Tost Hooks
Guy Corbett
hooks must be replaced in our Ventus 2CT(at a
cost of £320) when they are 4 years old because
that is the life specified by the hook manufacturer.
When they reach this age the winch hook will
have done <30 launches and the aerotow hook around
200. It seems to me that the same hooks fitted
to a club two-seater would have done rather more
work by the time their life had expired.
Does anyone else change their apparently serviceable
hooks at 4 years?
Guy
Sent via Deja.com http://www.deja.com/
Before you buy.
RFR
you call Tost directly, you may be able to get re-manufactured hooks for
your Ventus. The cost is around £100 for a nose and cg hook.
Regards,
Rod
Tony Firmin
more than 4 years heavy use on aerotow. However the frustration of having to
replace this mid flying season is probably not worth the risk. They can be
hard to get at and get out.
As a result of seeing this we had both ours overhauled in Germany during a
recent Winter overhaul (after some 10 years of use) and it took 4-6 weeks to
get them turned around.
Guy Corbett <guyco...@my-deja.com> wrote in message
news:84f5no$7i4$1...@nnrp1.deja.com...
RFR
both hooks on my 301.
Jim Kellett
> Does anyone else change their apparently serviceable hooks at 4 years?
The CG Tost - used ONLY for aerotow, BTW - on my Cirrus failed after
about 400- 500 launches. We'd goofed - it had been in place for about 6
years, and we didn't catch it at the four year mark. The failure was
curious - the outer ring was severely dented and cracked (there was no
accident/incident to explain this). Easy to replace, though, and an
overhauled unit is not all that expensive in the US.
Made a believer out of me.
--
Jim Kellett
Skyline Soaring Club http://www.ssl.umd.edu/Skyline/
The Open Cirrus Association http://home.adelphia.net/~jimkellett/
"If Flying Were the Language of Man, Soaring would be its Poetry"
Sula
>The CG Tost - used ONLY for aerotow, BTW - on my Cirrus failed after
>about 400- 500 launches. We'd goofed - it had been in place for about 6
>years, and we didn't catch it at the four year mark. The failure was
>curious - the outer ring was severely dented and cracked (there was no
>accident/incident to explain this).
Despite the replacement/overhaul requirement, it seems like many pilots are
relying simply on inspecting the towhook. This raises some questions:
How frequent are Tost release failures?
What parts fail?
How many failures could not have been predicted by inspection?
What is done during an overhaul?
F.L. Whiteley
Sula wrote in message ...
twentieth or so pull. It was 1) clean 2) in apparently good condition and
3) many years old. It had about 600 total launches, 98% aerotow. It was a
CG/aerotow release on an Open Cirrus. Following removal, the only
discernable problem noted was a slight <1mm asymmetrical lateral movement in
the hook, no corrosion or broken springs.
The thing that REALLY bothered me about the incident was that the tow pilot
was completely oblivious to my wing waggle while flying nearly along his
left wing (I was amazed that the rope didn't back release at this point) and
I was getting a bit nervous that he would wave me off and turn back to his
base without noting my predicament. Fortunately, it released on the next
series of tries and I proceeded on to home plate.
This cast iron thermal resulted from being one thermal short of completing
the task and landing at a neighboring club.
I believe similar reports led Tost to establish a reasonable overall
interval. However, I too would like to hear it from them.
F. Whiteley
Colorado
"two hooks, too often"
RFR
aircraft.
Glad nothing serious happened to you.
Regards,
Rod
Dave Brunner
> more than 4 years heavy use on aerotow.
> The CG Tost - used ONLY for aerotow, BTW - on my Cirrus failed after
> about 400- 500 launches. We'd goofed - it had been in place for about 6
> years, and we didn't catch it at the four year mark.
>
> Not frequent, however, mine did fail to release on aerotow once, until the
> twentieth or so pull. It was 1) clean 2) in apparently good condition and
> 3) many years old.
Seems odd that the requirement is after 4-years, seems like after 300
launches would be a better choice. Now at 30 launches a year... well, you do
the math (for your own ships).
