On Mon, 18 Oct 2004 16:13:41 +0200, CV wrote:


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


I demonstrate to my students ground effect by approaching a 4200 foot
runway in a Blanik L-13 at about 55-60 knots. I would be at the
threshold a foot above ground. I could float over 3500 feet before I
would settle down and use the wheel brake to avoid running off the end
of the field. It is very effective. (There was little or no wind
when I did this.)

I once had to use this technique when I allowed myself to be
distracted on base leg. When I turned final I realized I was too low
to make the field but had plenty of speed. I dove toward the ground,
and put the glider in ground effect and made the field. (There were no
obstructions.)

A fellow instructor referred to ground effect as the last refuge of
the scoundrel glider pilot.