ATPL type question

[Captain N]

1-high altitude=low density=high engine efficiency

high temp=low density= low engine efficiency WHY?

[MrHorgy]

Difference in temperature. You'll frequently see performance limited operations at "Hot and High" airports - jet engines just don't work as well when it's hot. This problem doesn't occur at altitude, as it's rather cold :ok:

Horgy

[Blinkz]

Its not just to do with temperature. Jet engines are designed to be most efficient at high RPM and this RPM can only be reached at high altitude otherwise the thrust would be too much to balance the drag (since thrust decreases with altitude)

[bobster1]

No it covers, jet, turbo prop and piston theory. I believe the introduction of diesel powered engines to now, as they have started to become more relevant to aviation.
During our exam I was expecting plenty of questions on jets, but there where more on piston engines, but thats just the luck of the draw.