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I would like to ask about differences in the way that engine power decrease with altitude, but first some performance charts:
BWM 801D2
or Merlin 66:
http://www.spitfireperformance.com/merlin66hpchart.jpg
Both engines have 2-speed supercharger. We can see in both cases that the power of engine rise till FTH of the particular gear is achieved, then there is a power drop untill the second gear of supercharger is engaged.
However, on Jumo 213 E-1:
we can notice that there is a constant power decrease with altitude?
Where does these differences come from? Could we use all those charts for direct comparison of engine performance?
No - each manufacturer had superchargers designed differently - trying for high blower performance peak at different altitudes.. turbo superchargers were more efficient at high altitudes but had weight and size penalties which affected the airframe drag, and climb performance
Regards
PS. Sorry for my English - isn't as good as I want it to be.
On the other side we have Jumo 213 E-1 chart when at each gear the power of engine is pernamenlty dropping. What may be the reason of this?
Don't forget that Jumo hydraulic driven second stage that allowed change supercharging smoothly. So line of power between 1st 2nd stage max. power points is not so wavy as other have.Hello
On the other side we have Jumo 213 E-1 chart when at each gear the power of engine is pernamenlty dropping. What may be the reason of this?
Regards
Exhaust backpressure is not the only factor reducing the power under critical altitude. The main factor is air (mixture) density. As the manifold pressure regulator keeps MP constant air temperature after blower is higher at low altitude so the density that is proprtional to pressure/abs_temperature ratio drops.Each engine aircraft is built for a critical altitude, that is the altitude at which it can develop the maximum power.
At sea level, manifold pressure must keep below a certain level even if the supercharger could, in theory, pump more fuel air mixture, the limit being the ocurrence of self ignition before the piston reach the top dead center. What's interesting is that power at sea level is usually slightly lower than power at critical altitude becuase air is thinner and thus the expanding hot gases encounter less resistance during their trip down the bore, pushing the piston, and out of the exhaust (this factor is called 'back pressure').
As the manifold pressure regulator keeps MP constant, air temperature after blower is higher at low altitude, so the density, that is proprtional to pressure/abs_temperature ratio, drops.
I think the challenge is where to fit the turbo, and preferably, the intercooler.The single engined fighter with turbo V-1710: a missed USAAF's opportunity?