Meeting Abstract

20.5  Friday, Jan. 4  Direct aerodynamic force measurements in avian flight support active upstroke hypothesis LENTINK, D; Stanford University; Wageningen University; Harvard University dlentink@stanford.edu

Birds dynamically change the shape of their wing during the stroke, resulting in dramatic differences in wing shape between the up- and down-stroke. The wing is partially folded during the upstroke, which suggests that the upstroke of birds might not actively contribute to aerodynamic force production. This hypothesis is supported by the significant mass difference between the large pectoralis muscle that powers the down-stroke and the much smaller supracoracoideus that drives the upstroke. Previous workers used indirect or incomplete techniques to measure the total force generated by bird wings ranging from muscle force, airflow, wing surface pressure, to detailed kinematics measurements coupled with bird mass-distribution models to derive net force through second derivatives. I will present a new validated and verified technique that measures aerodynamic force directly time-resolved. It does not require exposing animals to laser light, surgery or sacrificing animals to obtain mass distribution – and is more precisely verified and validated compared to previously published methods. Results obtained for 5 slowly flying lovebirds (Agapornis roseicollis) show that the upstroke of birds is surprisingly active during slow hovering flight. The method is scalable and can be applied to all flying animals from birds and bats to insects. Other potential applications could include swimming.