Greg's Airplanes: Nakajima Ki-84 Hayate "Frank" History

AerialTorpedoDude69 said:

I am skeptical of the 386 MPH speed on a dash five as well. Given the Hellcat's weight, horsepower, and wing loading, I assume its top speed was probably over 400, even for a bog-standard production version.

Click to expand...

It was the largely common-place wing pylons, fuselage bomb/drop tank attachments, and rocket launchers found on the F6F-5 which reduced the maximum speed of factory fresh examples down from 400 mph into the 380 mph range.

According to wartime ACPs most -5s in fleet service were only expected to achieve around 390 mph in clean condition, which dropped to 380 mph with wing pylons and fuselage attachments. Rocket launchers reduced this further by another 5 maybe 6 mph at absolute critical altitude.

Just to add, the F4U-1D was also commonly configured with bomb racks and rocket launchers. With these devices maximum speed was reduced from 417 mph to around 400 mph.

DarrenW said:

Yes the different induction systems would definitely bring up new questions concerning the adaptability of each engine to higher manifold pressures but testing on both the F6F F4U concluded that higher ratings were definitely possible. My belief is that the upgrade wasn't necessary in the PTO due to the lower performance of Japanese aircraft compared to those found in Europe. Even fuel octane ratings remained 100/130 while 100/150 was standard on a host of combat aircraft operating in the ETO by the later half of 1944.

Click to expand...

Raising the performance of USAAF aircraft in Europe by using 100/150 octane was prioritized over raising the performance of the same aircraft in the Pacific. However, the other issue was that the USN wanted nothing to do with the British developed 100/150 octane, which contained N-monomethyl-aniline http://www.wwiiaircraftperformance.org/150grade/150-grade-spec.pdf. The problem was that this fuel must not be kept in contact with water and, I think, the aviation fuel tanks in American carriers used water to displace the fuel to prevent fuel - air mixtures occurring. After WW2, 115/145 octane fuel was developed which was not so sensitive to water (it contained xylidene).

Greg just finished up the series with Part IV. Part IV is a more nuanced video which analyzes the Ki-84's maneuverability and handling in a dogfight.

• Advantages: While it's a great low-altitude aircraft with superlative low-speed turn performance as well as sustained turn, the Hayate's main advantage is its climb performance, which allows it to maintain energy after a bounce.

• Disadvantages: it didn't have the dive speed, trained pilots, or the structural robustness to take on the Corsair or the Hellcat, even with it being at peak condition. And that hand-operated fuel pressure pump would have been an issue in a dogfight. Most interesting is the 5G maximum limit on acceleration, which is quite a bit below that of Allied fighters of the day. This 5G load limit severely limits initial (or instantaneous) turn speed. Greg thinks that this could be because of drop offs in quality due to late-war manufacturing standards. This seems to be the most likely answer, because some have mentioned that the Frank had a designed 7G limit on acceleration but Japanese documentation of the era shows a 5G limit. Also worth noting is that the combat flaps deployed at a much lower speed than the Corsair's. While the Frank's flaps were more effective and had little impact on sustained turn due to their low-turbulence design, a Corsair was much better at forcing overshoots due to its dive flaps or instantaneous turns due to its ability to pop the flaps at a higher speed therefore forcing high speed turns, which the Frank was poor at.

• Summary: The Allies probably would have had problems with the Frank were it encountered in larger quantities, with skilled pilots at the controls. A top-shape Hayate would potentially outmatch Allied carrier borne fighters (and perhaps even the P-51) at low altitude where there wasn't room for a dive, but at higher altitudes, it could only be a match against the Hellcat and the 1D Corsair. More or less, what limits the Frank's ability to exploit its massive climb rate is its 5G limit on acceleration. My takeaway is that pilots could less exploit advantages in altitude to perform "zoom" attacks because they couldn't maximize the sharp initial climb to throw guns off target, or keep guns on target during a climb. A better-made Hayate with a higher G-limit would have been extremely dangerous as it could dive with and outclimb a Corsair. On the deck, the Frank was probably the best fighter in the world. At altitude it was good too but poor manufacturing and undertrained pilots probably crippled its combat performance.

