UNSTEADY WIND-TUNNEL INTERFERENCE IN AIRCRAFT DYNAMIC EXPERIMENTS

An analysis of existing oscillatory and rotary test data was undertaken to identify the origins of the observed wind-tunnel interference effects and interpret the aircraft aerodynamic characteristics. Logical arguments based on the limited experimental data point to the existence of interference flow mechanisms involving the coupling between unsteady flowfields near the model, the tunnel walls, and around the model support. Oscillatory cross-coupling derivatives measured on the standard dynamics model were significantly affected at low angles of attack while the nonlinear yawing moment characteristics of the HIRM 2 aircraft configuration at high incidence were masked completely in rotary tests performed in a small test section. Both of these very different problems may be attributed to unsteady wind-tunnel interference. Analytical corrections are not feasible at present, but experimental solutions can be implemented. Predictions of vehicle dynamics at high alpha based on dynamic wind-tunnel data can be affected by the interpretation given to the prevailing interference flow phenomena.