Vortilon

The original pylons which wrapped around the leading edge of the wing had to be cut back to reduce excessive cruise drag.

[5] Vortilons consist of one or more flat plates attached to the underside of the wing near its leading edge, aligned with the flight direction.

[6] When the speed is reduced and the aircraft approaches stall, the local flow at the leading edge is diverted outwards; this spanwise component of velocity around the vortilon creates a vortex streamed around the top surface, which energises the boundary layer.

[10] The occurrence of span-wise flow at high angles of attack, such as observed on swept wings, is an essential requirement for vortilons to become effective.

[11] Vortilons were first introduced with the McDonnell Douglas DC-9 to achieve a strong nose down pitching moment just beyond the normal stall and their influence ceased to have any effect beyond 30 degrees angle of attack.