An analytical study on the effect of active wing folding and twist on the aerodynamic performance and energy consumption of a bio-inspired ornithopter

The vast majority of bird scale ornithopters still utilize single active degree of freedom wings in which the flapping motion is actuated at the root of the wing. Yet, as we look to nature, we see that birds utilize more than one active degree of freedom. The purpose of this study is to determine the effect of dynamic wing twist and wing folding on lift and thrust produced by a flapping wing as well as their effects on power consumption. The method of analysis this study utilizes is a version of MST, a Modified Strip Theory, in order to model the aerodynamics of the wing. Both non-folding and folding wing scenarios are considered where the parameters varied include dynamic wing twist amplitude, time averaged wing twist, and dynamic wing twist and flapping phase offset. Furthermore, unlike many other theoretical studies, when examining power consumption both the aerodynamic force as well as inertial effects are considered as inertial effects can be of the same order as aerodynamic force. Moreover, the negative power occurring on the upstroke cannot be always considered to lead to energy transfer back into the system as many studies assume. Thus, this study discusse the impact of negative power and its implications on ornithopter design.