Mechanics of multifunctional wings with solar cells for robotic birds

Abstract

Inspired by nature, Flapping Wing Aerial Vehicles (FWAVs), also known as Robotic Birds, use flexible compliant wings that deform while flapping to generate the aerodynamic forces necessary for flight. These vehicles sustain short flights due to the limited payload for on-board energy storage. Using flexible solar cells, energy can be harvested during flight to extend the flight of the FWAV. By integrating flexible solar cells into the wing structure of the FWAV, more electrical power is produced but at a cost. The solar cells increase the overall mass of the vehicle while also altering the deformation of the wing. These changes to the wing ultimately have an effect on the performance of the FWAV. In this paper, three different wing designs were designed, built and tested. The Robo Raven platform was used for each wing design. The first design was the original wing design without solar cells. The second design hosted 12 solar modules integrated into the wings. The final design was composed of 22 solar modules integrated into the wings. The aerodynamic forces generated by each wing design were observed in a wind tunnel while the FWAV was attached to a six DOF load cell. To understand how the wings changed with respect to deformation each wing was also observed in the wind tunnel 3D using Digital Image Correlation (DIC). The results from DIC demonstrated a correlation between the lift and thrust forces produced by the wings and the biaxial and shear strains observed on the wings surface respectively. By observing the power output form the solar cells while flapping, the corresponding wave form correlated well to the thrust force measurements. This allows th solar cells to also behave as sensors while flying. The resulting platform, Robo Raven III, is the first ornithopter to fly while using energy harvested from solar cells.