Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: 1K3 on July 01, 2005, 01:38:19 AM
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(very interesting...)
ZERO-SEN Model 21 Performance: Unraveling Conflicting Data
Richard L. Dunn © 2004
INTRODUCTION
The Mitsubishi Type Zero Carrier Fighter Model 21 was the fighter that opened the war in the Pacific over Hawaii and the Philippines . It was the primary fighter used by the Japanese navy from the beginning of the war until early 1943 and remained in front line service until well into 1944. As important as this fighter was in the Pacific air war there is little agreement in published sources about some aspects of its performance. In particular, the aircraft's maximum speed is given by different post-war publications in a range from 316 mph to 345 mph. This disparity of nearly 30 m.p.h. is sufficiently broad that at the lower end the aircraft might be deemed relatively slow by 1942 fighter standards and at the upper end it might be considered relatively fast and definitely competitive. This article attempts to unravel conflicting data and provide a likely, if not definitive, answer to the question of the Zero's maximum speed[...]
http://www.j-aircraft.com/research/rdunn/zeroperformance/zero_performance.htm
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Interesting. If true it would explain why the Zero was seen as such a threat in a way that AH's A6M2 cannot.
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It would also explain why the lightning succes should not be underestimated.
Hence zero's where too slow to compare to the uber luftwaffe aircraft.
As well the enemy faced in the PTO was at least as dangerous as in the ETO.
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Hi 1K3,
http://www.j-aircraft.com/research/rdunn/zeroperformance/zero_performance.htm [/B]
While this article is really nice to read, I think it is hard to reproduce Dunn's conclusion because he has fragmented the data sets in his article.
Unfortunately, some speeds are given without the corresponding altitude, and these don't help much :-(
The attempt to build A6M2 speed data based on combat reports is hardly reliable, though it could be used as a sanity check. One problem is that the F4F engines apparently were modified at some point, allowing them to run with the first supercharger stage in neutral gear, which boosted sea level speed considerably. The use of indicated air speeds is problematic since they are typically reading too high in the top speed range.
Let me try to re-build Dunn's data sets:
SET A
Intelligence Summary No. 85, December 1942:
(3) 321 m.p.h. at 20,000 ft. (Mikesh, p. 123);
(4) 326 m.p.h. at 16,000 ft. (Reardon, p.113);
Condition: Intelligence Brief #3 "It is probable that the airplane in original condition was somewhat faster than is indicated here, due to lack of flush fit at wheel well fairings and cabin enclosure in the overhauled plane, and the addition of non-specular paint."
Boost for the flight tests: +150 mm Hg (rated)
Overboost: +250 mm Hg
SET B
275 knots at 4,400m
(JICPOA Item No. 5981, dated October 1943, captured on Kwajalein February 1944).
SET C
289 m.p.h. at 15,000 feet @ 2050 rpm
(Holloway)
SET D
Zero rated 2500 r.p.m, maximum take-off rating of 2550 r.p.m.
(no source)
Regards,
Henning (HoHun)
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Hi again,
After checking it against a British report, it seems that the airspeed indicator of the P-39 indicated around 10 mph too high at sea level top speed, which casts a slightly different light on the combat reports quoted in Richard Dunn's article.
I've tried to find information on A6M performance, and it seems there were a few tests of captured aircraft of this type, many of which were problematic in one way or the other.
Here is my evaluation and a calculation for A6M performance, based on the drag of the airframe in the best condition and the TAIC data on the Japanese engines. (I'm not sure how trustworthy the latter is.)
http://hometown.aol.de/HoHunKhan/A6M_Speed.png
Note 1: Neumann's Zero was limited to 2050 rpm by a malfunction of the constant speed propeller. Only the 10000 ft data point was using full boost, and it coincedes with the Akutan Zero at the ca. 80% that were available.
Note 2: The Akutan Zero data is from the A6M2 that crashed on one of the Aleutian Islands. It was restored to a good, though maybe not perfect condition. My estimates are based on the assumption than all Zero models had the drag of this Zero.
Note 3: The Akutan Zero was found to be as fast as an F4F-4 in neutral gear at sea level. According to my calculations, it would be a bit short of that, and that's at WEP which the TAIC manual quotes as cleared for 60 s only. I assume in the comparative trials, it was used for longer than these 60 s or the F4F-4 comparison would make little sense. (Apparently, US combat pilots at Guadalcanal felt the A6M was superior to the F4F-4 at sea level, and from what I've read neutral gear operation was pioneered at Guadalcanal.)