Twopence worth
Dave Brunner - I fly a 1-26 anyway!... hmmm must check the tension on the
release mechanism.
David Starer
I have heard it suggested by one glider repairer that, in the UK at least,
failing to carry out a manufacturer's recommentation like Tost's could
invalidate your C of A and therefore also your insurance. This particular
repairer was not willing to sign off a C of A knowing that the hooks were
out of date, on the grounds that he might incur liability if an accident
occurred. Knowing the rip-off propensities of insurers, I would expect them
to try to wriggle out of paying out whether the accident had anything to do
with the hooks or not.
It might therefore be bad economics to hang on to time-expired Tost hooks
unless you have absolutely no intention of having any sort of accident
whatsoever!
Happy new (soaring) year.
David Starer
Guy Corbett <guyco...@my-deja.com> wrote in message
news:84f5no$7i4$1...@nnrp1.deja.com...
> The UK Schemp-Hirth Agent tell me that both the Tost
> hooks must be replaced in our Ventus 2CT(at a
> cost of £320) when they are 4 years old because
> that is the life specified by the hook manufacturer.
> When they reach this age the winch hook will
> have done <30 launches and the aerotow hook around
> 200. It seems to me that the same hooks fitted
> to a club two-seater would have done rather more
> work by the time their life had expired.
> Does anyone else change their apparently serviceable
> hooks at 4 years?
>
Robertmudd1u
who set the overhaul time for tow hooks. It seems that some time ago there was
a period when no overhaul time was stated. After a few years the rate of
problems increased dramaticly, and this led to the L.B.A. setting an overhaul
time.
During their winter months Tost overhauls an average of 300 hooks per week.
If you ever visit Munich be sure to stop at Tost and get a tour. All the tow
hooks are made in a facility that has grown up inside an apartment building
right in the heart of Munich. Standing on the sidewalk and looking at the
building you would never guess the world's largest supplier of tow hooks is
there.
Robert Mudd
F.L. Whiteley
Frank
RFR wrote in message <84hqas$43a$1...@pollux.ip-plus.net>...
Rich Carr
: aircraft.
Overall, radios are a net benefit, but as an additional piece of
equipment they can cause their own problems.
I'd say instead everybody involved in an operation should be
proficient and have undergone recent recurrency training in any
procedures being depended upon. Frequently, towpilots are not and
have not. Club safety checks too often ignore towpilots.
- Rich Carr
Nolaminar
stamp on the edge.
R.E. Gaines
Doug Bell
<gre...@greeleynet.com> writes:
>Not frequent, however, mine did fail to release on aerotow once, until the
>twentieth or so pull. It was 1) clean 2) in apparently good condition and
>3) many years old. It had about 600 total launches, 98% aerotow. It was a
>CG/aerotow release on an Open Cirrus. Following removal, the only
>discernable problem noted was a slight <1mm asymmetrical lateral movement in
>the hook, no corrosion or broken springs.
How, why did you attribute the failure to release to the tow hook? I had a
similar experience, but it was a problem with the release cable housing
slipping in it's mounting bracket.
BTW. I had the same problem with the tow pilot. I did everything I could to
get his attention and signal "unable to release", to no avail (the tow plane
was not radio equipped even though I was). We just kept climbing. Finally
released by twisting my foot/leg so that I could hook the tip of my shoe on the
release cable (it makes a 180 degree bend from out the back of the instrument
panel to the belly tow hook) and pushed with my toe while I pulled on the
release knob. Had to pay for a 5000 foot tow!
KD (remove NOSPAM from address to reply)
J. Cunningham
springs are in constant tension. Being in continual tension the
spring can fatigue and break. The good news is that failure mode if
the spring breaks is to keep the release mechanism closed.
I am in a club that had a TOST hook failed in mid season. It took
over a month for me to get the proper parts and get the plane flying
again. I did notice that the springs on the rebuilt hook were about
50% larger in there wire diameter than the old one we replaced.
F.L. Whiteley
Doug Bell wrote in message <20000101043958...@nso-ff.aol.com>...
