Ki-61/100 Hien Performance (1 Viewer)

[Shortround6]

How could such a slender, delicate wing be so rugged? The weights of the Ki-61/100 in comparison with similar fighters do not indicate heavier structure.
How were three spars possible without being heavier?
I thought the Me 109 had a main spar with two auxiliary spars as well.

3 small spars might be both stronger and lighter than 2 big spars. Remember that the skin handles some of the load/spreads it out.
It is going to cost more to make however.

auxiliary spars are sometimes just places to hang the flaps and/or ailerons. they sometimes to not transfer torsional loads into the fuselage or the opposite wing structure.

Please note the Ki-61/Ki-100 did not have large gun bays interrupting things in middle of the wing.

 

[spicmart]

The details about the Ki-61-I/Ki-61-II/Ki-100 structure:

The forward wing spar must have been almost identical with the wing leading edge.

@ Shortround6 It looks like the Ki-61 also had more of 1 main wing spar and 2 (or just 1?) auxiliary spars on this illustration rather than what one would call 3 spars.
And the Ki-61/100 did have midwing cannons (you meant that?).

 

[AerialTorpedoDude69]

I recently came across a reference in Japanese Wikipedia that the Ki-61-II's Ha-140 engine used water methanol injection. Does anyone know if this is true?

Here's the Bing English translation of the Japanese Wikipedia article on the Ki-100:

In the spring of 1942, the Ha-140 was developed, a 1,500 horsepower liquid-cooled inverted V12 engine while retaining the basic structure of the Ha-40. This new engine increases the intake pressure to increase the engine speed from 2,500 rpm to 2,750 rpm, and increases the take-off power from 1,175 horsepower to 1,500 horsepower[16]​, to cool the larger supercharger. Water-methanol injection device was introduced[16].​ However, the production of this engine was very difficult. The first model equipped with this engine, Ki 61-II, was discontinued after 8 prototypes from September 1943 to January 1944[17]​[16]​, and from the ninth aircraft Ki 61-II was revised. , Type 3 fighter Type 2 was produced, but by August 1944, even after 30 additional prototypes[17],​ Production of the Ha 140 engine, which is still not stable, has not been stabilized. Captain Tomoo Natori of the Examination Department, who went to the Akashi factory to investigate the trouble, also thought that the Ha 140 had no prospects, and as a mechanic, he could not say that he would fly on it[18​].

I am surprised that they achieve a higher HP rating not by drilling it out the Ha-140 but by increasing RPMs, boost presssure, and adding WM injection. Germany had struggled with adding WM injection to the DB 603 because of cylinder cracking. I guess injecting water into the supercharger was more reliable?

The Japanese entry on the Ha-40 also claims that the Ha-140 had the same cylinder sizes and just added WM50 injection, higher RPMs, higher boost pressures, and (also) a higher compression ratio, which suggests it required a higher octane fuel.

 

[tomo pauk]

I recently came across a reference in Japanese Wikipedia that the Ki-61-II's Ha-140 engine used water methanol injection. Does anyone know if this is true?
Here's the Bing English translation of the Japanese Wikipedia article on the Ki-100:

I am surprised that they achieve a higher HP rating not by drilling it out the Ha-140 but by increasing RPMs, boost presssure, and adding WM injection. Germany had struggled with adding WM injection to the DB 603 because of cylinder cracking. I guess injecting water into the supercharger was more reliable?

The Japanese entry on the Ha-40 also claims that the Ha-140 had the same cylinder sizes and just added WM50 injection, higher RPMs, higher boost pressures, and (also) a higher compression ratio, which suggests it required a higher octane fuel.

The DB 603 had the water-alcohol injection in the eye of the S/C, too (when installed).
Spinning the DB 601 faster, along with many other changes, was also done by DB, when 601A became 1st 601N, and then 601E.

 

[AerialTorpedoDude69]

The DB 603 had the water-alcohol injection in the eye of the S/C, too (when installed).
Spinning the DB 601 faster, along with many other changes, was also done by DB, when 601A became 1st 601N, and then 601E.