Note 4: The Australian Hap was flown at lower rpm and higher boost than given by the TAIC WEP data. This might account for the low full throttle height. Estimating the power fraction it got from these settings, it confirms the drag assumption for the A6M2.
Note 5: The Patuxent River A6M5 was tested twice, once by the US and once by the UK (Royal Navy, I suppose, as they tested against a Seafire.) The US reports warns against airframe damage and high drag, but provides a sea level WEP speed that's only 12 km/h lower than my estimate. The UK report has data that's 10 - 20 km/h faster than the US report, but a lower full throttle height and no indication of using the supercharger low gear.
Note 6: I don't know whether the TAIC engine data is realistic. Especially the A6M5 full throttle height appears to be rather high. I get a top speed of more than 600 km/h for the A6M5, which tops all popular books. On the other hand, the popular books might be based on the sub-standard US tests, so who knows?
Note 7: I'm aware of one other test of an A6M5 that was captured on the Phillipines. It might be quoted in Mikesh's "Zero" book, but I don't have that at the moment. If someone could provide the data, that might help me with the data evaluation :-)
Henning (HoHun)
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One problem is that the F4F engines apparently were modified at some point, allowing them to run with the first supercharger stage in neutral gear, which boosted sea level speed considerably. The use of indicated air speeds is problematic since they are typically reading too high in the top speed range.
Note 3: The Akutan Zero was found to be as fast as an F4F-4 in neutral gear at sea level. According to my calculations, it would be a bit short of that, and that's at WEP which the TAIC manual quotes as cleared for 60 s only. I assume in the comparative trials, it was used for longer than these 60 s or the F4F-4 comparison would make little sense. (Apparently, US combat pilots at Guadalcanal felt the A6M was superior to the F4F-4 at sea level, and from what I've read neutral gear operation was pioneered at Guadalcanal.)
I'm not following you, or you misunderstand how the P&W 2-stage/2-speed superchargers worked. There would be no need to modify the supercharger to run in neutral blower at SL.
The R-1820 in the F4F-4, as well as the R-2800-8 and -10 in the F4U and F6F all had an integral supercharger ALWAYS running at a single fixed gear ratio off of the crankshaft. They also had an aux stage blower with three settings; neutral, low and high blower. Neutral blower simply meant that the aux stage was clutched out, and only the integral blower was running.
So you had three settings for the blower;
neutral with the aux stage clutched out and only the integral blower operating
low with the aux stage in low gear and the integral blower operating
high with the aux stage in high gear and the integral blower operating
Neutral blower typically had the intake air coming directly into the carb, then from there to the integral blower and into the intake manifolds leading to the cylinders. High and low blower had the charge air go through the aux stage blower, then the intercooler and finally into the carb, integral blower, intake manifolds.
If you look at a power curve for the P&W figther engines there are three distinct steps in it, as opposed to two for a two-speed blower drive like RR used. Neutral, which was used from SL up to perhaps 5000 ft, low blower used from there up to around 15,000 ft or so, and hi used above that level.
Greg Shaw
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Hi Greg,
>I'm not following you, or you misunderstand how the P&W 2-stage/2-speed superchargers worked.
Most probably the latter :-)
>So you had three settings for the blower;
I was aware of that, I just mis-interpreted some read-and-half-remembered comment on the genesis of this system and thought it resulted from a field modification of a two-speed, two-stage system.
So the F4F-3 would have had the same neutral gear power curve as the F4F-4?
>Neutral blower typically had the intake air coming directly into the carb
Ah, thanks, that was new to me! :-)
Regards,
Henning (HoHun)
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Would be interested to see an HTC response on this one myself
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Hi Widewing,
I think this thread is better suited for our analysis of the A6M than the great Luftwaffe thread where we originally started :-)
For reference:
http://www.hitechcreations.com/forums/showthread.php?s=&threadid=165257
(http://hometown.aol.de/WBHoHun/A6M_Speed.png)
Originally posted by Widewing
The Patuxent River A6M5 (yellow plot) data came from Naval Air Tactical Note 106, distributed to Royal Navy F6F squadrons deployed to the Pacific. The tests were performed by TAIC at Patuxent River, which the RN used to generate NATN 106. As far as I know, only the Patuxent River facility used independent air speed measuring equipment. I seem to recall that field tests performed by TAIC in the war zone relied on aircraft instrumentation for speed data. However, my memory is vague on this. Do you have any info on test methodology?
