A6M2 with overboost?

[Krusty]

I think you'd be hard pressed to prove to us average folks that the zero went 350mph. Even the Japanese ace (forget which one, was posted recently in another thread) said that the zero only had a top speed of 315mph.

[F4UDOA]

There are some other factors that play into the top speed of all A/C in combat especially in the PAC Theater. Namely maintenance and upkeep of the A/C at hand.

Conditions on forward operating bases were aweful and most A/C stationed there while flyable were probably not optimal in there performance. Combine that with the high humidity and the actual performance was probably not what it was stateside or even compared to European operations where the conditions of the bases even when poor were pobably better than say Gaudacanal in 1943.

Combine that with the fact that the F4U was new and complicated for it's time and I would say that the perofrmance of the average F4U in the VF-17 was not what it could have been. Carrier A/C had better conditions for maintanace and would have been better.

Even with that the stated speed by Ken Walsh was appropriate for an F4U and well above that of a Zero of any year.

[HoHun]

Hi F4UDOA,

>This chase was at speads from 400MPH down to about 300MPH for an extended period of time and he could never get far beyond firing range of at least one Zeke.

Wow, that's pretty impressive. The only explanation I can offer is that Walsh might have involuntarily zigzagged in order to keep his pursuers in sight around the fuselage spine, losing a bit of speed and allowing them to take a shorter path in pursuit. (I know that's what always happens to me in the simulators :-) Since 300 mph is mentioned as low-end speed, that would support the idea that he did in fact lose some speed to manoeuvres.

>Where did you get the speeds for the A6M5 at Pax River? I have the full report of the Army and Navy test of the A6M5 but I don't have the speed chart but your speeds for the TAIC test seem to slow especially at sealevel.

Hm, I guess I wrongly ascribed this data to the Patuxent River test since I have a PDF that has the Patuxent River test and the Eglin Field Army test in one file, and it's actually Eglin Field data. The speed chart is "inclosure 3" of the Eglin Field test and noted as "not reduced to standard". A free air temperature graph is given, though, so that it should be possible to calculate standard day speeds from that.

("Inclosure 4" repeats the assertion that the Zeke 52 is powered by a Sakae 31A, by the way. Is it really certain that no 31A was ever used? I'd think if they got hold of the aircraft, the engine plate should tell them the exact version.)

>I have the Army flight test climb and speed chart of the A6M5 with HP curve and MAP but that was a broken A/C according to the AAF and was not running at full MAP as well as having drag problem because of structural defects.

Hm, that's probably not the test I have because 42" Hg boost pressure is charted. On the other hand, "certain airframe discrepancies" are noted that "prevented obtaining maximum speed and climb performance", which seems to fit your description.

>I do not have the Navy test results except for specific altitudes.

>335MPH at 18K for the Zero.

That seems to be the data from the "UK" report for which Widewing provided the exact reference.

>Note the F4U was listed as being 48MPH faster than the A6M5 at sealevel. It is hard to find a report that shows the F4U any slower than 350MPH at sealevel so the A6M5 in this test would have been unusually fast.

Indeed. That's probably an error, it wouldn't match the rest of the speed graph.

>I will post the full test when I can.

Thanks! :-)

Regards,

Henning (HoHun)

[Squire]

There are several obvious points of contention with the report cited in the initial thread, and with many of the comments that have come after.

The first of which is that the cited combat reports simply mention "Zero", with no confirmation on wether they are A6M2, A6M3, or A6M5 varients being engaged. With some of the early combats, undoubtably they are A6M2s, but not the later ones.

All three served in the Solomons from 1943-44, the A6M5 being first based from Rabaul in August of 1943, and saw action against most of the allied fighter types then. Both the A6M2 and the faster A6M3 were used in New Guinea in 1942-43, and any combat report citing "Zeros" could easily be any of them.

Secondly is that no mention of the fuel grades for any of the allied tests are mentioned, and I find that odd.

[Widewing]

Originally posted by Grits
I have a VHS tape about VF-17 from 1990 and it has clips from the surviving members. In one clip Roger Hedrick talks about the F4U and says "The corsair had a slight speed advantage over the Zero". When he said "slight" he stressed that word to make clear the difference was not great.

I dont usually put much stock in anecdotal accounts of aircraft performance, but with the current accepted wisdom of the speeds of the F4U and A6M we have now, I cant see anyone calling it a "slight" speed advantage.

I've read a similar account where a P-51 pilot was unable to chase down a Bf 110. However, when he returned to base hours later his crew chief found that the prop governor had failed, not allowing full rpm. Some pilots (far more than you might imagine) had absolutely no clue as to the mechanicals of their aircraft. Believe me, I flew with knuckleheads just like that. This particular pilot never even noticed that he was down 400 rpm.....

The account credited to Walsh defies common sense. All he had to do was establish a high speed climb and he would have rapidly opened the distance AND climbed high enough to avoid overheating his R-2800. Something else was going on here, something beyond Walsh's ability to figure out. P-40 pilots used a high speed climb to distance themselves from Zeros, and this was SOP. Maybe Welch misidentified the enemy aircraft. Ki-44s were much faster than Zeros on the deck.

I had a pilot complain that he was unable to obtain full throttle in our C-1A. It took me 10 seconds to discover that he over-tightened the throttle tensioner and couldn't push the throttles forward the last 15 degrees to the stops. He was apoplectic about it... and damned sorry he made a fool of himself. This was his NATOPS check ride and the evaluator pilot was unimpressed.

