Krueger flap

Krueger flaps deployed from the leading edge of a Boeing 747 (top left and right in photo)

Krueger flaps are lift enhancement devices that may be fitted to the leading edge of an aircraft wing. Unlike slats or drooped leading edges, the main wing upper surface and its nose is not changed. Instead, a portion of the lower wing is rotated out in front of the main wing leading edge. Current Boeing aircraft, and many others, use this design between the fuselage and closest engine, where the wing is thickest. Outboard of the engine, slat flaps are used on the leading edge. The Boeing 727 also used a mix of inboard Krueger flaps and outboard slats, although it had no engine between them. Most early jet airliners, such as the Boeing 707 and Boeing 747, used Krueger flaps only.

Operation

While the aerodynamic effect of Krueger flaps may be similar to that of slats or slots (in those cases where there is a gap or slot between the flap trailing edge and wing leading edge), they are deployed differently. Krueger flaps, hinged at their foremost position that once deployed actually become their trailing edges, hinge forwards from the under surface of the wing, increasing the wing camber and maximum coefficient of lift.^[1] Conversely, slats extend forwards from the upper surface of the leading edge. Also, when deployed, Krueger flaps result in a much more pronounced blunt leading edge on the wing, helping to achieve better low-speed handling. This allows smaller-radius wing leading edges, better optimized for cruise.

The Krueger flaps developed for the Boeing 747 were constructed from fiberglass honeycomb material and were designed to be intentionally distorted into an aerofoil section on deployment.^[2]

History

Krüger flaps were invented by Werner Krüger in 1943 and evaluated in the wind tunnels in Göttingen, Germany.^[3] One of the earliest applications was the Boeing 707 in 1954. The flap was added to prevent wing stall with an extreme attitude take-off with the tail dragging on the runway, a scenario that had already caused two deHavilland Comet accidents. A preliminary flight test had been made on the Boeing 367-80 using a fixed flap and a skid on the after-body.^[4]

Krueger flap operation
Slat operation

Boeing commenced a series of test flights on 17 March 2015 with a modified Boeing 757, incorporating new wing-leading-edge sections and an actively blown vertical tail.^[5] The left wing has been modified to include a 6.7 m-span glove section supporting a variable-camber Krueger flap which will be deployed during landing and which protrudes just ahead of the leading edge. Although Krueger flaps have been tried before as insect-mitigation screens, previous designs caused additional drag; the newer design being tested is variable-camber and designed to retract as seamlessly as possible into the lower wing surface. Increasing the use of natural laminar flow (NLF) on an aircraft wing has the potential to improve fuel burn by as much as 15%, but even small contaminants from insect remains will trip the flow from laminar to turbulent, destroying the performance benefit. The test flights have been supported by the European airline group TUI AG and conducted jointly with NASA as part of the agency’s Environmentally Responsible Aviation (ERA) program.

References

Wikimedia Commons has media related to Krueger flaps.

Notes

↑ Gary V. Bristow (2002). Ace the Technical Pilot Interview. McGraw-Hill Professional. ISBN 0-07-139609-8. Retrieved 2009-02-16.
↑ Taylor 1990, p. 114.
↑ Niels Klußmann; Arnim Malik (2012). Lexikon Der Luftfahrt. Springer. pp. 193–. ISBN 978-3-642-22500-0.
↑ "The Road to the 707" Cook, William H., TYC Publishing Company, Bellevue, 1991, ISBN 0-9629605-0-0, p.249
↑ "'757 EcoDemo Focuses On Laminar And Active Flow'". Aviation Week. 23 March 2015. Retrieved 23 March 2015.

Bibliography

Taylor, John W.R. The Lore of Flight, London: Universal Books Ltd., 1990. ISBN 0-9509620-1-5.

Aircraft components and systems

Airframe structure	Aft pressure bulkhead Cabane strut Canopy Cruciform tail Dope Empennage Fabric covering Fairing Flying wires Former Fuselage Hardpoint Interplane strut Jury strut Leading edge Lift strut Longeron Nacelle Rib Ring tail Spar Stabilizer Stressed skin Strut T-tail Tailplane Trailing edge Triple tail Twin tail Vertical stabilizer V-tail Y-tail Wing root Wing tip Wingbox

Flight controls	Aileron Airbrake Artificial feel Autopilot Canard Centre stick Deceleron Dive brake Electro-hydraulic actuator Elevator Elevon Flaperon Flight control modes Fly-by-wire Gust lock Rudder Servo tab Side-stick Spoiler Spoileron Stabilator Stick pusher Stick shaker Trim tab Wing warping Yaw damper Yoke

Aerodynamic and high-lift devices	Active Aeroelastic Wing Adaptive compliant wing Blown flap Channel wing Dog-tooth Droop Flap Gouge flap Gurney flap Krueger flap Leading edge cuff LEX Slats Slot Stall strips Strake Variable-sweep wing Vortex generator Vortilon Wing fence Winglet

Avionic and flight instrument systems	ACAS Air data computer Airspeed indicator Altimeter Annunciator panel Attitude indicator Compass Course deviation indicator EFIS EICAS Flight data recorder Flight management system Glass cockpit GPS Heading indicator Horizontal situation indicator INS Pitot-static system Radar altimeter TCAS Transponder Turn and slip indicator Vertical Speed Indicator Yaw string

Propulsion controls, devices and fuel systems	Autothrottle Drop tank FADEC Fuel tank Gascolator Inlet cone Intake ramp NACA cowling Self-sealing fuel tank Splitter plate Throttle Thrust lever Thrust reversal Townend ring Wet wing

Landing and arresting gear	Arrestor hook Autobrake Conventional landing gear Drogue parachute Landing gear Landing gear extender Oleo strut Tricycle landing gear Tundra tire

Escape systems	Ejection seat Escape crew capsule

Other systems	Aircraft lavatory Auxiliary power unit Bleed air system Deicing boot Emergency oxygen system Entertainment system Environmental control system Hydraulic system Ice protection system Landing lights Navigation light Passenger service unit Ram air turbine Weeping wing

This article is issued from Wikipedia - version of the 10/30/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.