Wingtip device

Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag. Although there are several types of wing tip device, which function in different manners, their intended effect is always to reduce an aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan. Extending the span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan (e.g., available width at airport gates).Boeing 747-400 canted wingletAirbus A320 sharkletBoeing 767-400ER with raked wingtipsAirbus A310 wingtip fence'Winged rotor' on AgustaWestland AW101 Merlin helicopterC-130J Super Hercules showing scimitar propellers with raked tipsDetail view of the wingtip device on a wind turbine rotor-bladeCeiling fan with wingtip devices Wingtip devices are intended to improve the efficiency of fixed-wing aircraft by reducing drag. Although there are several types of wing tip device, which function in different manners, their intended effect is always to reduce an aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without greatly increasing the wingspan. Extending the span would lower lift-induced drag, but would increase parasitic drag and would require boosting the strength and weight of the wing. At some point, there is no net benefit from further increased span. There may also be operational considerations that limit the allowable wingspan (e.g., available width at airport gates). Wingtip devices increase the lift generated at the wingtip (by smoothing the airflow across the upper wing near the tip) and reduce the lift-induced drag caused by wingtip vortices, improving lift-to-drag ratio. This increases fuel efficiency in powered aircraft and increases cross-country speed in gliders, in both cases increasing range. U.S. Air Force studies indicate that a given improvement in fuel efficiency correlates directly with the causal increase in the aircraft's lift-to-drag ratio. The initial concept dates back to 1897, when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices. In the United States, Scottish-born engineer William E. Somerville patented the first functional winglets in 1910. Somerville installed the devices on his early biplane and monoplane designs.Vincent Burnelli received US Patent no: 1,774,474 for his 'Airfoil Control Means' on August 26, 1930. The earliest-known implementation of a Hoerner-style downward-angled 'wingtip device' on a jet aircraft was the so-called Lippisch-Ohren (Lippisch ears), allegedly attributed to the Messerschmitt Me 163's designer Alexander Lippisch, and first added to the M3 and M4 third and fourth prototypes of the Heinkel He 162A Spatz jet light fighter for evaluation. This was done in order to counteract the dutch roll characteristic the marked three degrees of dihedral angle for each wing panel that the original He 162 design's wings possessed. As production of the Third Reich's chosen turbojet-powered emergency fighter was of prime importance at the start of 1945, disruption of the production line to make other types of changes to correct such a problem were not likely to have been available, and the added wingtip devices became a standard feature of the approximately 320 completed He 162A jet fighters built, with hundreds more He 162A airframes going unfinished by V-E Day. Following the end of World War II, Dr. Sighard F. Hoerner was a pioneer researcher in the field, having written a technical paper published in 1952 that called for drooped wingtips whose pointed rear tips focused the resulting wingtip vortex away from the upper wing surface. Drooped wingtips are often called 'Hoerner tips' in his honor. Gliders and light aircraft have made use of Hoerner tips for many years. The term 'winglet' was previously used to describe an additional lifting surface on an aircraft, like a short section between wheels on fixed undercarriage. Richard Whitcomb's research in the 1970s at NASA first used winglet with its modern meaning referring to near-vertical extension of the wing tips. The upward angle (or cant) of the winglet, its inward or outward angle (or toe), as well as its size and shape are critical for correct performance and are unique in each application. The wingtip vortex, which rotates around from below the wing, strikes the cambered surface of the winglet, generating a force that angles inward and slightly forward, analogous to a sailboat sailing close hauled. The winglet converts some of the otherwise-wasted energy in the wingtip vortex to an apparent thrust. This small contribution can be worthwhile over the aircraft's lifetime, provided the benefit offsets the cost of installing and maintaining the winglets. Another potential benefit of winglets is that they reduce the intensity of wake vortices. Those trail behind the plane and pose a hazard to other aircraft. Minimum spacing requirements between aircraft operations at airports are largely dictated by these factors. Aircraft are classified by weight (e.g. 'Light,' 'Heavy,' etc.) because the vortex strength grows with the aircraft lift coefficient, and thus, the associated turbulence is greatest at low speed and high weight, which produced a high angle of attack. Winglets and wingtip fences also increase efficiency by reducing vortex interference with laminar airflow near the tips of the wing, by 'moving' the confluence of low-pressure (over wing) and high-pressure (under wing) air away from the surface of the wing. Wingtip vortices create turbulence, originating at the leading edge of the wingtip and propagating backwards and inboard. This turbulence 'delaminates' the airflow over a small triangular section of the outboard wing, which destroys lift in that area. The fence/winglet drives the area where the vortex forms upward away from the wing surface, since the center of the resulting vortex is now at the tip of the winglet. Aircraft such as the Airbus A340 and the Boeing 747-400 use winglets while other designs such as later versions of the Boeing 777 and the Boeing 747-8 have raked wingtips. The fuel economy improvement from winglets increases with the mission length. Blended winglets allow a steeper angle of attack reducing takeoff distance.