Dragan,

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

It has to accelerate the mass to the speed at which positive lift occurs then it only has to overcome air friction (drag) to maintain speed.

>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.

I'd love to find the original reference and re-read it. Considering that > 99.99999% of all mass transport we humans do involves air and/or water and/or surface friction rockets in a vacuum can be neglected.

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

A jet powered dirigible now there's an idea worth investigating. *bg*

Seriously though the He only overcomes gravity, the propulsive force is relatively inefficient piston driven props.