In order to fulfill these restrictions it is a common practice to use thick airfoils (airfoil thickness to chord ratio: t/c > 0.25) and even circular section geometries.
The main problem is that the modified airfoil has a larger airfoil thickness and a smaller camber per chord length.
The airfoil modification method consists of symmetrically adding thickness to an airfoil in such a way that the "nose" geometry, airfoil thickness and camber remain the same, but obtaining a blunt trailing edge.
A signal to noise ratio study based on Taguchi methods  is presented to show the main effect on aerodynamic performance of the different trailing edge thicknesses under different modification methods, as well as to give an idea about the opposite effects between camber, airfoil thickness and trailing edge configuration.
The main advantage of these methods of airfoil modification is that they preserve important geometric aspects of the airfoil such as airfoil thickness, camber line, chord line orientation and "nose geometry" .
This family was selected because its airfoils can be parameterized using three values: mean camber (first digit), camber position (second digit) and airfoil thickness (third and fourth digits).
Trailing edge thickness increases the maximum lift coefficient and the critical angle of attack, whereas airfoil thickness produces the opposite effect.
Mean camber reduces the [alpha]@[C.sub.lo], hence producing a higher [C.sub.l] curve, while airfoil thickness increases the [alpha]@[C.sub.lo].
The cutting off method produces modified airfoils with higher airfoil thickness, smaller mean cambers and a new chord line orientation.
* Maximum lift coefficient and stall angle of attack increases are the result of an overlap effect between opposite effects: trailing edge thickness increases both, but airfoil thickness and lower camber decrease them both.
The added thickness method produces airfoils that conserve the airfoil thickness, camber line distribution and chord line orientation; consequently the lift curve displacement is not present.