Originally Posted by barit1
G SXTY's got it. It's not that the
engine is more efficient at altitude, but that the engine is best matched to the
aircraft at altitude. The machine is bloody overpowered at takeoff, is working hardest at top of climb, and happiest in cruise.
Then consider an underpowered aircraft - say a twin with one engine out or a trijet with one or two engines out, or a quadjet with two engines out. Assuming that the inoperative engines are properly shut down, they burn no fuel and no fuel is leaking.
After the plane has descended to its ceiling and continues on a cruise... the remaining engines are working harder than in normal cruise, therefore burning more fuel each, but the inoperative engines burn none at all.
Does the aircraft then lose efficiency and therefore range? Does a plane cover longer distance with all engines operative cruise or some engines out cruise, given the same fuel load?