Are Weak Links really Necessary for Aero Tow?

Doug Haluza wrote:
Oh, my, where to start?

KM wrote:


After an upset, the towplane will enter an unrecoverable dive, and if
the rope does not break, the speeds will quickly increase beyond
maneuvering speed.

Where do you come up with this?I have NEVER flown an airplane that
could not be pulled out of a dive. Another thing to consider is that the
tow pilot would just release by this point.The tost hook will release
at vitually any angle, and even if the plane had a Schweitzer hook, by
forcing the tail up you will change the angle on the rope and the pilot
could then release it.

You can't pull out of the dive if the glider is still attached to your
tail by a rope that won't break. And if you have a Schweizer hook on
the tail, it may not release after the upset because the pull is
greater and may no longer be straight back. There have been several
cases of upset where the tow pilot could not make the hook release, and
the dive would have been unrecoverable if the rope did not break.



I recall that John Campbell did a detailed analysis of this issue
(loads on a Schweizer towplane release mechanism) when he was a
postDoc. There were a couple of pretty sobering conclusions IIRC:

1. There is a critical angle (not a particularly steep one) beyond
which the vertical component of the force applied by the towrope will
overcome the force available from the emergency release cable on the
towplane side. In other words, once the glider kites up to a certain
angle, the towpilot may (probably won't) be able to release. Anyone
who has ever eyeballed the Schweizer release will immediately be able
to see why this is the case.

2. The force required for this was significantly less than the
breaking strength of a typical towrope. I could probably rough out
the numbers for this, but it is intuitively makes sense.

Maybe somebody has a copy of this analysis handy?

P3