Hello everybody,

I have a question for those familiar with the Xfoil program.
Can someone tell me in which frame are computed the lift and drag coefficient CL & CD?
Is it in the wind frame or the in the body (airfoil) frame ? The difference between the two being the rotation worth the incidence alpha.

Thanks for the help.

Regards,
Paul

By definition, the lift coefficient, Cl, is perpendicular to the velocity vector and drag coefficient, Cd, is parallel to it. The nomal force coefficient, Cn (or Cz), is defined as being perpendicular to the chord line and axial force Ca (or Cx) is parallel to it. XFOIL results depict Cl and Cd by the above definitions.

Thanks a lot.

Best regards,
Paul