[JoeF]

Sock Series
The best I surmise to date: Sock 1 to Sock 2 to Sock 3 from 1983-1986.
"The Yvon Perret Sock hang glider appeared in 1985"
========================
Sock 2
Sock 3

http://all-aero.com/index.php/63-hang-glider-paraglider/16761-yvon-perret-sock
==================
https://www.delta-club-82.com/bible/758-hang-glider-sock-3.htm
==================
https://www.delta-club-82.com/bible/760-hang-glider-sock.htm

Sock 3

The manufacturer and pilot tester of the Sock 2 is Alain Jacques. After a few tests on the slope school, he had taken off directly from the north hill in St Hil.

Sock 2
Wing area: 15.21 m²
Wing span: 11.6 m
Aspect ratio: 8.8
Hang glider weight: 36 kg
Packed length: 3 m
Nose angle: 138°

=====================================

13tsyk1pSock.png (245.33 KiB) Viewed 2366 times

Regarding a later project called Piuma Project
by Yvon Perret, a PDF had the clip showing noting his earlier Sock. Piuma was not a HG.
=============================================