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A.T.I.G. Report No. 45 - Nakajima Engine, Design and Development is worth a read.Supposedly it was a problematic engine. Eg. Wikipedia says: However, the tight design of the engine made it difficult to maintain quality in manufacturing, and unreliability in the field was a significant problem; actual output of early models at altitude was in the range of 1300 hp (970 kW), far below the designed capability.
Questions: what was the actual Japanese view on the Homare? Any Allied report on the engine that can confirm it to being unreliable?
Design was good but production.Supposedly it was a problematic engine. Eg. Wikipedia says: However, the tight design of the engine made it difficult to maintain quality in manufacturing, and unreliability in the field was a significant problem; actual output of early models at altitude was in the range of 1300 hp (970 kW), far below the designed capability.
Questions: what was the actual Japanese view on the Homare? Any Allied report on the engine that can confirm it to being unreliable?
I'm sorry for going off topic, but I'm constantly seeing the 388-mph figure as well for the Ki-84. As far as I can tell, the reason is that everyone sources Rene J. Francillon's book, "Japanese Aircraft of the Pacific War". Unfortunately, much of the information in it doesn't seem to match Japanese records or TAIC data.All the accounts I have seen show that the Homare engined Nakajima Ki.84 had a top speed of 388mph. The Americans tested one and they got it up to 427mph on "WEP" (War Emergency Power). Water/Methanol? The Kawanishi N1K and the Mitsubishi J2M also exceeded 400mph in American testing.
- Did the Japanese quote engines with WEP running and aircraft without?
- The performance charts on WWIIAircraftPerformance.com say "92 Octane". Did the Americans really have 92 octane fuel lying around? Why?
Did the Japanese quote engines with WEP running and aircraft without?
Probably. There were a lot of refineries and oil sources in the US and Canada in the 40s and not all of them used the fluidic cracking method which produced 100 octane. So they definitely had supply of the fuel and it would be reasonable to conclude many air bases stored a wide range of octanes although I don't know for certain.
- The performance charts on WWIIAircraftPerformance.com say "92 Octane". Did the Americans really have 92 octane fuel lying around? Why?
For some reason most countries that used water/alcohol injection used a 50/50 mixture...or 49.5 + 49.5 + 1 percent (roughly) oil, anti corrosion etc. A few may have used 30/70 + anti corrosion stuff. You can't use pure water or the tank will freeze at high altitude so the alcohol is pretty much an anti-freeze. On the other hand water (per pound) will suck up more heat out of the intake mixture so pure alcohol doesn't provide as much cooling per pound.Similarly, the claim that Japanese engines were designed to run on MW50 also seems specious and without a source.
There were a lot of refineries and oil sources in the US and Canada in the 40s and not all of them used the fluidic cracking method which produced 100 octane. So they definitely had supply of the fuel and it would be reasonable to conclude many air bases stored a wide range of octanes although I don't know for certain.
Be careful here. The BMEP of the Homare engine is consiistent either with the 100/130 octrane fuel the RAF and USAAF were using in Europe, or with water methanol injection. If all the Americans have to test Ki.84s is 100/130 octane fuel, they may have used those boost pressures. Note the 1946 date. This is an analysis of Japanese technology, not an analysis of an opponent in combat.I'm sorry for going off topic, but I'm constantly seeing the 388-mph figure as well for the Ki-84. As far as I can tell, the reason is that everyone sources Rene J. Francillon's book, "Japanese Aircraft of the Pacific War". Unfortunately, much of the information in it doesn't seem to match Japanese records or TAIC data.
Thanks Howard. I have seen people mentioning BMEPs for the Homare but I'm not sure which are true. Can you point me in the general direction of a source? Or were you talking about this source: http://www.wwiiaircraftperformance.org/japan/ATIG-Report-45.pdfBe careful here. The BMEP of the Homare engine is consiistent either with the 100/130 octrane fuel the RAF and USAAF were using in Europe, or with water methanol injection. If all the Americans have to test Ki.84s is 100/130 octane fuel, they may have used those boost pressures. Note the 1946 date. This is an analysis of Japanese technology, not an analysis of an opponent in combat.
I worked it out.Thanks Howard. I have seen people mentioning BMEPs for the Homare but I'm not sure which are true. Can you point me in the general direction of a source? Or were you talking about this source: http://www.wwiiaircraftperformance.org/japan/ATIG-Report-45.pdf
I did not see manifold pressures listed in it though, but I could have missed it.
The 427 mph figure has been discussed ad nauseum here. It is the calculated maximum level speed of the Ki-84 using data such as aerodynamic drag coefficients and peak horsepower ratings. The captured aircraft was never tested to find these limits in performance.I'm sorry for going off topic, but I'm constantly seeing the 388-mph figure as well for the Ki-84. As far as I can tell, the reason is that everyone sources Rene J. Francillon's book, "Japanese Aircraft of the Pacific War". Unfortunately, much of the information in it doesn't seem to match Japanese records or TAIC data.
There are numerous reasons why that book shouldn't be treated as a primary source. But above all other reasons, I can't find an appendix or list of sources in it. That means any source based on it is potentially false since we can't vet the information in it. I would be very appreciative if someone could locate the sources of that book,
Thanks for addressing this question. I read the TAIC report as well as a summary of one of the two specimens recovered from Clark Field (as I can't find the original report). I've also seen the Francillon quote regarding the 388 mph speed on the prototype. There are a number of problems with this information but among these are:The 427 mph figure has been discussed ad nauseum here. It is the calculated maximum level speed of the Ki-84 using data such as aerodynamic drag coefficients and peak horsepower ratings. The captured aircraft was never tested to find these limits in performance.
