Ki-61 II-Kai Versions (1 Viewer)

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I'm not sure if this is on-topic, but perhaps worthy of discussion. The TAIC Report 154B estimates the maximum level speed of the Ki 61-II at 423 mph at 28,000 feet. Seems to me that this is one of their less reliable estimates. Seems to me that this plane should go no faster than about 380-390 mph estimated from the power increase over that of the Ki-61-I.

Does anyone here have any good data on the subject?

- Ivan.
 
Hi all, well after reading in this forum for while this is my first post! I hope many more will follow.

To get on topic, I have always found the ki-61 to be one of the most fascinating aircraft of wwII. It is a beautifull aircraft but never lived up to it's expactations. But I think that with the right engine it could have been much more competetive. This bubble canopy version of the ki-61II is new to me, but why is it performance so bad with a new 1500 hp engine? It looks like it is hardly faster then the old version, don't know about climbing speed etc, but it looks like that hasn't improved much either. This is a general problem for Japanese aircraft. Does anyone have an explanation for this? Has it to do with their engine designs?
 
Yep, the ratios between declared engine powers and declared max speeds are quite fuzzy for the Japanese planes. Eg. it's quoted at many sources that Ki-84 was able to do 630 km/h with 1900 HP, or 590 km/h for Ki-100. Perhaps Shinpachi-san could shed some light on this :)

Welcome to the forum, BTW.
 
I have often wondered about this, too. I assume the real power output of Japanese series production engines was somewhat lower. This may be true for most Western engines as well but in Japan it seems it was worse than elsewhere (steel?). Then it also would be interesting what effects fuel quality and superchargers had.
 
I have often wondered about this, too. I assume the real power output of Japanese series production engines was somewhat lower. This may be true for most Western engines as well but in Japan it seems it was worse than elsewhere (steel?). Then it also would be interesting what effects fuel quality and superchargers had.

Firstly, the main problem was that Japanese used lower graded fuel (due to deteriorating war situation). Ki-84 with 87 octane fuel achieved 630kph on the battlefield, while when tested in USA with 150 octane fuel it easily achieved 680kph.

Next, Japanese standard testing of their aircraft performance was done at military power, not war emergency power, which was a standard in the rest of the world.

This two factors alone brought in a lot of confusion in regard of Japanese fighter performance.
 
Ok, so I understand. But this octane thing in fuel is also debated as I have understood from reading this forum.
And to understand your post correctly, WEP is full power en MP is a lower throttle setting with the extra throttle setting still available? This would mean then that Japanese planes could go faster then tested.
 
From what has been available to most western writers the Japanese fuel situation has not been sorted out very well.
there is no mention of lean vs rich ratings like western 100/130.
What is known is that the fuel from Dutch East Indies was very rich in aromatics which gave a good rich mixture response. This may have offered performance benefits over and above what what straight western 87 octane fuel allowed.
Octane ratings established with different test engines also vary a bit. this makes it difficult to directly compare from one nation to another in years just before or during WW II.

This does not mean I am saying that Japanese fuel was as good as American or British fuel, just that comparison are hard to make. It is also hard to make comparisons because the octane scale is not linear.
For example in testing in 1931 a P&W engine showed an increase in power of 25% when going from 91 octane fuel to 98 octane fuel. and other points in the scale a change of 9 points does not show anything like that increase.
IF the "Java" fuel allowed a rich response into the high 90 range ( and British aviation fuel from the same source when modified to have a lean rating of 100 showed a rich response of 115-120) and IF the Japanese knew of this and IF they modified/operated their engines to take advantage of it, it might explain some of the performance they were able to get from their engines from "87" octane fuel.
A lot of IFs though :)
 
Hello Folks.
Octane ratings need to be done with the same methodology. If you look at the pumps at your local gas station, you will find that the octane rating is (R+M)/2. What this means is that it is an average of Research Octane and Motor Octane. I believe Motor Octane is really what we are interested in here. Another question is what rating we are really looking for: Lean Mixture or Rich Mixture. Fuel will typically rate much higher at Rich mixture settings because the extra unburned fuel tends to cool the charge and reduce preignition (pinging / knocking / detonation).

In the US Test of a FW 190, there was a statement that the US equivalent to the German C3 (96 or 100 octane) fuel was much superior to the typical 100 octane US fuel. My point is that numbers really don't mean much unless they were obtained by the same methods.

From what I have read, the typical Japanese aviation fuel was 91 to 92 octane. There was one location (I believe the Phillipines) where the typical captured fuel tested out at 94 or 95 octane which isn't bad.

Higher octane fuel isn't necessarily superior. The octane rating is just resistance to ignition. Higher octane fuel typically has less energy content than lower octane because it has more additives (like tetraethyl lead) and less burnable stuff. It just allows higher compression, supercharger / throttle settings, and more timing advance before it starts to detonate and damage the engine. Perhaps it even allows you to use hotter spark plugs.

