Modeling a Flapping Wing MAV: Flight Path Reconstruction of the Delfly II

Abstract

Flight identification techniques were used to excite the modes of a Flapping Wing Micro Air Vehicle the Delfly II. The flapper was flown in a flight chamber, where the position of eight markers placed on its structure was captured using high fidelity external tracking system, at 200Hz. The flight tests comprised step, doublet and triplet inputs on the control surfaces that were commanded by the autopilot during trimmed steady flight. The first step of the Two Step Method, known as Flight Path Reconstruction, was used to reconstruct the inputs and states, after assessing the quality of the recorded data, by means of differentiation and filtering. It was possible to identify two oscillatory modes: one longitudinal, similar to a phugoid, with a period of 1 second and a coupled lateral directional mode with a period of 0.9 seconds. The general aircraft equations of motion were used to estimate the aerodynamic forces and moments that act on the flapper during the maneuvers, under a set of non-flapping rigid body assumptions. The results point to coherent estimation of the aerodynamic forces. The moments around the lateral (y) and downwards (z) body axes, M and N moments respectively, seem to be well estimated for both the longitudinal and lateral/directional inputs on the elevator and rudder. However, the L moment around the longitudinal (x) body axis seems to have missing information around the maneuvers, due to the reconstruction method of the roll angles and roll rates. The good results point to the possibility of applying the second step of the Two Step Method for linear and non-linear aerodynamic model identification.