ORIGINAL: RFJ
By the way, just to be fussy - this difference in wing and tail angles is called longitudinal dihedral. Decalage is the angular difference between the top and bottom wings of a biplane.
Not that I'd disagree with anything said here, on the contrary, I totally agree. Just to thank you, Ray, for illuminating a word I was musing about for a long time: decalage.
I adopted its meaning from a trustworthy source but was still in doubt. Now I remembered having a glossary of aeronautical definitions, and there's your definition of decalage. Nevertheless, American sources define decalage as "the difference in zero lift angles" (or chord lines, for that matter) "between the wing and horizontal stabilizer". So does [link=http://en.wikipedia.org/wiki/Decalage]Wikipedia[/link].
Now I searched in the glossary for a translation of our German term
Einstellwinkeldifferenz (abbreviated EWD), which means the difference of chord line (incidence) angles of wing and stab. The glossary translates it to "tail-setting angle", referring to British Standard 185, Sect. 5, No. 5211. The whole book is based on BS. Maybe our American friends really call that thing decalage while we in old Europe are a bit out of style.
This is all quite off-topic but nevertheless interesting, at least for me. Thanks again...