMW VII of 600/750-800 hp (despite the identical designations, this engine differed from the original German BMW VII). Initial combat sorties in China revealed the Type 92’s poor performance at low-speed (particularly during takeoff and landing) and an ­array of teething problems, especially in the difficult winter conditions. In addition, its performance was inferior to the latest foreign machines such as the British Hawker Fury or the American Boeing P-26. The outcome was a demand formulated in June 1933 by Koku Hombu tasking Kawasaki with the development of a more modern successor.

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Kawasaki Ki-5 monoplane
The initial design of the new aircraft, which Koku Hombu assigned the designation Ki-5 (according to the new designation scheme known as Ki Go), was developed by Takeo Doi under the supervision of Richard Vogt. Following Dr Vogt’s return to Germany further project work was directed by Doi alone. The first of the four prototypes (five according to some sources) to be built was completed in February 1934. This was a machine totally different from earlier Japanese fighters, being an all-metal cantilever low-wing monoplane with partial fabric covering. The wings had an inverted gull configuration. The cockpit was of the open type, and the classic fixed landing gear featured a tail skid. The main wheels were protected by wide fairings. The Ki-5 was powered by the liquid-cooled twelve-cylinder V-type Kawasaki Ha-9-I (aka BMW IX) rated at 720/800-850 hp, a developmental version of the German BMW engine manufactured by Kawasaki. Armament consisted of two 7.7-mm fuselage-mounted machine guns.
All the Ki-5 prototypes, which differed from one another in various constructional details (e.g. wing dihedral angle, pilot’s seat placement, landing gear and radiator construction), underwent exhaustive flight tests. However, in September 1934 the IJAAF stopped further development of the aircraft, as it was considered unlikely to make a satisfactory fighter despite its quite good performance (e.g. maximum speed was 360 kph, ceiling 9,000 m, and the aircraft climbed to 5,000 m in eight minutes). Unfortunately, the Ki-5 had poor low speed characteristics and suffered from engine vibrations. The cooling system was also a source of problems, while maneuverability was judged to be poor. The latter feature was a basic prerequisite with the Japanese air forces. Indeed a fighter that was assessed as lacking in the agility stakes had no chance of gaining the approval of the Koku Hombu..

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The biplane prevails
With the abandonment of the Ki-5 project, the Koku Hombu again turned to Nakajima and Kawasaki in the fall of 1934 with a request for a replacement for the Type 91 and Type 92. This time, having learned the Ki-5 lesson, engineers Takeo Doi and Isamu Imachi of Kawasaki returned to a tried and tested configuration. Their new fighter, for which Koku Hombu chose the designation Ki-10, was a classic strutted biplane with an open cockpit and fixed landing gear with a tail skid. It was an all-metal structure with partial fabric covering. Armament consisted of two 7.7-mm Type 89 fuselage-mounted machine guns. The Ki-10 was powered by the liquid-cooled twelve-cylinder V-type Kawasaki Ha-9-IIa (Ha-9-II Ko) of 720/850 hp. Four prototypes of the type were built in the spring of 1935.
The Ki-11 from Nakajima (factory designation PA) was much more competitive, designed by a team directed by Yasushi Koyama and Shinroku Inoue. It was a low-wing monoplane with wire bracing, modeled on the American Boeing P-26. It had an all-metal fuselage and the wings were of mixed, metal-and-wood construction with plywood and fabric covering. The aircraft incorporated a fixed two-wheel landing gear with a tail skid, and featured an armament of two 7.7-mm machine guns. The cockpit was open on the first three prototypes, whereas the fourth was equipped with a rearwards sliding canopy, a quite novel innovation for a Japanese fighter. The machine was powered by an air-cooled nine-cylinder radial, the Nakajima Kotobuki 3 rated at 550/710 hp. Four prototypes were built between April and December 1935; they were subjected to comparison tests with the Ki-10.