Low approaches in ground effect

Gerhard Wesp wrote:
nafod40 wrote:

Interesting observation. Flying in ground effect places the center of
pressure of the wing at about mid-chord, while out of ground effect the


Are you sure? Note that a forward CG implies a pitch down moment which
would have to be compensated by negative lift on the tail. Hence
performance degradtation, contrary to what ground effect is supposed to
create.

That part would be minor, more than compensated for by decrease in
induced drag and increase in lift.

I'm still searching for a good explanation of ground effect :-)

Here's a killer page describing the aerodynamics of it. Follwoing is a
short excerpt from the page.
http://www.se-technology.com/wig/htm...en=aero&code=0

Two phenomena are involved when a wing approaches the ground. Ground
effect is one name for both effects which is sometimes confusing. The
two phenomena are sometimes referred to as span dominated and chord
dominated ground effect. The former results in a reduction of induced
drag (D) and the latter in an increase of lift (L). The overall effect
is an increase of the L/D ratio. This ratio is a measure for the
efficiency of an aircraft which can be expressed as the amount of power
(thrust) that is required to propell an aircraft of a certain weight.
Since thrust is equal to drag and weight is equal to lift in stationary
flight this efficiency can be expressed as the L/D ratio. As the L/D of
a wing increases with decreasing ground clearance the craft becomes more
efficient in ground effect.