It was common to put them on flight test aircraft too. MD80 fuselage
909 (RIP) had one on the center windshield. More like a cord than the
light yarn we use. I don't remember how it was attached, probably to
one of the windshield bolts. One use may have been to maximize single
engine climb performance for the cert numbers.

I see more pictures these days of flight test aircraft with an extended
test probe on the nose. It looks like it carries alpha and beta vanes
so they probably don't bother with the string any more.

Andy