Earlier, JJ Sinclair wrote:

Its been a long time now, but a group was
auto-towing a Cherokee at Air Sailing, NV...

I'm not sure, but I believe that was actually a Don Mitchell design
called the Nimbus III-B (no relation to the later Schempp-Hirth
product of similar name). That was in 1973:

http://www.ntsb.gov/NTSB/brief.asp?ev_id=85473&key=0

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com