Hello P-39 Expert,
This is looking a lot like the movie Groundhog Day.
Hopefully you might learn something like Bill Murray did.
You obviously don't know how the carburetors work in these aircraft.
Obviously.
The Auto Rich setting gives a slight margin for detonation under maximum throttle settings and the automatic mixture controls also compensate for altitude (air density) changes with varying flight conditions.
To achieve the extra 25 HP and 3 extra MPH, the pilot had to switch to manual mixture control and lean out the mixture.
This might work just fine if you are flying along straight and level with nothing else is going on, but in COMBAT, this is just plain STUPID. Without the automatic mixture control working, the pilot would need to compensate for any altitude changes immediately. Losing a few thousand feet of altitude and finding that your engine is now detonating or burning valves is a pretty lousy way to find you need to walk or swim home.
As in the test all the pilot had to do was adjust the mixture control slightly. It was a lever on the throttle quadrant. Again we're talking about 3mph.
You are correct. IIS 85 is not the correct reference.
You are also not reading the report correctly. It actually says 326 MPH.
I was off by one line. 326mph is not 335mph.
It is interesting though that the actual information that was eventually distributed more widely was 332 MPH.
332mph is not 335mph.
This is a better reference.
Glad you finally found your 335mph reference. Most other references say 330mph. You're fighting over 5mph like it won or lost the war.
Memorandum 23 Oct 1942
Note that maximum speed in this report is 335 MPH @ 16,000 feet and the test aircraft is still achieving 331 MPH at 20,000 feet.
P-39K did 370mph at 16000' and was still achieving 364mph at 20000'.
Do you remember my comment that if you didn't like a comparison of climb rate with the A6M5 at 15,000 feet, you would like the comparison with the A6M2 even less?
Note that the climb rate is 2480 feet/minute at 15,000 feet. How does that compare with the P-39D????
Look at the P-39K graph in post #1006. I think you'll find the climb rates very comparable.
The most interesting information listed in this memorandum report is the note at the bottom which states that the manifold pressure was limited to 35 inches Hg. This is only +129 mm boost which isn't even Military Power.
Military Power would be +150 mm or 35.83 inches Hg
Emergency Power would be +250 mm or 39.76 inches Hg
I had missed this note in my earlier readings.......
This is why I am tending to believe now that Mr. Dunn's argument is probably correct considering that a rebuilt wreck can achieve 335 MPH without even using MILITARY power and with a carburetor that wasn't working correctly.
Probably?
Correct or not, you're talking 5mph.
First of all, the source of information that is listed in that table is a book from 1981.
Second, your conversion isn't entirely correct. Speed should be 331.5 MPH (288 Knots).
331mph is not 335mph.
Third, you should read the footnote to that entry. The information that is listed there suggests that the author is a bit confused:
"The speed was increased after thickening the outer wing panel"? How does THAT improve speed?
Sounds like he was confusing level speed with maximum diving speed..... There is much more detail to this discussion about the authors errors that is beyond the scope of this discussion.
Note also that earlier speed was specified as 275 Knots. This was NEVER the maximum speed as we understand the term here.
275 Knots (316 MPH) was the maximum speed under "Normal Power" settings of +50 mm boost at 2350 RPM.
316mph is not 335mph.
One report shows 335mph, most others show 330mph. Or less. Take your pick.
If you have information that can confirm that the P-39D-1 in the test was loaded to 7850 pounds please post it.
7850lbs was the listed weight of the P-39D-1.
Considering that the pilot in the test was willing to try 70 inches Hg at Take-Off to prove he could beat the Zero off the line suggests that they were not above a few tricks.
More tricks? The pilot overboosted the engine at takeoff indicating he either was new in the P-39 or was a lousy pilot.
In any case, 7250 pounds was not the loaded weight of operational P-39D-1 in service and your hypotheses are not proven and irrelevant.
I have always stated that this weight was easily achievable at forward bases and this was hypothetical. You have not proven anything either.
- Ivan.