tow hook limitation question

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

Chris wrote:
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?

Max weight of the two pilot? :-)

Jeremy

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
oups.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

It is not the max weight of the glider, but the max tension applied to the
hook.
That said, the "weak link" should not be stronger than 1200#.
It does not take 1200# of "pull" to tow a 1200# glider.

Cindy has the formula.. and I'm looking for my reference.

BT

"Chris" wrote in message
oups.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

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
roups.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

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

Bill, I missed where the Grob 103 "recommended" weak link is 1650 lbs.
Our Grob 103 POH does say "max" rating of 1662 lbs. at Max Gross weight of
1279 lbs, perhaps we have different models of the G-103?

Based on FARs, 80-200% factor for weak links, that makes it as low as 1032
lbs or as high as 2558 lbs, much higher than Grob recommends.

We run a weak link that is "about" 1200 lbs when brand new, after a few
flights it is lower from initial use. This allows us to tow most everything
on the same weak link material. Yes we have them built up for both Tost and
Schweizer rings.

Have you seen an approved STC or Form 337 to put a TOST tow assembly on a
Pawnee?
I would be interested, as our last Schweizer hook wears out.

BT

"Bill Daniels" bildan@comcast-dot-net wrote in message
. ..
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
egroups.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

Talk to Tom Knauff, he recently put a Tost on his Pawnee and Scout



"BT" wrote in message
...
Bill, I missed where the Grob 103 "recommended" weak link is 1650 lbs.
Our Grob 103 POH does say "max" rating of 1662 lbs. at Max Gross weight of
1279 lbs, perhaps we have different models of the G-103?

Based on FARs, 80-200% factor for weak links, that makes it as low as 1032
lbs or as high as 2558 lbs, much higher than Grob recommends.

We run a weak link that is "about" 1200 lbs when brand new, after a few
flights it is lower from initial use. This allows us to tow most
everything on the same weak link material. Yes we have them built up for
both Tost and Schweizer rings.

Have you seen an approved STC or Form 337 to put a TOST tow assembly on a
Pawnee?
I would be interested, as our last Schweizer hook wears out.

BT

"Bill Daniels" bildan@comcast-dot-net wrote in message
. ..
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
legroups.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

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.


Many years ago there were tests of Schwiezer releases that showed that
they did, indeed jam. These should all be replaced ASAP. Anyone with
a brain can look at a Schwiezer release and see why it will jam under
high loads.

2c

wrote in message
oups.com...
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.


Many years ago there were tests of Schwiezer releases that showed that
they did, indeed jam. These should all be replaced ASAP. Anyone with
a brain can look at a Schwiezer release and see why it will jam under
high loads.

2c


I'll bite....why will it jam under high loads?