The bottom line is that unless your engine is designed for it, or unless you start retuning the engine by changing the timing or unless you run higher boost, you really aren't going to see a difference.

Another consideration is that aircraft sometimes use two different fuels. There may be a small tank with a different grade of fuel for starting or priming the engine. This fuel will have a LOWER octane than the stuff in your main fuel tank because when the engine is cold, it won't vaporise the fuel as well and you need something that lights off more easily. There is also the possibility that if your engine is designed to use lower octane fuel, its ignition system may not be powerful enough to fire off a charge of higher octane fuel.

Hope this clarifies a few things.
- Ivan.

Methane, Pentane, Hexane, Heptane, Octane........
 
" Fuel will typically rate much higher at Rich mixture settings because the extra unburned fuel tends to cool the charge and reduce preignition (pinging / knocking / detonation)."

That is not why there is a rich mixture rating. Use fuel to cool the engine was noted and used in WW I. Some "air cooled" engines would actually start to "glow" if the mixture was leaned out. The V-8 Renault was a prime example and used about twice the amount of fuel as was needed for combustion.
In the very late 30s or 1940 with the first use of 100 octane by the Americans the American fuel specification called for no more than 2% aromatics in the fuel mixture because the aromatic compounds tended to dissolve gaskets and tubing and other rubber products. British specification 100 octane fuel in contrast was required to have a minimum of 20% aromatics, because the British had noted the improved rich response but hand't really measured it yet. there was more than one batch of American 100 octane that actually measured lower in octane rating at rich mixtures than at the lean setting.

The same fuel will show different numbers if tested in different engines. Different bore to stroke ratios (which give different volume to cylinder wall ratios), valve sizes and location and different spark plug locations can affect results as can piston shape and construction. All affect local "hot spots".
The US and the British were able to standardize on one particular single cylinder test engine and get them built in numbers early so the various fuel suppliers and receiving stations could be sure they testing the various batches of fuel to the same standards.

"Higher octane fuel isn't necessarily superior. The octane rating is just resistance to ignition. Higher octane fuel typically has less energy content than lower octane because it has more additives (like tetraethyl lead) and less burnable stuff"

One of the specifications for aircraft fuel (out of many) was the number of btu's per gallon. While it is possible for the heat value of gasoline to vary depending on it's components, the manufacturers/blenders knew what the goal/requirement was and blended accordingly. In practice nobody was ever going to be able to tell the difference if there was one.
Lets use a little common sense too, 5-6 cc of lead was a LOT of lead (lead content was also specified, manufacturer could not just keep adding lead to poor base stock to get the required octane rating) and that is per gallon. 1 gallon is a bit under 4 liters (3.79) so 6cc is .15%, that is 1 1/2 tenths of one percent. The displacement of that much burnable stuff is going to go un-noticed.

Two aircraft that I know of, the FW 200 Condor and the Spartan Executive, there may very well be others, used the two tank/ two fuel system. Both used 87 octane to start and take-off on and switched to 80 octane fuel to cruise on. The 87 oct. gave the needed performance and the 80 oct was cheaper to fill the tanks with.
Volitilty was another aspect of the fuel that was in the requirements and could be met with the right blending and it had little or nothing to do with the octane rating by the start of WWII. In the WW I era it may have but at that time many aspects of fuel were not understood and sometimes all that was know was that gasoline from the XXX oil field behaved differently than the gasoline form the ZZZ oil field and gasoline from the BBB oil field was different still. Nobody yet knew why.
 
I often wondered how the ki-61 would have performed with a DB605 instead of the HA140. Although they are closely related I suspect (no more then that) that it would have performed better. It seems to me that the Japanese lost a lot of time (and quality) by not building the engine in licence by copying it. Any thoughts?
 
I often wondered how the ki-61 would have performed with a DB605 instead of the HA140. Although they are closely related I suspect (no more then that) that it would have performed better. It seems to me that the Japanese lost a lot of time (and quality) by not building the engine in licence by copying it. Any thoughts?

The Japanese (Kawasaki) were working on a DB605. It was called the HA 240, only two built and under test at the time the factory was destroyed.

The "problem" with building things under licence is that, while the basic engine design is already done, the manufacturing design/equipment is not. The licencee needs to be able to produce casting and forgings to the original specification and produce bearings, both roller and plain, to original quality and specification.

See: http://www.wwiiaircraftperformance.org/japan/ATIG-Report-39.pdf
 
I often wondered how the ki-61 would have performed with a DB605 instead of the HA140. Although they are closely related I suspect (no more then that) that it would have performed better. It seems to me that the Japanese lost a lot of time (and quality) by not building the engine in licence by copying it. Any thoughts?
Would've been interesting. Also could it take the DB 603? Now that would've been a late-war fighter to look out for.
 

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