Spoiler Ailerons

Spoiler ailerons project upward from the upper surface of one wing, reducing lift on that wing and thus producing a rolling moment (Figure 5.10). Spoiler ailerons are often the same surfaces used symmetrically to reduce lift and increase drag on large jet airplanes for rapid descents and to assist braking on runways. Spoiler ailerons are generally used either to free wing trailing edges for full-span landing flaps or to minimize wing twist due to aileron action on very flexible wings.

The aerodynamic details of spoiler operation are still not completely understood, even after years of experiment and theoretical studies. The aerodynamics of a rapidly opened spoiler has two phases, the opening and steady-state phases.

Spoiler Ailerons

Figure 5.10 Plug-slot spoiler ailerons used on the Northrop P-61 BlackWidow airplane. An attempt to devote most of the wing’s trailing edge to landing flaps, rather than ailerons. The small guide aileron provides stick force feel. (From Toll, NACA Rept. 868, 1947)