One thing that stood out to me was the use of a fuel-cooling system. You'd think that they'd use the fuel cooling intake to pressurize the fuel tanks using ram-air forces, but there's nothing in the documentation to suggest this.

Another thing One thing that I didn't see was any reference to the Homare Ha-45-23 low-pressure, fuel injected engine, which was in some of the final versions of the Hayate. So I'm not sure whether the Homare -23 required hand pumping or whether that was automated.

It would have been faster if the IJA applied balkenkreuzs.

Greg got a little defensive with me when I questioned his remark about Hellcats being unable to catch the Frank. He's obviously under a lot of strain concerning this last group of videos...

AerialTorpedoDude69 said:

Greg just finished up the series with Part IV. Part IV is a more nuanced video which analyzes the Ki-84's maneuverability and handling in a dogfight.

• Advantages: While it's a great low-altitude aircraft with superlative low-speed turn performance as well as sustained turn, the Hayate's main advantage is its climb performance, which allows it to maintain energy after a bounce.

• Disadvantages: it didn't have the dive speed, trained pilots, or the structural robustness to take on the Corsair or the Hellcat, even with it being at peak condition. And that hand-operated fuel pressure pump would have been an issue in a dogfight. Most interesting is the 5G maximum limit on acceleration, which is quite a bit below that of Allied fighters of the day. This 5G load limit severely limits initial (or instantaneous) turn speed. Greg thinks that this could be because of drop offs in quality due to late-war manufacturing standards. This seems to be the most likely answer, because some have mentioned that the Frank had a designed 7G limit on acceleration but Japanese documentation of the era shows a 5G limit. Also worth noting is that the combat flaps deployed at a much lower speed than the Corsair's. While the Frank's flaps were more effective and had little impact on sustained turn due to their low-turbulence design, a Corsair was much better at forcing overshoots due to its dive flaps or instantaneous turns due to its ability to pop the flaps at a higher speed therefore forcing high speed turns, which the Frank was poor at.

• Summary: The Allies probably would have had problems with the Frank were it encountered in larger quantities, with skilled pilots at the controls. A top-shape Hayate would potentially outmatch Allied carrier borne fighters (and perhaps even the P-51) at low altitude where there wasn't room for a dive, but at higher altitudes, it could only be a match against the Hellcat and the 1D Corsair. More or less, what limits the Frank's ability to exploit its massive climb rate is its 5G limit on acceleration. My takeaway is that pilots could less exploit advantages in altitude to perform "zoom" attacks because they couldn't maximize the sharp initial climb to throw guns off target, or keep guns on target during a climb. A better-made Hayate with a higher G-limit would have been extremely dangerous as it could dive with and outclimb a Corsair. On the deck, the Frank was probably the best fighter in the world. At altitude it was good too but poor manufacturing and undertrained pilots probably crippled its combat performance.

One thing that stood out to me was the use of a fuel-cooling system. You'd think that they'd use the fuel cooling intake to pressurize the fuel tanks using ram-air forces, but there's nothing in the documentation to suggest this.

Another thing One thing that I didn't see was any reference to the Homare Ha-45-23 low-pressure, fuel injected engine, which was in some of the final versions of the Hayate. So I'm not sure whether the Homare -23 required hand pumping or whether that was automated.

Click to expand...

Thanks for the excellent review of the video. Your summation helps wrap things up very nicely!

DarrenW said:

Greg got a little defensive with me when I questioned his remark about Hellcats being unable to catch the Frank. He's obviously under a lot of strain concerning this last group of videos...

Click to expand...

IMO - Greg does make good videos (not perfect, but good, and some very good among them). However, him accepting anything than praise for his work is not at the table.

But he did made an efford worth while i think. Even for the better in the know.
Now that is something in Tube land.
So go see.

