Saint Evil said:
So what is the actual explanation for Ground Cushion?
Let's start with a simple answer, courtesy of Nick Lappos from
this thread.
"For the record, the effect is not due to a "ground cushion" or "air pressure" or "a bubble of air" under the helo. The ground bends the air flow coming off the rotor, and this bend makes the rotor blades work at a lower angle to produce the same lift. The lower angle needs less power, so we see the ground effect."
For further reading, here are some threads where this issue has been discussed and the pressure bubble folks (sorry mil guys) have been sent home with tails firmly between their legs.
Helicopter Urban Myths #11 (Post 69 and onwards)
Ground effect/Urban myth
Varying degrees of IGE
OGE Hover, Service ceiling