I always assumed that the DB 603 issues with WM injection had to do with the Bosch patent on injection directly into the combustion chamber. IIRC, the Bosch process provided more of an increase in performance but it caused more damage to the engine. Supercharger injection seems far less risky due to there being less of a change in temperature and less microfracturing.

But all the sources that I've checked do state that the Ha-140 was not a licensed copy of the DB 605 but rather a modification of the 601 series. But then that doesn't make sense because the Ki-61-II had an enlarged wing to compensate for the increase in engine size. But that little factoid makes even less sense because Kawasaki reverted back to the original wing in the final production version of the Mk II model and apparently everything was gravy. That just doesn't happen if the center of gravity has shifted. So it seems a lot of the available data isn't really all that reliable.

 

[tomo pauk]

I always assumed that the DB 603 issues with WM injection had to do with the Bosch patent on injection directly into the combustion chamber. IIRC, the Bosch process provided more of an increase in performance but it caused more damage to the engine.

That was a direct fuel injection thing, not the injection of the MW 50 mixture.
An increase in performance was achieved via the greater valve overlap, that allowed for better cylinder scavenging. About 10% more power was the gain.
Carburated engines didn't work well (or at all) with the big valve overlap since that would've meant that the un-burned fuel is also dumped through the exhausts.

But all the sources that I've checked do state that the Ha-140 was not a licensed copy of the DB 605 but rather a modification of the 601 series.

From what I've read about the Ha 140 (and that is not much), it was the improvement of the Ha 40.
OTOH, just how many Ha 140s were tested by the Allies - who knows?

But then that doesn't make sense because the Ki-61-II had an enlarged wing to compensate for the increase in engine size. But that little factoid makes even less sense because Kawasaki reverted back to the original wing in the final production version of the Mk II model and apparently everything was gravy. That just doesn't happen if the center of gravity has shifted. So it seems a lot of the available data isn't really all that reliable.

Can you double-check the wing sizes?

 

[AerialTorpedoDude69]

That was a direct fuel injection thing, not the injection of the MW 50 mixture.
An increase in performance was achieved via the greater valve overlap, that allowed for better cylinder scavenging. About 10% more power was the gain.
Carburated engines didn't work well (or at all) with the big valve overlap since that would've meant that the un-burned fuel is also dumped through the exhausts.



From what I've read about the Ha 140 (and that is not much), it was the improvement of the Ha 40.
OTOH, just how many Ha 140s were tested by the Allies - who knows?



Can you double-check the wing sizes?

Thank you that makes a lot of sense. I must have misread the entry on the 603's development.
This is from English Wikipedia:

Compared to the Ki-61-I, the Ki-61-II had 10% greater wing area, used more armour and was powered by the Kawasaki Ha-140 engine generating 1,120 kW (1,500 hp). After overcoming initial fuselage and wing stability problems, the new interceptor reverted to the original wing and was put into service as the Ki-61-II-KAI. However, the Ha-140 engine had severe reliability problems that were never fully resolved, and around half of the first batch of engines delivered were returned to the factory to be re-built. A US bombing raid on 19 January 1945 destroyed the engine factory in Akashi, Hyōgo, and 275 Ki-61-II-KAI airframes without engines were converted to use the Mitsubishi Ha-112-II radial engine, resulting in the Ki-100. While the Ha-112 solved the problems encountered with the Ha-140, the new engine still had a major weakness: a lack of power at altitude, which diminished its ability to intercept high-flying B-29 Superfortresses relative to the Ki-61-II.[12]​[16]​

So they're saying that the II-Kai used the original wing and the Ha-140 engine.​

Japanese Wikipedia (the source isn't adequately displayed) states that The Ki-61 II Ko and Otsu had a 10% larger wing. And the Ki-61-II Kaizen reverted to the Ki-61-I Tei wing. It also states that the wing area is 20 meters squared. Furthermore, it states that it's unknown why the larger wing was adopted and then quickly abandoned. Some sources claim that the large wing had poor flight characteristics and others claim that it was to fit 20mm in the wing.​

The source is:​
Doi, Takeo (1999), "Design and Development of Type 3/Type 5", Hiyan and Type 5 Battle, Illustrated Military Aircraft Series, 2, Kojinsha, ISBN 4-7698-0911-5

 

[Ivan1GFP]

