Nakjima Homare - what's the verdict?

[DarrenW]

2. The Fancillon data is for the prototypes, which lacked thrust augmentation exhaust stacks, used an unspecified fuel type (probably 92 octane), had 1,800 HP engines (as you mentioned), used an unknown test methodology, etc... So these are not indicative of actual performance either. Also, I could not find any of Francillon's sources. I'm not sure where he got his data from.

It's always good to question sources. However, Francillon's book is still considered the benchmark when discussing Japanese WWII aircraft mainly because he did search out official Japanese documents whenever possible. In addition, Nakajima Ki-84 a/b Hayate in Japanese Army Air Force Service (Bueschel) reiterates these same performance stats and his book had a multitude of aviation researchers involved, many of whom were of Japanese descent. So I suspect that this data is as accurate as humanly possible.

I also read that the added thrust from the modified exhaust could provide up to an extra 10 mph in top speed but the addition of wing mounted pylons negated some of this. Speed was increased to 394 mph at 21,800 feet, an improvement of 6 mph in pre-production machines. But like you said, this could only be attained by aircraft under strict testing parameters and not by those in the field.

 

[DarrenW]

Where does methanol water injection fit into all of this? The Ki.84 had it. It is the only explanation for the engine's rated BMEP.

To achieve the rated 2,000 hp water injection would definitely be required. Furthermore, because of the poor quality of Japanese fuels it was common to utilize it for even lower power levels to reduce detonation.

 

[DarrenW]

An adequately maintained Ki-84 with a properly functioning engine and quality fuels could likely hit 390 mph around 20,000 ft.This is quite fast by Japanese standards.

There is data out there suggesting that the Ki-84 with the model 23 engine reached 416 mph. This was the low pressure fuel injection version of the Homare but was similar to the model 21 in most other respects including output power. But without knowing the testing parameters it wouldn't be prudent to accept this figure as possible by even a well maintained Ki-84 in the field.

The Homare model 11 was MAP rated at +350mm military and +400mm war emergency (1,850 hp at sea level). Model 21 increased war emergency MAP to +500mm (1,990 hp at sea level).

 

[tonycat77]

To elaborate on what Shinpachi mentioned, Japan's conscription policy did not exclude critical workers, such as skilled machinists and mechanics who would otherwise contribute to engine production. As a result, as the war progressed, engine quality fell off the map as critical skilled labor was rapidly replaced with child and newly trained workers.

Additionally, it's mentioned in multiple sources that the Homare ran best on 100 octane fuel. I'm not sure why that is because that implies it was designed from the outset to use 100 octane fuel.

But pretty much all of Japan's high horsepower engines were maintenance nightmares. If you look at the serviceability of planes with the Homare, the Kasei, or early model Tenzans (B6N1), they're all reported to be terrible. Why else would pilots prefer the Kinsei 64 over the Homare?

Sounds like a really dumb policy, USSR was in much dire straits for most of the war and they didn't do that, not on that scale anyway, most of the soviet aircraft early problems seem to be factories not used or trained in producing the more advanced airframes.

 

[Ivan1GFP]

Gentlemen,
I am a bit disappointed in this discussion because I see pretty much the same people for the most part and it seems to be going about the same place as it usually does. Folks seem to forget what has already been presented in prior threads on the same subject.
Here is a link to the Middletown Test Report of a Homare engine removed from a Ki 84, serviced to correct issues and then bench tested. Folks in this discussion seem to be forgetting that the Japanese use of Water Methanol wasn't quite the same as that of other nations. They basically used it whenever the throttle settings were pushed over our equivalent of Maximum Continuous power. For details, read the report. I uploaded this over 4 years ago.
Japanese Aircraft Performance

From this report I believe it is reasonable to conclude that the power claims of 1990 HP for this engine were reasonable if everything was working as designed which usually was not the case. As for the maximum speed that was reached at this power level, I have been in way too many discussions of this one type to join in again. Just keep in mind that Japanese performance testing was done at equivalent of Military Power settings which were way below their Take-Off power settings.

- Ivan.

 

[Shinpachi]

Shinpachi might know more.

I think I have mentioned basic matters in my old thread "Data base Japanese aircraft engines."
Nakajima was a sort of gambler or entrepreneur in a good sense like its founder Chikuhei Nakajima while Mitsubishi was a group of steady engineers as a traditional combine.

Nakajima aero-engines

Data Base: Japanese Aircraft Engines

Seems like a good place to put these manuals, I don't have the first one but does talk about engine oils, superchargers and other stuff.

ww2aircraft.net

Mitsubishi aero-engines

Data Base: Japanese Aircraft Engines

Engine for the Intercontinental Bomber "Fugaku" - challenging 5,000hp

ww2aircraft.net

 

[DarrenW]

Folks in this discussion seem to be forgetting that the Japanese use of Water Methanol wasn't quite the same as that of other nations. They basically used it whenever the throttle settings were pushed over our equivalent of Maximum Continuous power.

