Free-motion wind tunnel testing using a three-degree-of-freedom magnetic suspension system

A magnetic suspension system is developed for free-motion wind tunnel testing. An external magnet-yoke open magnetic circuit produces a levitation force acting on the disk magnet in the model, and stable suspension of the model is achieved by PID feedback control using two coils. The suspended models are free from support interference and move in three degrees of freedom in the wind tunnel. The pitch rotation around the y-axis and the translational motion in the xz plane under the influence of unsteady aerodynamic forces are observed using the motion capture technique. Parameter identification methods using Fourier analysis of the motion capture data are developed to determine the moment slope \(C_{\textrm{M}\alpha }\) $C_{\text{M}\alpha }$ , lift slope \(C_{\textrm{L}\alpha }\) $C_{\text{L}\alpha }$ and drag coefficient \(C_{\textrm{D}}\) $C_{\text{D}}$ . The standard deviations of the identified values of \(C_{\textrm{M}\alpha }\) $C_{\text{M}\alpha }$ , \(C_{\textrm{L}\alpha }\) $C_{\text{L}\alpha }$ and \(C_{\textrm{D}}\) $C_{\text{D}}$ are less than 5%, 8% and 6% of the respective means.