We are trying to see if our club gliders meet spec on the force needed to activate our G-72 tost release. See the specs below.

How do you safely restrain a glider while you do this test? In particular we have Grob Twin Astirs and Grob Twin IIs.

"Checks after installation
After installing a release, and as part of the periodic aircraft inspections, these checks must be carried out:
1. You must. be able to open the unloaded release completely by applying a force of 7.5 + 1.5 daN (16.5 + 3.3 Ibs.) - measured on a spring balance- on the manual release tever in the cockpit over the full travel of the release actuation arm.
2. When the release hookis under a load of approx. 150 daN (330 Ibs.), you should still be able to operate the manual release lever in the cockpit with the same force, i.e., 7.5 + 1.5 daN (16.5 + 3.3 Ibs.).
3. If both a nose and a center-of-gravity release are connected to the same release cable, the manual force required to operate them from the cockpit may not exceed 17 daN (37 ibs.), even if one of the releases is under. a load of 150 daN (330 ibs.)."

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I've never done the test, but maybe you could put the main wheel on a surface, then gradually increase the slope of the surface until you get the desired load on the rope.

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On Monday, April 11, 2022 at 12:36:20 PM UTC-7, son_of_flubber wrote:

I've never done the test, but maybe you could put the main wheel on a surface, then gradually increase the slope of the surface until you get the desired load on the rope.

How about a big wheel chock that is high enough to be above the axle………..chock would need to be secured to the ground/pavement! Then pull on the tow rope by applying force required ? Common way to test aircraft cables is to secure one end of a 2X4
that is 12’ long, with a pivot point at the 1 foot mark. Then, apply 1/10th the desired force at 11’ mark with a bathroom scale. Get the picture? It’s a 10 foot pry-bar that applies 10 times the force applied.
Hope this helps,
JJ

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Thanks guys. JJ you're confirming what I was thinking: the main wheel structure can easily take 300 lbs of force directed aft. I think we can just wrap long webbing or rope around the main wheel axle structure and tie the glider back to a structure or
vehicle while we pull on the tow release

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I would do the low level test, then I would remove the hook and do the high level testing with it mounted to a secure structure.
Then it can be reinstalled if your happy with the results.
I would not want the possibility of damaging the ship by coming up with some hopeful way of securing the aircraft.
If you do secure the aircraft for the high level check it will need to be secured in the reverse direction as well so it doesn't back into something when the release is pulled.

I'm very sure Tost checks their releases on a test stand, not in a glider.

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P.S. That's a very good point about securing the glider both directions.

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JJ the specs require a test release from the cockpit. In fact we're concerned about cable routing friction in the rear seat release. This is "must" be done periodically (per the manual), so there must be a simple way to hold a glider back with 300 lbs
force or they wouldn't write the test as it is.

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On Tuesday, April 12, 2022 at 1:24:03 PM UTC+10, bret...@gmail.com wrote:

P.S. That's a very good point about securing the glider both directions.

Here in Australia, some clever bloke deveoped a jig that lets you test the Tost . Its put in a big enginners vice, and a threaded device is turned to simulat load.
The Tost needs to be removed from the glider, which makes this a good time to clean inspect lubracte, change springs etc. Doing it in the aircraft sounds like a can of worms to me.

Mark

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On Monday, April 11, 2022 at 10:24:03 PM UTC-5, bret...@gmail.com wrote:

P.S. That's a very good point about securing the glider both directions.

If it passes the low level test then the cable routing and cable friction is good. Adding loading to the hook will not add any friction to the cables. It will load the release itself. I was just saying how I would proceed, but your welcome to do it as
you feal is best.
Is this test requirement in the manual in the section for continued airworthiness? or just in the body of the MM?

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The test is in the manual for the tow release, G72.  

We are concerned about the force needed to release during winch launching seeming to be much more than in aerotow. We have a small pull scale we might use in flights, but the only specs we have are this test in the release manual.

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On Monday, April 11, 2022 at 10:50:40 PM UTC-5, bret...@gmail.com wrote:

The test is in the manual for the tow release, G72.

We are concerned about the force needed to release during winch launching seeming to be much more than in aerotow. We have a small pull scale we might use in flights, but the only specs we have are this test in the release manual.

Awesome - then I again default to, Im sure Tost test there hooks on a bench not in a glider. You might reach out to Tost to get advice from them. Your winch will be putting loads on the release in a different direction than an aero tow. They are most
likely a higher tension at release than that of an aero tow as well.

