• NACA 2.5411-PT (Fig. 12.62)
The NACA 2.5411 is a four-digit NACA section with 2.5% maximum camber at 40% of chord, and 11% thickness.
The drag polar shows that the overall drag is low, and this gives a good first impression. However as shown in Fig. 12.63, the stall characteristics are undesirable. There is a smooth, continuous increase in lift up to a sharp and abrupt stall. Flight near maximum lift with this section would be exceedingly difficult because there is virtually no angle of attack margin between maximum lift and stall.
As mentioned in the discussion of the MB253515, a lift plateau with the associated high drag is desirable, as it provides warning that stall is imminent. Unless measures such as stall strips on the leading edge are used to alleviate this problem, the NACA 2.5411 and closely related sections (NACA 2412, NACA 24159) are not recommended for slow, thermal duration flying. However, its performance at high speed, such as is needed in windy conditions, is very good, and stall strips make the thermalling performance at least acceptable.
Also see: E374, CLARK-Y, DF101, SD5060 Digitizer plot: Fig. 10.23 Polar plot: Fig. 12.62 Lift plot: Fig. 12.63
Thickness: 11.00% Camber: 2.50%