"CV" wrote in message
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Dave Martin wrote:
Don't know whether this answers your question!

No bearing on the question, really, though it is
slightly related, and interesting as well.

Ground effect does work with a low wing glider, other

I don't know of any low-wing gliders. Most are mid-wing
and some older types are high-wing, but that difference
is so small I wouldn't expect it to matter. In the
situation I asked about we'd want a safety margin
of perhaps 5 feet or so off the ground in any case.

AFAIK ground effect starts being significant from
approx. half a wingspan off the ground, the effect
being to increase performance, as if you had greater
span.

lived. A few hundred yards rather than miles, but then
I have never tried to go miles.

A few hundred yards would be sufficient for what I had
in mind, provided that the other factors balanced out
and resulted in a net gain in how far you can glide.

Cheers CV

The rule I learned was that ground effect became measurable at one wingspan
above the ground and near the ground could double the L/D. Running in
ground effect is a lot of fun but you'd better be very smooth on the
elevator since the pitch control gets 'twitchy'.

(I strongly suspect that unanticipated elevator sensitivity in ground effect
is a secondary cause of some of the G103 "PIO" accidents.)

The best glide stretching technique is to approach the ground at slightly
better than best L/D speed leveling off a couple of feet above the ground.
Diving to the ground is dangerous and wastes energy that could better be
spent at best glide. Maintaining the usual approach speed seems to work
best.

Of course, all this assumes that the approach and runway under-run are
completely free of obstacles like wires or fences.

Bill Daniels