By the end of 1940, the Imperial Japanese Navy, asked Mitsubishi to start designing a 16-shi carrier fighter that would replace the A6M Zero already in service. However, at that time there wasn't any reliable high-output compact engine suitable to be used in a fighter. Furthermore, Jiro Horikoshi's team (the team designer of the famous A6M Zero, among others) was busy fixing all the production issues of the A6M2b version of the Zero that was already under production, developing the A6M3 Zero and the 14-shi interceptor, that would eventually become the Mitsubishi J2M Raiden. Due to that, work on the A7m was pushed back until January 1941.
In April 1942, as the work on the A6M3 was already complete, the Imperial Japanese Navy ordered Mitsubishi to retake the works on the Zero's successor and shortly after, in July, the Navy issued a specification:
It had to fly faster than 345Kn (639km/h; 397mph) above 6000m (20000ft) in less than 6 minutes, it had to be as maneouvrable as the Zero and it had to be armed with two 20mm cannons and other two 13mm cannons.
One of the main obstacles was the engine selection, as in order to comply with the specification, it had to produce at least 2000hp (1500Kw) of power, narrowing that way the choices down to Nakajima's NK9 that was still under development and would later become the Homare, or Mitsubishi's Mk9 that was also under development.
With that choice of engines, wing loading became also an issue as the specification stablished a maximum of 150kg per square meter but desired 130kg per square meter complicating even more design considerations. With the Nk9, they could achieve less than 150kg, but with the less power, it wouldn't meet the maxomum required speed, however, it was concluded by the engineers that with the Mk9 it could fulfill the requirements. However, production of the Mk9 was delayed in comparisson with the Nk9 and the Navy ordered Mitsubishi to use the Nk9.
The aircraft was delayed further when Mitsubishi's factories prioritized production of the Zero and the G4M bomber as well as addresing issues on the Raiden. Due to those factors, the 17-shi, which became A7M1 flew officially for the first time on 6th May 1944, as late as four years after the development started. It showed excellent handling and maneouvrability, but, as Mitsubishi's engineers feared, was underpowered with a maximum speed similar to the A6M5 Zero.
As it was disappointing, the Navy ordered development to stop on 30th July 1944, but Mitsubishi got permission to continue with the development using the Ha-43 engine, so the prototype flew with such engine and the designation of A7M2 Reppu (Strong Gale) on 13th October 1944. It now achieved a top speed of 628km/h (339kn; 390mph) and surpassed in climbing and other areas the Zero which made the Navy to change their mind about the aircraft. It was also equipped with automatic flaps, which were previously used on the Kawanishi N1K-J improving maneouvrability even further. An earthquake on 7th December 1944, plus Allied bombings, delayed the development of the aircraft even further.
In June 1945 Japanese Ace pilot Saburo Sakai was ordered to Nagoya to test the aircraft and declared to be the fastest aircraft he had ever seen, capable of surpassing anything in the air, Japanese or American. He claimed also that it could fly in circles, while ascending around a Hellcat or a Mustang and it could fight at up to 12000m.
Further versions were proposed and even worked on, like the A7M3, that would've featured a mechanically driven three-speed supercharger Mitsubishi Ha-43 engine rated at 2250hp (1680Kw), and, unlike the previous variants it would've operated from land bases. Work on the prototype of this variant was underway, however the end of the war halted any development.
Another land based variant the A7M3-J Reppu-Kai was planned around the turbo-supercharged Ha-43 engine, rated this time at 2200hp (1600Kw) including an inter-cooler with a maximum speed of 648km/h (402mph) and armed with six 30mm Type 5 cannons, four wing mounted and two oblique-firing mounted in the fuselage, copying the German Schäge Musik system. A full-scale mock-up was built but no prototype was produced.
When Japan surrendered in September 1945, every development was halted.
Edit: We've just updated the drawings today, on 30th May 2020.
1. https://en.wikipedia.org/wiki/Mitsubishi_A7M
2. Salamander Books - The Complete Book of Fighters
No comments:
Post a Comment