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Wing 113
13-3.1 Lift
The wing lift is defined in terms of lift-curve slope CLα and maximum lift coefficient CLmax (based
on wing planform area). The three-dimensional lift-curve slope is input directly or calculated from the
two-dimensional lift-curve slope:
CLα =
cℓα
1+cℓα(1 + τ)/(πAR)
where τ accounts for non-elliptical loading. The effective angle-of-attack is αe = αwing + i − αzl, where
αzl is the angle of zero lift; in reverse flow (|αe| > 90), αe ← αe − 180 signαe. Let αmax = CLmax/CLα be
the angle-of-attack increment (above or below zero lift angle) for maximum lift. Including the change of
maximum lift angle caused by control deflection, Amax = αmax +Δαmaxf and Amin = −αmax +Δαmaxf.
Then
⎧
CLααe +ΔCLf
Amin ≤ αe ≤ Amax
⎪⎨
π/2 −|αe|
(CLαAmax +ΔCLf )
αe >Amax
CL =
π/2 −|Amax|
⎪⎩
π/2 −|αe|
(CLαAmin +ΔCLf )
αe 90), αe ← αe −180 signαe. For angles of attack less than a transition angle αt, the drag coefficient
equals the forward-flight (minimum) drag CD0 plus an angle-of-attack term and the control increment.
If the angle-of-attack is greater than a separation angle αs αs; and otherwise
CDt = CD0 (1 + Kd|αt| Xd + Ks(|αt|−αs) Xs )+ΔCDf
π |αe|−αt
CDp = CDt +(CDV − CDt) sin
2 π/2 − αt