What could cause extremely high effort to release a Tost CG hook on aTwin Astir?

The scenario is winch rope break practice with the instructor pulling the release to simulate rope breaks.

I'm not talking about just an ordinary hard pull. This is a maximum-effort, adrenaline pumped, two-handed strain to get the release to work.

On the ground, the CG hook checks out as a little stiffer than one might prefer but otherwise normal. But trying for a mid-winch launch release it requires all the strength I can muster using both hands. Tost CG hook pull effort is not supposed to be dependent on rope tension.

The pull cable runs and pulleys have been checked and re-checked. The Tost CG hook itself is new and seems to work as advertised. There is nothing obvious one can see with the seat pans and instrument pedestal cover removed.

Any ideas?

I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain.. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

On Sunday, May 31, 2015 at 6:58:47 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

FWIW, CS-22 regs say a CG hook operating force can't exceed 140N (31.5 Lbs-F) I'm guessing this one takes 200 Lbs-F or more.

On Sunday, May 31, 2015 at 7:02:37 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:58:47 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

FWIW, CS-22 regs say a CG hook operating force can't exceed 140N (31.5 Lbs-F) I'm guessing this one takes 200 Lbs-F or more.

New hook, correct hook? Correctly installed? Cracked plates? Is replacement of plates logged? Sounds like hook could be rotating under tension but you can't duplicate on ground. Cracked or broken mount plates could perhaps cause this. See these SB's
http://www.ltb-lindner.com/g-103-ad-...ofG%20hook.pdf
http://www.ltb-lindner.com/g-103-ad-...ofG%20hook.pdf

On Sunday, May 31, 2015 at 7:02:37 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:58:47 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

FWIW, CS-22 regs say a CG hook operating force can't exceed 140N (31.5 Lbs-F) I'm guessing this one takes 200 Lbs-F or more.

Has this changed since winch testing and training started, or remained consistent?

Frank W

On Sunday, May 31, 2015 at 7:46:35 PM UTC-6, Frank Whiteley wrote:
On Sunday, May 31, 2015 at 7:02:37 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:58:47 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

FWIW, CS-22 regs say a CG hook operating force can't exceed 140N (31.5 Lbs-F) I'm guessing this one takes 200 Lbs-F or more.

New hook, correct hook? Correctly installed? Cracked plates? Is replacement of plates logged? Sounds like hook could be rotating under tension but you can't duplicate on ground. Cracked or broken mount plates could perhaps cause this. See these SB's
http://www.ltb-lindner.com/g-103-ad-...ofG%20hook.pdf
http://www.ltb-lindner.com/g-103-ad-...ofG%20hook.pdf

Aircraft log show compliance with both AD's on Apr 6, 2013

On Sunday, May 31, 2015 at 7:58:26 PM UTC-6, Frank Whiteley wrote:
On Sunday, May 31, 2015 at 7:02:37 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:58:47 PM UTC-6, Bill D wrote:
On Sunday, May 31, 2015 at 6:43:19 PM UTC-6, Bill T wrote:
I believe I remeber a Kestral that had a "stiff release" issue. He removed the seat pan and discovered that the pan was depressing with his weight in it and binding the cable. But you said you have removed the seat pans and checked all of the cables.

My second guess would have been that there was a worn spot or nick in the "jaws" of the TOST release that might be catching on the ring under strain. But you said the TOST was fairly new. Is the TOST ring in fairly good shape and not one of the imposters that were on the market a few years back?

It would be great if you could have a cable under load at GS=0 to visually watch the release mechanism, but that is not a safe venture without a lot of precautions in set up.

BillT

Both the CG hook and the ring pair are brand new. My only guess (AKA pure speculation) is an improper (and unrecorded) repair left the whole forward fuselage weak so it is deforming under winch launch loads causing the yellow-ball to CG hook cable system to bind. FWIW, I do not suspect the hook itself.

Bill D

FWIW, CS-22 regs say a CG hook operating force can't exceed 140N (31.5 Lbs-F) I'm guessing this one takes 200 Lbs-F or more.

Has this changed since winch testing and training started, or remained consistent?

Frank W

No change.

Hate to launch again as an "experiment " without knowing what is really going on.
You said the instructor "rear" seat release pull took what you estimate is a 200 lb pull.
Is the front seat release having a problem?
Any problems with an auto back release at top of climb?

BillT

On Sunday, May 31, 2015 at 8:12:52 PM UTC-6, Bill T wrote:
Hate to launch again as an "experiment " without knowing what is really going on.
You said the instructor "rear" seat release pull took what you estimate is a 200 lb pull.
Is the front seat release having a problem?
Any problems with an auto back release at top of climb?

BillT

Yes, rear seat release.
The front seat release hasn't been tested in flight.
The "back-release" function seems to work well at the top of the launch.