The great disadvantage of a fat plate as a rudder is the fast low separation; the low will separate already at small angles of attack. A fat plate stalls already at a small angle of attack. A wing section thickness, t, of 9 percent of the chord length, c, is often considered as a practical minimum value, so t=c > 0:09:
The lift, drag and moment coefficients (CL, CD and CM) of symmetrical NACA (National Advisory Committee for Aeronautics) wing sections for 0:06 6 t 6 0:18 and an aspect ratio