However the 388 mph figure can be found in official Japanese data, for the prototype during service trials. A provisional pilot's handbook dated January 1944 captured at Clark Field Philippines concurs with this speed. Apparently 394 mph was obtained by the second prototype.
Getting back to the main thread, I've read numerous documents about horrendous issues with the Homare in combat conditions. For example, there was apparently an issue with the carburation system; during high negative-G maneuvers, IIRC and this could be apocryphal, the fuel system would cut out on occasion. The Homare 23 supposedly resolved the issues with the 21, by moving to a low-pressure direct injection system, but whether or not that's true, I don't know. But basically the Homare had a combination of quality control issues as well as design issues. When everything was running smoothly it was highly regarded by the Japanese. In a situation where there are supply shortages and daily air raids, the Homare became less well liked.It has been stated elsewhere that 400 mph+ was possible with the more powerful model 21 engine and everything in good working order but the problem was this never seemed to be the case.
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.The 427 mph figure has been discussed ad nauseum here. It is the calculated maximum level speed of the Ki-84 using data such as aerodynamic drag coefficients and peak horsepower ratings. The captured aircraft was never tested to find these limits in performance.
However the 388 mph figure can be found in official Japanese data, for the prototype during service trials. A provisional pilot's handbook dated January 1944 captured at Clark Field Philippines concurs with this speed. Apparently 394 mph was obtained by the second prototype. It has been stated elsewhere that 400 mph+ was possible with the more powerful model 21 engine and everything in good working order but the problem was this never seemed to be the case.
Perhaps the final verdict would/could/should have been a comprehensive fly-off between the Ki-116 and the Ki-84. I suspect that even with a well-manufactured and properly maintained Homare engine, the latter would have been 20-30mph faster than, but not as maneuverable and certainly not as available for use as, a Ki-116 with a properly manufactured and maintained Kinsei engine. Even a Ki-100 might have been a better all-round fighter.Thanks for addressing this question. I read the TAIC report as well as a summary of one of the two specimens recovered from Clark Field (as I can't find the original report). I've also seen the Francillon quote regarding the 388 mph speed on the prototype. There are a number of problems with this information but among these are:
1. The TAIC report doesn't mention how they performed their speed calculations, simulated or unsimulated. There's one sentence where it mentions maximum speed tests were not conducted, but it's not clear whether they meant in dives or level flight, or whether that was just one test flight or all test flights.
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.
3. The summary of two Ki-84s recovered from the Philippines mentions that speed tests were not performed as the landing gear collapsed after the first flight. It's mentioned there was a second aircraft but there's no test data from that aircraft and I can't find any records of it either. But basically, I can't find this document (unless it's the speed-at-altitude charts).
Getting back to the main thread, I've read numerous documents about horrendous issues with the Homare in combat conditions. For example, there was apparently an issue with the carburation system; during high negative-G maneuvers, IIRC and this could be apocryphal, the fuel system would cut out on occasion. The Homare 23 supposedly resolved the issues with the 21, by moving to a low-pressure direct injection system, but whether or not that's true, I don't know. But basically the Homare had a combination of quality control issues as well as design issues. When everything was running smoothly it was highly regarded by the Japanese. In a situation where there are supply shortages and daily air raids, the Homare became less well liked.
I had read that the Homare 23 was not a true direct-injection engine, but I don't know if that's true either. Whatever the case, the Homare 21 was an example of not enough development time, shoddy mass production standards, poor-quality materials used in place of components that required advanced metallurgy, and declining standards in metal quality. It goes without saying that a Ki-84 with a lemon engine was likely to have significantly worse performance than a prototype or well-built aircraft. However, I think most history buffs are interested in knowing the design speed as well as the operational performance of the aircraft. I think it would be like judging the late-war German aircraft by their operational performance, rather than what Allied testing found later on.
That's a good question. It may be that the Kinsei 62 was so well regarded because it needed fewer of the alloys that a high RPM engine required. After all, it was considered to be reliable by the Japanese and of superior quality by Americans. But I don't know. Shinpachi might know more.Perhaps the final verdict would/could/should have been a comprehensive fly-off between the Ki-116 and the Ki-84. I suspect that even with a well-manufactured and properly maintained Homare engine, the latter would have been 20-30mph faster than, but not as maneuverable and certainly not as available for use as, a Ki-116 with a properly manufactured and maintained Kinsei engine. Even a Ki-100 might have been a better all-round fighter.
Yeah... I have been wondering a lot about the alloys issue... What was the big difference in the engine materials?... And the more I read, the more I think that Japan should have concentrated its fighter engine development on the Kinsei (and its 18-cylinder derivative) than wasting all that time trying to beef up the Sakae, Ha-41, Mamoru, Homare, etc... Of course hindsight is always 20-20 or even 20-10.That's a good question. It may be that the Kinsei 62 was so well regarded because it needed fewer of the alloys that a high RPM engine required. After all, it was considered to be reliable by the Japanese and of superior quality by Americans. But I don't know. Shinpachi might know more.
I do know that the Kinsei 62 is regarded as one of the few (possibly also certain models of Kasei or Homare) Japanese WW2 engines that had full direct fuel injection. Because fuel injection requires very high levels of precision and technical sophistication, it may be that the Kinsei was just a technically superior engine compared to its stablemates.