Low approaches in ground effect

It strikes me that an additional benefit of this (assuming you
don't hit anything early on) is that at the point
one perhaps inadvertently stalls, one is quite low (2 feet?)

The fatal accidents I've read commonly involve either stalls at
above 2 feet and/or hitting a wing first (not a wings-level touchdown).

In article ,
CV wrote:
Kirk Stant wrote:
CV wrote in message ...

I see. So if the results as reported here apply to calm conditions
it would mean the ground-effect technique wins out whenever there
is any significant wind gradient.

Actually, no. If I remember correctly, the test concluded that in
order to achieve any noticeable benefit from ground effect, the glider
had to be flown extremely precisely at VERY low altitude - only a

I should have worded that differently.

What makes the difference there is less headwind close to
the ground. The ground effect would of course not increase
on account of the wind gradient.

couple of feet above the ground. None of this "half a wingspan" - so
unless you are stetching your glide over the Bonneville salt flats,
just keeping out of the usual bushes, fences, stray airport dogs, etc
would eliminate any ground effect benefit.

With bushes and fences it's not on. I was thinking more along the
lines of a big plowed field, perhaps with some ditches crossing
and maybe just a low fence between the field and the runway.

If there is some ground-effect benefit at 2 ft though, it won't
be magically "eliminated" at 2,5 ft. The effect will decrease
gradually with height.

If the wind gradient is that strong, the turbulence at ground level
would make any precise low flying sporting and inefficient, anyway.

It doesn't have to be very turbulent there. We are assuming
flat ground. When the gradient is strong the surface wind is
much weaker than winds aloft. That is the meaning of "gradient".

I think pilots confuse the distance a glider will "float in ground
effect" (with the dive brakes closed) with the simple low drag glide
angle as the glider slows down - and if over the runway this may be
helped a little by ground effect,

The slowing down factor is a valid point. And ground effect may
help a little, or more than a little, if it is true that it can
doube the L/D as someone mentioned.

but remember this "float to the end
of the runway" is usually started at a relatively low speed, so the
drag penalty of diving down to a high speed is not felt.

Try a constant altitude decelleration from Vne to Vstall at altitude
some time; it's amazing how long and far you go! (helps when you get
above the MSH...yeah I know you're not supposed to do it!)

I suspect at altitude I wouldn't be able to appreciate the exact
distance covered and fail to be amazed.

CV



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Mark J. Boyd