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