Aircraft Winglets Explained

Aircraft Winglets Many of us who fly regularly have most probably seen a so-called winglet or wingtip device at the end of the wing of an airliner at least once. It is showing up more and more often on more and more types of aircraft, thus we felt it’s time to give an overview to our readers about these sometimes funny, sometimes cool and stylish looking aircraft parts. History, Reason and Benefits The initial theoretical concept goes back to times before even the Wright Brothers first took to the skies in 1905, but it was picked up and developed by Richard T.

Whitcomb of NASA after the 1973 oil crisis – in order to reduce fuel consumption.

The first tests were carried out in 1979/80 in cooperation with the U. S. Air Force. At almost the same time, but independent of any U. S. military organization, a private jet producer, LearJet exhibited a prototype in 1977: the LearJet 28 that featured the first winglets on a jet and a production aircraft.

Flight tests made with and without winglets showed that the winglets increased range by about 6. 5 percent and also improved directional stability for the LearJet- these two factors are the major reasons behind using this facility at any fixed wing aircraft ever since.

A winglet is a (near) vertical extension of the wing tips. The upward angle of the winglet, its inward angle as well as its size and shape are critical for correct performance – this is why they can look quite different. Air rotating around the wing strikes the surface of the winglet that directs it in another direction – thus creating an extra force, basically converting otherwise wasted energy to thrust.

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This is a small contribution but can save a lot for an operator in an aircraft’s lifetime. Another potential benefit of winglets is that they reduce the strength of wingtip vortices, which trail behind the plane.

When other aircraft pass through these vortices, the turbulent air can cause loss of control, possibly resulting in an accident. Winglet Types In general any wingtips that not end the wing simply horizontally are considered as some kind of a winglet. Even though in strictly technical terms Wingtip Fences are not real extensions of the wing, and Raked Wingtips do not have a vertical part, they are still widely considered as winglet variants. WINGTIP FENCES are a special variant of winglets, that extend both upward and downward from the tip of the wing.

Preferred by European plane-maker Airbus, it is featured on their full product range (except the A330/340 family and the future A350). The Airbus A300 was actually the first jet airliner to feature this kind of solution by default, but it was a very small version of the tool. Provided that most of the Airbus planes (including all A320 family jets) feature such wingtip fences, this may be the most seen and most produced winglet type. Even the new Airbus A380 double-decker features wingtip fences. Airbus Winglets as seen from the outside

Airbus Winglets as seen from onboard BLENDED WINGLETS (the real “Winglets”) are the most popular winglet type, leveraged by Airbus, Boeing, Embraer, Bombardier but also by Russian Tupolev and Iljushin. Blended winglets were first introduced on the McDonnel Douglas MD-11 aircraft in 1990 with launch customer Finnair (it also features a smaller winglet at the bottom side of the wing). In contrast to Airbus who applies the wingtip fences by default on most of their aircraft (and the winglets on the A330/340 family), lended winglets are considered by Boeing for example as an optional extra feature on their products, except for the Boeing 747-400. For some of the older Boeing jets (737 and 757) such blended winglets have been offered as an aftermarket retrofit, these are the newer, tall designs and do not connect to the tip of the wing with a sharp angle, but with a curve instead. These winglets are popular among airlines that fly these aircraft on medium/long haul routes as most of the real fuel savings materialize while cruising.

Longer flights mean longer cruising, thus larger fuel savings. And they also server as marketing surface for airline logos or web addresses usually. Just recently the Boeing 767-300ER has received 3. 4 m high (! ) winglets produced by Aviation Partners Inc. with American Airlines as the launch-customer with Air New Zealand and Hawaiian Airlines following with orders of 5 and 8 aircrafts respectively. 141 shipsets have been pre-sold already as the forecasted fuel savings range around 4%-6% for medium/long-range flights.

Airbus earlier tested similar blended winglets designed by Winglet Technology for the A320 series, but determined that their benefits did not warrant further development and they stayed with the wingtip fences instead. Aviation Partners Boeing claims that winglets on 737s and 757s have saved a collective 1. 2 billion gal. of fuel since they were introduced and 11. 5 million tonnes of CO2 while reducing those types’ noise footprint by 6. 5%. It has sold winglets to 140 airlines and 95% of all 737NGs are fitted with them.

It is working on four winglet concepts for the 777 and hopes to finalize a design for that aircraft type by December, 2008. Blended Winglets on Several Aircraft Types RAKED WINGTIPS are the most recent winglet variants (they are probably better classified as special wings, though), where the tip of the wing has a higher degree of sweep than the rest of the wing. They are widely referred to as winglets, but they are better described as integrated wingtip extensions as they are (horizontal) additions to the existing wing, rather than the previously described (near) vertical solutions.

