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

On Monday, June 1, 2015 at 11:26:28 AM UTC-4, Dan Marotta wrote:
Perhaps a pulley mounted to a 2 x 12 of sufficient length that the
glider sits on the board to hold it down.** Position the glider on
the board to get the desired angle and put a couple of people in the
cockpit.* Use a spring scale and come along to set the desired
tension.



snip


We're thinking along those lines too. However, to check a CG hook at the rope angles normally experienced, the pull angle has to be something line 45 degrees down from horizontal. That's going to be complicated.





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Dan Marotta

Yup. Was involved in a similar exercise many years ago when John Campbell was investigating critical angles on Schweitzer releases. If the glider is assembled, you can get a group of folks together and lift it onto some tall saw horses supporting the wings near the root. Use big pads to avoid crushing the skin. Even better would be to take the wings off and support using the lift pin hardpoints. If you do this over a solid tie down (airport tiedown ring), you'll only need a small pulley and you can move the fuselage forward or backwards to get the required angles.

On Monday, June 1, 2015 at 8:45:14 AM UTC-7, Papa3 wrote:
On Monday, June 1, 2015 at 11:26:28 AM UTC-4, Dan Marotta wrote:
Perhaps a pulley mounted to a 2 x 12 of sufficient length that the
glider sits on the board to hold it down.** Position the glider on
the board to get the desired angle and put a couple of people in the
cockpit.* Use a spring scale and come along to set the desired
tension.



snip


We're thinking along those lines too. However, to check a CG hook at the rope angles normally experienced, the pull angle has to be something line 45 degrees down from horizontal. That's going to be complicated.





--

Dan Marotta

Yup. Was involved in a similar exercise many years ago when John Campbell was investigating critical angles on Schweitzer releases. If the glider is assembled, you can get a group of folks together and lift it onto some tall saw horses supporting the wings near the root. Use big pads to avoid crushing the skin. Even better would be to take the wings off and support using the lift pin hardpoints. If you do this over a solid tie down (airport tiedown ring), you'll only need a small pulley and you can move the fuselage forward or backwards to get the required angles.

A variation of Dan's idea is pretty simple. Take a 12 ft. or so plank with one end under the main wheel and an eyebolt at the desired point under the CG hook. Let the free end of the plank extend beyond the nose of the glider and link the hook to the eyebolt so that the plank is held up at the nose end. That allows someone to sit on the tail and another person to put tension on the rope by pushing down on free end of the plank.

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

Update,

I finally got knowledgable help to do a better ramp test. Pulling on a strop by hand at a typical winch angle, I can feel a noticible step in the release process as the yellow knob is very slowly pulled. It seems like there is some irregularity in the "beak" part of the hook which may be large enough to cause the hard release problem. Since this glider has never seen winch launch before, it could be the CG hook was used for tie-down or an old hook was used as a "box check" to get through an annual. More investigation results to follow.

- Mountings bolts/nuts overtightened during installation(some earlier Tost
releases do not have the mounting bolt bushings inside the hook)?
- Nose-release blocked (had this on an ASK-21 with a sheared off
M6-bolthead fallen inside the release, very hard to find)?
- Actuator-arms of new release not in the same position as before removal
of old release (they are adjustable) causing pre-tension on actuation
cable?
- Dirt/debris in any actuating cable jackets (e.g. Bowden)?
- Wrong hardness mountings bolts (4.6) fitted, distorting bolts?

If release just installed, mounting bolt tightening or actuator arm
position usually to blame.