Conclusion and Recommendations
NACA airfoils and two-parameter s-shaped airfoils are studied in ground effect.
Lift coefficient of airfoils increase when they approach to the ground. But for airfoils with concave lower surface, a sudden decrease in lift coefficient occurs at some very close ground clearances for low angles of attack.
Aerodynamic center in angle of attack of airfoils moves towards the trailing edge when the ground clearance decrease.
None of NACA profiles obeys to Irodov’s stability criterion.
The increase in the lift coefficient of the s-shaped airfoil with convex lower surface is more considerable than that of the airfoil with concave lower surface.