Winglets or Sharklets (term for winglets at Airbus ) are mostly outer wings at the ends of the wings of aircraft that extend upwards and more rarely upwards and downwards . They ensure better lateral stability, reduce the induced drag and thus improve the glide angle and the rate of climb at low speed.
- less induced drag at high lift values, high angles of attack (low speeds),
- better stability around the vertical axis ( yaw axis ), because winglets always sit behind the aircraft's center of gravity and thus have a vertical tail effect,
- greater maneuverability due to the slightly lower moment of inertia around the longitudinal axis ( roll axis ),
- the increased resistance at high speeds.
When the lift is generated by wings of finite extension, the pressure difference between the top and bottom creates vortices , from which wake vortices arise in the outer area of the wing . The air flows from the underside of the wings, where there is overpressure, up around the wing tips, where there is negative pressure. With a positive wing sweep , the vortices are strongest at the tip of the wing and roll up (depending on the flight condition) to form a tip vortex. The vortices induce a downward force at the location of the wing, which creates an induced drag. Winglets now reduce the influence of these vortices by dividing the tip vortex (part goes off at the wing-winglet junction, part at the winglet tip) and deflecting it outwards through their profile. The total strength of the eddies remains the same because it is directly connected to the generation of lift. The desired reduction in air resistance is ultimately due to the fact that the wing is better used and can work more efficiently. An aircraft equipped with winglets can operate at a lower angle of attack (compared to one with an identical wing without a winglet) for a given weight and speed, because the wing tips generate more lift, so the induced drag is reduced.
Winglets must be adapted for each type of aircraft, taking into account the wing area and the expected flight speeds. For example, the additional flow around the surface develops more additional friction and pressure resistance at high speeds than it saves in terms of induced air resistance.
Winglets lead to a certain increase in the aircraft curb weight. If you want to retrofit an aircraft with winglets, there are costs for the installation. In the past, an extension was not always worthwhile; In view of the high oil price , the break-even point is reached relatively quickly today.
According to Boeing , the use of winglets can cut fuel consumption by three to five percent.
Winglets vs. Enlargement of the span
Contrary to what is often assumed, the winglets do not bring any aerodynamic advantages compared with an equally large extension of the span. If the winglets were to be folded outwards, the aircraft would have a better glide angle and lower fuel consumption.
However, increasing the range brings the following disadvantages:
- Larger floor space required
- Stronger bending moments on the wing (the bending moment is already increased by the winglets, but not as much as with the same extension of the span)
- Poor maneuverability due to higher mass moments compared to winglets around the longitudinal and vertical axis
Winglets are more often installed or retrofitted in aircraft that have already reached the maximum wingspan of a certain class, such as gliders with a wingspan of 15 m or 18 m as well as cargo and passenger aircraft with a wingspan of
- 80 m (A380-800)
- 65 m (A350, B747-400, A340)
- 36 m (A320neo, B737NG)
The loss of lift due to air flow around the wing edge arches had been known for a long time. After the Second World War, for example, tests were carried out on some STOL aircraft with wing tips, which mostly consisted of only one sheet of metal (e.g. PZL-101 ). These stood a few centimeters above the wing tip profile and made it difficult to flow around it. Similar effects were hoped for from so-called edge clubs such as on the Let L-13 , which were also used as wing tip tanks .
Although the geometry is greatly simplified, modern winglets are modeled on the wing tips of certain bird species. Long flight feathers, which are spread fan-shaped and staggered in height, ensure better slow flight characteristics, especially for birds of prey. Louis B. Gratzer called these upwardly curved ends winglets. He was head of aerodynamics at Boeing, examined the aerodynamics of the wings in birds and noticed the similarities (see also bionics ).
Winglets are not a modern invention. The basic idea of the winglets was even registered for a patent by Frederick W. Lanchester in 1897 ; Before the Second World War there were aircraft with winglet-like wing tips. During the Second World War they were first used in the series under the name "Henschelohren" ( Heinkel He 162 ), where they were bent downwards, contrary to today's standard construction.
In passenger aircraft construction, Airbus' winglets were introduced on the A310-300 in the form of small wing end caps (so-called “wingtip fences”). In contrast to these original end caps on the wings, today's winglets often have special profiles, which can significantly improve the desired effects. For the wing tips of the A380 , however, wingtip fences similar to those of the A310-300 were used, as newer winglet designs would have increased the wingspan to a level unsuitable for commercial airports.
Around 1980, some hang-glider manufacturers began to equip them with winglets. One manufacturer even tested "wings with feathered wings".
There are different winglet designs and constructions, which are shown below in an overview with examples.
- Classic winglets (angular, straight or angled upwards). Examples:
Blended winglets (with a smooth transition from the wing to the winglet). Examples:
- Boeing 737NG (not available on 737-600, except not standard on 737-900ER), BBJ . Can now be retrofitted on Boeing 757 , Boeing 737-300 , Boeing 737-500 and 767 . Airbus has been calling its newly developed winglets for the A320 family Sharklets since the end of 2009 because of their shape reminiscent of shark fins. With the 2.4 m high and together weighing 200 kg, fuel savings of at least 3.5% are possible, according to the manufacturer.
