A quick question about that. Aren't jet engines (I'm thinking aircraft here) effectively turbines that spin blades to pull air through a compression chamber (with a few extra things going on) to result in very high speed exhaust? Does this mean that a jet plane's ability to push itself through the air doesn't really scale with a lower speed? (I'm probably misunderstanding something basic here)
Phew, difficult one. Since in the terms of aircraft there is just so many things that needs to be looked into. While the engine is part of "moving the plane forward", there are just too many things besides that to look at. Like the flight-height of the plane. In higher heights the air is thinner, with that the engines doesn't need as much power for the same forward movement, seen on a plane which flies not that high.
I'm no mechanical engineer, but what I know is that most fuel and engine power is used in the take off of the plane. When it's actually in the air, at it's travel-height and just uses the engine for moving forward it uses alot less engine-power.
However I think the problem might be here, that while "jet engine" always sounds like it's used in aircrafts, the ones that are used for electricity are actualy "modified" versions of what you find at planes.
So you cannot simply take a jet engine which is used for making shaft-power to create electricity and build a plane with them. Even though many of them actually were taken from old jets once, the modifications doesn't really make them the "same as plane engines", as far as I understand (really a complicated topic, when you're not really into aircraft engineering, heh)
So I think the confusing part here is, that while the name is pretty much the same, there is still a difference between jet engines used in planes and the same'name engines used for creating electricity.