Vortilon

{{Short description|Aerodynamic device}}

Image:Raytheon hawker 850xp ei-kjc arp.jpg]]

Vortilons are fixed aerodynamic devices on aircraft wings used to improve handling at low speeds.{{Cite book|title=Aerodynamics for engineering students|url=https://archive.org/details/aerodynamicsfore00houg_081|url-access=limited|last1=Houghton|first1=Edward Lewis|last2=Carpenter|first2=Peter William|date=2003|publisher=Butterworth-Heinemann|isbn=0750651113|edition= 5th|location=Oxford|pages=[https://archive.org/details/aerodynamicsfore00houg_081/page/n530 514]|oclc=50441321}}

The vortilon was invented{{Cite web|url=https://patents.google.com/patent/US3370810|title = Stall control device for swept wings}} by aerodynamicists working at Douglas Aircraft who had previously developed the engine pylons for the Douglas DC-8. The original pylons which wrapped around the leading edge of the wing had to be cut back to reduce excessive cruise drag.https://www.scribd.com/document/50976964/Applied-aerodynamics-at-the-Douglas-Aircraft-Company, Fig.23 Wind tunnel testing of the next Douglas commercial aircraft, the Douglas 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).https://arc.aiaa.org/doi/abs/10.2514/3.43770, p.Fig 13

Vortilons consist of one or more flat plates attached to the underside of the wing near its leading edge, aligned with the flight direction.{{cite book |title=Aircraft Design: A Conceptual Approach |url=https://archive.org/details/aircraftdesignco00raym_515 |url-access=limited |first=Daniel P. |last=Raymer |edition= 3rd |year=1999 |publisher=American Institute of Aeronautics and Astronautics |location=Reston, Virginia |isbn=1-56347-281-3 |page=[https://archive.org/details/aircraftdesignco00raym_515/page/n99 183] |chapter=8.2 Aerodynamic Considerations in Configuration Layout}} 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. A more turbulent boundary layer, in turn, delays the local flow separation.

File:Vortilons on a Cozy MKIV.jpg

Vortilons are often used to improve low-speed aileron performance, thereby increasing resistance to spin. They can be used as an alternative to wing fences, which also restrict airflow along the span of the wing. Vortilons only stream vortices at high angles of attack{{cite book |title=Aircraft Flight |url=https://archive.org/details/aircraftflightde00hr |url-access=limited |last1=Barnard |first1=R.H. |last2=Philpott |first2=D.R. |edition= 4th |year=2010 |publisher=Prentice Hall |location=Harlow, England |isbn=978-0-273-73098-9 |page=[https://archive.org/details/aircraftflightde00hr/page/n83 75] |chapter=Boundary layer and stalling problems on swept wings}} and produce less drag at higher speeds than wing fences. Pylons used to mount jet engines under the wing produce a similar effect.

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. According to Burt Rutan, vortilons installed on straight wings would not have any effect.Vortilons for Variezes, The canard pusher, n°42, October 1984

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.{{cite journal|title=The DC-9 and the Deep Stall|journal=Flight International|date=25 March 1965|page=442|url=http://www.flightglobal.com/pdfarchive/view/1965/1965%20-%200804.html|access-date=2011-10-07}}{{cite journal|first1=Richard S.|last1=Shevell|first2=Roger D.|last2=Schaufele|title=Aerodynamic Design Features of the DC-9|journal=Journal of Aircraft|volume=3|issue=6|date=November–December 1966|pages=515–523|doi=10.2514/3.43770}} They have been used on subsequent aircraft, including:

• McDonnell Douglas MD-80
• McDonnell Douglas MD-90
• Boeing 717
• Rutan VariEze, replacing leading edge cuffs (1984)
• Rutan Long-EZ
• Cozy MK IV
• BAe 125 1000 series{{cite journal|journal=Flying|page=88|date=February 1993|title=BAE 1000 Lifts Hawker Name to New Heights|first=J. Mac|last=McClellan|url=https://books.google.com/books?id=XPB1MpYNfPUC&q=Vortilon&pg=PA88|access-date=2011-10-07}}
• Hawker 800XP{{cite journal|journal=Flying|page=75|date=November 2002|title=Hawker 800XP|first=J. Mac|last=McClellan|url=https://books.google.com/books?id=R5uhU9wKe7wC&q=Vortilon&pg=PA75|access-date=2011-10-07}}
• Embraer ERJ 145 family{{cite journal|journal=Flying|page=75|date=July 2002|title=Unicom|url=https://books.google.com/books?id=cSZdKLCDb7kC&q=Vortilon&pg=PA58|access-date=2011-10-07}}
• Learjet 45
• Aériane Swift{{cite web|url=http://quest.nasa.gov/aero/question/aerotheory/Resources_for_Learning_about_Vortilons.txt|archive-url=https://web.archive.org/web/20101111120921/http://quest.nasa.gov/aero/question/aerotheory/Resources_for_Learning_about_Vortilons.txt|url-status=dead|archive-date=2010-11-11|title=Resources for learning about vortilons|first=Steve|last=Smith|publisher=NASA Quest|access-date=2011-10-07}}
• Experimental Vought F-8 Crusader with supercritical wing. The supercritical wing would have been prone to pitch-up as the wing had increased sweep and aspect ratio compared to the standard wing. No pitch-up problems were experienced with vortilons fitted.https://archive.org/details/DTIC_ADA247719 8-4https://www.nasa.gov/centers/dryden/pdf/88410main_H-1957V1.pdf,p.87 {{Dead link|date=February 2022}}
• Bombardier Challenger 300, later becoming the Challenger 350 & new 3500 series.