DarrenW said:

Greg got a little defensive with me when I questioned his remark about Hellcats being unable to catch the Frank. He's obviously under a lot of strain concerning this last group of videos...

Click to expand...

The weak and untranslated documentation out of Japan is probably not helping matters. And the Youtube commenters can be absolutely savage. It can make almost anyone defensive.

We should probably continue that discussion here. I'm of the mind that the majority of Franks and Georges were not capable of outspeeding a Hellcat -3 at any altitude in the Philippines in 1944 during the fighter sweeps over Cebu. The earliest preproduction models were apparently using the -11 version of the Homare, which lacked MW50 injection. That almost certainly means that they had to be detuned in order to use 87-92 octane fuel.

In fact, the latest book on the subject indicates that the George (and possibly the Frank) were just not capable of matching the Hellcat at low altitude in speed, although it's been reported by Hellcat combat pilots that they were similar in speed, with the 'cat having the edge. As far as I'm aware the early Franks had Homare-11 engines, whereas the Georges had Homare-21 engines. If that's true, then the Hellcat was probably capable of catching a Frank at some altitudes.

IMO, going off what Greg has mentioned, the Ki-84s flying out of Formosa (Taiwan) were likely capable of outspeeding a -3 Hellcat at all altitudes, if they were in peak condition, which means a preproduction model equipped with a -21 or -22 Homare engine. The Japanese had a 100-octane manufacturing facility somewhere around Taiwan (according to several reports, the synthetic fuel plants were located in Manchuria, Korea, and possibly Taiwan).

tomo pauk said:

However, him accepting anything than praise for his work is not at the table.

Click to expand...

I sometimes find it difficult to read the comments people leave for his videos. It borders on hero worship. That sort of thing will eventually lead to an inflated ego, if one didn't already exist before.

But then there's the occasional troll who attacks every single point he makes so there is that too.

The Type 4 Fighter was mass produced with the Ha-45, but the engine was restricted at the beginning of service to perform almost the same as Ha-45 Special. All service planes with that engine model were also subjected to this. The RPM and CR were both reduced.
(IJA Ha-45 Special = IJN Homare Mod.12 = Unified Ha-45-12) (IJA Ha-45 = IJN Homare Mod.21 = Unified Ha-45-21)
It's not really clear when/if the restrictions were removed on a large scale, but the reliability of the plane in service suffered until the end of the war because of inadequate maintenance capacity and also factors out of their control.

I enjoy Greg's videos and his explanations are always interesting, but 427mph / 687km/h was not obtained by performance testing. It was calculated by TAIC in early 1945, probably with generous air resistance and power curve.

The highest speed given in a known comprehensive performance test was what seems to be a Japanese test during the war with a fully rated Ha-45 and below gross weight. 634km/h at the military power full pressure alt of 6,650m (unusually high because the 2nd speed full pressure alt of Ha-45 is usually written as 6,100m).
Found here via this thread.
There's also the commonly written in Japanese books 631km/h obtained with the 4th prototype and a fully rated Ha-45 at 6,120m with gross weight, which checks out.

We can assume that these were planes with the old collective exhaust thrust and extrapolate performance with WEP and some arbitrary number for extra exhaust thrust, but I don't think it will come close to 687km/h, the WEP full pressure alt will be a bit lower as the RPM is the same in both conditions. I'm also skeptical of the common statement that the Ki-84-I Otsu prototype reached 660km/h, at least if it was in typical JP testing conditions.

Qaz said:

The Type 4 Fighter was mass produced with the Ha-45, but the engine was restricted at the beginning of service to perform almost the same as Ha-45 Special. All service planes with that engine model were also subjected to this. The RPM and CR were both reduced.
(IJA Ha-45 Special = IJN Homare Mod.12 = Unified Ha-45-12) (IJA Ha-45 = IJN Homare Mod.21 = Unified Ha-45-21)
It's not really clear when/if the restrictions were removed on a large scale, but the reliability of the plane in service suffered until the end of the war because of inadequate maintenance capacity and also factors out of their control.

