@blobrana
Not sure I understand your point.
Anyway, horizontal flight embraces three major forces:
Mass (gravity) which is down.
Lift (via the aerofoil or reaction to a down thruster) which is up.
Drag (air friction) which is backwards in the case of 'forward' motion through the air.
Provided lift exceeds mass, the craft will hover.
Provided the motive force exceeds the drag, the craft will move horizontally, ie: it will fly.
Aeroplanes get lift from the differential pressure above (low) and below the relatively vast wing aerofoil area. A very slow forward motion through the air will create a lot of lift if the aerofoil is pronounced (as in GA and typical gliders). A man has enough energy to achieve this lift if the total mass is low enough (as in GA). The craft also has to be designed with sufficient streamlining to allow drag to be minimised. Even so, GA flies very slowly, perhaps 10mph.
In the case of hovering, which only helicopters and vectored thrust planes can achieve, there is no drag because there's no motion. All the power of the engine is directed in opposition to the mass. In other words, the downthrust must equal the mass of the craft. The air is simply used as the down thrusting medium in the helicopter. In the Harrier, it's the high pressure exhaust stream.
So, no man has the energy to counterbalance the mass and can never power a hover. He can, however, power just sufficient forward motion, by overcoming the drag, and thereby get a hand from Mother Nature's lift as the air passes over the aerofoil.
As a matter of interest, the tips of a helicoper's rotor break the sound barrier. So yes, the stresses are immense.
Cheers,
JaX
