Ki-61/100 Hien Performance

tomo pauk said:

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??

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The answer to that is easy. The Germans never licensed anything but the DB 601Aa.

tomo pauk said:

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??

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It was an incorrect translation, thanks for pointing this out. Here's what Bing Translate wrote:

Atsuta developed and manufactured the DB 600 and DB 601 engines at Daimler-Benz in Germany around the time of World War II, under the direction of the Imperial Japan Navy (Japan Navy). It is a liquid-cooled engine for aircraft produced under license by Aichi Aircraft. The Atsuta Type 11 (Navy Code: AE2A), which produced the DB 600G under license, the Atsuta Type 21 (AE1A), which was produced under license from the DB 601A, and the Atsuta Type 32 (AE1P) as an improved version of the DB 600G. It was mounted on the carrier-based bomber Comet and the special attack aircraft Haruran. In addition, Kawasaki Aircraft's Ha40 is an engine that also domestically produced the DB 601 under the direction of the Japan Army.

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This was of course a complete mistranslation. Here's a generative AI translation:

The Atsuta was a liquid-cooled aircraft engine produced under license by Aichi Aircraft Company at the direction of the Imperial Japanese Navy during World War II. It was based on the German Daimler-Benz DB 600 and DB 601 engines. Variants included:

• Atsuta 11 (Naval designation: AE2A): A licensed version of the DB 600G.
• Atsuta 21 (AE1A): A licensed version of the DB 601A.
• Atsuta 32 (AE1P): An improved-performance variant of the Atsuta 21.

These engines were installed in aircraft such as the Yokosuka D4Y Suisei (Comet) carrier-based dive bomber and the Aichi M6A Seiran special attack aircraft.

In parallel, at the direction of the Imperial Japanese Army, the Kawasaki Ha-40 engine was developed as a domestically produced version of the DB 601.

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You were exactly right: The 600G was not developed into the Atsuta 32. The Atsuta 32 is based on the DB601A. The Atsuta 11 is actually a slightly pumped up 600G. (Some sources refer to the 11 series as the 12. But in either event, the HP is listed as 1,200. Oddly, the Japanese source does not list the 11's HP output.

EDIT: My best guess here is that the D4Y1 "Judy" used the Atsuta 21, which was the DB 601A copy and that there has been some mistranslation going on.

EDIT2: It looks like the D4Y1 initially used the Atsuta 11 but then quickly changed over to the Atsuta 21.

I am not sure if you all are familiar with fuel injection for gasoline engines. It isn't quite the same as for Diesels.
The injectors typically don't inject directly into the cylinder. Properly named, they would be called "Port fuel injection" because the injectors are in the intake manifold and aimed at the back side of the intake valve. The fuel is timed to inject when the valve is open and vaporizes as it hits the hot intake valve and is drawn into the cylinder by the incoming charge air.
This method in automobiles tends to result in really clean intake valves because no deposits of any consequence form there as would happen if the fuel came pre-mixed with charge air. I have looked at those intake valves on a couple auto engines which is how I know. The exhaust valves never form deposits because they run so hot.

This method doesn't work for Diesels because they rely on compression heat and sometimes a glow plug for ignition. If the fuel arrived at the same time as charge air, the exact time of ignition could not be controlled and you get pinging or simple destruction.

- Ivan.

From a post on this site back in 2015

all descriptions that I have sees say they DB engines used direct injection into the cylinders using an injector screwed into the head like a spark plug.
The world may have figured out better ways to do things since the early 40s.

Ki-61-I , Ki-61-II, Ki-100 series all have the same wings.
850km/h IAS maximum safe dive limit

Laurelix said:

View attachment 831878
View attachment 831879

Ki-61-I , Ki-61-II, Ki-100 series all have the same wings.
850km/h IAS maximum safe dive limit

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That is quite a high max safe dive limit for an airplane with such slender one-spar wings.
Higher than many other fighters have iirc.
I wonder how the Japanese designers managed to accomplish this?

spicmart said:

That is quite a high max safe dive limit for an airplane with such slender one-spar wings.
Higher than many other fighters have iirc.
I wonder how the Japanese designers managed to accomplish this?

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By using three spars instead of one, the front one being just before the leading edge and serving as a support for the landing gear, the main one at a third of the chord and the third at the back to support flap and aileron hinges.

spicmart said:

That is quite a high max safe dive limit for an airplane with such slender one-spar wings.
Higher than many other fighters have iirc.
I wonder how the Japanese designers managed to accomplish this?

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My understanding is that the sparring on Japanese aircraft were made from Extra-Super Duralumin, which is a 7000-series alloy, something equivalent to 7076 or 7075, depending on the source (I believe Wikipedia lists it as 7075).

It's been reported in Life Magazine, based on an analysis by TAIC of the Attu Zero, that Japanese aircraft didn't need very many attachment bulkheads for the wing because the fuselage and wing were built as a single structure. I interpret this to mean that the wing spars passed through the fuselage and were built as a single contiguous spar. They mention that this is more labor intensive but the structure is stronger and lighter (more "maneuverable").

At the time, Japanese industrial policy favored labor-intensive processes using skilled machinists. So, it's likely that all Japanese fighters used the wing spar as the carry-through spar (if my understanding of the structure is correct) in order to minimize attachment bulkheads. But I have yet to see a schematic of the Zero which demonstrates this feature, so I could be wrong.

If I'm right, then it's a big reason (along with having three 7075 spars) for the Ki-61's excellent dive performance.