P-39 Performance Thread

[Ivan1GFP]

I have a British (A&AEE) tests of:

Airacobra AH-573
7,830 pounds
Allison V-1710-E4
2600 rpm
37.2 inches of Hg.

2,000 feet - 2040 feet per minute
10,300 feet - 2040 feet per minute (critical altitude)
16,000 feet - 1385 feet per minute
22,000 feet - 795 feet per minute
29,000 feet - 120 feet per minute

I know this is an old thread, but thought I would still point out that the numbers quoted here are at very low throttle settings.
Full throttle is more like 47 inches MP and 3000 RPM.

 

[Neil Stirling]

I know this is an old thread, but thought I would still point out that the numbers quoted here are at very low throttle settings.
Full throttle is more like 47 inches MP and 3000 RPM.

Those were the limitations at the time http://www.wwiiaircraftperformance.org/P-39/AH573.pdf

Neil.

 

[tomo pauk]

British were not testing the climb rates on full throttle RPM, at least not early in the war?
The 3000 rpm and 44.5 in Hg was a 5 minute rating ('Emergency maximum'; later renamed 'Military' rating - not to be confused with 'War emergency' rating, introduced in late 1942) in the early V-1710-Es, rather useless if the plane need to intercept something that is flying at, say, 20000 ft. As witnessed by USAF units in SE Asia/Pacific in 1942?
The 'Military' rating was allowed to 15 minutes some time in 1942 for the V-1710s.

 

[Shortround6]

And even then, the use WEP was required to be noted in log books and times to overhauls shortened and extra maintenance could be triggered (more frequent changing of spark plugs for one) so more normal climbing powers were used when they could be. Granted these figures do not tell us what the plane could do in combat but then the WEP power settings don't tell us what the plane could do in normal operations either. Using WEP for every intercept or climb to altitude is going to run you out of engines or at least spark plugs fairly quick let alone enemy action.

 

[Venturi]

Spark plugs are a very quick replacement, easy to access and a normal wear item, and I'm sure nearly anybody operating these ac had spares. You're right on the log books but without a "wire" to break it is up to the pilot to tell the crewchief what he's done. So on those engines without an automatic manifold pressure regulator (early P39s) there is some question as to how realistic adherence to the published engine limits actually was in combat. It is worth noting that the basic Allison used in the P39D for instance, minus gearbox for mid aircraft placement, was nearly identical to those used in P40Es and Mustang Is (usually had a automatic MAP regulator) and these had a reputation for being pushed pretty hard by their operators.