>In article <RwWa4.4$1o8.17...@news.frii.net>, "F.L. Whiteley"
><gre...@greeleynet.com> writes:
>
>>Not frequent, however, mine did fail to release on aerotow once, until the
>>twentieth or so pull. It was 1) clean 2) in apparently good condition and
>>3) many years old. It had about 600 total launches, 98% aerotow. It was
a
>>CG/aerotow release on an Open Cirrus. Following removal, the only
>>discernable problem noted was a slight <1mm asymmetrical lateral movement
in
>>the hook, no corrosion or broken springs.
>
>How, why did you attribute the failure to release to the tow hook? I had a
>similar experience, but it was a problem with the release cable housing
>slipping in it's mounting bracket.
>
more times on the ground following this incident and got a couple of
repeats. It was not the cable. Replacement was 75UKP exchange through
London Sailplanes in 1993. The replacement worked without difficulty on the
same hookup.
Frank Whiteley
MarkGrubb
built in a "safety valve" so that they get a look at the hooks periodically and
also get paid well to do it. Haivng them dimensionally checked is not a bad
idea but the spring fatgue theory seems a little, shall we say, weak (grin).
Properly sized springs made from the correct material will NOT "fatigue" due to
static loads in only 4 years. I have seen Tost hooks that were 30 years old
that functioned perfectly for several thousand hours.
John Giddy
>
> The reason the TOST hooks need to be rebuilt every four years is the
> springs are in constant tension. Being in continual tension the
> spring can fatigue and break. The good news is that failure mode if
> the spring breaks is to keep the release mechanism closed.
I beg to differ. The spring which breaks most often is the return spring
which pulls the release lever back to the closed position. If this
spring breaks or becomes weak due to cracking etc., friction in the
cable to the release handle can result in the release lever not
returning to the fully closed position, and thus not placing the hook in
the correct over-centre locking position. This can mean a premature
release when a heavy load comes on the cable, e.g. a poor removal of a
loop in the tow cable.
John G.
--
John Giddy ( ) ) Mangalore Gliding Club
5/287 Barkers Rd ) ) ) http://www.gfa.org.au/vic/mgc/
Kew, Victoria, 3101 ( ) ) _
Australia ( ) '------8------'
Mike Koerner
Further, it will not yield no mater how long its held any operating
position.
Mike Koerner
Caracole
failed aft release return spring in a c.g. release. This release
showed signs of serious neglect. Dirt, rust and corrosion in
general.
After recently removing a nose release from a Grob. I did a load
test comparison between the freshly overhauled and 17 year old
original release. There was no difference between the spring loads.
For my own information I will try to routinely do this comparison.
That said, for liability reasons I will not sign off any glider unless it's
Tost releases meet the overhaul requirements of the gliders
maintenance manual, operating limitations, or type certificate.
A pilots statement that he never uses the c.g. release does not
waive it's overhaul requirements.
It would be a great idea if Tost would provide some alternative load
testing to establish the airworthiness of releases in service.
But the major negative impact on the number of overhauls the
factory could do per year. Makes the chances of this idea
highly unlikely.
However they should at least either become a U.S. certified repair
station or have someone with a U.S. airframe mechanics license
in their facility to sign off the overhaul on releases sent to the U.S.
Or provide the overhaul data and parts so that mechanics in the U.S.
could sign off the overhaul here themselves.
I am not an engineer. So how about some of you engineers out there
posting some supporting data in favor of Mark and Mikes position,
or the factories position?
Inquiring minds want to know.
M Eiler
>Mike Koerner wrote in message ...
John H. Campbell
cracked off) on the nose hook of a Grob G103. First time in 10s of 1,000s
of flights over 20 years at this place. The release was not far from the 4
year spec. since overhaul, but it had gone through many more cycles than the
1,000 cycle spec. (that ship flew a lot of rides). Not to worry, the break
cannot cause the release to open on tow but leaves it unable to close on the
next cycle, so the ship cannot be launched. An exchange unit was swapped in
within 3 days --JHC
Jim Husain
>break, and the unit *should* still work, but the return
>force will drop by half
On my old Pilatus B-4, I had a few unexpected releases. Not fun.
