The only solution for "negative g-bumps" are properly located and secured
lap straps.

"Bill Daniels" bildan@comcast-dot-net wrote in message
...
I've been following this thread with interest. Sholder straps anchored
high on the seat back prevent the pilot from moving up and forward but are
less effective in preventing up and back movements as might be encountered
in a winch launch or turbulence.

I like Nyal's original suggestion of two additional vertical straps
located between the pilots sholders and the sholder strap anchor points
holding down the sholder straps. The next time I have my glider out of
the trailer, I'm going to look carefully at this possibility. I think it
would only require straps and buckles attached to the landing gear frame -
simple, cheap and likely to be highly effective. Thanks Nyal!

Bert's suggestion of a "friction pad" behind the pilots's back to anchor
the additional straps is somewhat problematic since I would want the
solution to work for both winch launch and for negative G "bumps"
encountered in turbulence. In a negative G scenario the friction pad idea
is less likely to provide an anchor.

Bill Daniels


"Nyal Williams" wrote in
message ...
Bert,

As I lay awake this morning before getting up, I began
to understand your reasoning, and you might be quite
right. A thin layer of foam or rubber could provide
enough friction across the whole back or the 'chute
and against all of the slippery surface of the seat
pan/back rest and grip enough to prevent sliding.
This would probably work if the straps are really snug.
It is not a matter of spacing but of a large area of
friction.

My notion was to put the entire force against the shoulders
and straps; if this were the case the strap attach
points would have to be lower and/or a fifth attach
point in the crotch area to prevent strap movement
aft.

Best,

Nyal




At 08:00 20 October 2006, Bert Willing wrote:
Nyal, I do have read this thread.
If the attachment point of the shoulder straps are
too high, a thin layer of
foam or rubber on the seat pan is all what's needed.
Having double attachment points on the shoulder straps
is big means to solve
an easily solved problem - you go through a certification
loop, you need to
think about egress restrictions and all this stuff.

'Nyal Williams' wrote in message
...
Bert, I think you must not have read all this thread;
it was pointed out that shoulder strap connections
are too high and, while preventing the upper body
from
going forward, do not prevent an upward and aft movement.
With current setups, no amount of tightening will
prevent this for short/small persons.


At 14:42 19 October 2006, Bert Willing wrote:
I guess we just need to secure the shoulder straps
properly ? ...

'Nyal Williams' wrote in message
...
This is somewhat analagous to reported accidents by
Cessna pilots on takeoff; if the adjustable seats
are not properly locked in their rails the seat can
slide backward, making it impossible to push the yoke
forward.

Perhaps we need a two-point attachment for each of
the shoulder straps -- the one above the shoulders
that already is in place and which keeps the body
from
being thrown forward, plus a second one from be bottom
of the seat pan, and which would prevent the body
from
moving upward and aft. This second strap could also
protect against cranial collision with the canopy.


Anyone for seven-point harness?