I recently scratch built a Dirty Birdy-all balsa. I used Compufoil and made the root rib NACA 0015 and the tip rib NACA 0012. What does this do to tip stalling?

if all is straight and strong weight is held down - nothing to fear-
that design would fly fine with 10 % airfoils if the weight was held down and the wing were strong enough
all of that era pattern planes used kinda fat wings to allow for higher AOA on landings and to make em strong enough. we ended up doing 12% root and 10% tips on our last Tipo designs -also kept dropping weight - down to about 7 lbs - It all just got better .
Back when -I saw some of those at up to 11 lbs-

The planform often has more effect on tip stalling than aero-twist will. Since the Dirty Birdy has a slight taper to the chord, and was designed to be able to snap (so the wing was made to more easily tip stall than not) whatever effect won't be enough to change what you'd have gotten with the original airfoils. Or what that planform is going to do. Which is more often stall from the tips.

Anyway...... with symmetrical airfoils of the same family, thicker usually stalls at greater AOA. But if you look at the original plots NACA made back in 1931, you see those two stalled at about the same AOA. Same chord test profiles used, same tunnel, same atmospheric pressures, same RN. One went slightly over 22degrees. The other went slightly more than that, but obviously less that 23degrees.

Since your real life setup has one with less chord than the other, that might have more effect than the airfoils do. And the planform is going to have it's effects that a half-degree difference in stall angle won't even phase.

What might the change in profiles do in the fairly complex "environment" they've been built into? Probably nothing much compared to the effect the planform would have.

Dick & da Rock,

Thanks for the reply. If the plane seems to tip stall to quickly on landing, I at least now know I did not cause this condition by changing the tip root.

Bob