The performance enhancement of a vertical tail provided by aerodynamic flow control could allow for the size of the tail to be reduced while maintaining similar control authority. Decreasing tail size would create a reduction in weight, drag, and fuel costs of the airplane. The application of synthetic jet actuators on improving the performance of the vertical tail was investigated by conducting experiments on 1/9th and 1/19th scale wind tunnel models (relative to a Boeing 767 tail) at Reynolds numbers of 700,000 and 350,000, respectively. Finite-span synthetic jets were placed slightly upstream of the rudder hinge-line in an attempt to reduce or even eliminate the flow separation that commences over the rudder when it was deflected to high angles. Global force measurements on the 1/9th scale model showed that the flow control is capable of increasing side force by a maximum of 0.11 (19%). The momentum coefficient that created this change was relatively small (C_μ = 0.124%). Furthermore, for some conditions, when the individual jet strength was held constant, reducing the spanwise density of active actuators (e.g., turning on every other or every fourth jet) results in more control authority relative to when all jets are on. Scaling considerations were also studied by comparing the performance of actuation systems on the 1/9 th and 1/19 th scale models. Experiments showed better agreement in side force augmentation when the jet orifice cross-section and spanwise spacing are scaled dimensionally as opposed to non-dimensionally.
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