Mitsubishi A5M Claude

During tests the machine demonstrated a time to climb to 3,000 m of just over four minutes and a top speed at that altitude of 320 km/h. This less than impressive performance was mainly due to huge amounts of drag produced by the bulky radial and its cowling. Poor choice of wing fabric skins, underpowered engine and poorly designed propeller didn’t help either. In addition, flight test program revealed worrying stability issues and poor forward visibility from the cockpit, which all but disqualified the machine as a carrier-based fighter.
Comparative tests of the NK1F (Nakajima’s entry into the program – a mixed construction fighter in parasol configuration with a monocoque all-metal fuselage and fabric-skinned wings and tailplane) and the Mitsubishi fighter proved that both machines had various design flaws. The 1MF10 was 24 km/h faster than its competitor, but in the end it didn’t matter much: Kaigun Koku Hombu rejected both projects since neither of them fulfilled the 7 Shi requirements.

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Undeterred, Mitsubishi continued the flight test program of their fighter. In June 1933 the aircraft’s vertical stabilizer broke in flight during a recovery from a dive forcing the pilot to bail out. Amazingly, the aircraft didn’t crash, but glided back to the airfield for a more or less uneventful landing and suffered only minor damage. Following the incident the vertical stabilizer was strengthened and its fabric skins were made tauter, but that didn’t prevent the very same failure from happening again during another test sortie.
To further experiment with the new fighter’s design Mitsubishi built a second 1MF10 prototype with redesigned landing gear featuring carefully streamlined legs. The machine completed a full flight test program, but eventually proved to be a disappointment with its top speed 48 km/h below the requirements. In July 1933 the aircraft was lost in a crash after it had entered an unrecoverable flat spin forcing the pilot, Lt. Motoharu Okamura, to bail out. Finally the unsuccessful 1MF10 project was abandoned, but Horikoshi used the lessons learned in designing the machine in his work on the highly successful A5M fighter.

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9 Shi requirements – Nakajima A5N1
It appeared that all hopes for a quick acquisition of a new fighter and modernization of Japanese carrier aviation were lost with the fiasco of the 7 Shi program. Trying their best to save the day, Kaigun Koku Hombu contracted Nakajima to deliver a modernized version of the A2N fighter, which became the A4N – hardly an improvement on the original. The new fighter was indeed faster and more maneuverable than its predecessor, but its performance was still a far cry from what the Navy was hoping for. Nonetheless, reeling from the failure of the 7 Shi program and trying to respond to growing tensions in China, the Navy brass gave a green light in January 1936 for a full-scale production of the A4N.
Following the unsuccessful 7 Shi program Koku Hombu published new requirements (8 Shi), which were once again submitted to Mitsubishi and Nakajima in 1933. The program spawned a pair of two-seat biplane fighters: Nakajima NAF-2 whose prototype was delivered in March 1934 and Mitsubishi Ka-8 (first prototype built in January 1934). Not surprisingly, both fell short of the Navy’s requirements. Even the Nakajima A2N fighters already in service had better performance characteristics than either of the proposed machines and what the Navy was looking for was a modern fighter of a significantly better performance.
Koku Hombu, struggling to secure locally-manufactured modern carrier-based fighters, was forced to adapt stop-gap measures, such as continuing production of obsolete Nakajima A2N aircraft and its upgraded A4N version. That, however, couldn’t go on forever. In February 1934 a new set of requirements was published – 9 Shi, which was mainly the work of Lt.Cdr. Hideo Sawai. Yet again Mitsubishi and Nakajima were invited to take part in the program.

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This time the requirements were fairly straightforward and included little more than expected top speed, climb rate, fuel load, armament, types of radios to be used and dimensions dictated by the size of aircraft elevators. Interestingly, the program specified a single-seat fighter aircraft, rather than a carrier-based type, which freed the designers to build a machine without the constraints inherent to aircraft specifically designed for carrier operations. The idea was that the new design was supposed to be first and foremost an aircraft of superb performance, which then could be adapted as necessary to carrier operations. Lt.Cdr. Sawai firmly believed that the only way forward in aircraft design was to focus on the machine’s tactical characteristics, without imposing unnecessary limitations of weight, particular technological features or powerplants. This was a radical departure from a standard approach in which the designers’ ingenuity was often stifled by such limitations. Thus the 9 Shi requirements contained little more than expected performance parameters: top speed at 3,000 m – 350 km/h; time to climb to 5,000 m – no more than 6.5 minutes; internal fuel – no less than 240 l; armament – two 7.7 mm machine guns; communication radio; wingspan – no more than 11 m; length – not exceeding 8 m.
Mitsubishi’s entry into the program was PA-Kai, also known under its military designation “Experimental Single-Seat Navy Fighter 9 Shi” (A5N1). Nakajima’s entry into the earlier 7 Shi competition was a carrier fighter design based on the company’s Type 91 machine built for the Army. Nakajima used the same tactics in the single-seat fighter program submitting the aircraft based on their Ki-11 fighter designed for the Imperial Japanese Army.

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