Expert: Paul Soderman - 11/10/2009

Question
QUESTION: I have a model airplane that has a  polyhedral configured wing. I am considering changing the configuration to just have the dihedral. I don't need the increased stability. Will this change enhance the wing's lift?

ANSWER: Polyhedral and dihedral wings are configured for stability reasons. If the wings are disturbed from wings level the ensuing sideslip on a dihedral wing will cause increased lift on the lower wing and return the wing to level condition.  So, even though polyhedral and dihedral have a lot to do with lift in sideslip, they have no significant effect on level flight.  On the other hand, a polyhedral or dihedral wing would have a vector component of lift in the side direction.  Changing the wing angle would restore that small lift vector component to the vertical and could be easily calculated.  So, I believe the answer to your question is probably not - in normal flight polyhedral and dihedral effects do not affect lift except for the minor vector component in the side direction that would be changed if polyhedral or dihedral angles were removed.

---------- FOLLOW-UP ----------

QUESTION: Tank you for such a deliberate answer to my previous question. Second question. what effect will wing tiplets have on the lift performance of my polyhedral configured wing?  

Answer
I believe you mean winglets.  Winglets improve the efficiency of a wing primarily by reducing induced drag.  They have no direct effect on the lift.  However, if drag goes down you can reduce thrust and maintain speed or maintain thrust and increase speed.  If speed increases, lift increases so you can reduce angle of attack to maintain lift equal to weight in level flight.  Now you have less parasite and form drag.  It is all good.