Vortilons are fixedaerodynamic devices on aircraft wings used to improve handling at low speeds.[1][2]
The vortilon was invented[3] by aerodynamicists working atDouglas Aircraft who had previously developed the engine pylons for theDouglas DC-8. The original pylons which wrapped around the leading edge of the wing had to be cut back to reduce excessive cruise drag.[4] Wind tunnel testing of the next Douglas commercial aircraft, theDouglas DC-9 which had no under-wing engines, showed a cutback engine pylon would be beneficial to wing lift and upwash at the tail at the low speed stall. The pylon was reduced in size and became the vortilon (VORTex-generating-pYLON).[5]
Vortilons consist of one or more flat plates attached to the underside of thewing near its leading edge, aligned with the flight direction.[6] When the speed is reduced and the aircraft approachesstall, the local flow at the leading edge is diverted outwards; this spanwise component of velocity around the vortilon creates avortex streamed around the top surface, which energises theboundary layer.[6] A more turbulent boundary layer, in turn, delays the local flow separation.
Vortilons are often used to improve low-speedaileron performance,[1][7] thereby increasing resistance tospin. They can be used as an alternative towing fences, which also restrict airflow along the span of the wing.[1] Vortilons only stream vortices at highangles of attack[8] and produce less drag at higher speeds than wing fences.[9] Pylons used to mountjet engines under the wing produce a similar effect.[10]
The occurrence of span-wise flow at high angles of attack, such as observed onswept wings, is an essential requirement for vortilons to become effective. According toBurt Rutan, vortilons installed on straight wings would not have any effect.[11]
Vortilons were first introduced with theMcDonnell 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.[10][12] They have been used on subsequent aircraft, including:
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