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A wind tunnel experiment was performed to further investigate the potential of the dy­ namic manipulation of forebody vortices as a means of supplementing directional control of fighter aircraft at high angles of attack. Tests were conducted on a 65-deg delta-wing model fitted with a slender, pointed tangent-ogive forebody of circular cross-section and 12.8 deg semi-apex angle. Forward-blowing nozzles located near the apex of the forebody served as the means of manipulating the forebody vortices. As expected, forward blowing was very effective, i.e., little blowing effort was required to cause the forebody vortex on the blown side to assume the ‘high’ position. However, the magnitudes of yawing moment and side force developed by the slender forebody with blowing do not differ significantly from that of the no-blowing, baseline case. Moreover, blowing above a certain thresh­ old value produced an unexpected reversal, with blowing causing the vortex on the blown side to assume the ‘low’ position instead and the yawing moment and side force to change sense. The results have shown that the dynamic manipulation scheme is very successful in producing a linear variation of time-average yawing moment with a duty-cycle parameter, even with sideslip, for the aircraft-like model. The results also show that, by switching the vortex pattern rapidly, the linearity can be maintained up to a reduced frequency of at least 0.32, which is expected to be very satisfactory for practical applications. Cross-coupling effects were also identified between the control method and time-average rolling moment, pitching moment and normal force. The cross-coupling effects in rolling moment and nor­ mal force appear to benefit the flight mechanics, whereas the effect in pitching moment may not. Excellent effectiveness of forward-blowing in sideslip was demonstrated with nozzles located in close proximity to the apex of the forebody (xn/D = 0.095); a more aft location (xn/D = 0.159) may reduce effectiveness in sideslip but raises the threshold at which vortex reversal occurs and thus increases the margin for low blowing momentum coefficients. The preferred azimuthal position of 120 deg from the windward meridian

Dynamic manipulation of asymmetric forebody vortices to achieve linear control