On Sep 16, 5:45*am, wrote:
On Sep 15, 6:15*am, JJ Sinclair wrote:





On Sep 14, 5:11*pm, wrote:

On Sep 14, 8:05*am, JJ Sinclair wrote:

The ideal location for the trailing edge cuff is over the trailing
edge of the wing at a location where no control surface is located, as
in a standard class ship. On a 15 meter bird like the 27, the whole
trailing edge is either flap or aileron. I have used the trailing edge
cuff where the flap and aileron meet for years on my Nimbus-3 and LS-6
without causing any control surface damage. Any slight upward pressure
is restrained in the flap and aileron push-rods which are loaded in
tension as upward forces are trying to raise both control surfaces
together.

*I would however, reconsider pulling upward on the spoiler push-rod
which is quite strong in tension, but quite weak when bending loads
are applied.
JJ

Hey JJ,

I don't tie to the pushrod. I agree, it is is too long and not likely
stong in bending load. *Instead I thread the webbing around the 1.5-
inch long T that is the bottom of the whole pivot for the divebrake.
There is one inboard and one outboard on each divebrake - I tend to
tie to the outboard one. They are essentially the bottom corners of
the whole parallelogram that allows each divebrake to swing up out of
the box. Since they run chordwise inside the box and are anchored fore
and aft by 3/4" steel bearings set in carbon fiber next to the spar it
would seem to me to be one of the more stout parts on the whole wing
structure - certainly at least as strong as control surface hinges.
But since I have not cut into my wing to see how it's really put
together I can't be absolutely sure which is why I was asking around
from people who maybe have seen inside a -27 wing.

If it's still not totally clear which part I'm talking about I'll take
a picture when I get home. I've never had a problem with doing it this
way. On the other hand, I've never seen any tiedown actually rip off
of the airplane even though I've seen some pretty sketchy methods - so
lack of a catastrophe doesn't prove much.

Schleicher wisely recommends against using the spoilers as a tie-down
location because you are applying high loads to a butt weld which is
weak under side loads. The same loads will be present when using the
short drive arm to attach a web strap, although admittedly not as high
as attaching to the vertical arms. If you bend anthing in there, your
spoilers won't close and lock completery.............guess how I know
this to be true?

The loads applied using the trailing edge cuff are 90% forward and 10%
upward. As demonstrated by 20 years in use, the control hinges are
plenty strong enough to withstand the forward load and the control
mechanism is plenty strong enough to take the 10% upward load. The
cuff is well padded and bent to an angle that grips the sides before
the trailing edge seats fully.

What we're talking about here is the lesser of two evils while still
providing an acceptable solution to tying the ship down when
necessary.
JJ

I guess you can get away with putting the JJ rig at the flap/divebrake
intersection as long as there isn't a lot of play in the control
circuit so everything stays snug and aligned. But here's a thought
experiment - *I cup the cuff over the trailing edge and lay the web
across the top surface of the wing, then I squat in front of my glider
and yank on the strap from a low angle as hard as I can to simulate a
big wind gust trying to lift my glider up. Those -27 control surfaces
seem so thin and delicate - it makes me nervous to think about it. But
I don't glue gliders back together for a living so maybe I'm being too
squeamish.

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Thanks JJ - I'm going to take another look. I haven't seen a butt weld
in that location, so now I have something to look for.

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Andy,
I just took a look at an ASW-20 wing in my barn and although I don't
recommend it, it looks as though a web-strap that was shoved
completely under the outboard divebrake pivot bolt (sleeve), would
pass the tie-down loads into 2 vertical plywood blocks and then into
the upper spar cap and might be a satisfactory place to attach your
tie-down strap.
JJ
PS, I have a repaired 20A fuselage, both wings and a broken stab that
could be the makings of a nice re-build project for 4K, no trailer, no
instruments.