Unfortunately, I have few details on the tests. The Neumann Zero was tested in the field and made mention of relying on the original Japanese airspeed indicator, so at least for this test we know the instrumentation. I believe that is not an overly serious source of error as it would be possible to calibrate the airspeed indicator by either flying in formation with an aircraft with a sufficiently well-known indicator (standard operation procedure at test establishements at least) or by making a timed run over a known distance. I believe the runway length should normally be known accurately enough for the latter. Methodically, I imagine the latter might not yield perfect results for high altitude, but probably be quite satisfying for low altitude.
The Neumann A6M2, the Akutan A6M2 and the Australian A6M3 display good coincedence of their drag condition if you allow for the very different power settings they were run at.
I'd be confident that I could prepare a fairly good estimate of all A6M variants' speed curves using that data. It might be slightly on the low side because at least both A6M2s were (competently) patched up and not in optimum condition, but I believe that would be a minor factor.
However, such an estimate would have to be built on accurate engine power curves, which I haven't found yet.
The rest of the A6M tests paint a rather confusing picture, I haven't been able to learn anything useful from them so far :-(
I would like to ask you for your opinion on the following power curves, which I have derived from the TAIC intelligence data and which I regard with some suspicion:
(http://hometown.aol.de/HoHunKhan/Sakae_Power.png)
(Now that I prepared such a nice diagram, I notice that I have probably underestimated power drop above full throttle height. My mistake, not the TAIC's.)
Here is the original TAIC data I used as a basis:
Sakae model 12, TAIC 1944 p. 851
925 hp/2550 rpm/39.8" SL
925 hp/2550 rpm/39.8" SL
1010 hp/2550 rpm/39.8" 11000*
820 hp/2500 rpm/35.8" SL
935 hp/2500 rpm/35.8" 13800 ft
Sakae model 21, TAIC 1944 p. 852
1115 hp/2750 rpm/41.7" SL
1115 hp/2750 rpm/41.7" SL
1180 hp/2750 rpm/41.7" 7500*
1040 hp/2750 rpm/41.7" 18000*
995 hp/2700 rpm/37.8" SL
1085 hp/2700 rpm/37.8" 9350 ft
965 hp/2700 rpm/37.8" 19700 ft
Sakae model 31A, TAIC 1944 p. 853
1120hp/2800 rpm/41.7" SL
1120hp/2800 rpm/41.7" SL
1210 hp/2800 rpm/41.7" 8000*
1055 hp/2800 rpm/41.7" 20400*
995 hp/2700 rpm/37.8" SL
1085 hp/2700 rpm/37.8" 9300 ft
965 hp/2700 rpm/37.8" 21700 ft
The two main problems of the TAIC graphs are:
- 31A power gain over 21 in low gear (at just +50 rpm speed)
- 31A full throttle height gain in high gear without corresponding power loss
The only way I see for the 31A to achieve a higher full throttle height than the 21 is to use a longer high-gear drive ratio. That would however mean that effective power is reduced at the same time, resulting in a different power from the one I modelled from the TAIC data points.
In fact, since this data looks pretty generic, I'm actually having some doubts about the other data since it might be just as generic. TAIC data was wartime intelligence, which always is the best guess based on the currently available information at any moment.
I haven't been able to find anything substantial on the hardware of the Sakae engines either, such as supercharger dimensions, gear ratios etc., which could be used to double-check the TAIC data even in the absence of definite power curves.
A general statement TAIC makes on the engine data section:
"All ratings tabulated are taken from documents unless followed by asterisk (*). The latter are TAIC estimates.
Take-off - This is usually a one-minute rating.
W.E.P. - (War Emergency Power) - These ratings are in most cases estimated extrapolations based on take-off boost pressure. For most engines, documents indicate that take-off boost is permissible for one minute for either take-off or emergency. If one minute is permissible for take-off it is quite probable that under certain flight conditions, the period could be exceeded. Its exact duration is conjectural, but until better information is available, should, to be conservative from a tactical point of view, be considered as at least a five minute rating."
