It is a known fact you can improve the efficiency of fixed-wing aircraft by reducing drag.
Have you ever looked at birds in flight and wondered why their wings bend up at the tips, or the feathers flair out.
The intended effect is to reduce drag by partial recovery of the tip vortex energy.
NASA worked with manufacturers to experiment with technology to make more fuel efficient aircraft, and ultimately, engineers turned to nature for a solution.
If you extend the span, you 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 such as airport gates that limit the allowable wingspan.
Using wingtip devices and winglets, you can increase the effective aspect ratio of a wing without greatly increasing the wingspan.
Wingtip and winglet 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. Wingtip devices can also improve aircraft handling characteristics and also enhance safety for following aircraft by reducing wake turbulence.
Winglets reduce wingtip vortices, the twin tornados formed by the difference between the pressure on the upper surface of an airplane’s wing and that on the lower surface. High pressure on the lower surface creates a natural airflow that makes its way to the wingtip and curls upward around it.
A winglet is actually a wingtip device and are vertical extensions of wingtips. They are created as small airfoils and reduce the aerodynamic drag associated with vortices that develop at the tips as the aircraft flies.
Winglets are now a mainstay in commercial aviation. However, their journey has come a long way over the decades. Even though they have been conceptualized for over a century.
Here are some of the several different types of wingtip devices:
Wing end-plates
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.
Hoerner wingtips
Drooped wingtips are often called ‘Hoerner tips’ after Dr. Sighard F. Hoerner. He 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.
Gliders and light aircraft have made use of Hoerner tips for many years, such as seen on many Cessna and Piper singles.
The earliest-known implementation of a Hoerner-style downward-angled wingtip device was on a jet aircraft during World War II, the Heinkel He 162 in order to counteract the dutch roll characteristic, related to its wings having a marked dihedral angle.
Canted winglets
The 747-400 introduced in 1989, was the first commercial plane ever to feature canted winglets.
Boeing said that the aircraft’s winglets increased its range by 3.5% over the 747-300.
Canted winglets are short and are sloped upwards. They can be primarily seen on wide-bodies such as the Airbus A330 and A340 and 747-400. With several aircraft that deploy these winglets retiring, canted winglets are harder to come by these days.
Wingtip fence
A wingtip fence refers to the winglets including surfaces extending both above and below the wingtip. Both surfaces are shorter than or equivalent to a winglet possessing similar aerodynamic benefits. The Airbus A310-300 was the first airliner to sport wingtip fences in 1985.
Blended winglets
A blended winglet is attached to the wing with a smooth outward curve to reduce interference drag. A sharp angle between wing and winglet can interact with the boundary layer flow, causing induced drag, negating some of the benefit of the winglet.
Gulfstream pioneered blended winglets in the 1990s. However, most are commonly in use on modern passenger aircraft, such as several 737s and with 757s and 767s.
Along with extending range, Boeing states that they are proven to reduce drag, save fuel, cut carbon and nitrogen oxide emissions and reduce noise output.
Sharklets
Airbus introduced sharklets with its newer A320-family models. Despite the edgy name, the title is the primary difference with these winglets and Boeing’s blended offering. In fact, Airbus faced legal action over the patent of the design. Subsequently, the European manufacturer had to pay out following the dispute.
The A350’s sharklets do not resemble shark fins as much as the A320 family’s devices.
Spilt Scimitar winglets
Split scimitar winglets on seen on several Boeing 737 jets. These are also shaped below and above the wing. Notably, they are like blended winglets but have an added airfoil below the wing.
The Mc Donnell Douglas MD-11 was the first aircraft with split scimitar winglets in 1990.
Raked wingtips.
Here, the tip of the wing itself is swept back and has greater sweep than the rest of the wing. The usage is similar to winglets and aircraft such as the 787 Dreamliner, some 777s, and the 747-8 have these designs.
Altogether, there are several different modifications of wingtips. However, blended and canted are two of the most distinct variants. They nonetheless all serve the key purpose of reducing drag and improving fuel efficiency.
Like winglets, they increase the effective wing aspect ratio and diminish wingtip vortices, decreasing lift-induced drag.
Wingtip devices on rotating blades
Wingtip devices are also used on rotating propeller, helicopter rotor, and wind turbine blades to reduce drag, reduce diameter, reduce noise and/or improve efficiency. By reducing aircraft blade tip vortices interacting with the ground surface during taxiing, takeoff and hover, these devices can reduce damage from dirt and small stones picked up in the vortices.
The first homebuilt with winglets
Burt Rutan designed the VariEze, which first flew on May21, 1975. What made the VariEze unique was the winglets incorporated with rudders, well before NASA winglet flight tests. The canard aircraft rudders and vertical stabilizers are at the extremities of the swept wing. The VariEze pioneered glass reinforced plastic composite construction in homebuilt aircraft, simplifying winglet fabrication. Many other Rutan designed aircraft have similar features.
The first business aircraft with winglets
The Learjet 28/29 series was the first commercial aircraft with winglets.
Learjet exhibited the prototype Learjet 28 at the 1977 National Business Avaition Association convention with first winglets ever used on a production aircraft, either civilian or military. Learjet developed the winglet design without NASA assistance. Although the Model 28 was intended to be a prototype experimental aircraft, performance was such that it resulted in a production commitment from Learjet.