I finally took out the Tost release, inspected it, and found that one half of
the spring had broken.
Given how simple the mechanism is, why does not sell the spring alone? Its
very easy to replace.
Jim
N483SZ
gap...@aol.com
Sula
>a properly designed spring will never crack or fatigue.
>Further, it will not yield no mater how long its held any
>operating position.
This argues that if springs are breaking, the solution is replacement with
properly-designed springs, not periodic overhauls.
Has Tost made any recent changes in their springs?
Are there types of failures that don't involve the springs?
tom_systek
design. The solution is to redesign the mechanism, not to continue to repair
an inadequate mechanism. Springs are used in, literally, millions of
machines successfully without fail. One that comes to mind are all the valve
lifter springs in millions of push rod engines produced for decades. These
springs undergo untold millions of cycles at high temperatures with few
failures (just ask your local mechanic). Any mechanism can fail due to
defect. Are we to replace every component in our gliders at four year
intervals?
Tom Seim, 2G DG-400
Richland, WA
John Giddy <jgi...@melbpc.org.au> wrote in message
news:386FEA...@melbpc.org.au...
Stephen Kittel
Caracole wrote in message <1v3c4.175$nF1...@news2.randori.com>...
>During the 12 years I have been working on gliders I have seen 1
>failed aft release return spring in a c.g. release. This release
>showed signs of serious neglect. Dirt, rust and corrosion in
>general.
>
>After recently removing a nose release from a Grob. I did a load
>test comparison between the freshly overhauled and 17 year old
>original release. There was no difference between the spring loads.
>For my own information I will try to routinely do this comparison.
>
>That said, for liability reasons I will not sign off any glider unless it's
>Tost releases meet the overhaul requirements of the gliders
>maintenance manual, operating limitations, or type certificate.
>A pilots statement that he never uses the c.g. release does not
>waive it's overhaul requirements.
>
>It would be a great idea if Tost would provide some alternative load
>testing to establish the airworthiness of releases in service.
>But the major negative impact on the number of overhauls the
>factory could do per year. Makes the chances of this idea
>highly unlikely.
>
>M Eiler
A point of interest to the non Australian members of this group, gliders in
Australia do not go through the Tost factory overhaul procedure.
During the early eighties I believe the Tost position in Australia was that
release springs had to be replaced on a four yearly basis and that this had
to be done by the factory, no agents were available in Australia (of course,
the maintenance was not happening). I was told at the time that Tost would
accept no other maintenance scheme. There followed a number of accidents,
not all glider related (specifically a naval helicopter winch misoperation
and an IS28 write off are mentioned in the subsequent AD).
These accidents were attributed to lack of maintenance of the releases,
however, my understanding was that not just old releases but new ones (I
think the navy releases were less than 2 years old) as well were found to
have problems, not just with springs. [1]
The Gliding Federation of Australia had a long hard look at what was
practical in Australia and issued an AD (AD 277 for those interested). The
AD consists of a number of actions, simplified and described here briefly:
1. At annual inspections, if less than 200 launches have taken place since
the last action 1, inspect clean and lubricate the release.
If more than 200 launches then as above and carry out a "Main Spring" test
to determine that the spring has the correct strength spring when opening
and a "Pull Back" test to show there is correct spring tension to close the
release. These two tests show that the spring is not broken or non standard
or incorrectly installed. (This will catch the one side broken spring which
has been discussed in this thread, I have found broken springs using this
method). If the release has a back release you must also do the "Back
Release" test to show that the spring on the back release cage is also OK.
2.Each 4 years or 2000 launches, action 1 and an "Overcentre" test is
carried out with the release effort required for varying loads on the hook.
(I assume M Eiler carried out something similar to this test but at one
load). By plotting the load on the beak versus the effort to release on the
lever it can be determined if the correct amount of overcentre is set up in
the release.
This is a crude summary of an 11 page document and I have not described the
limiting values or the special equipment used, but it is roughly what we do
here.
