View Full Version : How reliably do CG hooks disconnect when the angle of the ropeexceeds the autorelease angle
Kenz Dale
June 4th 20, 10:33 PM
I understand that CG hooks are designed to autorelease when the angle of pull passes a certain critical angle. Is this a very reliable disconnect, or is more of an "Eh, it's nice to have but I've seen it fail too many times to trust it"?
Tom BravoMike
June 4th 20, 11:25 PM
On Thursday, June 4, 2020 at 4:33:29 PM UTC-5, Kenz Dale wrote:
> I understand that CG hooks are designed to autorelease when the angle of pull passes a certain critical angle. Is this a very reliable disconnect, or is more of an "Eh, it's nice to have but I've seen it fail too many times to trust it"?
From the PW-5 Flight manual:
"RELEASING
The sailplane is equipped with the self-releasing hook.
Two releasing techniques exist:
1) before the intended releasing release the stick to lower the cable
tension then pull the releasing handle in the cockpit;
2) before the intended releasing hold the stick in position till the selfreleasing occurs. After releasing recover immediately the glide and
check the cable releasing pulling the control handle."
It results that self-releasing is considered a normal and reliable procedure.
Dan Daly[_2_]
June 4th 20, 11:58 PM
On Thursday, June 4, 2020 at 5:33:29 PM UTC-4, Kenz Dale wrote:
> I understand that CG hooks are designed to autorelease when the angle of pull passes a certain critical angle. Is this a very reliable disconnect, or is more of an "Eh, it's nice to have but I've seen it fail too many times to trust it"?
Over a couple of hundred winch launches on TOST hooks in a variety of gliders, I have seen one problem, which was caused by one of the two springs inside the hook failing, and the failure caused the hook to release (on a friend's glider, not mine or the club's). I have every confidence in the TOST system when winching; our procedure was to release manually, but if a thermal kept the cable tight, the hooks automatically back-released very reliably.
Keeping track of the number of releases and getting the hook refurbished when due is smart, as is keeping it lubricated and clean.
son_of_flubber
June 5th 20, 05:19 AM
On Thursday, June 4, 2020 at 5:33:29 PM UTC-4, Kenz Dale wrote:
> Is this a very reliable disconnect,...?
It's very reliable if the Tost hook is maintained/rebuilt on the recommended schedule. But the maintenance costs money, so it is not altogether unheard of to delay the maintenance past the recommended interval. I know one IA who was OK with that because the total number of releases was very low for the elapsed time.
On Thursday, June 4, 2020 at 4:33:29 PM UTC-5, Kenz Dale wrote:
> I understand that CG hooks are designed to autorelease when the angle of pull passes a certain critical angle. Is this a very reliable disconnect, or is more of an "Eh, it's nice to have but I've seen it fail too many times to trust it"?
I have never heard of a TOST CG release failing to "back release". The back "jaw" of the TOST CG hook is held closed only by light spring tension. If there is any rearward pressure on it, it has to release. The spring tension is light enough that it is easy to attach the tow ring to the hook simply by pushing the ring against the back jaw of the release. Not many ways that it can fail. A foreign body or broken part falling into the mechanism could conceivably jam it and prevent it from opening. Some of the older TOST CG releases could have a problem with the tow ring jamming sideways in the release. Gliders with those model TOST releases require installation of small metal guides to prevent misalignment of the ring. Those metal guides also act as protective skids if one forgets to extend the landing gear upon landing (one guess as to how I know this).
I think most of the "failure to release" problems for gliders launching with the CG release have not actually involve the CG release as such. Rolling over the launch cable and entangling it in the wheel have been the cause of some incidents. That is why ground launch systems MUST have some means of quickly cutting the cable.
Martin Gregorie[_6_]
June 5th 20, 03:32 PM
On Fri, 05 Jun 2020 07:13:58 -0700, WB wrote:
> On Thursday, June 4, 2020 at 4:33:29 PM UTC-5, Kenz Dale wrote:
>> I understand that CG hooks are designed to autorelease when the angle
>> of pull passes a certain critical angle. Is this a very reliable
>> disconnect, or is more of an "Eh, it's nice to have but I've seen it
>> fail too many times to trust it"?
>
> I have never heard of a TOST CG release failing to "back release". The
> back "jaw" of the TOST CG hook is held closed only by light spring
> tension. If there is any rearward pressure on it, it has to release. The
> spring tension is light enough that it is easy to attach the tow ring to
> the hook simply by pushing the ring against the back jaw of the release.
> Not many ways that it can fail. A foreign body or broken part falling
> into the mechanism could conceivably jam it and prevent it from opening.
