OK, I'll accept that a Discus single place glider's minimum weak link
strength is 43 pounds less than the maximum rated strength for a Schweizer
hook - but I won't take much comfort from it. A typical 2-seater is a Grob
103 with a reccomended weak link of 1650 pounds.

Reccomended weak link strengths range up to 1000 kg force or 2200 pounds
force. A common safety factor is 50% which brings it to 3300 pounds or more
than 2.5 times the rated strength of the Schweizer hook.

I think (but I don't know) the Schweizer hook wouldn't actually break at
these loads but I suspect that the manufacturer had a good reason to put a
1200 pound limit on it. You don't size a tow hook for the average
glider, you size it for the maximum loads it will see in normal service plus
a safety factor. Common sense and good practice says don't exceed it. I'll
stand by my advice - get a Tost hook.

Bill Daniels

"Soarin Again" wrote in message
...
Bill's data is a bit skewed. The Discus is probably
the most common single place glider in the U.S. I
have flight manuals for both the Discus a and b as
well as a Discus 2a and b in front of me. Per the
mfg specs both manuals list the minimum weak link as
1157 lbs.
His other claim that exceeding the 1200 lb limit will
cause the schweizer release to jam is highly suspect.
The vast majority of tows in the U.S. are done with
schweizer releases with little if any actual complaints
by tow pilots. Several years ago in soaring magazine
there was an article about a glider kiting and the
tow pilot was unable to release. However the cause
was not that the schweizer release jammed, it was the
result of a poorly installed and secured release cable
housing. The cable ties used to secure the release
cable housing to the airframe failed, which then resulted
in excessive slack in the release cable. This excessive
slack meant that the tow pilots release handle was
incapable of pulling on the schweizer release lever.

At 16:30 30 January 2007, Bill Daniels wrote:
If you check glider manufacturers weak link requirements
as listed in the
respective POH's, you will find almost all are stronger
than the maximum
lond permitted on a Schweizer tug hook. Overload a
Schweizer hook and it
jams. To me, that says that all Schweizer tug hooks
are dangerously
obsolete and should be replaced with Tost hooks - preferably
with the tow
rope retract winch.

Bill Daniels

'Chris' wrote in message
groups.com...
Our club is looking at new tow plane. The plane has
a Schweizer tow
hook with '1200 lbs max' stamped on it.
Does anybody know what that relates to?
Is this the max gross weight of the glider or max
tow tension or...?
I've tried Schweizer, but they couldn't help since
they are no longer
making tow hooks.

Thanks for any insights.

Chris