How reliably do CG hooks disconnect when the angle of the ropeexceeds the autorelease angle

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"?

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.

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.

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.

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

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.

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

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'