Side Force Control At Large Angle Of Attack

Dynamic manipulation of forebody vortices as a means to obtain directional control of high-performance aircraft at large angle of attack is investigated. A tangent ogive shape of a slender body of the revolution and a full-aircraft model are chosen. The experiments are conducted at a low-speed wind tunnel. How the side force changed when the roll angle and the angle of attack vary is studied by surface pressure measurement and dynamic force measurement.A surface pressure measurement is performed on the slender body when the roll angle changes by rotating the nose tip. During the experiments, How the side force changed when the roll angle vary is studied. A nose-tip-perturbation and a transitional-strip are chosen to control the side force. The results indicate that the variation of side force versus roll angle shows two types: continuous change state and bi-stable state ,showing continuous change state among the angle of attack of 40-50 deg while bi-stable state above the angle of attack of 50 deg. In this paper, a special state is found. Through the axial direction, the variation of side force versus roll angle shows continuous change state,critical state and bi-stable state at the angle of attack of 50 deg. The nose-tip-perturbation can control the direction of the side force, but can not reduce the maximum of the side force, while the transitional-strip can reduce the maximum to a great extent.A dynamic force measurement is performed on the full-aircraft model to studied how the nose-tip-perturbation,side strip and perturbation-combined effect the side force. The results show that the single nose-tip-perturbation can also control the side force of the full-aircraft model, but due to the existence of the vertical tail , the direction of the side force changes when the angle of attack is very high(above 45deg),while double nose-tip-perturbations can prevent this phenomenon happens. The model still suffers large random side force even if the separation of the boundary-layer is symmetric caused by symmetric side strip. The perturbation-combined is very effective on controlling the side force.