Morphing activities at the DLR and future perspectives

Kurzfassung

For the past 20 years the DLR Institute of composite structures and adaptive systems is dedicated to the research on shape adaptation of all kinds of structures. Two projects that have been related to rotors and fixed wings are presented: active twist for higher harmonic control and morphing for leading edge devices. Regarding the active twist the goal of the current investigation is a high frequency (up to 6/rev) twist deflection of the blade for individual blade control with relatively small amplitudes. The basic princi-ple of this technology is the skin integration of patch type actuators to introduce shear strain into the skin. Piezoceramic d33 actuators are used for such purposes. The commercially available macro fiber composites were used for the DLR blades which are based on the passive BO 105 blade. Those blades are made of GFRP with a C spar and a rectangular plan form. The profile is NACA 23012. At the DLR such model rotor blades (radius 2 m) have been designed, built and tested. They show static tip twist amplitudes of ±2°, even under centrifugal loads. The dynamics needed to excite a blade at frequencies up to 100 Hz is given by the piezoceramic actuators. Cur-rently the blades for a fully instrumented rotor are being built so they can be tested in a wind tunnel in 2013. Large deformation morphing has been investigated with the goal to realize a smart seamless lead-ing edge for fixed wing aircrafts. This system consists of a kinematic chain which is holding the skin in place. The skin is designed flexible enough to be morphed into the take off and landing shape but strong enough to carry the aerodynamic loads into the substructure and to bare the strains of morphing. In order to do so, a skin design process is established, which allows to tailor the skin thickness in a way that the displacements introduced by the kinematics will morph the skin into the desired shape. Also the load introduction into the skin is of interest. In the end omega stringers are designed to distribute the load of morphing deflections into the skin, taking into account the string-ers stability and strength. The difference between the aerodynamically wanted target shape and the achieved shape is within tolerable limits. Besides the skin it is an important task to design the kinematics to deploy to a position of approx. 18 degrees. The kinematics has to follow the trajecto-ries given from structural investigations of the skin with minimum deviations. The experiences from these investigations are a great prerequisite for research towards rotor morphing.