Aerodynamics of flapping-wing micro air vehicles

TL;DR: In this article, the effect of a dihedral angle on the generated thrust and normal force of a flexible flapping wing was investigated for the 25 cm and 74 cm wing-span models at different airflow velocities and flapping frequencies.

Abstract: The research study outlined in the paper addresses the aerodynamic features of flexible flapping wings used in micro air vehicles called ornithopters. Aerodynamic force measurements were conducted for the 25-cm and 74-cm-wing-span models at different airflow velocities and flapping frequencies. A series of experiments were conducted on the 25-cm flapping-wing model without free stream airflow. In order to study the effect of a dihedral on generated thrust and normal force, the model was modified to accommodate three values of dihedral angle. It appeared that the thrust force is higher for higher dihedral angle. Effects of a wing’s bending stiffness and of the wing root constraint on the generated thrust force and required power were investigated. The aerodynamic forces on flapping wings were studied with the stroke plane angle varied from horizontal to vertical. An important result was found that flapping wings do not exhibit a typical, abrupt stall seen with the fixed wings. Experimental results were analyzed in the framework of the momentum theory. The results of this study were realized in micro ornithopter designs that was successfully flight tested.