# Ki-61 II-Kai Versions



## Tomt (Oct 7, 2010)

Hey I have a Question. 
I knowed that around 3 dozen KI-61 II-Kai has been built.
Some said the last Ki-61 II-Kai had a low-back like KI-100 "Otsu". 
Do you know any iformation about this?


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## Torch (Oct 7, 2010)

Don't know but 10 + 13 have nice profiles..


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## Tomt (Oct 7, 2010)

The KI-61 II-Kai (9. in Pic) was used. 
The cut down Fuselage on 10. was tested on the Ki 61 II-Kai, 
but was it used in combat?


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## krieghund (Oct 7, 2010)

Apparently only 69 examples of the Ki-61-II made it to combat units

One was modified with the cut down rear fuselage as it was tested for the planned Ki-61-III which was canceled

No idea if the canopy prototype saw combat on the Ki-61-II but it did on the Ki-100


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## windswords (Oct 8, 2010)

I have a book on the Ki-61 that says the -II Kai model with the cut down fuselage was sent to a fighter group - the 56th or 59th Sentai if I remember correctly. I will take a look at it when I get home this evening and post what I find.


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## windswords (Oct 8, 2010)

Found the book I mentioned above. Here's what it says:
According to Kawasaki Ki-61/Ki-100 in Japanese Army Airforce Service by Richard M. Bueschel (part of the Aircam aviation series) the bubble canopy version of the Ki-61 was to be called the Ki-61-III. The first ones built (prototypes?) were converted from Ki-61-II Kaib airframes and named Ki-61-II Kaic. Kawasaki built 4 of them and they were sent to the 56th Sentai (group) in the Osaka-Kobe area for "combat evaluation". I interpret this to mean that they flew them in combat. There is no further information as to how they performed with the Sentai or what the pilots thought about them.

I've included a color plate of the bubble top Ki-61 in the colors of the 56th Sentai (I don't remember where I got this image from).


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## Wayne Little (Oct 9, 2010)

I have 2 photo's of the 'Bubbletop' version neither show unit markings...


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## Shinpachi (Oct 9, 2010)

According to the Bunrindo's book,

31 prototype and 374 production type of Ki-61 II kai were to be manufactured from Sept.1944 but only 99 ha-140 engines were available for the production type.
The rest 275 airframe were converted to Ki-100 I with mitsubishi ha-112 radial engines.

How many late model or III with such bubbletop canopy is not described.


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## windswords (Oct 9, 2010)

Wayne,

Can you post those photos? I have never seen a pic of the Hien with a bubble canopy, only drawings.

Shinpachi-san,

I am not familiar with Bunrindo's book. Is it and the author reliable in your opinion?


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## Shinpachi (Oct 9, 2010)

windswords said:


> Shinpachi-san,
> 
> I am not familiar with Bunrindo's book. Is it and the author reliable in your opinion?



Hi, windswords.
It's more reliable than wiki at least


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## krieghund (Oct 9, 2010)

I believe the picture above is the same as the first picture below,l However I found a fuzzy B&W and some color profiles


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## windswords (Oct 9, 2010)

krieghund,

These are great thanks for posting! The color shot looks like it was taken after the war and the plane is a display at a base somewhere. The second B&W pic is the first I have ever seen of a bubble top Ki-61. The first color plate is used in my Bueschel Aircam book. The second color plate I also have. I got it from somewhere on the web and it supposedly is the the mount CO Capt Fudzitaro Ito of the 19th Sentai, 3rd Chutai, as it appeared in April 1945. According to Michael Reimer's website [ Imperial Japanese Army (1+ Sentais) ] the tail marking is his own. Addendum: There is Fujitaro Ito who flew a Ki-45 for the 5th Sentai. They are not the same man.

So, did the 19th Sentai also get Ki-61-II Kai bubble tops? The normal tail marking for a 19th Sentai airplane looks like this:


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## verner (Oct 9, 2010)

I'm sorry shinpachi but your pic is not a bubble-top. Look a little closer please. I almost got really excited as I don't believe I've ever seen one. Thanks though. Gettin red X's on Krieghunds' pics.


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## Shinpachi (Oct 9, 2010)

OK, verner.
This is of bubble top of army flight 56th sentai at Itami airfield, Osaka.
Same photo as #11 by krieghund, though.


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## verner (Oct 10, 2010)

Very nice. Thanks very much.


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## vikingBerserker (Oct 10, 2010)

That is a pretty aircraft. Great info fellas.


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## Shinpachi (Oct 10, 2010)

verner said:


> Very nice. Thanks very much.



You are welcome, verner.

These are relics of a crashed Ki-61 II kai of the 56th sentai.
Fuselage and wings are not found yet but I would like to believe it had the bubble-top canopy


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## Wayne Little (Oct 10, 2010)

Shinpachi's image in post 14 is one of the pics I have...can't see those others...Red X's...the other shot is definately a different aircraft...will post tomorrow...unless of course it is one of the Red X's..?


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## Civettone (Oct 10, 2010)

Nice stuff.


I also read recently that the problem with the Ha-140 engine was the crankshaft. I thought it would have been overheating of some sort. In any case, I never understood why they didn't upgrade their DB 601 copy to the 1350 hp 601E-version. 

