Thick Airfoil Design
The difficulty with thick airfoils is that the minimum pressure is decreased
due to thickness. This results in a more severe adverse pressure gradient
and the need to start recovery sooner. If the maximum thickness point is
specified, the section with maximum thickness must recover from a given
point with the steepest possible gradient. This is just the sort of problem
addressed by Liebeck in connection with maximum lift. The thickest possible
section has a boundary layer just on the verge of separation throughout
the recovery.
The thickest section at Re = 10 million is 57% thick, but of course, it
will separate suddenly with any angle of attack.
