The Nakajima Type 91 Fighter was a parasol wing monoplane that served as the main fighter aircraft for the Japanese army after its introduction in 1932.
The Type 91 had quite a lengthy development. In 1927 the Japanese Army held its first open competition to find a Japanese-designed fighter aircraft. Nakajima, Mitsubishi and Kawasaki all produced entries, in each case using a mixed Japanese and European design team. The new aircraft was expected to replace the Nakajima Ko-4, which was a licence-built version of the Nieuport-Delage NiD-29 equal span biplane.
The Nakajima team was led by Shigejiro Ohwada and Yasushi Koyama, with the French engineers André Marie and Maxime Robin providing assistance. This team produced a parasol winged aircraft with a tapering monocoque fuselage, powered by an air-cooled Nakajima Jupiter engine (Mitsubishi and Kawasaki both used water-cooled engines on their designs. The Nakajima aircraft had tripod main landing gear, with the struts for the parasol wing reaching the fuselage at the same place as the undercarriage struts.
The Mitsubishi Hayabusa, another parasol wing fighter, was ready by May 1928. During diving tests at Tokorozawa the prototype disintegrated in the air (Sumitoshi Nakao, the test pilot, became the first Japanese pilot to escape from an accident by parachute). The Japanese Army halted the tests on the Nakajima and Kawasaki designs and instead used the surviving prototypes for ground-based static structural tests. The two Nakajima NC prototypes were completed in May-June 1928 but were destroyed in these tests, which proved that none of the three designs were strong enough.
The disaster ended further work on the Mitsubishi Hayabusa and the Kawasaki KDA-3, but the Army asked Nakajima to continue working on their design, which was felt to be the best of the three. Between 1929 and 1931 Nakajima produced another five prototypes, all parasol-winged fighters, all with stronger structures. Nakajima used these aircraft to solve a problem with the design's centre of gravity and by 1931 the aircraft was judged to be ready for service.
In the autumn of 1931 the Nakajima NC was accepted for production as the Type 91 Fighter (for Japanese year 2591). It became the official standard fighting, replacing the Nakajima Ko 4. From 1932 it served alongside the Kawasaki Type 92 Fighter, which was seen as a better interceptor, while the Nakajima aircraft was used as an air superiority fighter.
The Type 91 was produced in two variants. The main one was the Type 91-1, which used the Nakajima Jupiter VII engine. A total of 320 were built by Nakajima between 1931 and March 1934. At the same time Ishikawajima built another 100 (or possibly 115) Type 91-1s. The Type 91-1 was revealed publicly in February 1932
In April 1933 Nakajima produced a single experimental aircraft.
Between July and September 1934 production switched to the Type 91-2. This had a Nakajima Kotobuki 2 engine and a Townend ring cowling. The new engine was more reliable and more powerful, but only twenty-two Type 91-2s were built before the Army accepted the Kawasaki Ki-10 as the Army Type 95 Fighter ('Perry'). This aircraft entered full production during 1936, giving the Nakajima Type 91 a front line career of four years.
The Type 91 saw service during the 'Shanghai Incident', and with four squadrons of the 11th Air Battalion, part of the Kanto Command in Manchuria. During the Shanghai fighting one aircraft fell apart in the air, reviving the earlier worries about the structural strength of the parasol winged fighters, but after that the aircraft appears to have been reliable, and it was popular with its pilots.
Engine: Nakajima Jupiter VII nine-cylinder air cooled radial engine
Span: 36ft 1in
Length: 23ft 10.25in
Height: 9ft 2in
Empty weight: 2,370lb
Maximum take-off weight: 3,373lb
Max speed: 187mph
Climb Rate: 4 minutes to 9,843ft
Service ceiling: 29,527ft
Armament: Two fixed forward firing 7.7mm machine guns