However, if you do decide do something like this, I don't think you need a block that provides lift. Rockets already do that :D. More importantly, since I read somewhere that you're planning to add drag,  why don't you just add a block that creates air resistance? That way, you can create aircraft, but also manipulate drag in other ways.

Or. 

http://www.youtube.com/watch?v=FExsR6Q_vAU

:D

Don't forget. This game is fundamentally a blow up/ car racing thing. Personally, I wouldn't use pistons, but something more like explosives, since it seems like there would be more interesting ideas using that.