Dynamics and Aeroelasticity of Hover-Capable Flapping Wings: Experiments and Analysis

This dissertation addresses the aerodynamics of insect-based, bio-inspired, flapping wings in hover. An experimental apparatus, with a bio-inspired flapping mechanism, was used to measure the thrust generated for a number of wing designs. Bio-Inspired flapping-pitching mechanisms reported in literature, usually operate in oil or water at very low flapping frequencies (~0.17 Hz). In contrast, the mechanism used in this study operates in air, at relatively high frequencies (~12 Hz). All the wings tested showed a decrease in thrust at high frequencies. A novel mechanism with passive pitching of the wing, caused by aeroelastic forces, was also tested. Flow visualization images, which show the salient features of the airflow, were also acquired. At high flapping frequencies, the light-weight and highly flexible wings used in this study exhibited significant aeroelastic effects. For this reason, an aeroelastic analysis for hover-capable, bio-inspired flapping wings was developed. A finite element based structural analysis of the wing was used, alongwith an unsteady aerodynamic analysis based on indicial functions. The analysis was validated with experimental data available in literature, and also with experimental tests conducted on the bio-inspired flapping-pitching mechanism. Results for both elastic and rigid wing analyses were compared with the thrust measured on the bio-inspired flapping-pitching mechanism

Whirl Flutter Stability of Two-Bladed Proprotor/Pylon Systems In High Speed Flight

The lack of polar symmetry in two-bladed rotors leads to equations of motion with periodic coefficients in axial flight, which is contrary to three or more bladed rotors that result in constant coefficient equations. With periodic coefficients, the analysis becomes involved, as a result very few studies have been directed towards the analysis of two-bladed rotors. In this paper, the aeroelastic stability of two-bladed proprotor/pylon/wing combinations is examined in high speed axial flight. Several parametric studies are carried out to illustrate the special nature of two-bladed proprotors and to better understand the mechanism of whirl-flutter in such rotors. The wing beam bending mode for two-bladed rotors is found to be stable over the range of parameters examined, a behaviour very different from three-bladed rotors. Also, the wing torsion mode exhibits a new type of instability similar to a wing torsional divergence scouring at I/rev frequency. This type of behaviour is not seen in three and more bladed rotors. The interaction between wing chordwise bending and torsion modes is found to be much greater in the case of two-bladed rotors and, over the range of parameters considered, these two modes govern the stability of the system

Collaborative Pazy Wing Analyses for the Third Aeroelastic Prediction Workshop

In this paper, collaborative aeroelastic analyses of the Pazy Wing are presented, which support the activities of the Large Deflection Working Group, a sub-group of the 3rd Aeroelastic Prediction Workshop (AePW3). The Pazy Wing is a benchmark for the investigation of nonlinear aeroelastic effects at very large structural deflections. Tip deformations on the order of 50% semi-span were measured in wind tunnel tests at the Technion - Israel Institute of Technology. This feature renders the model highly attractive for the validation of numerical aeroelastic methods for geometrically nonlinear, large deflection analyses. A distinguishing feature of the Pazy Wing is that its flutter speed is a function of the static deformation, and capturing this effect requires a nonlinear aeroelastic framework which allows for stability (flutter) analyses about steady states of large deformations. In particular, the flutter characteristics of the model are dominated by a hump mode which develops due to the coupling of the first torsion and the second out-of-plane bending mode; this hump mode moves towards lower airspeeds as the steady structural deformation increases. Different nonlinear aeroelastic solvers were applied by the authors to obtain static coupling and flutter results for a series of airspeeds and angles of attack. The results reveal that the decisive nonlinear effects were captured very well by the applied methods and computational tools