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This link might be useful. Paste it directly into your browser. All you ever wanted to know about Tost release maintenance.

http://www.doc.glidingaustralia.org/index.php?option=com_docman&view=download&alias=502-gfa-ad-277-issue-8&category_slug=gfa-ad-201-300&Itemid=101

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I'm sorry.... I just noticed that the AD info is provided by Mark. I thought it was from Bret and what was driving the original question.

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On Monday, April 11, 2022 at 11:13:14 PM UTC-5, Mark Fisher wrote:

This link might be useful. Paste it directly into your browser. All you ever wanted to know about Tost release maintenance.

http://www.doc.glidingaustralia.org/index.php?option=com_docman&view=download&alias=502-gfa-ad-277-issue-8&category_slug=gfa-ad-201-300&Itemid=101

That document says it was cancelled in May of 2017.

I read thru it and see nothing that says testing is to be done in the aircraft.

One section clearly says to disconnect it from the release cables as quoted next.....

"RELEASE OPERATING CIRCUIT:
The release operation circuit must be disconnected from the release.
For maintenance requirements of release circuits see Basic
Sailplane Engineering"

I'm of the opinion that this testing described in this cancelled AD was intended to be done outside of the aircraft on a bench.

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On Sun, 10 Apr 2022 16:36:56 -0700 (PDT), Bret Hess wrote:

We are trying to see if our club gliders meet spec on the force needed
to activate our G-72 tost release. See the specs below.

How do you safely restrain a glider while you do this test? In
particular we have Grob Twin Astirs and Grob Twin IIs.

When my club had a Grob Twin 2 Acro(*) I flew it a lot off the winch and
aero tow. I never noticed the cable release force being higher than it is
for an ASK-21 or Puchacz. If yours has noticeably higher cable release
forces, it may pay to have a close look at the release cable runs.

[*] it was airworthy when we sold it, but wear and tear and related
repairs had reduced its max seat load enough to impact its use for
training and trial flights. Pity because it was quite nice to fly and we
flew it in our Regionals to give recent solos a taste of xc flying.

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On Tuesday, April 12, 2022 at 5:58:43 AM UTC-7, Martin Gregorie wrote:

On Sun, 10 Apr 2022 16:36:56 -0700 (PDT), Bret Hess wrote:

We are trying to see if our club gliders meet spec on the force needed
to activate our G-72 tost release. See the specs below.

How do you safely restrain a glider while you do this test? In
particular we have Grob Twin Astirs and Grob Twin IIs.

When my club had a Grob Twin 2 Acro(*) I flew it a lot off the winch and
aero tow. I never noticed the cable release force being higher than it is
for an ASK-21 or Puchacz. If yours has noticeably higher cable release forces, it may pay to have a close look at the release cable runs.

[*] it was airworthy when we sold it, but wear and tear and related
repairs had reduced its max seat load enough to impact its use for
training and trial flights. Pity because it was quite nice to fly and we
flew it in our Regionals to give recent solos a taste of xc flying.

I remember a friend who auto towed a Gia glider several times, then he hooked it to a Cub. On tow, the ship went into a PIO but the pilot was unable to release! The 330# figure is testing to verify the pilot can release under tension!

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On Tue, 12 Apr 2022 07:15:33 -0700 (PDT), John Sinclair wrote:

On Tuesday, April 12, 2022 at 5:58:43 AM UTC-7, Martin Gregorie wrote:

On Sun, 10 Apr 2022 16:36:56 -0700 (PDT), Bret Hess wrote:

We are trying to see if our club gliders meet spec on the force
needed to activate our G-72 tost release. See the specs below.

How do you safely restrain a glider while you do this test? In
particular we have Grob Twin Astirs and Grob Twin IIs.

When my club had a Grob Twin 2 Acro(*) I flew it a lot off the winch
and aero tow. I never noticed the cable release force being higher than
it is for an ASK-21 or Puchacz. If yours has noticeably higher cable
release forces, it may pay to have a close look at the release cable
runs.

[*] it was airworthy when we sold it, but wear and tear and related
repairs had reduced its max seat load enough to impact its use for
training and trial flights. Pity because it was quite nice to fly and
we flew it in our Regionals to give recent solos a taste of xc flying.

Understood, but as others have already pointed out, the winch launch hook
is quite different to the aero-tow, both in mechanism and force vectors.

At my club, and every other UK club I've flown at, the winch hook is
tested for correct operation behaviour before every glider's first winch
launch of the day. When the pilot asks for 'cable on':

- the helper puts the cable on and says 'release checks: free drop'
at which the pilot should pull the release and the cable should fall
from the hook.

- If that was OK the cable is put back on (same procedure as before) and
this time the helper announces 'back release' and pulls the cable
toward the glider's tail with one hand to force a back release

- If that was OK the cable is put back on (same procedure as before) and
this time the helper announces 'tension release' as he pulls forward on
the cable with some force. The pilot then pulls the release knob. If all
three checks were satisfactory. the helper says 'checks OK'. The pilot
responds with 'cable on' and the glider is hooked on and launched.

