Concept of a variable chord-extension

Kurzfassung

Among all kinds of aircraft, helicopters are standing out due to their capability for both forward flight and hovering. Thisrange of flight conditions requires a special blade design, resulting in a rotor blade geometry, which represents acompromise between the different flight conditions. Morphing rotor blades could address this issue, by changing the rotorblade shape according to the demands of the current flight state. From rotor dynamic calculations it is known, that longerchord length at the blade root and increased pre-twist would increase the performance in hover [1,3], whereas shorter chordand less twist are beneficial for fast forward flight.Based on this assumption, a structural concept has been worked out for a blade design with a variable chord length in therotor root region. The model, which belongs to that concept forms the basis of a performance calculation.The structural concept consists of a pivot point at around 60% R and the chord extension is linearly increasing all theway to the blade root at 22% R. In this region an auxiliary spar is dividing the blade into a conventional rigid front part and amorphing rear part, whose structural design is the main focus of this paper. It consists of two components: a flexible skinmade of rubber-like EPDM material, which is reinforced in the spanwise direction by fibers, as well as an inner supportstructure.The design drivers for the skin thickness are shape accuracy on one end and actuator force to extend the mechanism andstretch the skin on the other end. The underlying support structure consists of vertical GFRP extending in span wisedirection. Design parameters for those webs are the distance between webs, which relates to the skin design, as well as thethickness of the members, which influences the overall stiffness of the design. The publication will present a workflow, inwhich the rotor is being structurally designed coming all the way from a generic CAD model, considering cg location as wellas elastic deformation of the elastic skin and calculating