Originally Posted by
dubbleyew eight
a wing does not have to be slipping for dihedral to have effect.
Absolutely!
You just need to think about the lift vectors when rolling a bit left or right.
With anhedral, the 'opposing' wing's Lift vector component in vertical direction will increase (Lift x cos(dihedral - roll)), whereas on the 'supporting' side it will decrease Lift x cos (dihedral + roll).
You get a self righting moment of the wing's lift. Then you need to consider the leverage of this stabilising force against the CG. If the CG is higher than the combined vertical position of where the lift is produced, these two moments will act against each other. If the postion where the Lift is applied is above the Cg the two moments will complement each other.
If you have anhedral, the effect will be inverse.
Therefore for a low wing aircraft you want to have rather dihedral if you don't want to go too aerobatic. With a low wing and no dihedral the aircraft will constantly try to roll off.
In a high wing design the leverage between Cg and the point where the Lift is applied will already cause a stabilising moment. This leads to increased aileron forces if you want to bank.
In order to avoid excessive self righting and thus excessive aileron forces for turning (which would increase drag and structural loads) high wing aircraft often get anhedral, especially bigger ones where the mentioned factors become significant.