Stability in Flapping Flight for Two Different Robotic Flappers

Passive stability has important implications for maneuverability during flight. To better understand bird and bat flight, and to aid in the development of controlled flight in flapping-wing drones, we characterize the static longitudinal stability of two robotic flapping systems operating in different parameter spaces. One flaps at high frequencies (~10 Hz) with light flexible wings (~0.5 grams) while the other flaps at moderate frequencies (~5 Hz) with heavier rigid wings (~10 grams). For each system, we mounted the robot in the wind tunnel test section and recorded triaxial forces and moments over a range of wind speeds, flapping frequencies, and pitch angles. Phase- and cycle-averaged data are recorded and used to assess static longitudinal stability as a function of flight kinematics, body and wing geometry. The results are compared with a quasi-steady blade element model and areas of agreement and disagreement are identified and explained.