The OP doesn't say what checks his club uses, but if they don't use a
similar procedure to the above, they'd be well advised to start doing so.

FWIW we do the same when aero-towing: do a tension release check on every glider before its first launch of the day, but I expect thats already SOP
in the US.

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If you do a low or no tension test on both cockpit positions and the release forces are acceptable, the cable runs and cable friction are good.

Adding tension over 300lbs will put tensions on the tost release mechanism, not on the cable system, unless the structure that the release is mounted to is compromised and twist or moves in a way that adds friction to the cables or connections.

So if low tension check is good, yet you feel that the release is difficult (high release pull pressures are required to release from tow) and the structure of the release mounting is good......the problem would be in the release mechanism itself, if in
fact there is a problem.

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If I was going to try to test as you are describing, I would look at putting the fuselage in a trailer. Nose securely in the nose cone structure of the trailer, tailwheel in the tailwheel divit, tail boom strapped down maybe some fore and aft straps
from the wing mounting structures. Then work up front applying the tensions you desire.

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The Gliding Federation Australia (GFA) AD277 was cancelled because it superseded by the inclusion of Chapter 16 'Tow releases' in the GFA Basic Sailplane Engineering' (BSE) publication. Search for Basic Sailplane Engineering AIRW-M05'. Lots of good
info there re Tost test procedures.

Also, here is Western Australia a clever glider/tug pilot & engineer has created a special tool that fits onto the Tost ring cage and applies the required force pushing against the ring.

Re winch Tost releases, one of the very important tests is the the back release functionality. This was wrongly described in AD277 but corrected in BSE.

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Using the "special tool that fits onto the Tost ring cage" would seem to defeat the purpose of the test. It is little different than a bench test since it does not load the mounting of the release to the glider, which appears to be the point of the 300-
lbs in-glider test.

...david

On Wednesday, April 13, 2022 at 9:06:41 AM UTC-4, bumpf...@hotmail.com wrote:

The Gliding Federation Australia (GFA) AD277 was cancelled because it superseded by the inclusion of Chapter 16 'Tow releases' in the GFA Basic Sailplane Engineering' (BSE) publication. Search for Basic Sailplane Engineering AIRW-M05'. Lots of good

info there re Tost test procedures.

Also, here is Western Australia a clever glider/tug pilot & engineer has created a special tool that fits onto the Tost ring cage and applies the required force pushing against the ring.

Re winch Tost releases, one of the very important tests is the the back release functionality. This was wrongly described in AD277 but corrected in BSE.

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On Tuesday, April 26, 2022 at 7:56:21 PM UTC+8, david.s....@gmail.com wrote:

Using the "special tool that fits onto the Tost ring cage" would seem to defeat the purpose of the test. It is little different than a bench test since it does not load the mounting of the release to the glider, which appears to be the point of the 300-

lbs in-glider test.

...david
On Wednesday, April 13, 2022 at 9:06:41 AM UTC-4, bumpf...@hotmail.com wrote:

The Gliding Federation Australia (GFA) AD277 was cancelled because it superseded by the inclusion of Chapter 16 'Tow releases' in the GFA Basic Sailplane Engineering' (BSE) publication. Search for Basic Sailplane Engineering AIRW-M05'. Lots of good

info there re Tost test procedures.

Also, here is Western Australia a clever glider/tug pilot & engineer has created a special tool that fits onto the Tost ring cage and applies the required force pushing against the ring.

Re winch Tost releases, one of the very important tests is the the back release functionality. This was wrongly described in AD277 but corrected in BSE.

I know of no TOST test that requires a loading of the release mounting system or tests the mounting integrity I think you misunderstand the test purpose.

The aim of the test is to prove that an average individual can operate the release pull with a reasonable pull force and achieve a rope release when under tow tension. It tests that the the mechanism is not too much over-centre, that the friction in
the operating cable/pulley system is reasonable and that the mechanical advantage at the release actuation lever is correct (ie the release cable is pulling at the correct arm length). It is a full system test with the release in situ.

I have separately sent you pictures of the special device.

Yes you can test overcentre with the release in a bench vice. If you do this, you should again insert a ring and apply tension. In Australia we do this at 3 different tension settings and measure the force required to trip the release. If the 3 data
points are plotted they should be a straight line.

You can also test the pilot's pull force with the release in situ to measure the system/pully friction plus release spring tension with no load on the release beak. What you are not testing here is the true situation when the release is loaded with
tension during the tow.

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