I enjoy Greg's videos and his explanations are always interesting, but 427mph / 687km/h was not obtained by performance testing. It was calculated by TAIC in early 1945, probably with generous air resistance and power curve.

The highest speed given in a known comprehensive performance test was what seems to be a Japanese test during the war with a fully rated Ha-45 and below gross weight. 634km/h at the military power full pressure alt of 6,650m (unusually high because the 2nd speed full pressure alt of Ha-45 is usually written as 6,100m).
Found here via this thread.
There's also the commonly written in Japanese books 631km/h obtained with the 4th prototype and a fully rated Ha-45 at 6,120m with gross weight, which checks out.

We can assume that these were planes with the old collective exhaust thrust and extrapolate performance with WEP and some arbitrary number for extra exhaust thrust, but I don't think it will come close to 687km/h, the WEP full pressure alt will be a bit lower as the RPM is the same in both conditions. I'm also skeptical of the common statement that the Ki-84-I Otsu prototype reached 660km/h, at least if it was in typical JP testing conditions.

Click to expand...

Something worth pointing out is that Greg uses primary source material.

Unfortunately, most of the Japanese source material, like Maru Mechanic, is not properly sourced and is oftentimes apocryphal. I'm not saying to throw it out, but rather, we have to pay closer attention to where information originates from.

Additionally, Greg mentioned that the Ki-84 tested at Middleton was not a standard model but rather a "Blueprint" rebuild, with slightly better fuel quality, run at full RPMs, at maximum manifold pressure (and a lot more).

He clearly states that this was not indicative of general Ki-84 performance but rather the maximum possible that a Ki-84 with a Ha-45-21 could achieve. His analysis is actually completely in-line with the comments in that thread as well as all the available speed estimates that you've provided as he's basically said that Ki-84s would have had huge differences in maximum performance due to large variances in fuel quality, as well as construction quality.

The reason why Greg's analysis is so unique is that he goes into the source material and explains some of the conventions and methods that TAIC's engineers used to calculate maximum speed (because he's an expert regarding engines).
One thing to point out is that the speed analysis comes from a 1946 bench test of the Homare engine under controlled conditions, which was based on hands-on measurements. Furthermore, the measurements of the Frank, PARTICULARLY FRONTAL DRAG, were similarly based on hands-on measurements.

I totally understand what you're saying and it makes a lot of sense (yes, it's possible that TAIC may have screwed up the measurement of the Ki-84). However, if you're going to claim that TAIC's 1946 analysis is bunk, you have to back that up with a source or some kind of evidence. Because as Greg has mentioned, the Middleton report is exhaustive, thorough, and currently represents the best available information on the Ki-84's performance.

AerialTorpedoDude69 said:

Additionally, Greg mentioned that the Ki-84 tested at Middleton was not a standard model but rather a "Blueprint" rebuild, with slightly better fuel quality, run at full RPMs, at maximum manifold pressure (and a lot more).

He clearly states that this was not indicative of general Ki-84 performance but rather the maximum possible that a Ki-84 with a Ha-45-21 could achieve. His analysis is actually completely in-line with the comments in that thread as well as all the available speed estimates that you've provided as he's basically said that Ki-84s would have had huge differences in maximum performance due to large variances in fuel quality, as well as construction quality.

The reason why Greg's analysis is so unique is that he goes into the source material and explains some of the conventions and methods that TAIC's engineers used to calculate maximum speed (because he's an expert regarding engines).
One thing to point out is that the speed analysis comes from a 1946 bench test of the Homare engine under controlled conditions, which was based on hands-on measurements. Furthermore, the measurements of the Frank, PARTICULARLY FRONTAL DRAG, were similarly based on hands-on measurements.

I totally understand what you're saying and it makes a lot of sense (yes, it's possible that TAIC may have screwed up the measurement of the Ki-84). However, if you're going to claim that TAIC's 1946 analysis is bunk, you have to back that up with a source or some kind of evidence. Because as Greg has mentioned, the Middleton report is exhaustive, thorough, and currently represents the best available information on the Ki-84's performance.

