Aerofoil or hydrofoil

An aerofoil or hydrofoil, comprising:

• a central panel having a central axis extending spanwise, said central panel being of symmetrical cross section of each side of said axis and having two opposite side edges;
• at least two lateral panels each having first and second side edges;
• means hinging each of said two lateral panels adjacent said first side edge thereof to said central panel at a respective one of said two opposite side edges of the central panel, to provide two alternative leading edges so that each lateral panel may pivot between an extended condition and a folded condition wherein the respective lateral panel is doubled back upon at least one of the central panel and the respective other lateral panel, to provide two alternative leading edges, the two lateral panels being of similar cross-section, and generally symmetrical with respect to said central axis, so that when said one lateral panel is extended and the other is folded an aerofoil or hydrofoil that is nonsymmetrical in cross-section is formed, which is substantially a mirror image of the aerofoil or hydrofoil which may be formed by extending said other lateral panel and folding said one lateral panel, tie means interconnecting the lateral panels to move in concert, as follows:
• said one lateral panel folds as said other lateral panel extends and said other lateral panel folds as said lateral panel extends;
• the effective leading edge of the aerofoil or hydrofoil incorporating said first side edge of whichever of the lateral panels as is in said folded condition.