On Tuesday, February 11, 2014 3:56:33 AM UTC-5, Chris Rollings wrote:

We did build an experimental hook and tried it, but,
set to an angle that prevented "Kiting" it occasionally dumped an
innocent glider in turbulence, and set to an angle that prevented that, it
didn't prevent the "Kiting". What was needed was a hook that
responded to the vertical component of the load, not the angle at which it
was applied, and that problem we decided was beyond us (at least in a form
robust and fool-proof enough to be attached to the rear end of a
tow-plane).

Thank you Mr. Rollings for your pioneering work with tow hooks and thank you for responding to my question.

(And thanks to all the people who deployed the internet and made conversations like this one possible. Wow.)