Click to expand...

I certainly know that Greg is more knowledgeable of the technical aspects than I am, but I just disagree with the use of the 687 km/h number as an accurate reference for a 'best case' Ki-84 for these reasons.

The 1946 'test data' that gave 687 km/h is an exact reprint of the TAIC early 1945 calculations:




^ TAIC Manual 1945


^ Ki-84 T-2 Report 1946


So in the first place, this speed was not obtained by a real flight test. It also is a wartime calculation based partly on intel, and we can't really know the accuracy of it, not mentioning that calculations with good data can be at variance with reality.
I don't think that this number should be used as a realistic ref for the speed of a top notch Ki-84 if no plane ever actually demonstrated it.

-

Now, looking at both of the 1946 Ki-84 test reports, although the above speed performance figures are given it is doubtful that maximum performance was tested/recorded at all.
Rather it seems that the objective was to determine handling characteristics.

In the 1946 T-2 Report with the copied TAIC estimate numbers:




In the 1946 Middletown report:

The climb time is only guessed, and assuming it's an average, at 6'40" to 6,100m (close to actual Japanese test values) it's almost a minute slower than the TAIC calc of 5'48" to 6,100.


As we can see, the 687km/h dataset in question was pretty certainly just calculations from the TAIC. I find it not credible due to the fact that it is exceptionally far from other existing data based on the fully rated Ha-45-21. As was a lot of TAIC data, like that of Shiden and that of Raiden. In general the claims of Japanese planes giving much superior performance in 'US testing' are often unfounded and lead back to the TAIC calcs.

While Japanese prototype performance tests were not done at WEP, they still naturally used adequate fuel for knock prevention and a well made airframe by their standards. Providing superior grade fuel by itself won't appreciably improve performance.

I'm not saying that the overall performance of Ki-84 couldn't be marginally improved in a US test, especially if it was rebuilt with better parts, excellent fuel/oil and so on, but there aren't real numbers for this. I believe 687 is very excessive considering that the highest Japanese test numbers are around 634 km/h, even though they're at mil power. Of course the extant Japanese test data is insufficient in many ways considering the amount of potential variance there was, but a theoretical number like 687 seems very unlikely unless the engine was uprated to produce greater than designed output.

Adding the materials in question:

TAIC Manual No.1

T-2 Report on Frank-1:

'Ki-84 Middletown Test'


And just to restate, I do agree that the Japanese test numbers we have currently are not satisfactory in context or detail. Considering the possible variances, to state a couple:

-the full pressure alt of the Ha-45-21 seems to have been changed over time
-the compression ratio of the Ha-45-21 has changed, possibly independently of other power restrictions
-the Ki-84 suffered propeller pitch issues and vibrational problems at points

However I don't think the 687km/h number is the place to start on the principle that it is a wartime calculation prior to extensive testing and doesn't seem to coincide with other data. It's also in the interest of the TAIC to calculate an enemy fighter's performance on the generous side, as they state in their manual.

qaz said:

-the compression ratio of the Ha-45-21 has changed, possibly independently of other power restrictions

Click to expand...

FWIW, see the post #12 here wrt. the compression ratio of the Homare 21.

tomo pauk said:

FWIW, see the post #12 here wrt. the compression ratio of the Homare 21.

Click to expand...

Certainly, based on this material I agree with the convincing theory written on warbirdperformance's blog:

That the compression ratio of mass produced/service Ha-45-21 was reduced to 7.17 by diverting the pistons of the prior Ha-45-12.
So resultingly:

Ha-45-12: 7.0CR
Ha-45-21 (Prototype/Initial): 8.0CR
Ha-45-21 ('Governed'): 7.17CR

What I meant to convey exactly is that even if the operating restrictions (2900 RPM and +250mmHg nominal boost) of the service Ha-45-21 were removed at some point, the compression ratio perhaps remained reduced. Therefore even in a fully rated test with +350mmHg, the compression ratio may still be decreased.

qaz said:

I enjoy Greg's videos and his explanations are always interesting, but 427mph / 687km/h was not obtained by performance testing. It was calculated by TAIC in early 1945, probably with generous air resistance and power curve.

