Question about the engine of the Ki-51 Sonia: Ha-26 or Ha-26?

[Johnny .45]

I know this question would be more appropriate in a place like J-aircraft.com, but I never heard back from them when I tried to sign up for their forum. Apparently they don't like me. http://www.ww2aircraft.net/forum/images/smilies/icon_confused.gif
Anyway, it was something I had thought of a while ago. The Wikipedia page for the Ki-51 Sonia says that it has an "Ha-26" engine. When you click on this link, it takes you to the page for the Mitsubishi Shinten engine. This engine is a up-stroked version of the Kinsei engine, and apparently one of it's designations is "Ha-26" (Japanese engine designations are very confusing). But I'm wondering if that's accurate; comparing scale models, the engine on the Ki-51 looks too small to be a Shinten.
I looked around a little, and I find that the Zuisei, which has the distinction of being the smallest-diameter Japanese engine of WWII, ALSO sometimes goes by the designation "Ha-26" (the Zuisei was used by the Ki-45 Toryu, among others). Is it possible that the Ki-51 engine is actually the Zuisei, not the Kinsei?
There are other clues.
The Kinsei is over 130cm in diameter, while the Zuisei is barely 111cm; that's a significant difference.
The Ki-51 is a slow and small aircraft, rated at about 950hp. The listings I find for the Zuisei are between 850hp and 1,050hp from 28L.
The Shinten is about 1,200hp from 36L. They could have derated it to 950hp, but it would be odd for a wartime aircraft, especially when the engine was designed to increase the Kinsei's 1,000hp to 1,200hp.
Can anyone confirm any of this? I'd like to change the Wikipedia article, but I have to know if it's right or not. I know damn well that a lot of stuff on Wikipedia is flat wrong; a couple weeks ago, I pointed out that the link from the A6M Zero's page for it's cowl-mounted "Type 97 machine guns" goes to the page for the Japanese Army's "Type 97" light machine gun, a small bipod-mounted, magazine fed weapon. Apparently no one noticed that it was physically impossible for that gun to be mounted as a synchronized aircraft gun, even if the army and navy ever shared any weapons, which they didn't. Ever. Now someone has created a page for the "Type 97 aircraft machine gun" and the link is corrected, but I hate to think how long it was like that before I brought it up.

 

[GregP]

The Japanese engine designations can be fairly confusing, but there is some order there. There were separate IJA (Army) and IJN (Navy) designations and they had a unified code while an engine was in development. The "Ha" designation means "Hatsudoki," or "engine."

There are 4 parts to a development designation.

Part 1 is "Ha."

Part 2 is 1 thru 9. 1 is an air cooled inline. 2 is an air cooled, single row radial. 3 is an air cooled, 14 cylinder, 2-row radial. 4 is an air cooled, 18-cylinder- 2-row radial. 5 is an air cooled, over 18-cylinder multi-row radial. 6 is a liquid cooled 12 cylinder. 7 is a liquid cooled, over 12 cylinder. 8 is a diesel. P is a special engine.

Part 3 is a single digit bore and stroke identifier. 0 meant 130 / 160 bore and stroke (in mm). 1 meant 140 / 130. 2 meant 150 / 170. 3 meant 140 / 150. 4 meant 140 / 160. 5 meant 130 / 150.

Part 4 is a specific type identifier within the above groupings.

Once in production, the "Type" stayed and other identifiers were added.

If it made production for IJA, a "Type" was added. 1, 2, 3, 4, 5 meant 1941 thru 1945, 99 meant 1939, and 100 meant 1940. So a new engine designated "Ha 41 Type 100" was an air cooled, 18 cylinder, 2-row radial with bore and stroke of 140 / 130 mm, that entered production in 1940.

If it made production of the IJN, it got more complicated, The Navy used 2 systems. When an engine was in development, it got a 4 – 5 character identifier for manufacturer, type, design, and revisions. Once is production, it was given another type designator as follows:

First character: A, G, I, K, M, N, Y were Aichi, Hitachi, Ishikawajima, Kawasaki, Mitsubishi, Nakajima, and Air Technical Arsenal.

2nd character was D, E, K for diesel, liquid cooled, and air cooled.

3rd character was design.

4th character was revision code.

So there COULD be more than one Ha-26, but it also had a type designation if Army and a different designation if Navy. As far as I know, the Ha-26 was a Mitsubishi Army Type 99 engine. It was an Army engine and I can't explain the "6". The unified code was an Ha-31, signifying it was an air cooled, 14-cylinder engine of 140 / 130 bore and stroke. In most texts, it was the Zuisei.

 

[Johnny .45]

Thanks. I just was doing a couple google searches, and I found a page listing a Vector resin engine kit "Mitsubishi Mk2 Zuisei/Ha-26/31/102", and naming the Ki-51 as one of the aircraft it was used in (printed on the box, so it's not just a mistake from whoever was selling it). That confirms my theory. But besides finding that I don't get anything listing the Shinten and "Ha-26" together, I also find a table of Japanese engines; there is two "Ha-26's". One is the Type 99 Kinsei, and one is the Type 100 "Nu-Go (Water Cooling)" (which I intend to look into!). The Zuisei doesn't list any "Ha-26"....but again, I've found all sorts of odd variant numbers for engines that didn't match any of the three normal (Army, Navy, Unified) designations. So, I'm left where I began, except instead of being uncertain whether it's the Zuisei or Shinten, I'm now uncertain whether it's the Zuisei or the Kaisei! The Kaisei is a bit smaller than the Shinten, but not as small as the Zuisei, and since they are all Mitsubishi engines, I'm guessing they all have front-mounted camshafts and pushrods going back to the rear cylinders (Mitsubishi used that, while Nakajima used front and rear camshafts...a good way to tell engine families apart at a glance).
I'm still inclined to think Zuisei, but I still need better proof.

 

[cherry blossom]

I think that the identification of the Mitsubishi Shinten with Ha-26 in Wikipedia is just a typo. Unfortunately, I don't know how to change the name of a Wikipedia article and few people seem to be able to sort that problem out. The effect is that this is a common problem in Wikipedia.

If you look at Mitsubishi Shinten - Wikipedia, the free encyclopedia, you will note that the engine is described as a Ha-6. That is the earlier Army system identification rather than the combined Army-Navy system introduced in 1944 (?) which was described by Greg above. As the Shinten had been long forgotten by 1944, it was never given a combined designation.

Note that a single engine may have four names. Mitsubishi named an engine the Zuisei 瑞星. The Army called it the Ha-26 (model 1 or model 2) and Ha-102 as it developed. It was also called Type 99 for its year of adoption. The Navy called it the MK2A Zuisei to MK2D Zuisei as listed at Mitsubishi Zuisei - Wikipedia, the free encyclopedia. Finally, it would become the Ha-31 in the combined system as described.

ps. After looking at Mawhinney Book, I see that the unified system was established in 1942. We are all waiting for Robert Mawhinney's book to solve all our problems.

 

[cherry blossom]

I found that it was easier than I had thought to change the Wikipedia articles as I only had to alter the redirect page. Thus the mystery mention in post 1 has now magically vanished