A two element aerofoil, and wing element based thereon, is provided, including a primary aerofoil element including a leading edge of the aerofoil and a secondary aerofoil element including a trailing edge of the aerofoil. A gap is provided between the primary aerofoil element and the secondary aerofoil element. The primary aerofoil element has at least one of a profile, orientation and location with respect to a respective at least one of a profile, orientation and location of the secondary aerofoil element that is configured for minimizing or avoiding accretion of contaminant on the secondary aerofoil element when subjected to an airflow that includes the contaminant, at least at one design set of conditions. A method for designing a two element aerofoil is also provided.