The measurement of Magnus force and moment using a magnetically suspended wind tunnel model

The magnetic suspension system makes an ideal facility for the measurement of the aerodynamic Magnus force acting on a wind tunnel model which is spinning about an axis inclined at an angle to the air flow. The Southampton University system was modified to allow the suspended model freedom to spin whilst retaining control of the other rigid body degrees of freedom. Force and moment read-out was obtained from calibration of the suspension electromagnet currents. The model was spun up using air jets and the mechanism retracted leaving the model rotating and free from flow interference. The Magnus force signals were recorded on magnetic tape during the gradual decay of spin rate for subsequent digital analysis. Typical test data is presented showing a strong influence of tail region geometry on Magnus force. This indicates that a mechanical support at the tail should be avoided and illustrates the usefulness of magnetic suspension in aerodynamic testing.