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I'm not entirely sure what exactly 'putting Ki-84 on the back-burner' means, but if it implies slower development but somewhat later introduction of a more mature aircraft, that sounds reasonable enough. In 45 the Ki 44 will probably have become long in the teeth regardless.
I guess that many options for better engines exist, i trust you already indicated the most obvious. My two reservations is that the Ki-44 may not really have the range for escort, and that conservatism among pilots will result in the aircraft not being flown as much to its strengths as it should to really harvest the benefit.
The KI-84 (which turned out to be one of Japan's most formidable fighters) was intended to replace the KI-43.
The KI-44 was not as nimble as the KI-43 and not as good as the KI-84, so why not accelerate the Shoki's development and get it into service as quickly as possible?
Putting the Ki-84 in the back burner might allow for improvements of Ki-44 to be done - engine and armament upgrades.tweaks in fuel tanks, protection, etc.
The Ki-44 was not intended as the Ki-43 replacement; that was the Ki-84 as Dave pointed out, whereas the Ki-44 was considered a departure from traditional Japanese fighters in terms of its strengths in rate of climb and speed at the expense of manoeuvrability. It doesn't make sense to focus on one at the expense of another in this pair.
The KI-44-11 with four 20mm cannon should have begun replacing the Ki-43 in 1942 (completely replacing it by the end of 1943). Over this time, its engine should also have been more highly-tuned to improve its power (and thus top speed) and its supercharger improved by adding extra stages or speeds.
Of course, if the IJA/IJN were really smart and worked together, after 1941 they should have concentrated only on the Kinsei and Kasei engines (and their 18-cylinder derivatives) at the expense of all other engines (even replacing the Sakae starting in 1942!). By 1945 the Juisei engine would have come online (and inserted in the Ki-44), thus skipping the horrendously unreliable Homare engine in the Ki-84 and other IJA/IJN aircraft.
Interesting/thoughtful comments... Perhaps if there were better production control for the Homare, it wouldn't have been so unreliable (and thus be fully competitive with the R-2800)... But it seems that most roads to better high alt. performance lead to the IJA/IJN not having good enough superchargers... I've read that the US turbo-superchargers were pretty unreliable, so perhaps if could/should have copied the Merlin's????...Nakajima did some of improvements already, the Ha 109 was development of the Ha 41, sporting a big S/C that was now with 2 speeds, and with straightened internals so it can rev faster.
Granted, a 2-stage supercharged Ha 109 would've been a very interesting engine, perhaps the Japanese copying idea from a F4F-3 or -4 captured/crashed with a working engine? The water-alcohol injection is also needed, the Japanese fuel octane rating was in shambles in 1944-45.
Sakae should've been indeed mostly phased-out by some time 1943, and produced only for aircraft where the Ha 109 or Kinsei don't fit. Ditto for Suisei.
Kinsei was worse than Ha 109 for high altitudes. The switch at Nakajima so they produce Mitsubishi's engines would've cost the Japanese dearly. What might be needed is to have Kawasaki and Aichi continue make radials only instead of DB 601 copies.
Homare is a known quantity; flatly assuming that Juisei will work flawlessly under the bad conditions of the last 12 months of
is not what I'd do.
But it seems that most roads to better high alt. performance lead to the IJA/IJN not having good enough superchargers... I've read that the US turbo-superchargers were pretty unreliable, so perhaps if could/should have copied the Merlin's????...
Wow; you know a lot... So please tell me what "highly tuned" means... Tighter clearances/higher compression? Better lubricants? Better ignition? Better engine and oil cooling? I read that the Sakae was relatively highly tuned, while the Kinsei gradually became less well-tuned; and the Homare, too...US turbo-superchagers were very reliable past 1941. The control systems were sometimes misbehaving, that was sorted out by some time in 1942.
Copying the 2-stage S/C from Merlin 60 series is always a good idea. Japanese might capture the Wildcat's engine earlier than that of the Spitfire VIII?
Wow; you know a lot... So please tell me what "highly tuned" means... Tighter clearances/higher compression? Better lubricants? Better ignition? Better engine and oil cooling? I read that the Sakae was relatively highly tuned, while the Kinsei gradually became less well-tuned; and the Homare, too...