The stated purpose of this additional feature is to improve fuel economy, climb performance and to shorten takeoff field length. It does this in much the same way as “traditional” winglets do. In testing by Boeing and NASA, raked wingtips have been shown to reduce drag by as much as 5. 5%, as opposed to improvements of 3. 5% to 4. 5% from conventional winglets. Airliners to use raked wingtips: Boeing 747-8, Boeing 767-400ER, Boeing 777(-200LR; -300ER; and freighter versions) plus the new Boeing 787 Dreamliner and the Airbus A350.

The 747-8, the 787 and the A350 will have special, new kind of wings, which do not have a separate winglet, but have raked, and blended wingtips integrated – without a sharp angle between the wing and the winglet. Raked Wingtips on the new Boeing 787 and Airbus A350 As you can see, wingtips/winglets have developed and changed very much over the last 30 years, but are becoming the standard, which is not proven better by anything else than the wing designs of future aircraft by the largest airplane-makers that feature a built-in winglet at the tip of their new, evolutionary wings. Raked wingtip Boeing 787 Dreamliner rollout showing raked wingtip Raked wingtips are a feature on some Boeing airliners, where the tip of the wing has a higher degree of sweep than the rest of the wing. The stated purpose of this additional feature is to improve fuel efficiency and climb performance, and to shorten takeoff field length. It does this in much the same way that winglets do, by increasing the effective aspect ratio of the wing and interrupting harmful wingtip vortices. This decreases the amount of lift-induced drag experienced by the aircraft.

In testing by Boeing and NASA, raked wingtips have been shown to reduce drag by as much as 5. 5%, as opposed to improvements of 3. 5% to 4. 5% from conventional winglets. [16] While an equivalent increase in wingspan would be more effective than a winglet of the same length, the bending force becomes a greater factor. A three-foot winglet has the same bending force as a one-foot increase in span, yet gives the same performance gain as a two-foot wing span increase. [27] For this reason, the short-range Boeing 787-3 design called for winglets instead of the raked wingtips featured on all other 787 variants.

Raked wingtips are installed on, or are planned to be installed on: * Boeing P-8 Poseidon * Boeing 747-8 Freighter * Boeing 747-8 Intercontinental * Boeing 767-400ER * Boeing 777-200LR * Boeing 777-300ER * Boeing 777 Freighter * Boeing 787-8 Boeing 787-9 Anyway – The performance of a commercial transport airplane is typically measured in terms of mission capability and operating costs. Mission capability can be improved by reducing airplane drag during takeoff climb and cruise, and by utilizing designs that minimize structural weight.

Operating costs can be reduced by reducing airplane cruise drag (hence, resulting in less fuel burn and less fuel costs) and by utilizing designs that are inexpensive to manufacture and maintain. Further, for commercial operators, higher profits can be achieved by being able to transport more customers and/or goods for a given flight. Because the additional payload increases takeoff weight, it is even more desirable to reduce takeoff drag for takeoff-climb-limited missions. – nothing new here right ? The objectives of reducing drag, reducing weight, and reducing complexity (hence manufacturing and maintenance costs) are often in conflict.

Adding a wingtip extension member can reduce the drag of a given airplane, but this will usually require increasing structural weight – IE winglets bend the hell out of wing roots because of the increased moment arm – therefore you need to beef up the wing judiciously – on shitty wing designs – the weight increase can “washout” the efficiency increase by additing a winglet in the first place.. Sooooooo – Weight increases are due to the weight of the wingtip extension member and also due to strengthening required of the existing wing structure in order to support the increased bending moments exerted by the wingtip extension member.

Additional weight penalties can also occur if the extension exacerbates flutter. – IE if you fiddle with ANY WING design after flight test – you change its natural resonance – IE it becomes a new tuning fork – heaven forbid it will like to resonate at cruise mach – IE flutter.. 747 has a speed advantage over the A340 because of flutter – the old crusty 747 hauls ass – the A340 could haul ass if it didnt like to shake itself apart at VMO.. ( my personal opinion based on 2nd hand info .. This conflict between the benefits of reduced drag and the disadvantages of increased weight has motivated designers to find an optimal balance between the two when designing a wingtip extension member. One such attempt is described in U. S. Pat. No. 5,039,032, incorporated herein by reference. The ‘032 patent describes a number of wingspan extensions termed “High Taper Wing Tip Extensions”. These are also known as “raked wingtips”. Raked wingtips are generally characterized by leading-edge sweep angles that are greater than the main wing sweep angles and are significantly tapered (i. . , the chord length decreases in the spanwise direction. ) Raked wingtips offer several advantages, some of which are outlined in the ‘032 patent. These advantages include the aerodynamic benefit of drag reduction due to increased wingspan, and a number of weight-reduction advantages (relative to simply extending the wingspan of an existing conventional main wing. ) Two weight advantages are attributed to the wingtip taper. At high-load-factor structural design conditions, the smaller chords are subjected to less load and they result in less induced loading on the outboard main wing.

