A Revised Blade Element Model for Vehicles with Flapping Wings

A blade element model utilizes regions of constant dynamic pressure to compute the lift and drag due to air flow on a lifting surface. In fixedwing aircraft, for zero or small sideslip angles, the blade element regions are along the entire chord of the wing at fixed spanwise locations. This assumption has also been used for flapping wing vehicles. However, flapping wing motion is rotational in nature. Hence, at a fixed spanwise location, the velocities of points of the wing along the chord are not constant. This work takes into account the rotational motion of flapping wings to accurately compute the velocity of any point on the wing. A double integration, of the velocity of any point on the wing, is then performed to determine the lift and drag due to wing motion. The wing is assumed to have a fixed angle of attack, but this revised model shows that the actual angle of attack can differ from the fixed value. A comparison is made between the conventional and revised blade element models and shows the differences between lift, drag, and angle of attack.