Tost release failure

For the first time in my life I heard a 1st person story of a release failure.
The story follows:

The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs. The pilot eventually got a successful release by yawing the glider strongly.

AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way.

Operationally, should a roll-over happen again, we will release the rope and re-attach before proceeding with a launch. The release will get special attention in the annual inspection later this month. No chain links will be allowed for any purpose.

There are specific notes on my website and on TOST website warning of
possible damages due to the use of non-approved or badly worn Tost Tow rings
http://www.wingsandwheels.com/page30.htm
tim--
Please visit the Wings & Wheels website at www.wingsandwheels.com


"Bill D" wrote in message
...
For the first time in my life I heard a 1st person story of a release
failure.
The story follows:

The glider, an ASK-21, was jerked forward by the tug so the front wheel
rolled over the rope at the start of an aero tow. The slack was then taken
out and the tow was launched without inspecting the hook and release. The
working theory is that this somehow cocked the ring set in the hook so it
failed to release even with pilot and passenger pulling on the release
knobs. The pilot eventually got a successful release by yawing the glider
strongly.

AFAIK, the hook in question had not reached it's 2000 tow life limit nor is
there any history of repair or maintenance in the hook area. There had been
cases where a commercial operator had insisted on providing tows using a
chain link instead of a Tost ring set. We think it possible this had
damaged the hook in some way.

Operationally, should a roll-over happen again, we will release the rope and
re-attach before proceeding with a launch. The release will get special
attention in the annual inspection later this month. No chain links will be
allowed for any purpose.

Not enough information to form an opinion, but I would suspect a worn/
damaged or improper tost ring substitute was used, as opposed to the
hook being defective. If you can't see the stamp on the ring, it is
no good IMO.

On Monday, August 20, 2012 7:18:48 AM UTC-7, Bill D wrote:
For the first time in my life I heard a 1st person story of a release failure.

The story follows:



The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs.. The pilot eventually got a successful release by yawing the glider strongly.



AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way.


BTW I'm also aware of a Tost release failing to release due to corrosion within the release, I believe likely a combination of pee-tube spray and lack of proper care and maintenance. Pee tube spray may not be a factor in typicality ASK-21s but I suspect quite a few tow releases get only a cursory look over pre-flight and during the annual inspection.

And on chain-links just say no. Tim's web site is a great resource for Tost stuff.

Darryl

On Monday, August 20, 2012 7:42:38 PM UTC-6, Darryl Ramm wrote:
On Monday, August 20, 2012 7:18:48 AM UTC-7, Bill D wrote:

For the first time in my life I heard a 1st person story of a release failure.



The story follows:







The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs. The pilot eventually got a successful release by yawing the glider strongly.







AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way.





BTW I'm also aware of a Tost release failing to release due to corrosion within the release, I believe likely a combination of pee-tube spray and lack of proper care and maintenance. Pee tube spray may not be a factor in typicality ASK-21s but I suspect quite a few tow releases get only a cursory look over pre-flight and during the annual inspection.



And on chain-links just say no. Tim's web site is a great resource for Tost stuff.



Darryl

The particular ASK-21 is fairly new (2000)and in excellent condition. It has always been stored in it's trailer when not being flown by highly qualified pilots. There is no evidence of corrosion anywhere. Records are being checked but indications are the release life limit has not been exceeded.

I participated in the last annual and while the release was checked, it was not subjected to special scrutiny. (It will be this time.) The ring pair was not checked for authenticity but it will be.

On Monday, August 20, 2012 8:08:47 PM UTC-7, Bill D wrote:
On Monday, August 20, 2012 7:42:38 PM UTC-6, Darryl Ramm wrote:

On Monday, August 20, 2012 7:18:48 AM UTC-7, Bill D wrote:



For the first time in my life I heard a 1st person story of a release failure.







The story follows:















The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs. The pilot eventually got a successful release by yawing the glider strongly.















AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way.











BTW I'm also aware of a Tost release failing to release due to corrosion within the release, I believe likely a combination of pee-tube spray and lack of proper care and maintenance. Pee tube spray may not be a factor in typicality ASK-21s but I suspect quite a few tow releases get only a cursory look over pre-flight and during the annual inspection.







And on chain-links just say no. Tim's web site is a great resource for Tost stuff.







Darryl



The particular ASK-21 is fairly new (2000)and in excellent condition. It has always been stored in it's trailer when not being flown by highly qualified pilots. There is no evidence of corrosion anywhere. Records are being checked but indications are the release life limit has not been exceeded..



I participated in the last annual and while the release was checked, it was not subjected to special scrutiny. (It will be this time.) The ring pair was not checked for authenticity but it will be.

Bill, I did not specifically expect corrosion in this case, I'm much more worried by corrosion where pee tubes are involved with higher performance/XC gliders, including in cases where there may be pee-tube vents into the gear well/on the U/C legs or gear doors and stuff spray around in in unpredictable ways (I don't like some style pee tubes that vent near the gear well) or where the pee tube exit is in front of the (CG) release and just does not poke out far enough.


Darryl

Hi

The initial message mentiones a rollover - problem there is that the tow rope can wind itself around the main wheel axle and tightens up severly when towed in this way. Nothing to do with Tost or other releases. Any Rollover - rope should be released immediatly and checked that above did not occur. Simple

I've seen a few fail to release. All of them were either the result of
using incorrect (homemade, worn, deformed, etc.) rings (see Tost's website,
which has considerable documentation on this), lack of maintenance
(corrosion related to pee tubes, extremely wet fields, and dirt jamming the
moving parts) and even illegal maintenance (involving readjusting the
overcenter to compensate for beak wear, the owner won't be doing that
again!). Also seen a few broken springs under 2000 launches, but these were
due to operators having a different checklist, using the release 6 times
per flight, and only 10.000 actuations are allowed.

