Boundary layer suction 5272076 198816369 2008-03-17T08:40:18Z Arnero 233665 /* See also */ '''Boundary layer suction''' is technique in which an [[air pump]] is used to extract the [[boundary layer]] at the [[wing]] or the [[inlet cone|inlet]] of an [[aircraft]]. Improving the air flow can reduce [[drag (physics)|drag]]. Improvements in [[fuel efficiency]] have been estimated as high as 30%. ===The boundary layer=== The air molecules at the surface of a wing are effectively stationary (see the [[no-slip condition]]). If the flow is smooth, known as [[laminar flow]], the velocity of the air increases steadily as measurements are taken further away from the surface. However the smooth flow is often disturbed by the boundary layer breaking away from the surface and creating a low pressure region immediately behind the airfoil (see [[flow separation]]). This low pressure region results in increased overall drag. Attempts have been made over the years to delay the onset of this flow separation by careful design and smooth surfaces. ===Use of suction=== As flow separation results from the velocity deficit that is characteristic of boundary layers, suction attempts to remove the boundary layer from the surface before it can separate. The technology was first developed by [[Werner Pfenninger]] in the [[Second World War]] and has been researched almost continuously since. In the 1990s tests [http://www.nasa.gov/centers/dryden/pdf/88653main_H-2382.pdf] were done by [[NASA]] with a [[F-16 Fighting Falcon|F16XL]]. Loek Boermans is researching the technology for use in [[glider]]s at the [[Delft University of Technology|Technical University of Delft]]. However about 500 watts of power would be needed to drive the pumps and this would mean covering the glider with [[solar panel]]s and would increase the cost greatly. There are also structural problems to be overcome before the ultimate glider could be manufactured. == See also == * The [[pusher configuration]] is an alternative way to re-energize the boundary layer, but is only used on the fuselage. ==External links== * [http://www.dg-flugzeugbau.de/leistung-e.html DGflugzeugbau article] * [http://www.nasa.gov/centers/dryden/pdf/88653main_H-2382.pdf NASA report on F16 program] * [http://www.iag.uni-stuttgart.de/transition/publications/trans_publ-200Xwww.htm combination] of [[vortex generator]] with suction [[Category:Boundary layers]] [[Category:Wing design]]