An airfoil ( in American English ) or aerofoil ( in British English ) is the shape of a wing or blade ( of a propeller , rotor , or turbine ) or sail as seen in cross-section .
An airfoil ( in American English , or aerofoil in British English ) is the shape of a wing , or blade of a propeller , the blade of a ship 's screw or the shape of a sail as seen in cross-section .