> Some of the older TOST CG releases could have a problem with the tow
> ring jamming sideways in the release. Gliders with those model TOST
> releases require installation of small metal guides to prevent
> misalignment of the ring. Those metal guides also act as protective
> skids if one forgets to extend the landing gear upon landing (one guess
> as to how I know this).
>
Look at the belly of a Std Libelle to see this setup (s/n 110 or earlier).
There's now a UK annual inspection requirement to check that the guide
spacing is in tolerance.
> I think most of the "failure to release" problems for gliders launching
> with the CG release have not actually involve the CG release as such.
> Rolling over the launch cable and entangling it in the wheel have been
> the cause of some incidents. That is why ground launch systems MUST have
> some means of quickly cutting the cable.
--
Martin | martin at
Gregorie | gregorie dot org
George Haeh
June 6th 20, 12:09 AM
I use the back release to hook up and release for ground towing. Basically the cage rotates back and makes room for the tow ring to enter and engage when the cage rotates forward. Strong fingers needed.
Most hooker uppers can learn this - easier in small clubs than at a contest with many newbie volunteers.
Even if the cage spring breaks, back release will work.
Martin Gregorie[_6_]
June 6th 20, 01:00 AM
On Fri, 05 Jun 2020 16:09:47 -0700, George Haeh wrote:
> I use the back release to hook up and release for ground towing.
> Basically the cage rotates back and makes room for the tow ring to enter
> and engage when the cage rotates forward. Strong fingers needed.
>
So do I, but not with the hook model on my Libelle: its situated between
two fore/aft rails 32mm apart and the end of the back-release isn't a
grabbable cage, big enough or shaped suitably to be pulled back from the
outside.
On the ASK-21, Puchacz, Juniors and Discii its very easy to do.
--
Martin | martin at
Gregorie | gregorie dot org
son_of_flubber
June 8th 20, 01:33 PM
Does anyone have experience with non-Tost rings failing to release in Tost releases?
I've been warned about this possibility, and I know how to verify that a ring is genuine Tost. The explanation that I've been given is that 'hardware store rings' change shape with use and that at some point the elongation prevents the release.
On Monday, June 8, 2020 at 8:33:23 AM UTC-4, son_of_flubber wrote:
> Does anyone have experience with non-Tost rings failing to release in Tost releases?
>
> I've been warned about this possibility, and I know how to verify that a ring is genuine Tost. The explanation that I've been given is that 'hardware store rings' change shape with use and that at some point the elongation prevents the release.
That is correct - there is a good chance that a hardware store ring or a chain link can deform and kind of swage itself onto the beak inside the Tost hook, making it very difficult to release. That subject was discussed in great length in the 'winchdesign' forum.
Uli
'AS'
Also note that the small hookup ring can wear. If it gets deformed or reduced in size, it can jam or prematurely release. I looked for the specification on minimum thickness, but couldn't find it with a (very brief) search. Check with Wings & Wheels to see if they know the correct "go-no go" dimension.
On Monday, June 8, 2020 at 9:38:29 AM UTC-4, wrote:
> Also note that the small hookup ring can wear. If it gets deformed or reduced in size, it can jam or prematurely release. I looked for the specification on minimum thickness, but couldn't find it with a (very brief) search. Check with Wings & Wheels to see if they know the correct "go-no go" dimension.
Mark - according the the DIN-LN65091, the oval ring has a wire diameter of 8mm, +0, -0.3mm. The round ring has a wire diameter of 7mm, +0, -0.3mm. The O.D. of the round ring is 35mm, +-0.3mm, which would give it a nominal I.D.. of 21mm. If you do a quick tolerance stack-up using just min.-max. material conditions while neglecting any ovality, the I.D. could range from 21.9mm to 20.7mm
The material specifications call for a high carbon Chrome-Vanadium alloy. No welding is permitted.
Uli
'AS'
On Monday, June 8, 2020 at 11:16:32 AM UTC-6, AS wrote:
> On Monday, June 8, 2020 at 9:38:29 AM UTC-4, wrote:
> > Also note that the small hookup ring can wear. If it gets deformed or reduced in size, it can jam or prematurely release. I looked for the specification on minimum thickness, but couldn't find it with a (very brief) search. Check with Wings & Wheels to see if they know the correct "go-no go" dimension.
>
> Mark - according the the DIN-LN65091, the oval ring has a wire diameter of 8mm, +0, -0.3mm. The round ring has a wire diameter of 7mm, +0, -0.3mm. The O.D. of the round ring is 35mm, +-0.3mm, which would give it a nominal I..D. of 21mm. If you do a quick tolerance stack-up using just min.-max. material conditions while neglecting any ovality, the I.D. could range from 21.9mm to 20.7mm
> The material specifications call for a high carbon Chrome-Vanadium alloy. No welding is permitted.
