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

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!

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.

Originally Posted by WB

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'

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?

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.