That's all well and good but for the Japanese to get the expected performance from the Ki-84 (anything approaching 390 mph) the engine would require full obtainable horsepower so water injection would be utilized and that's what the discussion has been about.

 

[AerialTorpedoDude69]

Sounds like a really dumb policy, USSR was in much dire straits for most of the war and they didn't do that, not on that scale anyway, most of the soviet aircraft early problems seem to be factories not used or trained in producing the more advanced airframes.

tonycat77 It does seem like madness. But from the Japanese perspective, Japan's propagandists had glorified military service to the point where it seemed like the duty of all able-bodied Japanese men. I don't think they could have allowed for exceptions. Although there were exceptions. IIRC, families (it may have been agricultural families in rural areas only) with only one son were exempt from conscription. There was likely a political reason for this IMO as rural areas were in favor of the war, whereas people in the cities tended to be against it.

DarrenW The problem with Bueschel's book is that while he has an acknowledgements section, he doesn't cite any sources as well and it appears he merely copied Fancillon's data without attribution, as far as I can tell. In his acknowledgements section, there's references to entities that did not exist at the time the book was written, such as the Nakajima aircraft company. IMO, there appears to be some degree of creative license and liberal attitudes toward sourcing in that book. But as it stands, it should not be seen as an authoritative source.

Also, it looks like most of the acknowledgements section refers to Japanese aviation magazines, US individuals, and Japanese individuals. These appear to be the sources of the photos in that book and not sources of data, as the names are associated with photos and never data. There are no in-text references, actually.

Again, the problem is not what Bueschel wrote but rather his lack of proper attribution. This is a major issue with aviation scholarship of that period: poor attribution.

I Ivan1GFP thanks so much for sharing that document. That resolves some major questions that I had about the Homare's MW50 system. I'm a bit shocked that this resource didn't appear in my searches online. It just shows how poor Google's indexing system is for forums.

 

[DarrenW]

DarrenW The problem with Bueschel's book is that while he has an acknowledgements section, he doesn't cite any sources as well and it appears he merely copied Fancillon's data without attribution, as far as I can tell. In his acknowledgements section, there's references to entities that did not exist at the time the book was written, such as the Nakajima aircraft company. IMO, there appears to be some degree of creative license and liberal attitudes toward sourcing in that book. But as it stands, it should not be seen as an authoritative source.

Also, it looks like most of the acknowledgements section refers to Japanese aviation magazines, US individuals, and Japanese individuals. These appear to be the sources of the photos in that book and not sources of data, as the names are associated with photos and never data. There are no in-text references, actually.

Again, the problem is not what Bueschel wrote but rather his lack of proper attribution. This is a major issue with aviation scholarship of that period: poor attribution.

It seems that you could be making too many assumptions and dismissing the information in the book out right, but of course this is your choice.

For instance, when Bueschel mentions Nakajimi he could be giving credit because he was sourcing company documents. Hideya Ando was present at the Tachikawa Army Aviation Maintenance School during the war so I would think he could have provided some valuable first-hand information on at least the testing of the prototype/pre-production Ki-84s. And a plausible reason for why his data matches Francillon's is that they sourced the SAME data.

Those providing photographs could also have technical data to offer which was relevant as well.

My belief is that when there is less than desired information out there concerning a subject (i.e. Japanese aircraft performance data) it's important to consider the published works of authors until we find enough conflicting information to the contrary (case in point, Martin Caidin). Lastly published works, especially when this book was written, are normally not referenced down to every factoid (such as we currently find in Wikipedia articles). This doesn't automatically equate to an author doing anything unscrupulous or twisting the facts to suit a particular narrative.

 

[special ed]

I have specs and charts for the Ki-84 in Japanese publications. Although in Japanese, the speeds and altitudes can be figured.. as they are metric. Since these are over 30-40 years old, they may be data more from Japanese sources. I'll scan and post the pages if there is interest.

 

[AerialTorpedoDude69]

It seems that you could be making too many assumptions and dismissing the information in the book out right, but of course this is your choice.

For instance, when Bueschel mentions Nakajimi he could be giving credit because he was sourcing company documents. Hideya Ando was present at the Tachikawa Army Aviation Maintenance School during the war so I would think he could have provided some valuable first-hand information on at least the testing of the prototype/pre-production Ki-84s. And a plausible reason for why his data matches Francillon's is that they sourced the SAME data.

Those providing photographs could also have technical data to offer which was relevant as well.

My belief is that when there is less than desired information out there concerning a subject (i.e. Japanese aircraft performance data) it's important to consider the published works of authors until we find enough conflicting information to the contrary (case in point, Martin Caidin). Lastly published works, especially when this book was written, are normally not referenced down to every factoid (such as we currently find in Wikipedia articles). This doesn't automatically equate to an author doing anything unscrupulous or twisting the facts to suit a particular narrative.

