nick
you said> ground effect is not a cushion, and it does not involve perssure rising under the machine or any such thing.
the ground is resisting the airflow from the rotor, the same as clean air in foward flight, reducing induced flow. if you're pushing air down and it cant go anywhere it has to increase in presure, doesnt it?
ground cussion > in the hover air from the disc is forced downward but is stopped by the ground (ground effect) so then has to move horizontally away, inward and outward. the air that goes inward stops when it meets the air directly opposite coming in. so the air in the centre has reduced velosity theorfore increasing preasure in all directions i would think.
to prove it > creeping takeoff,- as foward movement is achieved, adjusting collective for the offset lift vector, an additional collective pull will be required to hold the helicopter up after the cussion is lost behind you and just before translation.
you dont give a reason for the reduced induced airflow. pressure is the reason!
DAVE
shockwaves might have somthing to do with tuned length exaust pipes and inlet runners but i think it has more to do with the volume that is moved and the inertia of that volume.
as for helicopter blades....na! the shock waves would miss the blades when i adjust rpm.