Meeting Abstract

28.6  Friday, Jan. 4  The cost of performance: power cost and aerodynamic force generated by varying wingbeat kinematics BAHLMAN, JW*; SWARTZ, SM; BREUER, KS; Brown University; Brown University; Brown University joseph_bahlman@brown.edu

Bats display a wide range of flight behaviors, including steady flight, rapid acceleration, sharp turns, and load carrying. These behaviors require different combinations of lift and thrust, which are achieved by varying wing kinematics. Although the kinematics associated with different flight behaviors have been studied, it has not been possible to directly relate specific kinematic parameters to force production because flapping animals change multiple parameters simultaneously. To isolate the effect of specific kinematic parameters on aerodynamic force, and measure the energetic cost associated with each flapping motion, we designed, built, and tested a multi-articulated robotic bat wing that was instrumented to measure net lift, thrust, and mechanical power. During testing in a wind tunnel, we varied five kinematic parameters: four affecting wing motion (wingbeat frequency, wingbeat amplitude, stroke plane, downstroke ratio), and one affecting dynamic morphology (wing folding on upstroke). For each kinematic parameter, we described its relationship with net lift, net thrust, and mechanical power as the parameter varied across most of the range observed in the model bat species, Cynopterus brachyotis . Each parameter affected lift, thrust, and power in a different manner. For example, increasing amplitude produced additional force at a lower power cost than increasing frequency. Wing folding on the upstroke increased net lift and decreased power cost albeit with reduced thrust. The different relationships between kinematic parameters with lift, thrust, and power can inform modeling of how all the kinematic parameters can collectively be varied to produce the combination of forces required for different flight behaviors.