Aerofoil structure

An aerofoil structure arranged for airborne flight under the influence of an air stream comprising an envelope of flexible light-weight material having leading and trailing edges with respect to air flow, the leading edge facing upstream in flight, said envelope having upper and lower surface members, a plurality of separator members between and joined to the surface members to divide the interior of the envelope into a plurality of elongate chambers, and an elongate opening along the leading edge between the surface members to permit the ingress of ram air to inflate the chambers, the separator members being shaped to cause the upper and lower surface members to assume an aerofoil section in the direction of flow of the air stream;

• an elongate spar positioned along the leading edge of the bottom surface member transverse the direction of air flow, the ends of the bottom surface member leading edge and the ends of the spar being arranged to form anchor points respectively and a pair of control lines, one secured respectively to each of said anchor points, the spar being sufficiently flexible to assume a degree of curvature when the structure is in flight.