A gurney flap arrangement comprises: an airfoil with an opening in a surface of the airfoil; a gurney flap having a first position in which at least a portion of the gurney flap extends through the opening and projects outwardly from the airfoil surface, and a second position in which the gurney flap does not project from the airfoil surface or projects outwardly from the airfoil surface to a lesser extent; and a seal disposed about the opening to seal a gap in the opening between the gurney flap and the airfoil.