Back to the TAIC A6M5 test for a minute. The document does describe the engine as a Sakae 31 without water injection. I must conclude that this is probably an error or typo as I can find no evidence that any A6M5 ever flew with that engine, much less in early 1944. If someone can dig up something that establishes otherwise, I'd be very interested in seeing it.

My regards,

Widewing

[Angus]

Does any of you have some data on the a6m roll rates?
As well as max allowable speed. (VNE)

I've read that they hardly roll at 250 mph+ and the VNE is about 400-450, but the info is old and scattered and I don't trust it completely.

[F4UDOA]

HoHun,

TAIC report

[HoHun]

Hi Widewing,

>Maybe Welch misidentified the enemy aircraft. Ki-44s were much faster than Zeros on the deck.

That's a very good point!

If we had more information on the date and location of his encounter, mybe we could cross-check wether there were other Japanese aircraft types deployed to the area.

>I must conclude that this is probably an error or typo as I can find no evidence that any A6M5 ever flew with that engine, much less in early 1944.

I think you are probably right there because the test data does not display the increased full throttle height one would expect from the 31A engine.

Regards,

Henning (HoHun)

[Squire]

Dug out my Zero book which is based on Sakais comments.

Title is "Zero Fighter" by Robert C. Mikesh.

In the acknowledgements he expresses thanks to the letters, books and personal contacts of Jiro Horikoshi and Saburo Sakai.

Lists the following data on the Zero series.

A6M1:
Zuisei 780 hp engine
Max Speed 275 knots at 3600 meters.

A6M2:
Sakae 12 950 hp engine
Max speed 288 knots at 4500 meters (331mph at 15,000 ft.)

A6M3 Type 32:
Sakae 21 1130 hp engine
Max Speed 294 knots at 6000 meters  

A6M5:
Sakae 21 1130 hp engine (with exhaust stubs)
Max Speed 305 knots at 6000 meters.

A6M7:
Sakae 21 or 31A
Max Speed 293 knots at 6,400 meters.

*Seems the stuff about the "confusion" is all about the author (jn the internet article), not paying attention to what varient is being reffered to. Sakai gives 275 knots to the *A6M1*, not the A6M2, hes not even quoting his own book correctly.

[hogenbor]

This might be a stupid question but does no JAPANESE data survive indicating how fast a particular Zero was supposed to go? Surely they had factory data and acceptance data too? Is there any? Is it likely to be inflated? If there is any, is it accesible to the public? Can someone translate? There appear to be some people who play AH2 that would be able to.

This reads like a detective novel, I hope the issue will someday be resolved

[Squire]

I think whatever data survived is in peices here and there, which is why some historians have interveiwed some of the surviving Japanese pilots in the past. There are good Japanese historians, but I have not yet seen a translated book on the Zero from them.

For me the matter is closed, it keeps popping up after somebody reads a few poor quality sources that have conflicting numbers, or some anectdotal claim, usually over generalised, crops up yet again (and they always seem to contradict each other), but Mikesh's book is one of the best imho, and has some very detailed data on the Zero series and the engines that were in them. It also clearly distinguishes between the sub types, it gives hp, weights, time to alt info and top speeds in knots with the alt listed.

[HoHun]

Hi again,

Here is a new A6M5 speed estimate:



It lists only the A6M5 data, except for the A6M2 data (red/green) which I have used to calibrate airframe drag.

The A6M5 estimate is based on A6M2 airframe drag and TAIC data on the Sakae 21 engine (with doubled exhaust thrust to account for the individual exhaust stubs).

Now we have three competing sets of data: The Patuxent River A6M5 (a double set of curves actually), the TAIC data, and my own estimate.

The Patuxent River A6M5 (probably should be called "Eglin Field A6M5" because it was turned over to Eglin field after being rebuilt at Patuxent River, and looks to have been a different aircraft from the one tested by the Navy) had problems with landing gear fairings and doors not staying closed at high speed, a rough skin and a distorted airfoil section. I guess that means it was a below-average aircraft, though it's not clear how serious these issues were.

The data set for this aircraft also has not been corrected to standard conditions. The error below full throttle height probably is about 2 km/h, but due to the higher temperature, full throttle height is down a bit. Though the report states "After complete ignition rewiring, specified power was available" and the test data shows that full boost was indeed reached, the speed graph does not conform with the TAIC engine chart at all.

This seems to coincede with the TAIC analysis, which suggests a considerably higher top speed for the A6M5 than both sets of flight test data from TAIC aircraft. Interestingly, the TAIC sea level data point for WEP is close to the data point for the Eglin Field aircraft, which was in poor condition according to the report. (Due to the non-standard conditions, the gap is a bit larger than it appears, but not more than 5 km/h.)

My own estimate achieves the same sea level power as the TAIC's at MIL instead of WEP. It's based on two prerequisites:

1) The A6M5 has the same basic airframe drag as the A6M2.
2) The Sakae 21 does indeed perform as specified by TAIC.

I don't see much that would make the A6M5 more draggy than the A6M2's, especially considering that the Akutan A6M2 itself was a crashed and rebuilt example that was not in perfect condition.

With regard to TAIC engine data, it's often inconsistent. However, the Sakae 21 data is not marked as extrapolation and its MIL figures can be considered to stem from Japanese documents. The TAIC estimate seems to suggest a power graph that's close to their own data, while it's rather far from the test aircraft's performance.

So I'm not overly unhappy with my latest estimate :-) I don't consider it final, though.

Regards,

Henning (HoHun)