In-game the P51D30 starts losing HP at 5500m which is surprising for me considering it was built for high-altitude escort. I haven’t checked the other variants but I assume they start losing HP at high altitudes too with the exception of the P51H variant probably. In my opinion, it is even more outclassed by BF109 in the usual characteristics other than top speed at altitudes above 6000m. Is this realistic?
All aircraft do. Thinner air means less oxygen to get into the cylinders.
For aircraft with turbochargers/superchargers designers have to design a charger for a specific altitude as well, too high and engine performance at lower altitudes suffers.
Also the less dense the air the less air a prop has to move in order to provide thrust to pull forwards or push. Depending on config of aircraft.
less air for the supercharger to suck in and less air for the props to push against. Yes its realistic.
Superchargers don’t completely counteract the power loss at high altitude, they just lessen it. It’s less “We don’t lose power at high altitude” and more “We lose less power than the other guy”.
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This is for the P-51H and is from http://www.wwiiaircraftperformance.org/mustang/p-51h-na-8284-pg12.jpg
You can see where the supercharger stages kick in - high altitude is on the horizontal axis, which is a little confusing 1st tiem you look at it!
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My current experience with P-51C-11-NT (China) in Air RB:
At very high altitude, say around 6k meters, maybe 6,5k, a huge drop in power, the engine stops working, a complete loss of power. I think the high RPM warning also started appearing at the same time as this massive performance drop. It happened to me not once, but repeatedly. In one case, I was being pursued by a Spitfire, I think it was a Spitfire Mk.IIB, and it didn’t happen to him, he immediately started catching up with me, so I had to quickly dive and running off. I wanted to set an energy trap for him, but it was probably a lost cause because with the performance of the P-51C-10 must be something wrong at this altitude, and it probably started earlier, maybe around 5k meters. That could explain why I couldn’t energy traping him. I was relying on my much better high alt performance compared to that Spitfire, but…
EDIT: it happened to me again yesterday, and it happened when I was on MEC (100% PP, 80% rads), I tried to switching to automatic and suddenly the engine power was back. So at altitudes above 5,000 meters, I will rather to turning off the MEC from now.
(NOTE: The P-51C-10 and its copy-paste siblings do not have the option to manually switching supercharger gear with MEC, so this can’t be the cause of it.)