The highest speed given in a known comprehensive performance test was what seems to be a Japanese test during the war with a fully rated Ha-45 and below gross weight. 634km/h at the military power full pressure alt of 6,650m (unusually high because the 2nd speed full pressure alt of Ha-45 is usually written as 6,100m).
Found here via this thread.
There's also the commonly written in Japanese books 631km/h obtained with the 4th prototype and a fully rated Ha-45 at 6,120m with gross weight, which checks out.

We can assume that these were planes with the old collective exhaust thrust and extrapolate performance with WEP and some arbitrary number for extra exhaust thrust, but I don't think it will come close to 687km/h, the WEP full pressure alt will be a bit lower as the RPM is the same in both conditions. I'm also skeptical of the common statement that the Ki-84-I Otsu prototype reached 660km/h, at least if it was in typical JP testing conditions.

Click to expand...

TAIC 687kph at 1850hp at 20000 feet doesnt seem anything out of ordinary to me.
F8F-1 does 698kph at 1850hp at 20000 feet.
Is Ki-84 really that much draggy than F8F-1?

Also this document is from Aug 1945 and states:


With several photos:

So they had a flyable ki84 before the end of the war and probably when the TAIC was done.
Clark Air Base was recaptured in January, TAIC dates as of March.

qaz said:

I certainly know that Greg is more knowledgeable of the technical aspects than I am, but I just disagree with the use of the 687 km/h number as an accurate reference for a 'best case' Ki-84 for these reasons.

The 1946 'test data' that gave 687 km/h is an exact reprint of the TAIC early 1945 calculations:


View attachment 703261
View attachment 703259
^ TAIC Manual 1945

View attachment 703257
^ Ki-84 T-2 Report 1946


So in the first place, this speed was not obtained by a real flight test. It also is a wartime calculation based partly on intel, and we can't really know the accuracy of it, not mentioning that calculations with good data can be at variance with reality.
I don't think that this number should be used as a realistic ref for the speed of a top notch Ki-84 if no plane ever actually demonstrated it.

-

Now, looking at both of the 1946 Ki-84 test reports, although the above speed performance figures are given it is doubtful that maximum performance was tested/recorded at all.
Rather it seems that the objective was to determine handling characteristics.

In the 1946 T-2 Report with the copied TAIC estimate numbers:
View attachment 703262
View attachment 703255
View attachment 703253

In the 1946 Middletown report:
View attachment 703256
The climb time is only guessed, and assuming it's an average, at 6'40" to 6,100m (close to actual Japanese test values) it's almost a minute slower than the TAIC calc of 5'48" to 6,100.


As we can see, the 687km/h dataset in question was pretty certainly just calculations from the TAIC. I find it not credible due to the fact that it is exceptionally far from other existing data based on the fully rated Ha-45-21. As was a lot of TAIC data, like that of Shiden and that of Raiden. In general the claims of Japanese planes giving much superior performance in 'US testing' are often unfounded and lead back to the TAIC calcs.

While Japanese prototype performance tests were not done at WEP, they still naturally used adequate fuel for knock prevention and a well made airframe by their standards. Providing superior grade fuel by itself won't appreciably improve performance.

I'm not saying that the overall performance of Ki-84 couldn't be marginally improved in a US test, especially if it was rebuilt with better parts, excellent fuel/oil and so on, but there aren't real numbers for this. I believe 687 is very excessive considering that the highest Japanese test numbers are around 634 km/h, even though they're at mil power. Of course the extant Japanese test data is insufficient in many ways considering the amount of potential variance there was, but a theoretical number like 687 seems very unlikely unless the engine was uprated to produce greater than designed output.