Hello All,
You already figured out that the -II used a larger wing and the -II-KAI reverted back to the Ki-61 wing.
The original -I wing was 20.0 M^2, The new wing which was used on prototypes was 22.0 M^2.
This is just a guess, but I don't believe the new wing was intended to mount 20 mm cannon because with the Ki-61-Id, the plane was already stretched in the fuselage to allow for larger ammunition boxes in the nose to feed the Ho-5 20 mm cannon mounted there. The Ki-61-II increased the ammunition load from 120 rounds per cowl gun to 250 rounds. If I recall correctly, it was to allow ammunition boxes to sit one behind the other instead of side by side as on -Id aircraft.

As for the Ha-140 versus Ha-40, the basic dimensions of bore and stroke are the same, but compression increased from 6.9:1 to 7.2:1.
I have not found a good diagram of the Ki-61-II to verify the location of a Anti Detonant Injection tank if any.
The Take-Off boost setting was +480 mm which is usually high enough to require ADI, but might be of such short duration as to not need it. The regular military power boost of +380 mm was just at the borderline of what I would expect to need ADI.

As for valve overlap and carbureted engines, there is no problem with that. This is actually done all the time with high performance street and race cars. The issue is that at low RPM, the vacuum signal to the carburetor for fuel metering is somewhat inconsistent and leads to a lumpy idle (misfires here and there). The solution sometimes is just to raise the idle speed a bit which you usually do anyway with a manual transmission, but it still.... Another solution is to use "Rhoads Lifters" which are basically just leaky valve lifters. They pump up when the oil pressure builds with higher RPM and you start to get full valve lift. Before they pump up, you get less lift than your cam would otherwise provide.
As for fuel-air mixture going out the exhaust valve, if the intake and exhaust runners are proportioned correctly with the engine displacement and RPM, what you really get is quite effective scavenging and possibly even a volumetric efficiency over 100% at certain RPM. It is really cool when that happens, but it does not happen often.

- Ivan.

 

[AerialTorpedoDude69]

Interesting stuff. Thanks for sharing.

I've read more regarding the Kawasaki Ha-140 and the Aichi Atsuta. It's very surprising. In Japanese records, the Aichi Atsuta was regarded as being vastly superior to the Ha-140. Apparently, Aichi (formerly a watch making company) had managed to adapt the 600 and 601 series to their own manufacturing processes with no difference from air-cooled engines, in terms of quality and reliability.

The reason was that Aichi had started to manufacture the DB 600G in 1938, at least a year before Kawasaki got their hands on the DB 601A. And so they had developed manufacturing processes that made inline engines as reliable as air cooled. Although it's also stated in the article that IJN ground crews were inexperienced with inlines. As a result, the serviceability of the Atsuta was slightly lower than radial engines. This is surprising because TAIC considered Aichi inlines to be trash compared to the Kawasaki models. But there were no reports of the IJN complaining about their Suiseis' reliabilities. The only naval inline engine that may have been unreliable was the 1,400 HP Aichi Atsuta Model 32. However, this variant was a pumped-up version of the DB 600 Ga, which normally only made about 1,000 HP.

This is interesting because the Atsuta 32 has the same stroke and bore as the DB600Ga. That means in order to get more horsies, Aichi engineers needed to pump up compression ratio, RPMs, and boost pressure on a carbureted engine. The 600G was basically a 600A (edit) 601A (edit) without fuel injection. While I want to say it was an unreliable engine, the entry on the Suisei specifically states that it was about as reliable as air-cooled engines. And, according to a major who worked on the engines, Atsuta 32s could have operational rates of up to 70%, meaning it was more reliable than many air-cooled engines. Some of the modifications that the Japanese made were using water rather than glycol for cooling. And changing the cooling system to a high-pressure system. But, unfortunately, there's no mention of how they got 40% more power.

If you're wondering why the Ki-61 didn't use an Atsuta 32, the reason is simple: Aichi's alloying process was time intensive. They had to remove nickel from the process, and they used some kind of quenching process to make their drive shafts more resilient. They knew that naval orders were constrained by IJN's dwindling number of carriers, but the army's demands far exceeded their capacity for building engines. However, the final version of Aichi's Atsuta series produced around 1,700 HP, although this was used in a recon aircraft in a ganged configuration (the Keiun). I'm a little curious as to what a Ki-61-III would have performed like using a more reliable 1,700 HP engine.

