The alternative is to blend the airfoils to get aerodynamic washout and decreased stall speed at the tips. Martin Simons book describes this by using more camber at the tips, then using geometric washout to bring the aerodynamic AOA back to the same value. I have taken to this by using something like SA7035 at the root (2.5% camber) and SA7038 at the tip(3.25%camber) with the SA7036 and SD7037 between and washing the whole wing out. It is a near continuous twist to about 0.75 degreees - the approximate 0.75 degree (estimate) difference in zero lift angle.
I built a 10 foot set of wings like this and it was a nice flyer. I used the same templates to make a 2M. I hope it flies just as well.
The base assumption of LiftRoll and Lift3Span is a single airfoil accross the wing. I think it is based on a sd7037, but I may have this confused with something else.
If you are designing strictly for minimum sink to be at the lowest possible, then don't worry about what it will do at 60 mph when the Cl is 0.3 instead of 1.0. Use LiftRoll to make sure you aren't designing in a deadly tip stall. This is another compromise with efficiency.
I do not know how to estimate the actual performance numbers of these complex section wings. I bet that we would be entering the world of finite element analysis and other fun methods.
Tom Koszuta Western New York Sailplane and Electric Flyers Buffalo, NY
I can adjust the planform twist to get eliptical lift distribution at one AOA
It is then off at a different AOA.
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