Click to expand...

Thanks for the informed rely. I've read your analysis before and very much enjoyed your thorough discussion of the topic.


There are a few things that I'd point out:


So getting back to TAIC and Middleton (MAMA) testing standards, the information that we're missing is the Homare 21 bench testing under controlled conditions. Do you have access to these documents? There are two AFAIK, one relating to the controlled bench test and one relating to the aircraft evaluation. AFAIK, these are the documents that Greg is primarily referencing and they are absent from your website's analysis. They've been linked to multiple times on this forum.


There are a few points that need to be made:

First, WW2-era pitot tube speedometers aren't always accurate due to differences in wind, heat, humidity, altitude, airflow over the tube, and other variables that can't be controlled for. So TAIC is likely testing engines in isolation, outside of aircraft, in order to avoid two issues. The primary issue is standardization and the secondary issue may be cost. However, Greg doesn't speculate as to why TAIC's engineers used controlled external bench testing conditions to generate the synthetic speed estimates of the Frank, but it's cheaper and it's more standardizable to run the engine up on the ground and then synthetically generate its top speed.

In fact, TAIC basically states in the beginning of their intelligence reports that they do not calculate speed in the air and that all calculations, unless otherwise stated, are done synthetically. But that said, their report on the Homare 21 is actually one of the most thorough and comprehensive reports available on a WW2 engine, according to Greg.

Second, Greg also gets into the 624 KPH numbers and explains why they're not as authoritative as MAMA's data. Basically, those numbers aren't as well understood as the Middleton data. Again, the Homare Ha-45-21 that was tested at Middleton was removed from the Ki-84, completely disassembled and rebuilt to the factory standard (likely using machined components if such components were bad on the original engine). The engine was then tested at Middleton WITHOUT an aircraft attached to the engine using 96 octane (so the issue with knock disappeared). Because it was run with 96 octane, the dash 21 was run at its maximum horsepower using full RPMs and manifold pressure. In other words, this was not indicative of an aircraft flown in the Philippines or Japan, where the majority of air combat occurred. There were only three synthetic fuel factories that could produce 100 octane fuel under Japanese control IIRC. One in Manchuria, Korea, and Taiwan. So if there were Frank fighters capable of similar performance, they would have likely been outside the major zones of conflict (except Taiwan). It's possible that some better conditioned Franks were flying in the 1944 Japanese offensive in China, but IDK.


I don't think the climb data similarity is proof that TAIC's information is incorrect. If it is incorrect, or a result of a patchwork methodology, it would take an aerospace engineer to figure out where the mistake occurred. We lack the calculations used by TAIC and only have their final analysis. Is it possible? It is, but we don't have authoritative data or primary sources to confirm that point. At present, we only have (thanks to your work) a working hypothesis that suggests there might be a mistake in their calculations. However, I believe that the MAMA report might shed additional light on this incongruity.

Third, the 96 octane fuel's impact on test data should have (according to Greg) lowered knock as it wasn't increasing manifold pressure or increasing RPMs. TAIC still ran the engine at its designed power settings. The performance-at-altitude curve that you observed was based on the supercharger settings and should, AFAIK, be pretty much the same. Greg even got into this and mentioned that the critical altitude was suggestive of (IIRC) good knowledge of the Homare's supercharger design. You'll have to watch the video to understand his point about this because I can't remember the details.


In summary, I think that Greg's data only indicates the theoretical maximum performance of the Frank and (as he claims) is not the actual combat performance of most Franks, which was likely heavily watered down by operational limitations. I do not think you are wrong but Greg's point is that he is interested in the theoretical maximum performance of the aircraft as that is the standard that we use to judge the engineering of WW2 aviation designs.


By the way, I believe that TAIC's last report was September of 1945 and that the TAIC report was based on interviews with captured aircrew/pilots and that the Middleton report was generated in 1946 based on benchtesting. So the MAMA report is the final say in all post-war analysis on the Frank.