sin αst

D
Airfoil
Figure D.1 displays the lift coefficient Cl, drag coefficient Cd and glide ratio GR = Cl/Cd of the
NACA 4412 airfoil as a function of the angle of attack �.
Coefficient of lift and drag, Cd, Cl [-]
Figure D.1: Lift coefficient Cl, drag coefficient Cd and glide ratio GR = Cl/Cd of the NACA 4412
airfoil
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0 10 20 30 40 50 60 70 80 90
Angle of attack, � [�]
From figure D.1 it can be seen that the onset of stall is at an angle �st of 13�. For angles of
attack less than this the airfoil data is obtained from [47] and conveniently approximated
by following 4th degree polynomial equation in the rotor design tool:
Cd �� l k0 � k1� k2� 2
� k3� 3
� k4� 4
=
�
C_l
C_d
GR
180
160
140
120
100
80
60
40
20
0
Glide ratio, GR [-]
(D.1)
143