... I just did - some live examples of biplane and
triplane -hedral, just as you would expect - you say you did
expect this, didn't you?

Yes, here's the essence of my original post:

"Friend of mine said at lunch today that the upper wings of biplanes
have no dihedral. .... I believe he was mistaken. ..... I think the
PT-17 and most other biplanes have dihedral in both wings."

My friend insists the PT-17, properly rigged, has no dihedral in the
top wing. My photo collection shows SOME PT-17s that clearly have
some dihedral, but perhaps they were modified.

It appears that the N3N, F3F and SBC had no dihedral in the top wing,
along with the Fokker D VII, Albatros D III and D V, but most WW I
biplanes and most biplanes in the museum at Pensacola did.

vince norris