Wingtip Fences (slightly smaller winglets, aligned vertically or diagonally up and down). Examples:
- Airbus A300-600R , A310-300 , A320 Family , A380 ; Airbus makes these wingtip fences approximately symmetrical, i.e. that is, they are aligned equally up and down. For the A320 family, normal and blended winglets were also tested in flight tests in 2006, but were not taken into series production because of the insufficient efficiency gain in relation to the additional weight of the winglets.
- The transition from wingtip fences to conventional wing endplates is fluid. In tailless aircraft , end plates can also act as vertical stabilizers.
- Raked wingtips (wing tips curved upwards and backwards). Examples:
- Spiroids (loop-shaped wing tips). So far, this winglet shape has been investigated on a few test vehicles. Spiroids are said to be able to save fuel.
- Airbus A350 ; this type has a mixed form of blended winglets and raked wingtips , i.e. H. specially shaped, raised wing tips, which are not as strongly angled as other winglet shapes compared to the rest of the wing
- McDonnell Douglas MD-11 ; this type has a large winglet that is oriented diagonally above, which is supplemented by a small winglet that is oriented diagonally below
- Airbus A380 , Boeing 737 , Boeing 757 ; For the versions -700, -800 and -900ER of the Boeing 737, Boeing has been offering another hybrid version called Split Scimitar Winglets since 2014, and for the Boeing 757-200 since 2016 in cooperation with Aviation Partners . This consists on the one hand of a conventional, upwardly folded blended winglet and on the other hand, an additional smaller winglet protrudes diagonally backwards / downwards, which, using the example of a Boeing 737-800, leads to a further fuel saving of 1.6–2.2 % leads. In 2014, the cost of the upgrade was $ 550,000. A further development of this variant is used on the Boeing 737MAX under the name Advanced Technology Winglet . In 2017, Airbus confirmed a similar winglet design (without a name for it) for the version of the Airbus A380-800 called the A380plus with increased take-off weight.
Winglets on a model of the MD-11 in the wind tunnel
Wingtip fence of an Airbus A319
Inclined winglet of an Airbus A350-900
Split Scimitar Winglet on a Boeing 737-800
Advanced split scimitar concept on a Boeing 737MAX
Other use cases
Winglets can also be found on the rotor blades of some wind turbines .
Subsonic military aircraft, like passenger aircraft, can benefit from winglets, which is why some newer types have been fitted with them at the factory. However, supersonic aircraft such as jet fighters do not use winglets.
- Hermann Schlichting , Erich Truckenbrodt : Aerodynamics of the aircraft 1 (classic of technology) . Springer Verlag, Berlin 2001, ISBN 3-540-67374-1 .
- Hermann Schlichting, Erich Truckenbrodt: Aerodynamics of the aircraft 2 (classic of technology) . Springer Verlag, Berlin 2001, ISBN 3-540-67375-X .
- b737.org.uk Sketch of the air flow with and without winglets
- mandhsoaring.com (PDF) very detailed explanation (English; 136 KB)
- Reduction of the induced flow resistance based on nature's example
- Active Winglets as Multi-Axis Effectors Why a Morphing Aircraft and What is it? University of Bristol.
- EU research project (2002-2006): "Modeling and Design of Advanced Wing tip devices" (M-DAW)
- New winglets for Boeing 737-800: 3–5% less fuel saves the environment ( memento of October 23, 2008 in the Internet Archive ), Boeing press release of February 20, 2000.
- Blended Winglets Improve Performance. In: AERO Magazine No. 3, 2009 by Boeing.
- Is a winglet better than an equal span extension? March 18, 2016.
- Helmut Kreuzer: Jetliner, from the Comet to the Airbus A 321 . Air Gallery Verlag, Ratingen 1991, ISBN 3-9802101-4-6 .
- z. B. Jos Guggenmos from Kempten in the Allgäu the model "Wings".
- Object 9464/01: Hang glider: Wings with feathered wings in the Otto Lilienthal Museum Anklam.
- Information on Sharklets on airbus.com ( Memento from February 17, 2014 in the Internet Archive ), accessed on January 29, 2011.
- United Moves Forward with 757 Scimitar Winglets Installation. In: airlinegeeks.com. October 27, 2016, accessed December 20, 2016 .
- Article on b737.org.uk , accessed September 13, 2015.
- 737 MAX AT winglet. In: Boeing.com. Retrieved March 1, 2017 .
- A380plus: Super winglets for the super Airbus. In: aero.de. June 18, 2017. Retrieved June 19, 2017 .
- F1 aerodynamic dictionary: From the airbox to the winglet. Image 28 from 31st auto-motor-und-sport.de, March 24, 2009, accessed on September 27, 2015 .