It would be interesting to hear more about the way the USN operated their radials and on what they considered advisable and possible. A one minute WEP duration doesn't seem to be of much combat value in my opinion.
Thanks for your help! :-)
Regards,
Henning (HoHun)
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The part that needs explaining from the "the A6M2 did 345mph" group is how it is that a radial engined fighter with a 950 hp engine comes within 5mph of the following inline engined machines:
Ki-61 Hien @348mph 1175 hp
Spitfire IIA @350-355mph 1175 hp (100 octane) capable of overboost
109E-4/N @350-355mph 1200hp capable of overboost
330mph at FTH to me seems reasonable as an upper limit to me. I think 345mph is fancifull at best especially considering the A6M5 did @351mph tops? and the fuel grades the Japanese were using was not equivilant at all to RAF and LW fuels during the war.
I could see it getting 345mph on 100 octane grades, being run overboosted, maybe.
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Hiya Ho-Hun,
One problem I am encountering is finding any references to the Sakai 31a engine ever attaining genuine production status installed in any model Zero. As far as I know, all models of the A6M5 were powered by the Nakajima Sakae 21 engine w/two-stage supercharger rated at1,130hp at take-off, 1,100hp at 9,350ft, 980hp at 19,685ft.
So, I'm somewhat dismayed that you have TAIC data for the Nakajima Sakae 31a, when all of my references say that this engine was never installed in any A6M5s.
A handful of 31a powered A6M6c fighters were built in late 1944 and early 1945, but appeared far too late to be captured and shipped stateside for testing in October of 1944.
A6M8 and A6M8c prototypes were flown with the Mitsubishi Kinsei Model 62 engine, but the war was just about over when these made their first flights.
What document reports the 31a powering an A6M5?
My regards,
Widewing
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Sakai 31A powered the A6M7. It had MW50.
The A6M7 was the last version to see service. The A6M6 was never put into production, neither was the A6M8. War ended before the order could be filled. The exact # of A6M7s is speculative at best.
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Hi Widewing,
>One problem I am encountering is finding any references to the Sakai 31a engine ever attaining genuine production status installed in any model Zero. As far as I know, all models of the A6M5 were powered by the Nakajima Sakae 21 engine w/two-stage supercharger rated at1,130hp at take-off, 1,100hp at 9,350ft, 980hp at 19,685ft.
Ah, thanks, that's a very important observation!
The TAIC summary states that the Sakae 21, Sakae 31A (without ADI) and possibly the Sakae 31 (with ADI) were used in the A6M5. I excluded the ADI-injected engine but failed to notice that not even the 31A was ever installed.
With the Sakae 21 in the A6M5, the only difference to the A6M3 in motive power would come from the additional exhaust thrust due to the individual exhaust stubs. I'll prepare a new analysis based on these assumptions :-)
Regards,
Henning (HoHun)
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I can remember reading a number of claims of Zero's being much faster in combat than during testing.
One of which is Ken Walsh (20+ kills) in a F4U-1 in mid 1943 running from a large number of A6M2's for miles starting at 5K and ending at sea level until his engine overheated and still having to do a hard break turn at high G to escape and head back toward home. 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.
Hohun,
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.
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.
I do not have the Navy test results except for specific altitudes.
The top speeds from the report are 413MPH at 20K for the F4U. 409MPH at 22,600FT for the F6F-5 and 335MPH at 18K for the Zero. 321MPH at 13K for the FM-2.
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.
It must also be noted than the F6F was unusually fast in the test as well. I think it's results may have been skewed at lower altitiudes.
I will post the full test when I can.
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Originally posted by F4UDOA
I can remember reading a number of claims of Zero's being much faster in combat than during testing.
One of which is Ken Walsh (20+ kills) in a F4U-1 in mid 1943 running from a large number of A6M2's for miles starting at 5K and ending at sea level until his engine overheated and still having to do a hard break turn at high G to escape and head back toward home. 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.
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.
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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.
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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.
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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)
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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.
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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
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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.
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HoHun,
TAIC report (http://mywebpages.comcast.net/markw4/TAICzero.pdf)
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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)
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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.
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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 :aok
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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.
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Hi again,
Here is a new A6M5 speed estimate:
(http://hometown.aol.de/WBHoHun/A6M5_Speed.png)
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)