Motion induced aerodynamics of a pitching delta wing.
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
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.