noel.wade wrote:

And regarding the positive lift on the tail: Your explanation makes
sense in light of the (basic) modelling I've done of spanwise lift
distribution... However the wing airfoil still exhibits a negative
(i.e. nose down) pitching moment. So something needs to counteract
that force - especially because positive lift from the tail would
amplify the nose-down trend. Are you saying that the CG is
sufficiently far aft that it provides the "counterbalancing force", to
put it in layman's terms? I hate to keep repeating his name (but his
book is the most comprehensive one that I've read) - however, Thomas
talks about "aft CG" a lot, and in his measurements you never see
anything further aft than about 50% of the MAC. And as a result of all
of this, doesn't a positive-lifting tail then limit your forward CG
position?

I think I had it backwards before - according to Thomas, the stabilizer
must provide upward lift when the wing is operating at a high lift
coefficient (like thermalling), and a downward load at a low coefficient
of lift (like cruising). This is on page 133 of my edition, in the
"Longitudinal trim in unaccelerated flight" portion.

--
Eric Greenwell - Washington State, USA
Change "netto" to "net" to email me directly

"Transponders in Sailplanes" on the Soaring Safety Foundation website
www.soaringsafety.org/prevention/articles.html

"A Guide to Self-launching Sailplane Operation" at www.motorglider.org