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Even the hottest early N models with the reduced fuel would have been a nonstarter at ETO altitudes against escorts with two speed or two stage superchargers or turbos.
Cheers,
Wes
And would the strength of the P-39 at 5000meters (16,400ft) be to dive down to 3000meters upon sighting the German fighters?OK,....In all my posts on this forum about the later P-39s with the V-1710-83 engine
I am pretty sure I never said it was a world beater even when it was first delivered in
November 1942. Although at that time until late 1943 it could hold its own against
most first line Axis fighters up to 5,000 m. provided it was flown to its strengths.
And would the strength of the P-39 at 5000meters (16,400ft) be to dive down to 3000meters upon sighting the German fighters?
Being a bit sarcastic, I will agree that the P-39 could display good performance at 3000 meters and below but 5000 meters is really pushing things.
View attachment 512061
From Mike Williams website Spitfire performance.
The P-39M-N-Q all used the same power section or had the power curves. they varied in reduction gear used and propellers used.
Unless the planes are flying level and at high speed much of the WEP power advantage goes away above 3000 meters. Leaving high level speed and diving as the only real strengths of the P-39.
Good trainer for transition to a 1st generation jet?AS you accelerate you pick up RAM effect and if you accelerate long enough you will get to that 1300hp level and the just about 400mph speed.
Once again, ALL the planes tested in official performance tests (not propeller comparison tests etc.) were lighter than their published weights reflecting an average fuel weight during the test flight. The British used 95% of takeoff weight as their "corrected" weight to reflect fuel burned. The P-39N test was a standard test and the figures should be respected.Some of those numbers look suspiciously high. Higher than the numbers shown in the tests at Spitfire performance?
And those number were done with planes that weighed less than they should have. The only way you get a P-39N down to 7300lbs is to fly with less than full internal tanks. For some weird reason even the test of the N seems to show abnormally high climb rates compared to the M and the Q, They changed reduction gears and props between the M and N and that might account for it? But then they mounted a single 50 cal under each wing and yanked the .30s and the climb fell back down to just about the level of the M. We are talking about a 400 fpm change in both directions at some altitudes.
So if you have time and are not immediately bounced, get "on the step" by continuing your climb to 13,000, then accelerating in a shallow descent back down to 12.5. I've done that in 99s and 1900s, as PT6 engines are somewhat sensitive to ram effect.Now say your P-39 has just climbed hard up to 12,500ft and is doing about 200mph and you level out. You don't have a bit over 1300hp, you have a bit over 1100hp due to lack of ram.
Yes, and the good guys wear white hats and always win!The P-39N test was a standard test and the figures should be respected.
So if you have time and are not immediately bounced, get "on the step" by continuing your climb to 13,000, then accelerating in a shallow descent back down to 12.5. I've done that in 99s and 1900s, as PT6 engines are somewhat sensitive to ram effect.
Cheers,
Wes
The P-39N test was a standard test and the figures should be respected.
So if you have 5 out 6 planes closely clustered in weight and using the same power engine and closely clustered in climb and the 6th plane using the same engine and only slightly less weight showing a major increase in climb rate what are you to believe?
That it was a good idea to take the four paint chippers out of
the wings like the Russians did?...
I seem to recall reading this instruction in a pilot's manual to increase cruise efficiency.So if you have time and are not immediately bounced, get "on the step" by continuing your climb to 13,000, then accelerating in a shallow descent back down to 12.5. I've done that in 99s and 1900s, as PT6 engines are somewhat sensitive to ram effect.
Cheers,
Wes
Perhaps the Russians goofed and the wing guns actually increase the rate of climb
Wow SR6, you might be on to something there. I'm going to have to
go into deep research now....
Actually, we are on the same page here. If you look at all the
P-39 tests they all mention the overheating problem when boosted.
At no time is it mentioned that the engine was not able to take
the punishment. It just says the USAAF didn't approve of it.
The test reports don't tell you whether the engine on that hot performing P-39N1 whose coolant temp "didn't conform to USAAF standards" suffered an engine failure in some subsequent flight or had to have its engine pulled early for overhaul. If the test was done in Niagara NY or Moscow RFSSR in winter, then the engine could probably take that abuse with limited hidden damage. With MSL OAT 60°-70°F below ISA, your density altitude is going to be only about 3/4 of your barometric altitude, and your engine's going to have more power and your radiators more efficiency, and the risk of thermal runaway much reduced. In fact the plane's going to think it really is at 3,000 meters when it's actually at 4,000.If the USAAF considered it to be a problem, then overheating the engine must have had consequences. I don't pretend to know what those consequences were, but I think it would be unwise to pretend that there were no consequences.
Under those conditions you gain total energy faster by climbing than by trying to accelerate from slow speed in level flight. The extra 500 feet can't take more than 20-30 seconds at the outside, and then gravity is helping you accelerate and enhancing the "bootstrap effect" of your increasing ram as your speed builds.But once above 3000 meters it becomes much less of a factor in anything except straight line flight.
The test reports don't tell you whether the engine on that hot performing P-39N1 whose coolant temp "didn't conform to USAAF standards" suffered an engine failure in some subsequent flight or had to have its engine pulled early for overhaul. If the test was done in Niagara NY or Moscow RFSSR in winter, then the engine could probably take that abuse with limited hidden damage. With MSL OAT 60°-70°F below ISA, your density altitude is going to be only about 3/4 of your barometric altitude, and your engine's going to have more power and your radiators more efficiency, and the risk of thermal runaway much reduced. In fact the plane's going to think it really is at 3,000 meters when it's actually at 4,000.
Now all it takes is for the conversion of the raw measurements to ISA conditions to get lost in the shuffle, and there's your anomalous "hot Cobra".
Cheers,
Wes