Hi Frank,

Didn't see the request on gliderforum.com. Where was it? What are you
thinking of putting one in?

There are lots of similarities between the Schreder hook and Applebay's
version. George made his so that it will auto-release if the pull is
too much "down". Trying to protect the towpilot.

Les, I suspect the issue is not so much the spring, but is it possible
that when you got high, you leveled off for a moment, and got slack in
the rope? The weight and drag of the loop may have caused the release?

A bit about the release.

There are two springs in the design. A torsion spring to close the
release, and a tension spring to hold the locking arm in position.
There is not any slope on the mating faces of the locking arm and the
forward, load carrying part of the hook, so it should not have released
unless there was a load to pull the rope down the slot, or the release
got tripped by the locking arm being pulled.

As for adjustments, remember, there are two ends to a spring. The
other end should be easily accessable at the top of the locking arm.
You can shorten this spring to increase the tension holding the locking
arm in place.

Craig, as Bob said, try pushing in at the back of the release. There
is plenty of room inside the nose for you to push it most of the way
into position from the back end of the release.

There is one improvement I think can be made to the design. It will be
much easier for the line crew to hook up if a mechanical stop is
installed that prevents the forward part of the hook from rotating aft
as you push the cover plate back to insert the tow ring. If you look
at the geometry, of the hook, you will see what I am talking about.
This stop can take several forms. The simplest is a change to the
shape of the forward part of the hook.

There is also one installed on a Mosquito at my field. My opinion is
they work just fine. I have never had any troubles with mine and I
have about 1100 hours in my Zuni and probably 300+ flights.

Steve Leonard
Zuni 2, Serial 28