Figure 5-13 plots L/D (lift to profile drag ratio here) against wing thickness. Again it is evident that efficiency changed according to angle of attack and thickness. Clearly L/D was highest at the shallower angles where lower drag was generated, but of more interest here is that in general, peak L/D occurred with a wing section of 16% thickness from 4๐ to 12๐ angle of attack. Intriguingly, at the steepest angle of attack, 16๐, maximum L/D occurred with 20% thickness, and this obviously due to the higher downforce generated in this case.