Not only do you have ground effect, but the runway might be pretty hot,
generating some nice lift.

Mike Schumann

"Don Johnstone" wrote in message
...
At 19:00 11 July 2006, wrote:
1. The sailplane is going 75 knots 10 to15 feet off
the ground with
the spoilers open. The spoilers are then closed and
the sailplane
travels maybe 4500 feet losing 10 knots of airspeed
(65 knots on
impact) and the pilot is slipping the sailplane for
some of that time.
How is that possible? That equates to an L/D of 300/1
to 450/1. I
understand the concept of ground effect but I'm not
sure that ground
effect can have that much impact. Nor do I believe
that reducing ones
airspeed from 75 to 65 can increase ones L/D tenfold.
Some of the
story is not making sense to me.

I can assure you that ground effect is real and will
keep you in the air far longer than you might think.
One of the demonstrations that I gave students was
an approach over the runway threshold with 65-70knots
at 5 to 10 ft in a Grob 103 no airbrake. I was able
to show that the glider would still be flying when
the end of the 10000 ft runway was reached. Admittedly
the second half of the runway is slightly downhill
but if the airbrakes were not opened we would 'miss'
the runway. It would be nice to know just how far it
would go but we don't have a long enough runway in
the UK to find out, well not one I have access to.
I could of course start further back but I dont fancy
the bill for all those lights and things.