 

[Ivan1GFP]

When you are looking for maximum speed performance, you are not really concerned with Sea Level horsepower levels unless you happen to be pylon racing. What is crucial is altitude performance at critical altitude. In the case of the Ki-61-I versus Ki-61-II, the low altitude performance was greatly in favour of the -II. The problem is that its advantage wasn't that great at altitude which is why it wasn't that much faster.
TAIC made the assumption that the Ki-61-II used a DB 605 equivalent with a good supercharger which is why they got such high speed estimates. The reality was that it was just a more highly developed DB 601Aa equivalent and the supercharger wasn't nearly as good as assumed.
The same thing applies to some American fighters such as the P-40E/K and early P-39. They were really nice at low altitude but ran out of supercharger by around 12,000 to 14,000 Feet.

- Ivan.

 

[wells]

I recently came across a reference in Japanese Wikipedia that the Ki-61-II's Ha-140 engine used water methanol injection. Does anyone know if this is true?

Here's the Bing English translation of the Japanese Wikipedia article on the Ki-100:


I am surprised that they achieve a higher HP rating not by drilling it out the Ha-140 but by increasing RPMs, boost presssure, and adding WM injection. Germany had struggled with adding WM injection to the DB 603 because of cylinder cracking. I guess injecting water into the supercharger was more reliable?

The Japanese entry on the Ha-40 also claims that the Ha-140 had the same cylinder sizes and just added WM50 injection, higher RPMs, higher boost pressures, and (also) a higher compression ratio, which suggests it required a higher octane fuel.

yes, there was a 95L methanol tank behind the cockpit

 

[tomo pauk]

If you're wondering why the Ki-61 didn't use an Atsuta 32, the reason is simple: Aichi's alloying process was time intensive. They had to remove nickel from the process and they used some kind of quenching process to make their drive shafts more resilient. They knew that naval orders were constrained by IJN's dwindling number of carriers but the army's demands far exceeded their capacity for building engines.

Aichi was supplying the Navy, while Kawasaki was supplying Army - that would've stood against the Ki-61 usage of the Atstutas even if there was enough to spare?

This is interesting because the Atsuta 32 has the same stroke and bore as the DB600Ga. That means in order to get more horsies, Aichi engineers needed to pump up compression ratio, RPMs, and boost pressure on a carbureted engine. The 600G was basically a 600A without fuel injection.

You probably mean 601A there.
The 601 were also with the variable speed drive for the S/C, while I believe that even the last 600 versions were with the 1-speed S/C drive. TAIC manual notes the variable speed drive on Atstuta 22 and 32, as well as the fuel injection.

yes, there was a 95L methanol tank behind the cockpit

Would you be so kind to provide a source for that?

 

[Ivan1GFP]

The fuel load of the Ki 61-Id was the following:
Ki 61-Id
Wings 2 x 170 Liter
Wing Center 1 x 160 Liter
Fuselage 1 x 95 Liter
Total Internal Fuel = 595 Liters

The references I have found all list the fuel tank arrangement of the Ki 61-II-KAI as the same as the -Id.
Diagrams do not show but one 95 Liter tank behind the cockpit, which is the Fuselage fuel tank, so unless there is another 95 Liter tank elsewhere, I don't believe the one behind the cockpit is for ADI.

- Ivan.

 

[wells]

Why couldn't that tank be used for ADI on the -II or ki-100 ?

Sources are attached, and then there's this http://www.wwiiaircraftperformance.org/japan/ATIG-Report-39.pdf

 

[Ivan1GFP]

Because if it were, the total fuel load would show 500 Liters instead of 595 Liters.

With a Take-Off boost pressure of +480 mm, it makes sense that Ha-140 SHOULD have ADI, but as your figures note, the fuel capacity numbers are in agreement with the Ki 61-1d, so if there is a 95 Liter Water / Methanol tank, One has to wonder where it might be. Perhaps the fuel was relocated somewhere else? I haven't been able to find a drawing or description of changes to the fuel system or mention of a ADI tank, but I don't read Japanese at all.
Perhaps it was a system like C3 Einspritzung which used direct fuel injection into the supercharger for charge cooling and and anti detonant? That would explain the lack of an extra tank.

