write:The third airfoil shape has a relatively low maximum thickness and is more typical of those used in high speed airplanes with swept wings. As its AOA is increased toward its critic

even at low angles-of-attack. Despite its inefficien-cy in turning dynamic pressure into lift
this airfoil shape has one redeeming safety-re-lated characteristic; its stall is gradual. CL falls off relatively slowly as the critical AOA is exceeded.The third airfoil shape has a relatively low maximum thickness and is more typical of those used in high speed airplanes with swept wings. As its AOA is increased toward its critical angle of attack
a vortex should form shortly aft of its leading edge. Although this vortex will normally reattach the flow and delay the stall
it can also “burst” and allow the airflow over virtually the entire wing to separate. The sudden flow separation will cause an abrupt stall.The last airfoil shape to be covered takes the typical general aviation wing airfoil and gives it a relatively small or sharp leading edge radius. This smaller leading edge radius will precipitate premature separation
and it will do it in a rather abrupt man-ner. This not only decreases CLmax
it also increases the abruptness of the stall
causing the CL versus AOA to drop sharply as the AOA moves past the critical AOA. When properly designed into the airfoil
a sharp leading edge over a small portion of the wing can provide the pilot with a passive (it has no moving parts and requires no power) stall warning device. Look at the stall strip on the leading edge of many general aviation aircraft and even some military airplanes. However
when mother nature modifies the leading edge of an airfoil
perhaps by adding some ice
the consequences can be tragic.Figure 27-2. Camber Changing and Energy Adding High Lift Devices.Figure 27-3. Effect on of High Lift Devices on an Airfoil’s CL – AOA Curves.