Don't know whether this answers your question!

A Russian airforce pilot perfected this technique for
getting home on minimum fuel using ground effect to
prolong his flights. His ideas were developed into
ground effect vehicles which the Russians built in
a variety of forms.

The largest being the size of 747's and were named
the Caspian Sea Monsters. The intended development
was for military use. the end of the cold war stopped
production of the big ones. Some smaller craft have
been produced.

Briefly the idea is that you force air under the craft
with huge forward mounted jet engines, which provide
both the air cushion and thrust. Not quite the same
as just using ground effect to prolong an approach!

Ground effect does work with a low wing glider, other
than using the effect to float along way across flat
airfields I have never used it to prolong a final glide
over rough ground. But practice suggest that you have
to be very low to get the best effect and is only short
lived. A few hundred yards rather than miles, but then
I have never tried to go miles.

For Kranoplan information see

See http://aeroweb.lucia.it/~agretch/RAFAQ/WIG.html

First a disclaimer: I understand the security issues
involved
in the following and would not encourage anyone to
try this
at home, but I am interested in the theoretical side
of it.

Imagine you get things wrong and are caught out low
on final,
still a fair distance out, and it looks marginal whether
you
are going to reach the runway or not.

One technique I have sometimes heard described is to
dive for
the deck and complete the remaining distance in ground
effect.
For the sake of the argument we can assume fairly flat
ground,
free of obstacles, though not necessarily landable.

The advantages claimed are usually better glide performance
in
ground effect and less headwind and absence of downdrafts
close
to the ground.

On the other hand you'll be travelling at higher than
optimal
airspeed for most of the distance.

I am wondering how much truth there actually is to
this
technique. Would it significantly increase your range
and
improve your chances of reaching the field or not ?

Would it perhaps work better against a strong wind
gradient
(as I suspect it might), and maybe not help a lot in
calm
conditions ?

I'd be interested in any hard data/analysis or otherwise
enlightening comments on this.

Please note though, that I am not talking about high-speed
competition finishes, rounded off with a beatup and
a sharp
pullup and all the dangers and other issues involved
in that.

Cheers CV