The 2 stage supercharger is not the panacea that some people seem to think it was.
you have two things going with a 2 speed supercharger.
Yes you have much more boost going into the intake manifold.
You also have much more heat going into the intake manifold.
If you cannot control the heat (hotter intake charge) your gain in power is going to be minimal as the boost pressure will have to be restricted to control detonation.
The allies had the high performance fuel and the intercoolers and (on the radial) water injection to go with the two stage superchargers.
Look at the P-63, even using 100/300 fuel and a lot of water injection the two stage super charger on the P-63 moved the Full throttle height from 15,000 to to 25,000(Or a bit less). Very useful but well over one year compared to a Merlin 61.
Now try using 92 octane (or 96 or?) fuel in the two stage supercharger had run the intake manifold temperature a few hundred degrees hotter?
Yes you can more performance than the single stage supercharger and maybe that will enough for some of the interceptors to get into firing position to shoot at bombers.
You need a lot more to actually fight American fighters at 25,000-30,000.
IM0, the Ki-44 should have begun replacing the Ki-43 in 1942... And Kinsei-powered Zeros (ala the A6M8) should have started replacing Sakae-powered Zeros by the end of that year.. The Sakae was a light, long-range carrier plane well-suited for the offensive operations of 1942, but thereafter the IJN needed a plane with an engine more capable of carrying armour, bigger guns, etc. And with refinement of its engine, the Shoki might have been almost as good as the J2M Raiden (which didn't go into service until two years later---- way too late).I don't use the term "highly tuned". Seems too vague.
We know that 2-stage supercharging worked with 87 oct fuel if the compression was kept at modest levels (6.5:1 on the Jumo 213E and F), and if there was an intercooler (213E) or the water-alcohol injection was used (both 213E and 213F). Japanese were using water injection, however their superchargers in wartime service were firmly in the 1-stage land.
(power chart for the Jumo 213F posted here, scroll down a bit)
It was IIRC a jump to 22500 ft for the 1st gen of 2-stage V-1710s vs. the latest V-1710s with 1-stage S/C that topped at 15000 ft. A major increase (7500 ft) in anyone's book.
1st step might be that IJA admits to themselves that Ki-43 and Sakae are obsolete by late 1943, and that copy of DB 601 is late by now.
1) Weren't they trying to do just that and they may have had too many things on their plate? 2) It's not like they could just duck out and use NACA's wind tunnel when theirs were busy or burn gallons of high octane for testing engines. 3) Wasn't Jiro Horikoshi hospitalized with fatigue from designing new planes and updating old ones? I'm thinking he probably wasn't the only one. As you can tell I'm not up on this stuff.
I know Jiro Horikoshi worked for Mitsubishi (read his book, saw some documentaries, love the cartoon!) but I'm guessing his counterparts at Nakajima, Aichi, Kawanishi, etc were in the same predicament. And now I know that problems were exacerbated by building everything under one roof! Not a Willow Run sized roof either.1) That was the exact problem - flood of separate designs coming basically one year after another. Eg. Nakajima was making 3 fighter types in 1941-44 for the Army - yes, the old Ki-27 was still being made in December of 1942. All in one factory. Ki-43 was still being made in August of 1945 (not by Nakajima anymore, but still), while the Ki-44, a fighter far more suited for modern air combat, was phased out in 1944. (shaking my head in disbelief)
Nakajima was also making Zeros, they made more Zeros than Mitsubishi.
2) Japanese aircraft were reasonably streamlined. What was not there was engine power above 20000 ft. Lack of hi-octane fuel can be circumvented by a good deal with water-alcohol injection, however there was no circumventing the lack of modern superchargers or turbochargers the West had in use.
3) Mitsubishi (where Jiro Horikoshi was working) was not making fighters for the IJA. IJN mis-guided purchase policy is a topic of their own (a big topic).
I know Jiro Horikoshi worked for Mitsubishi (read his book, saw some documentaries, love the cartoon!) but I'm guessing his counterparts at Nakajima, Aichi, Kawanishi, etc were in the same predicament. And now I know that problems were exacerbated by building everything under one roof! Not a Willow Run sized roof either.