coefficient modification

Hello !

In his article about VPP (1) mr. Oliver states that: ' empirically derived lift and drag coefficients ( such as those in IMS ) implicitly acount for some average leeway...when leeway is actually incorporated in the wind triangle, empirical sail coefficients are no longer correct and must be modified to remove the built-in mean leeway.'
Does it mean that we must find lift and drag coefficients as function of sail incidence angle and not as functions of apparent wind angle, and how we can modify IMS coefficients for that purpose?

Sincerely,

Fradrigo

(1) Oliver,J.C. & Claughton,A.R.
' Development of multi-functional VPP for sailing yachts'
International Conference CADAP, RINA 1995