This idea came to me in a most peculiar dream, and I was wondering if it would be possible: Basically, it would be a backpack that you strap on with arms that come down (like a car seat) with controls at the ends. You start up the little engine in the backpack and mini helicopter blades extend up and outwards, just powerful enough to lift yourself and the engine. The retractable blades would mean you wouldn't have to tie up the contraption like a bike when entering buildings. Is there an engine that could be powerful enough to do this (yet light enough to carry around?) If so, it could have tremendous implications for personal transit.