[1] IIRC the navy release operated as it had not enough overcentre set when
it arrived from the factory. Newer (ie 80's and onward) Tost releases had an
allen screw adjuster with a lock nut. Varying this can set the amount of
over centre, too much over centre and the release is too hard to operate
under high loads (implicated in a fatal tug upset accident in Tasmaia IIRC),
too little over centre and high loads can cause the hook to open
spontaneously, the case with the navy helicopter. Older releases relied on a
part of the release body casting as the overcentre stop. When these are out
of limits they can be adjusted by careful filing away or weld building of
the body casting or quadrant plate. This is really the reason behind action
2 of the AD.
At the time the AD was first published a considerable amount of effort went
into release maintenance in Australia which has upped the general level of
knowledge about these things and paid off in the subsequent years.
Stephen Kittel
Port Augusta Gliding Club
http://www.adelaide.net.au/~kittsw/
Tim Mara
"tom_systek" <tom_s...@email.msn.com> wrote in message
news:ecpXCInV$GA.223@cpmsnbbsa02...
> If these springs are failing at such a high rate there is a problem with
the
> design. The solution is to redesign the mechanism, not to continue to
repair
> an inadequate mechanism. Springs are used in, literally, millions of
> machines successfully without fail. One that comes to mind are all the
valve
> lifter springs in millions of push rod engines produced for decades. These
> springs undergo untold millions of cycles at high temperatures with few
> failures (just ask your local mechanic). Any mechanism can fail due to
> defect. Are we to replace every component in our gliders at four year
> intervals?
And these releases are also used in literally thousands of applications and
have had probably several millions of functions without failures..and had
some failures as well..this does not change anything, they are certified
based on the overhaul periods specified and the manufacturers
certifications........rather than going on and on about what someone thinks
"should" be...this is the way it is....if someone feels so strongly that
they "Should" be this or "Why", then it is a free world and you are
certainly able to design, certify and offer to anyone your new and improved
mechanism at whatever cost you wish and whatever liability you are willing
to bare........if however, you choose not to do so, you can use what someone
else has made available and either accept their recommendations or if you
wish go against them and accept your own liability for doing so.
tim
tom_systek
Tom
Tim Mara <t...@wingsandwheels.com> wrote in message
news:84tii...@enews3.newsguy.com...
John Giddy
<<snip>>
> release springs had to be replaced on a four yearly basis and that this had
> to be done by the factory, no agents were available in Australia (of course,
> the maintenance was not happening). I was told at the time that Tost would
> accept no other maintenance scheme. There followed a number of accidents,
> not all glider related (specifically a naval helicopter winch misoperation
> and an IS28 write off are mentioned in the subsequent AD).
Just to add to Stephen's excellent summary of our system in Oz, I
understand that the detailed research work which resulted in the AD he
mentions, was done at the Aeronautical Research Laboratories (ARL) in
Melbourne, and was triggered by the helicopter accident he mentioned.
(ARL is a government research organisation, mainly dealing with defence
matters) I mention this to add some level of confidence that our
procedures are based on good science, and not just "these strange
colonials going their own way" :-)
Sula
>rather than going on and on about what someone thinks
>"should" be...this is the way it is....if someone feels so strongly that
>they "Should" be this or "Why", then it is a free world and you are
>certainly able to design, certify and offer to anyone your new and improved
>mechanism at whatever cost you wish and whatever liability you are willing
>to bare........if however, you choose not to do so, you can use what
someone
>else has made available and either accept their recommendations or if you
>wish go against them and accept your own liability for doing so.
Or you could do what the Australians appear to have done - research the real
causes of failures, and find efficient solutions to them.
Emilis Prelgauskas
We are a long way away from the factory source, and have therefore had
to deal with release systems for many decades locally, usually at each
flying site.
Through this a system of self help supported by state and feceral
amateur gliding organisations has come about. Including the development
of spring and hydraulic testing equipment.
This equipment has to deal with the 3 main release systems used her _
- Blanik
_ Tost
_ an English system called 'Ottfur' built locally