This study investigated the feasibility of reducing control surface input power with the use of a tab-assisted flap. Wind tunnel tests were conducted at the University of Illinois at Urbana-Champaign (UIUC) on a NACA 3415 airfoil model with a flap including a trim tab. Measurements were taken for two configurations: a baseline fixed tab case where tab deflection was zero and a tabbed case where multiple flap and tab angle combinations were tested. Hinge moment measurements were taken for both the flap and tab for comparison between the two cases. In addition; lift, drag and moment measurements along with surface pressures were acquired to aid in the analysis of the concept and provide flow diagnostics. The data were compared to computational results which compared well with the exception of flap and tab deflection cases where large regions of unsteady separated flow were present. All data were taken at a Reynolds number of 1.8 million and Mach number of 0.18.

To analyze the power-savings capability of a tab-assisted flap, several studies were conducted: a generalized tab performance study evaluating hinge moment reduction and a quasi-dynamic study using the static data to calculate work savings for two simulated flap deflections. The generalized tab performance study revealed large hinge moment reductions for each of the flap deflections when using the tab to actuate the flap. These reductions came at the cost of increased drag, reduced lift and loss of flap effectiveness. The quasi-dynamic study produced significantly large work savings for both simulated flap deflection schedules. Even though this study ignored the effect on lift and drag, as well as the unsteady aerodynamics and control surface inertia, it suggests the large power-savings potential of a tab-assisted flap. A flow visualization analysis was performed to further assess the loss of flap effectiveness observed in the tab performance calculations as well as the non-linear behavior in the lift, drag and hinge moment data. The results of the analysis showed the complex flowfield behavior in cases where the flap and tab deflections were of opposite sign and larger magnitude and identified the cause of behavior in other cases where data non-linearities existed.