I didn't mean to imply that Bueschel is some kind of Martin Caidin who would fabricate information. And you make a good point about Nakajima being the source of the records, although we don't know for certain (because it wasn't adequately sourced).

So while we can't throw his book out the window, I'm saying we can't treat it with the same weight as a primary source, a primary source being Nakajima, the designers, a pilot who flew the plane, etc.... By the way, I say this as someone who read and loved Bueschel's book.

In fact, my only criticism of his work is that it lacks adequate sourcing. Bueschel in general wrote high quality books, regardless of the plane. So his credibility is not in question. What's in question is where he got his information from. As it was not uncommon for aviation scholars of that era to get things wrong on occasion. I can point to dozens of errors in Francillon's book as an example.

 

[DarrenW]

I didn't mean to imply that Bueschel is some kind of Martin Caidin who would fabricate information. And you make a good point about Nakajima being the source of the records, although we don't know for certain (because it wasn't adequately sourced).

So while we can't throw his book out the window, I'm saying we can't treat it with the same weight as a primary source, a primary source being Nakajima, the designers, a pilot who flew the plane, etc.... By the way, I say this as someone who read and loved Bueschel's book.

In fact, my only criticism of his work is that it lacks adequate sourcing. Bueschel in general wrote high quality books, regardless of the plane. So his credibility is not in question. What's in question is where he got his information from. As it was not uncommon for aviation scholars of that era to get things wrong on occasion. I can point to dozens of errors in Francillon's book as an example.

I apologize for misunderstanding you and agree with the premise of your argument. One thing for certain is that there's definitely more to be uncovered concerning the Frank and other Japanese WWII aircraft as well.

 

[special ed]

There was some discussion of the Ki-84 performance. I go to references from the original country when they seem reasonable and accurate. This source is Japanese from 1956 and the first English companion translation. I think I bought this set in 1962.

 

[special ed]

The preface-- The Publication is " General View of Japanese Military Aircraft in the Pacific War", published for "Airview"


Source pages include some well known names:

 

[special ed]

 

[special ed]

This is a fold out chart with the Ki-84 at the top:

 

[special ed]

The other Japanese publications are from "Bunrin-Do" one from 1971 the other from 1985, mostly same data.
Another in only Japanese only on the Ki-84 Published by "Model Art" 1997.
Finally, a Koku-FAN Illustrated No.92 from 1997 with maybe (I can't read Japanese) updated 2000.

If interested further, I can scan the specific performance data and post.

 

[AerialTorpedoDude69]

The other Japanese publications are from "Bunrin-Do" one from 1971 the other from 1985, mostly same data.
Another in only Japanese only on the Ki-84 Published by "Model Art" 1997.
Finally, a Koku-FAN Illustrated No.92 from 1997 with maybe (I can't read Japanese) updated 2000.

If interested further, I can scan the specific performance data and post.

Thanks for sharing those pages! It's great seeing a source from the 50s derived from the original designers' data. I would guess that this document is what informed most American aviation scholarship on the subject, including Bueschel and Francillon.

Also, the sourcing on this document is better than what I've seen from the post-war era, and it all appears to originate with primary sources. The only criticism that I have is that it doesn't match up to modern sourcing methods (such as footnotes) although that's besides the point.

I'm curious, though, aren't we still running into test methodology issue? Like, for example, some mentioned (without attribution) that the Japanese may have tested VMAX without water injection (which seem specious, as thanks to the documents provided by I Ivan1GFP , we know they had water injection set to auto at around 2600 RPMs).

It would seem we could validate those numbers by finding an aircraft on that list that had been tested by TAIC and comparing Japanese test results to American results.

Also, those numbers are for the Homare 11 and not for the Homare 21/23/25. The Soviet archives, by the way, might contain information on captured Ki-84s with 23/25 engines. It's just a matter of time before scholars translate that info though.

EDIT: By the way, do you mean the specific-altitude performance data? That's really comprehensive, if so.

 

[special ed]

The Japanese volume is thicker, more pages, than the English translation volume so I would expect more detail for Japanese readers.
In addition I'll find "Genda's Blade", an excellent source for the problems with fuel and parts for the Navy's N1K1 in 1945. The fuel was so bad that when scrambled to stop U.S. attacks, many had to turn back when climbing due to engine problems or outright engine failure. At the end of the book when the three N1K1 aircraft were to be flown, under escort, to a port for shipment to the U.S. the Japanese pilots realised with the US fuel, 145/115, that their engines and fighters could show how well they they run on good fuel. The three N1K1 were to be escorted by four late model F4U-4s armed, while the Japanese planes had guns with no ammo. The seven aircraft took off together but the Japanese arrived at the port 20 minutes before the Corsairs.

 

[special ed]

The KOKU-FAN Illustrated No.92 from 1997 appears to give the same data as the 1956 Airview book, so they must trust their sources.

A brief interruption because of problem pulling up the page.