Changes in Control Characteristics withnChanges in Flow Pattern at High Subsonic Speeds. Test on an EC. 1250 Aerofoil with 25 per cent Concave Control Flap Parts I and II

摘要

This report describes results obtained in wind-tunnel tests where it was found that considerable changes in flow pattern and pressure distribution around an aerofoil with control flap occurred in certain conditions for a small increase in speed or change in incidence or control angle. The changes were found first1 between M =0-85 and 0-87, when the shock-stalled flow, which had developed at lower speeds, was replaced, on one surface only, by streamline flow extending almost to the trailing edge. When the flow adhered in this way an inclined shock-wave or Prandtl-Meyer flow was established at the flap hinge which deflected the flow smoothly along the flap. The changeover to this regime took place for a change in speed, M, of only about 0-01 to 0-03 and was accompanied by very large changes in the pressure distribution over the rear of the aerofoil and on the flap. These regimes were established only when the pressure distribution over the surface was favourable ahead of the hinge and appeared to require a local Mach number of about 1-25 for the Prandti-Meyer and 1 -4 for the hinge-shock regime.