Kris


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## Shinpachi (Oct 10, 2010)

I heard, though it might be slightly wrong, that the crankshaft contained no chrome because of army's instruction to save the resources. The shaft is said broken after 100 hours running.

Also, no time to update the engine because those necessary technical data and samples had to be delivered by submarine between Germany and Japan. It took months and almost sunk by the allies.


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## Civettone (Oct 10, 2010)

Yet they had time from mid 41 to 45. And for the Db 605 from mid 42. And if you can deliver 800 MG 151/20s?


Kris


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## Shinpachi (Oct 10, 2010)

No more idea, Civettone.
Sorry.

... but It was not until end 1944 or early 1945 when the Japanese fighters encountered B-29s at super high altitude that they understood the true value of liquid cooled engines.


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## Civettone (Oct 10, 2010)

and the true value of turbochargers 

Kris


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## Shinpachi (Oct 10, 2010)

Utterly, Kris.
Thanks.


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## verner (Oct 11, 2010)

Does anyone know if there are any other pics of a "Bubble-top III" ?


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## Wayne Little (Oct 11, 2010)

Here is that other pic...

Source : Famous aircraft of the World Ki-61


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## verner (Oct 11, 2010)

Thanks very much. I would love to do a model of this plane. There used to be a site where someone kitbashed one together but I don't think it exists anymore. Thanks again.


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## Wayne Little (Oct 12, 2010)

Your welcome!


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## Capt. Vick (Oct 12, 2010)

If I'm not mistaken, Fine Molds does it in 1/72 scale...


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## windswords (Oct 12, 2010)

I've never seen a kit myself. It seems you could take a kit of Ki-61 and Ki-100-Ib and do some "plastic surgery". 
Besides the front of Ki-61 mated to the back of the Ki-100 you would have to attach the air scoop under the fuselage. It would be a lot of work but it would look really cool.


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## davparlr (Oct 12, 2010)

Shinpachi said:


> No more idea, Civettone.
> Sorry.
> 
> ... but It was not until end 1944 or early 1945 when the Japanese fighters encountered B-29s at super high altitude that they understood the true value of liquid cooled engines.



Of course those B-29s used air cooled radials and the air cooled P-47s could easily intercept them. I think the real key was the turbo-superchargers, however, the Ta-152 did quite well with nitrous.


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## Shinpachi (Oct 12, 2010)

I heard that the heat exchange efficiency of R-3350 was superior to the Japanese engines which easily overheated.


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## Capt. Vick (Oct 12, 2010)

Capt. Vick said:


> If I'm not mistaken, Fine Molds does it in 1/72 scale...



Found it!

(See picture below)

Also found this listing of "all" Ki 61 kits:

Kawasaki Ki-61 Fighter


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## Civettone (Oct 13, 2010)

davparlr said:


> Of course those B-29s used air cooled radials and the air cooled P-47s could easily intercept them. I think the real key was the turbo-superchargers, however, the Ta-152 did quite well with nitrous.


I have my doubts about that. As far as I know the Ta 152 was never used operationally at high altitude, so the GM-1 was never used either. GM-1 on the Bf 109G-6/U2 or on the Fw 190B proved unpopular, I don't see why it would have been succesful on the Ta 152 series. Then again, I don't know what the problem was with it in the first place. Too much weight?


Kris


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## verner (Oct 13, 2010)

Thanks Cappy. Don't really do much 72nd stuff. Thanks though. Do mostly 48th. Found some pics of the kit-bash but the page is gone. Some guy named Galler used two Otaki kits. If this should go in modelling I'll move it. Cheers


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## tomo pauk (Oct 14, 2010)

That's neat


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## Capt. Vick (Oct 14, 2010)

Man that's sweet! 8)


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## vikingBerserker (Oct 14, 2010)

Now that is pretty impressive!


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## Wayne Little (Oct 18, 2010)

Rather well spliced....


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## verner (Oct 18, 2010)

Yep, he did an excellent job on this. Here's a couple a more shots. cheers.


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## Capt. Vick (Oct 19, 2010)

Man I don't know if this inspires me to build...or quit!


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## Ivan1GFP (Oct 27, 2010)

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.


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## windswords (Oct 29, 2010)

According to my Aircam book by Bueschel the top speed of the -II was 372 MPH at 19,685 feet.


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## ar250artist (Nov 1, 2010)

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?


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## tomo pauk (Nov 1, 2010)

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.


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## riacrato (Nov 3, 2010)

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.


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## TinyTim (Nov 10, 2010)

riacrato said:


> 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.


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## ar250artist (Nov 10, 2010)

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.


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## TinyTim (Nov 10, 2010)

ar250artist said:


> 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.



Precisely.


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## Shortround6 (Nov 10, 2010)

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


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## ar250artist (Nov 12, 2010)

TinyTim said:


> Precisely.



Thanks!


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## Ivan1GFP (Nov 12, 2010)

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........


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## Shortround6 (Nov 12, 2010)

" 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.


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## ar250artist (Nov 15, 2010)

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?


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## Shortround6 (Nov 15, 2010)

ar250artist said:


> 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


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## riacrato (Nov 15, 2010)

ar250artist said:


> 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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