Speed Discrepancy between Ki-43-II and A6M3/A6M5

[Laurelix]

ソース(Source) 「キ43飛行性能表」『飛行第５９戦隊整備関係資料』防衛研究所蔵
(Library of National Institute for Defense Studies)
"Ki43 flight performance table" from "Maintanance documents relating
to 59th FR"
登録番号(registration number) 陸空-濠北方面-84

高度 最高速度 上昇力
(Alt.) (Max. speed) (Clim. speed)
1000m 463km/h 1'13"
2000m 481km/h 2'25"
3000m 498km/h 3'30"
3340m 504km/h
4000m 504km/h 4'35"
4800m 500km/h(supercharger switching altitude)
5000m 503km/h 5'49"
6000m 515km/h 7'24"
6080m 515km/h
7000m 514km/h 9'12"
8000m 508km/h 11'09"
9000m 497km/h 13'36"
10000m 478km/h 17'20"

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Based on these figures we can estimate the SL max speed is roughly 445km/h at Military Power and 515km/h at 6000m
Now... the A6M3 features the same Sakae 21 / Ha-115 engine....

According to TAIC...
A6M3 Hamp has 457km/h at SL with WEP which is with 1130 Horsepower, this corresponds to 440km/h at SL at military power with 1010 Horsepower. A6M3 Hamp is given 557km/h max speed at optimal altitude with WEP.

The issue here is... Ki-43-II is supposedly faster at SL with 445kph at military power which would correspond to 562km/h max speed with WEP at optimal altitude. However the japanese source only lists 515km/h at 6000m at military power and at best youre getting 530-532km/h with WEP with that Military Power figure.

The issue is that with 515km/h at 6000m at military power, with the Ha-115 power curve i would expect only 420km/h at Sea Level, but then there would be the issue of it being slower than Ki-43-I at Sea Level despite having bigger wings (more drag) and weaker engine. So either 515km/h is just wrong... or the Ki-43-II critical max altitude ended up being a lot lower than that of the A6M's despite using the same engine.

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According to JICPOA
A6M3 Mod 22 has
520km/h (281knots) at 3250m
541km/h (292knots) at ~6000m at military power
Based on Power Curve the Sea Level Speed is somewhere between 445-452kph at military power.
Ki-43-II is listed at basically 445 at SL as well but its optimal alt speed is a lot lower.


Ki-43-II supposedly has
504km/h at 3250m
515km/h at 6000m at ~6000m

 

[taly01]

That US JICPOA Zero data table is made from the captured Japanese documents from Kwajalein Atoll , Marshall Islands 1944. It is thought the Zero 52 in that table is the earliest version without thrust pipes.
Also the Ki43-II 515kph speed is thought to be from its earliest version, with the long wings and less streamlined cowling.
All those speeds are at military power.

There is some evidence the JAAF Ha115/Sakae 21 used a lower military power rpm/boost (-200rpm) than the JNAF, which would account for lower altitude for peak speeds.

US TAIC data as many have now realised is calculated guesstimates and not to be taken too seriously.

 

[Laurelix]

So apparently...

Sakae 21 and Ha-115 are indeed different engines. They are variants of the same engine.

Sakae 21 was more fuel efficient achieving maximum of 1130 Horsepower and featured 2 stage supercharger
Ha-115 was more optimized for tactical operations and was more efficient achieving 1150 Horsepower, however it only had a single stage supercharger

This could explain why Ki-43-II speed is struggling after 3340-4000m altitude compared to A6M3 despite having similar Sea Level Speeds....

 

[ThomasP]

This is from the 'History of Nakajima Aircraft Engines'. According to this both variants of the Ha-115 - the Sakae 21 and Sakae 31 - had single-stage 2-speed superchargers. The only significant differences were the propeller reduction ratios, and the late-war availability of water-methanol ADI on the Sakae 31.

 

[Laurelix]

This is from the 'History of Nakajima Aircraft Engines'. According to this both variants of the Ha-115 - the Sakae 21 and Sakae 31 - had single-stage 2-speed superchargers. The only significant differences were the propeller reduction ratios, and the late-war availability of water-methanol ADI on the Sakae 31.

View attachment 829626

Ha-115 did later adopt 2 stage supercharger but that was later

 

[tomo pauk]

Sakae 21 was more fuel efficient achieving maximum of 1130 Horsepower and featured 2 stage supercharger

Ha-115 did later adopt 2 stage supercharger but that was later

No 2-stage S/C for either of those.
There was no Japanese aero engine with a 2-stage S/C that was used in ww2 flying combat missions.

 

[MIflyer]

Here is some engine comparison info from the book "A History of Aircraft Piston Engines"