Spoiler Steady-State Aerodynamics

Separation behind an opened spoiler on a wing upper surface causes distortion of the external or potential flow that is similar to the effect of a flap-type surface with trailing-edge-up deflection. In the latter case, streamlines above the wing are raised toward the wing trailing edge. The effective wing camber is negative in the trailing-edge region, causing a net loss in circulation and lift. The difference in the two cases is that the effective wing trailing edge in the spoiler case is somewhere in the middle of the separated region, instead of at the actual trailing edge, as in the flap-type surface case.

5.10.1 Spoiler Operating Forces

The hinge moments of ordinary hinged-flap and slot lip spoiler ailerons are high; brute hydraulic force is used to open them against the airstream. Retractable arc and plug spoiler ailerons are designed for very low hinge moments and operating forces. Although aerodynamic pressures on the curved surfaces of these ailerons are high, the lines of action of these pressures are directed through the hinge line and do not show up as hinge moments. Hinge moments arise only from pressure forces on the ends of the arcs and from small skin friction forces on the curved surfaces.