The lateral-directional characteristics of a 74-degree delta wing employing gothic planform vortex flaps

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Virginia Polytechnic Institute and State University

An investigation to determine the low-speed lateral-directional characteristics of a generic 74-degree delta wing-body configuration employing the latest generation, gothic planform vortex flaps has been conducted. In addition, the theoretical estimates from VORSTAB were compared against experimental data to aid in documenting this new method. VORSTAB is an extension of the Quasi-Vortex-Lattice Method of Lan which empirically accounts for vortex breakdown effects in the calculation of longitudinal and lateral-directional aerodynamic characteristics.

The experimental results indicated that leading-edge deflections of 30 and 40 degrees significantly reduce the magnitude of the wing effective dihedral relative to the baseline for a specified angle of attack or lift coefficient. For angles of attack greater than 15 degrees, these flap deflections reduce the configuration directional stability despite improved vertical tail effectiveness. Asymmetric leading edge deflections are shown to be inferior to conventional ailerons in generating rolling moments. Asymmetric leading-edge deflections are effective in producing side force at moderate to high angles of attack.

VORSTAB lateral-directional calculations provide ballpark estimates at low to moderate angles of attack. The theory does not account for vortex flow induced, vertical tail effects at high angles of attack and should not be used for this angle of attack region. The empirical formulae for predicting vortex burst effects are not reliable in their present form. Although the basic trends are correct, the magnitude of the predicted vortex burst effect is typically over-estimated.