PRESSURE MEASUREMENTS ON A HALF DELTA-WING OSCILLATING IN PITCH

A rigid, 55 degrees sweep, half delta wing has been oscillated in pitc h at subsonic speeds, and the unsteady pressures on both the upper and lower surfaces recorded for pre-stalled conditions. The oscillations were of low amplitude and at frequencies equivalent to a typical wing first bending mode for full scale applications. When compared to a qua si-steady approximation. the unsteady pressures on the upper surface o f the wing lag the steady case along the line of the primary attachmen t. The lag represents a constant convective time from the leading-edge with increasing frequency of oscillation. A further localised area of lagging flow is observed beneath the vortex burst point. the location of which is a function of mean angle of attack. The magnitude of the unsteady pressure variations was seen to increase linearly with the am plitude of the pitching oscillation while the phase lag was seen to in crease linearly with frequency parameter.