>Dragan,
>
>>For a jet, it still has to work a lot against gravity etc.
>
>No the lift of the wings does that. A jet engine is very efficient at converting fuel to thrust (ie expanded volume hot air). A ramjet (no moving parts) is the best, but it requires supersonic speeds to begin operation.

It still has to invest a lot of power to gain speed which would be sufficient to produce a liftoff.

I think the original comparison (rocket in vacuum vs bicycle vs anything else) was in total energy consumption per unit of transported mass per distance. In that light, I think that despite the jet engine being as efficient as it is, it still loses because it has to lift the heavy airplane.

Though, it would be nice to have a comparison for dirigibles. These things may sound promising.