Physical simulation of free-flight in captive wind tunnel tests

The ‘manoeuvre rig’ is a multi-degree-of-freedom dynamic wind tunnel test rig under development at the University of Bristol to facilitate research into nonlinear flight dynamics and control. One objective of the rig is to allow for the direct physical simulation of model aircraft responses within the wind tunnel, i.e. to obtain the same responses on the rig as if the model were in free flight in the same degrees of freedom. This study explores two influences the rig exerts on the aircraft’s motion in terms of reaction forces, as well as possible means to reduce them using the rig’s aerodynamic compensator. This will be attempted using reaction feedback measured via a load cell. The first effect is caused by the rig’s inertial and aerodynamic characteristics, and the second due to inherent kinematic constraints. The techniques derived were simulated in Matlab Simulink and the results are presented here. The study focuses on motion in the longitudinal sense. The results show that reaction force feedback can be used to improve the short period motion of a constrained aircraft model on the manoeuvre rig, such that its motion matches an equivalent free-flying aircraft at constant ground speed. Time delays within the system have an adverse affect on this match.