- Ivan.

 

[wells]

Because if it were, the total fuel load would show 500 Liters instead of 595 Liters.

With a Take-Off boost pressure of +480 mm, it makes sense that Ha-140 SHOULD have ADI, but as your figures note, the fuel capacity numbers are in agreement with the Ki 61-1d, so if there is a 95 Liter Water / Methanol tank, One has to wonder where it might be. Perhaps the fuel was relocated somewhere else? I haven't been able to find a drawing or description of changes to the fuel system or mention of a ADI tank, but I don't read Japanese at all.
Perhaps it was a system like C3 Einspritzung which used direct fuel injection into the supercharger for charge cooling and and anti detonant? That would explain the lack of an extra tank.

- Ivan.

Fair enough. The way the data is given, seems to imply that there may be an additional 95L tank. But yeah, I don't know where it would be. The same source also gives 95L for the methanol tank on the Ki-100. Maybe we need to look at that airplane instead.

 

[wells]

Because if it were, the total fuel load would show 500 Liters instead of 595 Liters.

With a Take-Off boost pressure of +480 mm, it makes sense that Ha-140 SHOULD have ADI, but as your figures note, the fuel capacity numbers are in agreement with the Ki 61-1d, so if there is a 95 Liter Water / Methanol tank, One has to wonder where it might be. Perhaps the fuel was relocated somewhere else? I haven't been able to find a drawing or description of changes to the fuel system or mention of a ADI tank, but I don't read Japanese at all.
Perhaps it was a system like C3 Einspritzung which used direct fuel injection into the supercharger for charge cooling and and anti detonant? That would explain the lack of an extra tank.

- Ivan.

There's something in this drawing that is bigger than the oil tank, outlined in blue. It may be the best clue. Perhaps it is beside/under the oil tank on the starboard side? Or maybe, that's just an access panel. We may never know!

 

[AerialTorpedoDude69]

The 601 were also with the variable speed drive for the S/C, while I believe that even the last 600 versions were with the 1-speed S/C drive. TAIC manual notes the variable speed drive on Atstuta 22 and 32, as well as the fuel injection.

Thanks again.

If TAIC has the Atsuta 32 as having direct injection, then either Aichi retrofitted a 600G with direct injection (Daimler supposedly designed the DB600 series to be upgradeable to DI) or the Atsuta 32 was based on the 601A and Japanese wikipedia is in error.

EDIT: Or the more likely scenario that TAIC got bad information somehow.

 

[tomo pauk]

Thanks again.

If TAIC has the Atsuta 32 as having direct injection, then either Aichi retrofitted a 600G with direct injection (Daimler supposedly designed the DB600 series to be upgradeable to DI) or the Atsuta 32 was based on the 601A and Japanese wikipedia is in error.

EDIT: Or the more likely scenario that TAIC got bad information somehow.

Japanese Wikipedia says this:

Speaking of Atsuta, the Atsuta 21 and 32 types, which are licensed products of the Daimler-Benz DB 601, are famous, but in general, when it is said that the license production rights were acquired at the direction of the Navy, it is often referred to the DB 601. Prior to this, however, the Navy had purchased the license rights to the DB 600, which was actually produced in small quantities.

...that immediately pops a question: the Type 32 was exactly what DB 601 version??

 

[Ivan1GFP]

View attachment 806301
There's something in this drawing that is bigger than the oil tank, outlined in blue. It may be the best clue. Perhaps it is beside/under the oil tank on the starboard side? Or maybe, that's just an access panel. We may never know!

Keep in mind the relative sizes of tanks. The fuselage is much narrower behind the cockpit, but that rather large object is a 95 Liter Tank. Maybe the extra size is for self-sealing material. I suspect there really isn't all that much room on one side or the other of the oil tank because its capacity is 48 Liters.
The fuel capacity of the Ki 100 is listed as 595 Liters as well, so it is the same as the Ki 61-id and Ki 61-II-KAI.

- Ivan.