Experimental Determination of Ornithopter Membrane Wing Shapes Used for Simple Aerodynamic Modeling

Abstract

This paper addresses a method to analyze flapping membrane wing aerodynamics using kinema tic data. An alternative to computational fluid dynamics, this experimental method places small reflective markers on a wing and tracks them using a Vicon motion measurement system. The dynamic membrane shapes of the ornithopter wing are then quantified as moving points in a three dimensional coordinate system. This motion tracking process was completed for two ornithopters with approximately one meter span rip -stop nylon wings over a series of flapping frequencies. Aerodynamic loads were recorded in additi on to wing shape data to confirm the aerodynamic modeling results. The wing shape data was used to form an analytical aerodynamic model that uses blade element theory and quasi -steady aerodynamics to account for the local twist, stroke angle, membrane shap e, wing velocity and acceleration. Results from the aerodynamic model show good correlation between the magnitude of lift and thrust produced but some phase errors exist between the measured and calculated force curves .