Current trends in modem combat aircraft design have seen a move towards canard configurations with all moving foreplanes, providing a manoeuvre advantage with reduced stability. At the same time, with rapid advances in the field of assisted flight control and emphasis now placed on computer controlled, fly-by-wire aircraft, there is an unprecedented requirement for detailed knowledge of motion dependent aerodynamics, such as may be experienced on a foreplane undergoing rapid corrective motions.
In this study, investigations have been carried out into the rigid body, motion dependent aerodynamics of a 55° delta wing, undergoing small amplitude pitching oscillations. Steady and unsteady surface pressures have been measured on the wing under low speed, pre-stalled conditions, for a range of mean incidence and oscillation frequencies, up to frequencies approximating a full scale foreplane under low speed conditions, such as landing approach.
Relationships between the motion of the wing and the unsteady pressures have been identified, and it has been shown that they may not be approximated by a simple quasi-steady model due to significant phase shifts in specific regions of the flow. The lower surface flow is shown to be highly dependent on the effective incidence of the wing. The vortical flow of the upper surface has a more complex response to the pitching motion, with the shear layer and burst motion reacting at different rates.
There is also significant attenuation/overshoot and phase in the unsteady loads and moments (obtained by integrating the pressure data) relative to the quasi-steady. These are shown to be highly dependent on the pitching oscillation frequency and the location of the pitch axis. It is suggested that there may be a pitch axis location such that quasi-steady loading may be obtained under oscillatory conditions.
Application of the key findings to a simple all moving control surface shows that the stability of the control system is strongly influenced by the pitch axis location.
|Date of Award||1997|