Rotor blade system

A rotor blade system having a plurality of rotor blades,

• wherein at least one of the rotor blades includes an outer surface having generally opposing first and second surfaces, the rotor blade including a fluid flow altering surface positioned relative to one of the first or second surfaces which is moveable between first and second positions, the fluid flow altering surface forming a substantially continuous surface of the first or second surface when in the first position,
• wherein movement of the fluid flow altering surface is effected by an expandable member made from a resiliently flexible material and which is inflatable and deflatable, the expandable member including a cavity for receiving a fluid,
• wherein the fluid flow altering surface is a surface of the expandable member,
• wherein the expandable member is positioned at or close to a tip edge of the rotor blade,
• wherein the fluid flow altering surface includes or is connected to a stiffening member for providing resistance to forces experienced by the member or the surface arising from airflow,
• wherein the stiffening member is attached to an inwardly facing surface of the fluid flow altering surface,
• wherein the respective one of the first or second surfaces includes a recess to receive the whole or a part of the stiffening member and to receive the whole or a part of the expandable member.