The belt-rib concept: A structronic approach to variable camber

The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a "mechatronic" solution with hinges or linear bearings a "structronic" solution is chosen, where distributed flexibility allows the desired shape changes. The resulting system is not only easier to maintain due to the absence of wear, but also is structurally more reliable and substantially lighter. The new concept evolves from the classical wing structure. The classical rib, which is in charge of the wing section's stiffness, is replaced by a "belt rib," which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged. The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. After a first development stage, in which mainly the system's shape adaptability and the overall stiffness properties were investigated, further steps followed, focused on manufacturing, weight optimization and strength aspects. Recent developments dealt with the construction of a model with solid-state hinges, realized as hybrid glass fiber-carbon-fiber reinforced composite structure. The model is actuated mechanically by cables, which can be replaced by multifunctional actuators-like shape memory wires-in the future. The paper opens with an introduction about shape control of aerospace structures and variable camber in particular, in which the major advantages of a "structronic" approach with respect to classical solutions are discussed. Then the fundamentals of the belt-rib concept are sketched, with some significant results of the feasibility proof phase, followed by the description of the last developments. The conclusion summarizes the potential of a structronic approach to shape control with an outline of possible future work.