>
> Uli
> 'AS'
Thanks!
Charlie M. (UH & 002 owner/pilot)
June 8th 20, 08:14 PM
Soooo....."no welding allowed"......how do they make the ring? Just asking......usually round "wire/rod", bent, welded together.....
Shrug....
On Monday, June 8, 2020 at 1:14:41 PM UTC-6, Charlie M. (UH & 002 owner/pilot) wrote:
> Soooo....."no welding allowed"......how do they make the ring? Just asking......usually round "wire/rod", bent, welded together.....
> Shrug....
Forging a ring involves bending the stock in a circle with varying amounts of overlap- sometimes one or more full circles, but more often a lap of about 1/3 the circumference. Then it is heated to a bright, glowing temperature and beaten into the final shape. Hardening is sometimes done by quenching in oil. Linked rings are made by forging the first ring and looping the second though it and forging by the same method.
Ventus_a
June 9th 20, 12:59 AM
On Thursday, June 4, 2020 at 4:33:29 PM UTC-5, Kenz Dale wrote:
I understand that CG hooks are designed to autorelease when the angle of pull passes a certain critical angle. Is this a very reliable disconnect, or is more of an "Eh, it's nice to have but I've seen it fail too many times to trust it"?
I have never heard of a TOST CG release failing to "back release". The back "jaw" of the TOST CG hook is held closed only by light spring tension. If there is any rearward pressure on it, it has to release. The spring tension is light enough that it is easy to attach the tow ring to the hook simply by pushing the ring against the back jaw of the release. Not many ways that it can fail. A foreign body or broken part falling into the mechanism could conceivably jam it and prevent it from opening. Some of the older TOST CG releases could have a problem with the tow ring jamming sideways in the release. Gliders with those model TOST releases require installation of small metal guides to prevent misalignment of the ring. Those metal guides also act as protective skids if one forgets to extend the landing gear upon landing (one guess as to how I know this).
I think most of the "failure to release" problems for gliders launching with the CG release have not actually involve the CG release as such. Rolling over the launch cable and entangling it in the wheel have been the cause of some incidents. That is why ground launch systems MUST have some means of quickly cutting the cable.
Before I bought my Ventus a, the previous owner rotated the hook backwards as per Schempp instructions to reduce early back releasing. The slot the back release hook moves in wasn't enlaged to the rear and the next time the glider was winch launched it wouldn't release backwards or via a pull on the release.
The process of rotating the hook had also effectively lengthened the release cable and it ended up bottoming out the lever arrangement, that transferred the pull back to the hook, against a bulkhead.
The winch driver didn't cut the cable and the winch was getting destabilised as the glider went through about 45 degress down towards the ground behind the winch. Going through about 400' with lots of frantic pulling on the release and the stick the cable finally let go and the day was saved.. Some badly shaken people and the hook installation got a good working over to ensure that it couldn't happen again
Colin
On Monday, June 8, 2020 at 3:30:08 PM UTC-4, wrote:
> On Monday, June 8, 2020 at 1:14:41 PM UTC-6, Charlie M. (UH & 002 owner/pilot) wrote:
> > Soooo....."no welding allowed"......how do they make the ring? Just asking......usually round "wire/rod", bent, welded together.....
> > Shrug....
>
> Forging a ring involves bending the stock in a circle with varying amounts of overlap- sometimes one or more full circles, but more often a lap of about 1/3 the circumference. Then it is heated to a bright, glowing temperature and beaten into the final shape. Hardening is sometimes done by quenching in oil. Linked rings are made by forging the first ring and looping the second though it and forging by the same method.
I am just speculating here but two interlocking rings could be easily made as an investment casting (lost wax casting). Given that it is a Cr-Va alloy, the raw cast product can be heat treated and quenched in oil, which would explain the blackened appearance when new.
I will see if I can get my hands on a discarded pair and have our metallurgists take a look at.
Uli
'AS'
son_of_flubber
June 9th 20, 01:46 PM
On Monday, June 8, 2020 at 1:16:32 PM UTC-4, AS wrote:
>...according the the DIN-LN65091, the oval ring has a wire diameter of 8mm, +0, -0.3mm. The round ring has a wire diameter of 7mm, +0, -0.3mm. The O.D. of the round ring is 35mm, +-0.3mm, which would give it a nominal I.D. of 21mm. If you do a quick tolerance stack-up using just min.-max. material conditions while neglecting any ovality, the I.D. could range from 21.9mm to 20.7mm<
For those of us who know how to use a pair of calipers, and not much else, what is a quick way to determine that a ring is worn out?
