WI: alternative IJA fighters

[nuuumannn]

Thankfully for the US it had the R-2800, which from the very beginning of the war provided 2,000 hp.

Agree, the R-2800 was a world beater.

I want the IJAF fighter to be a variant of the IJN's fighter.

Give the IJA Zeroes! Beez has a point here though. One thing the Japanese did not do was work its industries together. There were bitter rivalries between army and navy production and resource provision. Nakajima was a firm that produced its own metals, engines and airframes, but was largely controlled by army needs, conversely Mitsubishi with the navy and thus a rivalry grew between them. If both the army and navy require a land based interceptor, which thery both did, surely choosing a common airframe would have made sense within the limitations of Japanese production. The Mitsubishi J2M and Kawanishi N1K1 and 2 (preferrably the N1K2) were the navy's answer to this, could the army not use these types?

 

[Admiral Beez]

Agree, the R-2800 was a world beater.



Give the IJA Zeroes! Beez has a point here though. One thing the Japanese did not do was work its industries together. There were bitter rivalries between army and navy production and resource provision.

Easiest fix, through imperial decree in the 1920s de-establish the IJAAF and the IJNAF and create the IJAF, a separate military wing responsible for all aircraft development, procurement and operations regardless of use over sea or ground. The IJAF presents the Army and Navy with one fighter to replace its biplanes; a combo of the Ki-27 and A5M.

Though this will be a tall order to get done. Even today, the Japanese navy through the JMSDF retains control over its own aviation assets, separate from the JASDF.

 

[nuuumannn]

one fighter

A6M3 front

 

[tomo pauk]

Another plan, let's call it 'back-up plan', might be getting as much mileage from Sakae. It was a good, lightweight and reliable engine, with decent altitude performance, but it was also installed in relatively big fighters so raw performance of those left a lot to be desired sometimes, especially as the Pacific war (per Western beligerents) was closing to it's 3rd year. So basically I'd suggest that Sakae is installed in small-ish airframe, say something size of Ki-44, Ki-60, or the 1st prototypes of Fw 190. Best-case, it would've meant that IJA has a fighter that performs no worse than the Swedish J.22 already by mid-1942.
Another appeal of Sakae vs. Ha-41 was that Nakajima was asking 25000 Yen for the Sakae vs. 50000 Yen for Ha-41 in 1941; granted, the price discrepancy was just 20% by late 1942. It might also be possible to install Kinsei, or indeed the water-injection kit for the Sakae itself later in the war (details about historical, actual combat use of ADI on Army Sakaes are as good as non-existing, unfortunately; seems Navy Sakaes never got ADI?).

 

[cherry blossom]

Another plan, let's call it 'back-up plan', might be getting as much mileage from Sakae. It was a good, lightweight and reliable engine, with decent altitude performance, but it was also installed in relatively big fighters so raw performance of those left a lot to be desired sometimes, especially as the Pacific war (per Western beligerents) was closing to it's 3rd year. So basically I'd suggest that Sakae is installed in small-ish airframe, say something size of Ki-44, Ki-60, or the 1st prototypes of Fw 190. Best-case, it would've meant that IJA has a fighter that performs no worse than the Swedish J.22 already by mid-1942.
Another appeal of Sakae vs. Ha-41 was that Nakajima was asking 25000 Yen for the Sakae vs. 50000 Yen for Ha-41 in 1941; granted, the price discrepancy was just 20% by late 1942. It might also be possible to install Kinsei, or indeed the water-injection kit for the Sakae itself later in the war (details about historical, actual combat use of ADI on Army Sakaes are as good as non-existing, unfortunately; seems Navy Sakaes never got ADI?).

The problem with arguing for the Sakae over the larger Ha-109 is that the Ha-109 was not developed to give the best possible performance because the Sakae and Homare were Nakajima's main priorities and time was wasted on the Mamoru and its 18 cylinder derivative.

The most powerful Sakae was the Sakae 31 which was intended to use the Homare's technology to give 1360 ps but actually gave 1230 ps. The Ha-109 never gave more than 1520ps for takeoff and production and development stopped in 1944.

However, the later Ha-44 with 18 of the 146mm x 160mm (5.75" x 6.30") cylinders (48.2L) was much more powerful and of course much heavier at 1150kg (2,535lbs). It gave 2450 ps at 2800rpm and 550mm (51.6") Hg for takeoff. My point is that a developed Ha-109 (Ha-34) with Ha-44 technology should give 1900ps and, in general, vibrations are less of a problem with a 14 cylinder engine than with an 18 cylinder. The weight might rise from 720 kg to 900 kg using the 14/18 ratio to allow 2800 rpm instead of 2650 rpm.

Thus we can imagine Nakajima continuing to develop the Sakae, the Ha-109 and the related Ha-44 instead of the Homare (Ha-45) and the Mamoru and producing an alternative and more reliable family of engines.

 

[tomo pauk]

The problem with arguing for the Sakae over the larger Ha-109 is that the Ha-109 was not developed to give the best possible performance because the Sakae and Homare were Nakajima's main priorities and time was wasted on the Mamoru and its 18 cylinder derivative.

I'm not trying to argue for Sakae at expense of Ha 109. The Ha-41/109 series of engines was IMO under-produced and under-utilized, while a lot of aircraft either gotten the Sakae or Zuisei, or were hampered with waiting for newly fanged engines to materialize.

The most powerful Sakae was the Sakae 31 which was intended to use the Homare's technology to give 1360 ps but actually gave 1230 ps. The Ha-109 never gave more than 1520ps for takeoff and production and development stopped in 1944.

However, the later Ha-44 with 18 of the 146mm x 160mm (5.75" x 6.30") cylinders (48.2L) was much more powerful and of course much heavier at 1150kg (2,535lbs). It gave 2450 ps at 2800rpm and 550mm (51.6") Hg for takeoff. My point is that a developed Ha-109 (Ha-34) with Ha-44 technology should give 1900ps and, in general, vibrations are less of a problem with a 14 cylinder engine than with an 18 cylinder. The weight might rise from 720 kg to 900 kg using the 14/18 ratio to allow 2800 rpm instead of 2650 rpm.

Thus we can imagine Nakajima continuing to develop the Sakae, the Ha-109 and the related Ha-44 instead of the Homare (Ha-45) and the Mamoru and producing an alternative and more reliable family of engines.

The Ha-109 with tech from Homare (steel crankcase, dynamic ballancers, ADI) would've also been handy.
A reason why I've stated that just historcialy produced engines are to be used is to keep the thread simple - Japanese have had good & very good engines in production lines, but usage of those engines was not the best possible on aerodynamic & structural tech of the day.

 

[tomo pauk]

As for the Homare itself - don't go overboard with compression ratio. Instead of 7:1, later increased to 8:1, decrease it. Say, closer to 6:1 than to 6.5:1. It will help with low-octane fuel the Japanese are saddled with.

 

[tomo pauk]

Alternative Japanese fighters by the late Just Leo (1st is based on J2M that is navalized and has the 'regular' Kasei, another is a 'big wing Ki-44'; obviously the IJA will not need a navalized fighter):
picture