Out-of-plane permalloy magnetic actuators for delta-wing control

INTRODUCTION The goal of this project is t o demonstrate that a collection of micro-machined actuators can control a macro object, provided that a proper controlling mechanism exists. In our case, we intend t o use a linear array of out-of-plane magnetic actuators t o crea te a rolling moment on a tail-less delta-wing model, utilizing a known mechanism in delta-wing theory that allows micro actuation to have an amplified, macro effect. A delta-wing is one of the fundamental configurations for generating lift forces and its aerodynamic control is of great importance t o the aeronautics society [1,2]. When laminar air flow hits the two leading edges of the wing at a certain angle-of-attack (30" in our case, Fig. la,b), two counter-rotating leading-edge vortices are separated from the laminar flow and propagate over the wing's top (Fig. IC). These two high-momentum, low-pressure vortices contribute identical vortex lifting forces on the two sides of the wing, the sum of these being -40 % of the total lifting forces. The strength and position of these two vortices are determined by the boundary layer conditions near their separation points. A boundary layer is roughly 1-2 mm thick at a windtunnel flow speed of less than 20 m/s; the thickness will decrease when the flow speed is increased. Two linear arrays of surface micro-machined out-ofplane actuators (micro-flaps) are placed along two leading edges at the bottom of the wing (Fig. Id) . When un-deflected, flap arrays remain a t the bottom of the boundary layer, having no effect on the flow and vortices; when one array is deflected downward, however, it interacts with the boundary layer and changes the separation point of the corresponding leading-edge vortex. The span-wise vortex structures over the top of the wing become unbalanced, and an overall rolling moment can be created. The delta-wing has a 38-cm span and a 67 O top angle; it is tested in a wind-tunnel with a top speed of 20 m/s. Silicon micro-machined actuators are chosen here because of their added advantages of light weight and potentially large bandwidth. To control this wing, micro-flaps are required to deflect 1-2 mm out-of-plane (or t o match the boundary-layer thickness), and withstand large aerodynamic loading on the order of several hundred pN. Magnetic actuation is used because it is known to generate stronger and longer-range forces [3, 4, 51 compared with most other driving methods. Several types of magnetic micro-actuators have been previously demonstrated, but none can readily fulfill the current system requirements. Beneck et . al. [6] performed post-processing manual attachments of permanent magnet pieces on micromachined plates and actuated the magnet with an external magnetic field generated by in-plane coils. The manual assembly is unsuitable for us because a large number of ac-