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114 Wing<br />
Optionally there might be no angle-of-attack variation at low angles (Kd = 0and/or Ks = 0), or<br />
quadratic variation (Xd =2), or cubic variation for the separation term (Xs =3). For sideward flight<br />
(v B x =0) the drag is obtained using φv = tan −1 (−v B z /v B y ) to interpolate the vertical coefficient: CD =<br />
CD0 cos 2 φv + CDV sin 2 φv. The induced drag is obtained from the lift coefficient, aspect ratio, and<br />
Oswald efficiency e:<br />
CDi = (CL − CL0) 2<br />
πeAR<br />
Conventionally the Oswald efficiency e can represent the wing parasite-drag variation with lift, as well<br />
as the induced drag (hence the use of CL0). The wing-body interference is specified as a drag area, or a<br />
drag coefficient based on the wing area. Then<br />
<br />
<br />
D = qSCD = qS CDp + CDi + CDwb<br />
is the drag force. The other forces and moments are zero.<br />
13-3.5 Wing Panels<br />
The wing panels can have separate controls and different incidence angles. Thus the lift, drag,<br />
and moment coefficients are evaluated separately for each panel, based on the panel area Sp and mean<br />
chord cp. The coefficient increments due to control-surface deflection are calculated using the ratio of<br />
the control-surface area to panel area, Sf /Sp = ℓf fb. The lateral position of the aileron aerodynamic<br />
center is ηabp from the panel inboard edge, so y/(b/2) = η E(p−1) + ηabp/(b/2) from the wing centerline.<br />
Then the total wing coefficients are:<br />
CL = 1 <br />
SpCLp<br />
S<br />
CM = 1<br />
Sc<br />
Cℓ = 1<br />
S<br />
CDp = 1<br />
S<br />
SpcpCMp<br />
SpCℓp<br />
SpCDpp<br />
The three-dimensional lift-curve slope CLα is calculated for the entire wing and used for each panel.<br />
The induced drag is calculated for the entire wing from the total CL.<br />
13-3.6 Interference<br />
With more than one wing, the interference velocity at other wings is proportional to the induced<br />
velocity of the wing producing the interference: vF int = KintvF ind . The induced velocity is obtained<br />
from the induced drag, assumed to act in the kB direction: αind = vind/|vB | = CDi/CL = CL/(πeAR),<br />
vF ind = CFBkB |vB |αind. For tandem wings, typically Kint =2for the interference of the front wing on<br />
the aft wing, and Kint =0for the interference of the aft wing on the front wing. For biplane wings, the<br />
mutual interference is typically Kint =0.7 (upper on lower, and lower on upper). The induced drag is<br />
then<br />
CDi = C2 <br />
L<br />
+ CL αint =<br />
πeAR C2 <br />
L<br />
+ CL Kintαind =<br />
πeAR C2 <br />
L<br />
+ CL<br />
πeAR <br />
CL<br />
Kint<br />
πeAR<br />
where the sum is over all other wings.<br />
other wing