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for slender conical bodies and predicted that vortices over a flat-plate delta wing at high angles of attack with zero sideslip were conical, symmetric, and stable but adding a low dorsal fin to the wing would destabilize the vortices and therefore render the originally symmetric vortices asymmetric. The wing is assumed slender so that no vortex breakdown occurs on the wing. An experimental study using a six-component internal strain-gage balance is conducted to verify the validity of the theoretical predictions and shows the force development versus angle of attack. A sharp-edged flat-plate delta wing of 82.5 • sweep angle is tested in a low-speed wind tunnel at angles of attack up to 32 • and sideslip within ±10 •. The same tests are performed on an identical delta wing model but with a low dorsal fin mounted vertically in the incidence plane of the wing. Two fin heights are tested. The ratios of the local fin height to the local wing semi-span are 0.3 and 0.6. The measurement of the aerodynamic forces and moments clearly indicates that a force-asymmetry onset occurs over the wing-fin models at zero sideslip, providing for the first time force measurement evidence of the theoretical predictions and depicts that the force-asymmetry onset can be followed by a force-unsteadiness onset.

Duty cycle modulation of the alternating blowing from two opposite facing plasma actuators on the leeward surface near the apex of a cone of semi-apex angle 10• to control the mean lateral force and moment and the flow control mechanisms are presented. The pressure distributions over the cone forebody are measured using steady and unsteady pressure-tappings. The flowfields are visualized by a two-dimensional particle image velocimetry. The experiments were perfomed in a 3.0 m × 1.6 m open-circuit wind tunnel at 45• angle of attack and Reynolds number of 5 × 10 4 based on the cone base diameter. The opposite bi-stable vortex patterns appear when the port or starboard actuator is activated while the other is kept off during the test. The phase-locked (locked to the plasma duty cycle) averaged flow induced by the duty-cycled plasma actuation is periodic and varies smoothly between two opposite states like the bi-stable states but much smaller in amplitude. The ensemble-averaged pressure from sampling times as low as one second becomes a constant no matter the plasma actuation is steady or unsteady. However, the phasedlocked average of plasma duty cycle requires much more sampling time to reach a limit. α = angle of attack θ = meridian angle measured from windward generator, positive when clockwise τ = fraction of time when starboard actuator is on over a duty-cycle period ψ = phase angle of duty cycle Ω = reduced angular frequency of duty-cycle, 2πf D/U ∞

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