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I checked in Squadron/Signal Zero and the A6M3 -> A6M5 did change air intake slightly higher and wider on same cowl shape. The A6M7 cowl appears have an even higher upper cowl line and a bulge in lower cowl, but I had to look so hard my eyes hurt! Model 62/63 is a very confusing model, and I think engineers rather work on A6M8 or A7M!
Osprey Aces Ki-43 has pilots claims that the last Ki-43-II which came with wing racks was slower than earlier Ki-43-II (no racks) and state "some 15mph slower" (although japanese army would have used kph). It must have been with the bomb claws attached.
Found some new comprehensive Jp.wiki data
栄 (エンジン) - Wikipedia
Ha-115/Sakae.21 all used +200mm as standard boost and +300mm as T.O. boost, so the Anti-Detonant-Injection water only increased power by "evaporative cooling density change of compresed intake air". All 7.2:1 compression all peak T.O. at +300mm boost and 2750rpm
A6M6 Sakae 31 T.O. 1300hp ***failed engine***
A6M7 m.62/3 Sakae 31a/b T.O. 1210hp
Ki-43-IIa (early) Ha-115 T.O. 1130hp
1st stage peak 1100hp @ 2850m +200mm
Ki-43-III Ha-115-II T.O. 1300hp
1st stage peak 1230hp @ 2800m +200mm
So at 200mm boost Ki-43-IIa vs Ki-43-III is 1100 vs 1230 = 12%
So at 300mm boost Ki-43-IIa vs Ki-43-III is 1130 vs 1300 = 15%
Nice improvement!
There is very little data on late model Ki-43 (or A6M5c/7) and no defined speed effects of racks. I found actual tests on wwiiaircraftperformance.org where P-51 and F6F lost 11-13mph with racks so its a relevant baseline.It sounds like you are making the assumption that the speed loss was exactly the same with the wing bomb racks on -II and -III and the result
Regarding power figures, the power differences are enough that I am wondering what else may have changed in these engines.
There is very little data on late model Ki-43 (or A6M5c/7) and no defined speed effects of racks. I found actual tests on wwiiaircraftperformance.org where P-51 and F6F lost 11-13mph with racks so its a relevant baseline.
The 12% change from the 1100-1230hp at low altitude first speed on same boost is plausibly due to the water-injection effects (~6%) and better exhaust stacks cylinder scavenging (~6%), hypotheticallyIts second speed power is harder to compare as heights are different due to different supercharger speed gearing.
Sakae 21/31b & Ha115
Two speed 980 hp / 2,700 rpm / boost + 200 mmhg (altitude 6,000 m)
Ha115-II
Two speed 950 hp / 2,700 rpm / boost + 200 mmhg (altitude 6,800 m)
Yes thats probably true,I am not at all sure that once you go to positive pressure in the intake manifold that the exhaust system back pressure is quite as important as on a naturally aspirated engine
I also reply to an earlier question why lower exhaust back pressure may be kinder on exhaust valves, that is by a Pressure drop results in a temperature drop in a gas... basic gas laws. Oh course theory and practice are sometimes different., reducing back pressure and such are not going to reduce the heat load on the exhaust valves even if they reduce the heat of the exhaust manifold.
I suspect the often quoted 351mph speed for A6M5 was a pre-production test machine.
I also reply to an earlier question why lower exhaust back pressure may be kinder on exhaust valves, that is by a Pressure drop results in a temperature drop in a gas... basic gas laws. Oh course theory and practice are sometimes different.
).
Guessed Lucky and found this!
Mitsubishi Zero: Japan's Legendary Fighter By Peter C Smith p.159
A prototype was converted from a model 22 machine and made its debut in August 1943 achieving a maximum speed of 351.07mph (565kph).
The page above appears to be a Sakae 2x series engine from hp shown and seems to be for 87 octane only and peaked at +270mm, The text says on MW50+87 octane it could reach +500mm boost?! Unfortunately that graph was not translated
If Water / Methanol is being used as a charge cooler and detonation happens eventually ANYWAY but is just delayed a bit, it sounds more like the charge cooler is reducing the heat buildup in the engine so that it takes longer for the engine to heat soak and that is really all we are seeing.
- Ivan.
Some radials (and few V-12s) used extra mixture as a both a charge cooler and an internal engine coolant. Any picture showing a piston plane taking off with black smoky exhaust probably means they are using excess fuel as a coolant. They sure aren't burning it.
A number of American engines, R-2800s in particular, used significantly less fuel when the water injection was activated. They had de-enrichment circuits added to the carb or injection unit.
The alcohol is mainly to keep the water from freezing. Water soaks up a huge amount of heat when it flashes to steam, much more than the same amount (weight) of gasoline.
as far as exhaust scavenging goes on supercharged engines, look at the difference between the incoming air/mixture pressure and the outgoing.
On an unsupercharged engine the difference between the pressure in the exhaust ports/pipes and the intake manifold is slight, in fact the pressure before the exhaust valve opens might even be higher (most unsupercharged engines operating at under 14.7lbs in the intake manifold) and a lot of the movement of the gases in under momentum?
Perhaps the US test used the markings on the gauge as the "red zone", it would explain why they got ~15mph less than the book values for the A6M5 top speeds.
Perhaps the US test used the markings on the gauge as the "red zone", it would explain why they got ~15mph less than the book values for the A6M5 top speeds.
Model Speed Altitude
A6M2-21 275 Kts 4400 m
A6M3-32 290 Kts 6150 m
A6M3-22 292 Kts 5900 m
A6M5-52 294 Kts 5900 m
There is no reason why there should be excessive vibration at a diving speed of only 250 Knots.
It does seem the later Zeros the allieds tested, A6M3 had a tired engine/supercharger.....
I have seen people say that the widely quoted 351mph for A6M5 meant it could go even faster "as Japanese tested at military power", however its clear 336mph is the actual military power speed.
A few months ago I found part of a memoir on the web from a Japanese pilot where he got to test the late A6M5 at the test centre in Japan, and he said it could be dived at 400kt, but he said he wouldn't try that in actual combat! I assume he meant it was basically uncontrollable at that speed.