Tost failures other than these are pretty rare, and should be brought to
the attention of the manufacturer.


At 14:18 20 August 2012, Bill D wrote:
For the first time in my life I heard a 1st person story of a release
failu=
re. =20
The story follows:
=20
The glider, an ASK-21, was jerked forward by the tug so the front wheel
rol=
led over the rope at the start of an aero tow. The slack was then taken
ou=
t and the tow was launched without inspecting the hook and release. The
wo=
rking theory is that this somehow cocked the ring set in the hook so it
fai=
led to release even with pilot and passenger pulling on the release
knobs.
=
The pilot eventually got a successful release by yawing the glider
strongl=
y. =20

AFAIK, the hook in question had not reached it's 2000 tow life limit nor
is=
there any history of repair or maintenance in the hook area. There had
be=
en cases where a commercial operator had insisted on providing tows using
a=
chain link instead of a Tost ring set. We think it possible this had
dama=
ged the hook in some way.

Operationally, should a roll-over happen again, we will release the rope
an=
d re-attach before proceeding with a launch. The release will get
special
=
attention in the annual inspection later this month. No chain links will
b=
e allowed for any purpose.

On Monday, August 20, 2012 10:18:48 AM UTC-4, Bill D wrote:
For the first time in my life I heard a 1st person story of a release failure. The story follows: The glider, an ASK-21, was jerked forward by the tug so the front wheel rolled over the rope at the start of an aero tow. The slack was then taken out and the tow was launched without inspecting the hook and release. The working theory is that this somehow cocked the ring set in the hook so it failed to release even with pilot and passenger pulling on the release knobs. The pilot eventually got a successful release by yawing the glider strongly. AFAIK, the hook in question had not reached it's 2000 tow life limit nor is there any history of repair or maintenance in the hook area. There had been cases where a commercial operator had insisted on providing tows using a chain link instead of a Tost ring set. We think it possible this had damaged the hook in some way. Operationally, should a roll-over happen again, we will release the rope and re-attach before proceeding with a launch. The release will get special attention in the annual inspection later this month. No chain links will be allowed for any purpose.

Lets look at the mechanics of things when the glider gets bumped and rolls over the rope: The rope is pulled with an incredible force down- and backwards. The large ring which is held half way inside the rigid cage of the release is reacting against that cage with a huge force, so it is not unreasonable to assume that the entire housing gets deformed plastically. This could possibly allow the position of the small ring in relation to the moving beak to change and it doesn't take a whole lot to pinch in the ring and lock up the entire mechanism.
We had a release failure on a 2-33 after an new member was allowed to hook up the line using the large Tost ring. The line force was enough to make the ring slide up the wedge shaped release hook and lock itself onto it and not letting go even after the release was pulled. I know that these two mechanisms are completely different but it demonstrated how small deformations combined with wedge shaped bodies can result in very strong connections.
In other countries, the tow ropes are much thicker and stronger than the ones used in the US (following the 80-200% rule, which is total B.S. to begine with) but the manufacturer's stipulated weak-link (part of the POH) is right at the double ring. In the desribed scenario, the weak-link would have broken and the whole episode would have not happened.

GM

Good post.

I always get funny looks when the line crew says, "Open, close... Check
release", and I say, "No, I just checked it when I opened it for hookup. It
may have only one more operation left and I want it to work when I release
the rope in flight."

It should have occured to me that there's a manufacturer specified life
limit (number of tows) and, while a ground release is not as stressful as an
in-flight release, you're still wearing springs and mating surfaces, cables,
etc. Why wear it out with ridiculous, extra operations? Maybe I should
pull my rip cord before getting into the glider to be sure my parachute will
open when I need it... ;-


"Eric Munk" wrote in message
.com...
I've seen a few fail to release. All of them were either the result of
using incorrect (homemade, worn, deformed, etc.) rings (see Tost's
website,
which has considerable documentation on this), lack of maintenance
(corrosion related to pee tubes, extremely wet fields, and dirt jamming
the
moving parts) and even illegal maintenance (involving readjusting the
overcenter to compensate for beak wear, the owner won't be doing that
again!). Also seen a few broken springs under 2000 launches, but these
were
due to operators having a different checklist, using the release 6 times
per flight, and only 10.000 actuations are allowed.

Tost failures other than these are pretty rare, and should be brought to
the attention of the manufacturer.


At 14:18 20 August 2012, Bill D wrote:
For the first time in my life I heard a 1st person story of a release
failu=
re. =20
The story follows:
=20
The glider, an ASK-21, was jerked forward by the tug so the front wheel
rol=
led over the rope at the start of an aero tow. The slack was then taken
ou=
t and the tow was launched without inspecting the hook and release. The
wo=
rking theory is that this somehow cocked the ring set in the hook so it
fai=
led to release even with pilot and passenger pulling on the release
knobs.
=
The pilot eventually got a successful release by yawing the glider
strongl=
y. =20

AFAIK, the hook in question had not reached it's 2000 tow life limit nor
is=
there any history of repair or maintenance in the hook area. There had
be=
en cases where a commercial operator had insisted on providing tows using
a=
chain link instead of a Tost ring set. We think it possible this had
dama=
ged the hook in some way.

Operationally, should a roll-over happen again, we will release the rope
an=
d re-attach before proceeding with a launch. The release will get
special
=
attention in the annual inspection later this month. No chain links will
b=
e allowed for any purpose.