windhund116
Senior Airman
- 360
- Jul 3, 2017
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Hey guys,
Thanks for the reply. The Japanese characters 零戦 do seem to mean 'zero fighter' via Google translate.
Attached please find a performance graph for the P-39K which had the same 8.8 supercharger gears as the P-39D. Also attached is a P-39D performance test. The numbers are virtually the same.
As you can see from the graph the top speed of the K model was 370mph up to 16000'. The A6M2 is commonly listed at 330mph at 15000' with speed falling off at higher altitudes at the same rate as the K. That's a 40mph difference at all altitudes.
The climb numbers on the chart and the report show that power was reduced from combat power (3000rpm) to normal power (max. continuous) when the 5 minute limit was reached. This limit was increased to 15 minutes in mid 1942, just after these tests. The red dots represent rate of climb at combat power 3000rpm. This closely approximates the A6M2 climb rate.
Pardon me, I'm comparing the 1942 P-39s and A6M2. The A6M5 was later and should be compared to the P-39N of late 1942 early 1943.
Try reading P-39/P-400 vs A6M3 Zero New Guinea 1942 by Michael John Claringbould. It has some good combat accounts, some of which will say the P-39 and A6M were close in speed, some were the P-39 was faster, likely due to acceleration being close for the two aircraft. But the main reason to read the book is the in-depth look at combat records; the P-39 and A6M were even in the win-loss stats. That surprised me.
Shows the top speed of an A6M2 as 330mph at 15500'.Kanji 零戦 means Zero Fighter. "Reisen" is a contraction of Reishi Kikanjo Sentouki.
Reishi Kikanjo Sentouki
How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.So your numbers mean nothing then, just fluff.
Please expand above.Hello P-39 Expert....
Why do I get the feeling I have been here before?
The test report you gave on the P-39D is actually quite interesting. You should actually read it for content instead of just picking the maximum speed figures out of it.
Please note the following:
These people were tweaking manual mixture controls to get the P-39D up to 368 MPH. This is not something that is done in combat. With Auto Rich, it was doing 365 MPH which is still pretty good though. Just the pilot slightly varying the mixture control to get the best power based on feel and sound. Why wouldn't that be done in combat?
From other test reports (358 MPH), it is pretty obvious that maximum speed varied a bit as one might expect for production aircraft.
If you are still going with the "commonly listed" number for the A6M2, you obviously are forgetting the IIS 85 test report you claim to have read or don't understand it.
If a crashed and repaired A6M2 can achieve 335 MPH in tests (corrected down to 332 MPH for dissemination) while NOT running War Emergency Power, then 330 MPH for a fighter in good condition in Japanese service is unlikely. Highest speed listed in that report is 321mph at 18000'.
Here is a pretty good discussion along with anecdotes from combat encounters that supports a substantially higher number.
I just went through the article again and am more inclined to believe Mr. Dunn's conclusion is correct. See Windhund's post #1020, 330mph at 15500'.
A6M2 Performance
Please note that the manifold pressure conversions are not quite correct. I contacted him years ago about this issue and he acknowledged the issue but never corrected the article.
The IIS 85 report was based on testing after mid 1942 and shows P-39D climb rate as distinctly slower past about 12,500 feet or so. That was the D-1 model that weighed 7850lbs. Could have easily weighed 7250lbs after removing redundant or unnecessary equipment. Read the chart in my post #1006 and compare those climb numbers to IIS 85 test. That P-39 weighed 7650lbs.
- Ivan.
Quite likely partly due to differences in test conditions buried in the small print. Achieving identical test conditions (or correction factors to compensate if not achieved) is more involved than it may seem to the uninitiated.How do you account for the additional 1000fpm climb?
It was a postwar Vespa, made from the scrap metal of the P-39s crashed by the Italians after the USAAF gave them some.That depends. Is that Vespa from 1942? When the war had only been going for a year?
Both were official performance tests conducted at Wright Field by the AAF on brand new airplanes. Larry Bell was back in Buffalo. No "shenanigans" would account for a 1000fpm difference in climb rate. One was 836lbs lighter than the other.Quite likely partly due to differences in test conditions buried in the small print. Achieving identical test conditions (or correction factors to compensate if not achieved) is more involved than it may seem to the uninitiated.
Who actually conducted each test? Where and when? Corrected to standard atmosphere values? A P39C prepped at the Bell plant and tested in wintertime in Niagara will certainly put up better performance differential numbers vs a P39D in combat trim randomly selected from the flight line at Langley in summertime than the actual difference in the aircrafts warrants. Larry Bell was not above "detailing" a plane about to be tested to maximize performance. How do you KNOW such shenanigans didn't happen?
How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.
Same propeller. Cooling was a problem with most AAF fighters. Backfire screens were eliminated in mid 1942 on Allison engines without turbochargers, and in September on turbocharged P-38s. If the backfire screens were installed in the P-39C then performance would have improved with their removal. Even better climb."Airplane equipped with Allison V-1710-35 engine and 3-bladed constant speed propeller, blade design No. 614CC1.5-21, blades are not equipped with cuffs."
"Oil and Prestone temperatures do not meet Air Corps requirements in climb"
http://www.wwiiaircraftperformance.org/P-39/P-39C_40-2988.pdf
The test on the P-39D did not evaluate cooling, and so whether it met the required standards was unknown.
"Airplane equipped with Allison V-1710-35 engine and 3-bladed constant speed propeller, blade design No. 614-1C1.5-21."
"Individual port backfire screens not installed in engine."
http://www.wwiiaircraftperformance.org/P-39/P-39D_41-6722_PHQ-M-19-1325-A.pdf
But, by all means remove self sealing tanks, armour plating, armoured screen, ditch the radios and IFF, lose the .30" mgs. Then you will have an aircraft with 40 extra gallons of fuel and that extra 1,000fpm climb. It should be able to take the Luftwaffe on over Berlin!
While an interesting and compelling argument, I think I read somewhere that it's not quite that easy.300lbs lighter at 1.2fpm per pound would mean adding 360fpm to the values on the chart in my post #1006.
A different 'dash' number means there was a difference in the part.Same propeller.
How do you account for the additional 1000fpm climb? The only difference in the two planes was their weight. Same engine, propeller and airframe. Same HP at same altitude. One weighed more because it had different internal components (self sealing tanks, armor plate and glass, more .30cal MGs.) None of those internal components had any effect on performance other than their weight.