Päivää!
Jukka wrote:
"But consider Brewster Buffalo, it had excellent stall characteristics though it had NACA 23018 at root and 23009 at tip!"
Lavochkins had more tapered wing planform (lower tip chord / root chord -ratio) than Brewster and so more prone to drop their wing tips. I do not know if Brewster and Lavochkins had geometric twist (washout). Washout would tame the stall.
You (Jukka) surely remember the Brewster-type wing for VL Pyry (the type had elliptical wing). The new wing cured the wing drop problem, but new wings were more expensive than modifying the elliptical wings with leading edge slots.
For wing design see also this:
http://www.desktopaero.com/appliedae...ingparams.html
(Don't know if it is the best or even good one, but was the first suitable one I found with quick search on Internet).
tv.
Kari