Dan Marotta
June 9th 20, 03:08 PM
I was taught that, if unable to release, the glider should circle the
winch rather than slingshot towards the ground.Â* And why wouldn't the
driver cut the cable as soon as the glider overflew the winch and
started down?Â* Training...
On 6/8/2020 5:59 PM, Ventus_a wrote:
> he winch driver didn't cut the cable and the winch was getting
> destabilised as the glider went through about 45 degress down towards
> the ground behind the winch. Going through about 400' with lots of
> frantic pulling on the release and the stick the cable finally let go
> and the day was saved.. Some badly shaken people and the hook
> installation got a good working over to ensure that it couldn't happen
> again
>
> Colin
--
Dan, 5J
A quick way is to only use a TOST ring set where you can still read (most) of the TOST part number stamped on the side of the small ring. With dimension change due to wear&tear, the part number will become unreadable.
This has the dual benefit of also ensuring you are being hooked up with a proper TOST ring set and not a home made or repaired set.
PS- Remind me to take a calipers out to the airfield next visit and validate a suspect worn ring’s dimensions. Thanks, whoever posted the spec dims.
Dan Daly[_2_]
June 9th 20, 07:07 PM
On Tuesday, June 9, 2020 at 1:27:45 PM UTC-4, wrote:
> A quick way is to only use a TOST ring set where you can still read (most) of the TOST part number stamped on the side of the small ring. With dimension change due to wear&tear, the part number will become unreadable.
> This has the dual benefit of also ensuring you are being hooked up with a proper TOST ring set and not a home made or repaired set.
> PS- Remind me to take a calipers out to the airfield next visit and validate a suspect worn ring’s dimensions. Thanks, whoever posted the spec dims.
It's on the oval ring on my ring pair... and TOST is stamped at the bottom of it.
While inspecting, look for small (maybe 1/32 inch?) cracks.
That seems to happen before noticeable wear changes.
Ventus_a
June 9th 20, 11:45 PM
I was taught that, if unable to release, the glider should circle the
winch rather than slingshot towards the ground.Â* And why wouldn't the
driver cut the cable as soon as the glider overflew the winch and
started down?Â* Training...
On 6/8/2020 5:59 PM, Ventus_a wrote:
he winch driver didn't cut the cable and the winch was getting
destabilised as the glider went through about 45 degress down towards
the ground behind the winch. Going through about 400' with lots of
frantic pulling on the release and the stick the cable finally let go
and the day was saved.. Some badly shaken people and the hook
installation got a good working over to ensure that it couldn't happen
again
Colin
--
Dan, 5J
Hi Dan
The winch driver was an older gentleman and he bailed out of the winch. I suspect lack of familiarity with the cutting system and a sense of his own vulnerability prevailed. Since then a more robust training system is in place for winch drivers
On Tuesday, June 9, 2020 at 1:27:45 PM UTC-4, wrote:
> A quick way is to only use a TOST ring set where you can still read (most) of the TOST part number stamped on the side of the small ring. With dimension change due to wear&tear, the part number will become unreadable.
> This has the dual benefit of also ensuring you are being hooked up with a proper TOST ring set and not a home made or repaired set.
> PS- Remind me to take a calipers out to the airfield next visit and validate a suspect worn ring’s dimensions. Thanks, whoever posted the spec dims.
Welcome!
Uli
'AS'
Dan Marotta
June 10th 20, 06:40 PM
Us older guys need to step up our game!
On 6/9/2020 4:45 PM, Ventus_a wrote:
> Dan Marotta;1022870 Wrote:
>> I was taught that, if unable to release, the glider should circle the
>> winch rather than slingshot towards the ground.Ă‚* And why wouldn't the
>> driver cut the cable as soon as the glider overflew the winch and
>> started down?Ă‚* Training...
>>
>> On 6/8/2020 5:59 PM, Ventus_a wrote:-
>> he winch driver didn't cut the cable and the winch was getting
>> destabilised as the glider went through about 45 degress down towards
>> the ground behind the winch. Going through about 400' with lots of
>> frantic pulling on the release and the stick the cable finally let go
>> and the day was saved.. Some badly shaken people and the hook
>> installation got a good working over to ensure that it couldn't happen
>> again
>>
>> Colin-
>>
>> --
>> Dan, 5J
> Hi Dan
>
> The winch driver was an older gentleman and he bailed out of the winch.
> I suspect lack of familiarity with the cutting system and a sense of his
> own vulnerability prevailed. Since then a more robust training system
> is in place for winch drivers
>
>
>
>
--
Dan, 5J
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