The nonlinear aerodynamics associated with differentially actuated spoilers on the F-111C aircraft are examined. Results from a Stepwise Regression identification technique are compared with wind-tunnel data and the physical interpretation assessed. As an introduction to spoiler aerodynamics, a brief background on past experimental research is first given, followed by a summary of the relevant aspects. The identification approach is outlined, including the topics of data partitioning and Mixed Estimation. This biased technique was implemented into a Stepwise Regression procedure, in order that the 'weaker' terms in the model kept realistic values and any problems arising from collinearity amongst the variables would be suppressed. Of the results from the flight cases available, five were selected to be discussed in detail. Unique partitioning approaches were chosen using wind-tunnel data and applied to each case. It was found that, in general, the flight-estimated coefficients compared well with the wind-tunnel data. However, a difference in Reynolds numbers often produced a lower estimated spoiler effectiveness than the scaled model results. This was particularly evident at elevated angles-of-attack, where the expected (from wind-tunnel) control reversal was not identified.
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