thank bmathews,

i think i maybe understand a bit now.

still a bit confused though.

i use a program call liftroll to dising wing and i dising wing with c/l lower toward tip (my mistake in writing to say c/l higher) so lower c/l curve toward tip shows increased lift than at root.

root should then stall first correct? then tip keep flying and tip stall reduced even though tip airfoil is thinner and no washout is applied.

or what if use thinner airfoil at root and accross span of wing and then use thicker airfoil at tip with washout to compsate for zero lift angle difference of airfoils so even though tip is thicker and washout used then wing 'sees' same zero lift angle accros span?

so tip stall prevented and wing works at same effecency accross span and drag reduced.

i read some book by martin simons and i not sure if i understand what he is saying but i think he tell that above is good method.

rcuniverse is a great help and many thanks to all. i learning much now.



Hai Dang