These are both factors that reduce the bending moment that the inboard wing must support. Two more weight advantages are attributed to leading-edge sweep. The leading-edge sweep of a raked wingtip results in the center of pressure being located further aft than for a simple extension of an existing conventional main wing. At the high load-factor structural design conditions, this relative aft-movement of the center of pressure causes the sections of the main wing adjacent to the raked wingtip to be twisted more leading-edge-down, thus reducing the loading on these sections and the bending moment that the inboard wing must support.

The relative aft-movement of the center of pressure also acts to attenuate flutter. The raked wingtips described in patent ‘032 range from moderate span extensions (e. g. , 6% increase in span) to large span extensions (e. g. , 12% increase in span). It is the large span extensions that offer the greatest benefits. Regardless of these benefits, there are challenges in implementing raked wingtips on some aircraft. For example, on aircraft designed to operate at high subsonic Mach numbers (i. e. , at or greater than about 0. 0) there is a tendency for the boundary layer on the upper surface of each raked wingtip to separate under high-lift conditions (such as during takeoff climb or landing). This boundary-layer separation has the potential to increase drag and to generate premature buffet. The primary motivation for adding a wingspan extension is to increase the lift-to-drag ratio (primarily by decreasing drag), both during cruise and takeoff climb. If there is a significant drag increase due to large-scale boundary-layer separation under takeoff climb conditions, part or all of the takeoff-climb improvement is lost.

When the raked wingtip boundary layer separates, there is also a possibility of unsteady aerodynamic forces strong enough to vibrate the airplane structure and to be perceived by the airplane pilot as buffet indicating the onset of aerodynamic wing stall. If this form of buffet occurs prematurely (that is, within what would normally be the operating envelope), stall speed must be declared at a speed significantly higher than the aerodynamic wing stall, thus degrading airplane performance. The ‘032 patent acknowledges the tendency of the boundary layers on raked wingtips to separate under high-lift conditions.

In the ‘032 patent, raked wingtips are categorized into two groups, one group with leading-edge sweep angles between 40 and 50 degrees and another with leading-edge sweep angles between 50 and 60 degrees. For the first group, the ‘032 patent indicates that some form of a mechanical leading-edge high-lift device (such as a slat) is required in order to avoid premature low-speed buffet. The addition of a mechanical leading-edge high-lift device avoids premature boundary-layer separation, alleviating the buffet problem, but it adds profile drag, weight, complexity, and cost.

Under some circumstances, these disadvantages may outweigh the benefits of the raked wingtip. For the second group, the ‘032 patent indicates that the wingtip leading-edge sweep is great enough to trigger the formation of a stable leading-edge vortex, and that therefore premature buffet will not occur and no high-lift mechanisms are required. The inventors herein have discovered that under some circumstances, leading-edge sweep angles of 50 to 60 degrees may not be adequate to ensure the formation of a stable leading-edge vortex when conventional transonic airfoils are used for the raked wingtip geometry.

As used herein, “transonic airfoils” are those designed to operate at high subsonic freestream Mach numbers, with significant regions of locally supersonic flow. Additionally, even if the presence of a stable leading-edge vortex prevents premature buffet, such a vortex may result in higher drag than if the majority of the raked wingtip boundary layer could be kept attached over the range of typical operating conditions. Further, the technical viability of any raked wingtip would be improved greatly if there was no requirement for a leading-edge high-lift mechanism.

Thus, the evolution of the improved raked wingtip, particularly for use with aircraft that operate at high subsonic Mach numbers. The ideal raked wingtip would provide the aerodynamic benefits of an increase in wing span, while avoiding premature boundary-layer separation under high-lift conditions. Further, the optimal arrangement would not add significantly to wing weight or wing complexity. Both the raked wingtip ; the blunt raked wingtip are Boeing inventions. Airbus A330/A340 uses the 747-400 winglet.

The A320 family of airplanes uses the AIRBUS ( opps BAE – UK developed ) delta winglet that has an opposite plan-form camber on the upper ; lower half of the winglet – to gracefully control the direction of the vortices comming off the top ; bottom of the wings to kinda mesh them together non distructively – a clever design – by a company with a fine British aircraft heritage .. god save the queen .. All that being said – winglets on business jets regardless of eficiency increases are for sex- appeal ..