WINGLETS ON PASSENGER PLANES
Muratcan Savaskan
Martha Townsend, Writing 340
Abstract:
One of the most important yet simple innovations in aviation engineering has been the invention
and implementation of the winglet on the airplane wing. A simple mechanical piece, the winglet
reduces drag caused by swirling vortices of air around the tips of wings to increase efficiency,
range, and payload. As the technology becomes standardized, aviation industry companies have
begun retrofitting winglets to their fleets in order to see the benefits. This article discusses what
winglets are, their implementation, the benefits, and the industry uses.
Introduction
Increasing globalization has brought the world closer together. According to International
Air Transport Association statistics, in 2012 there were 26.2 million flights around the world.
People who are afraid of flying should feel more safe because the IATA states that there were
only 15 crashes during these 26.2 million flights, or to think about it differently, only
0.00000057% of flights crashed. As technology advances new aviation techniques are applied to
new designs, pushing the industry forward. Airplane manufacturing companies must compete
with each other to launch new and remarkable planes, such as Airbus’s A 380, the largest
commercial airplane ever built, or Boeing’s 787 Dreamliner which uses light and durable carbon
composites letting it consume 20 percent less fuel and produce 20 percent less emissions than
other planes in this category. These complex engineering projects rely on very small details; for
example, the 747 has six million parts that have to be produced, delivered and assembled. These
parts are very crucial and have very simple physical explanations, unlike other details in the
plane.
Electronics, such as flight software, have been used to control aircraft in new ways;
however there are still only a handful of mechanical devices that actually make the plane fly.
These mechanical devises are based on very simple physics. No developments have been more
important than these mechanical innovations in the airplane wing itself. Specifically, the smallest
details in wings, such as the elevator, flaps, wing twist, and maybe most importantly, winglets,
the upward curve on the tip of an aircraft wing. Winglets are perhaps the most simple innovation
with the greatest benefit. Fig. 1 shows the tip of a wing with a winglet.
Figure 1 Winglet on a United Airlines plane (www.latimes.com)
Principles of A Wing
What exactly are wings, and how do they make a plane fly? The wings are the main
components of a plane that allow it to fly by generating lift force. Wings are designed in a way
that the air flowing under the wing should generate more pressure than the air flowing above the
wing. When thrust causes the plane to move forward air moves past the wings and causes a
pressure difference between the top and bottom of the wing. Since the air flowing above is going
faster, the air pressure under the wings lifts the plane, because faster air causes less pressure on a
surface than slower air. The result is flight. In Figure 2, the airflow around the wing is illustrated
as you can see the wing from the side.
Figure 2: Airflow causing lift on a wing, from the side (www.engineeringexperts.com)
Winglets in Aviation Industry
Winglets are a small change to the design of wings that allow for greater efficiency,
speed, safety, payload, and range. When designing wings, there are many things to consider. In
the words of Airbus designers, “If the wings of the large birds like Steppe eagles were too long,
their turning circle would be too big to fit inside the rising columns of warm air which they use
to soar. The eagle’s wings perfectly balance maximum lift with minimum length by curling
feathers up at the tips until they are almost vertical. This provides a barrier against the vortex
(mass of swirling air) for highly efficient flight.” Similar to the curling feathers on the Steppe
eagle, a winglet is the curved-up tip of a wing. It is designed to reduce wingtip vortices, which
are tornados produced by the difference of air pressure on the bottom and top of a wing. These
tornados cause inefficiency, but winglets help reduce this by basically blocking airflow off a
wing’s tip and allowing it to flow back normally rather than in a vortex.
Winglets provide many other benefits in addition to efficiency. They give a performance
boost by reducing drag, which allows for a higher cruising speed. Since the development of
winglets aircraft are able to fly much faster and more efficiently. Winglets are also important for
the safety of aircraft. When the airflow around a wing reaches the wing tips, air from below the
wing moves to the top, which creates a vortex that reduces the lift force of the wings. This vortex
could even be strong enough to cause the wings to break, and at the least threaten the wings’
stability. Long wings are prone to flex, but strengthening them adds weight. Winglets are able to
give the effect of increased aspect ratio (relationship between wing span and distance from
leading edge to trailing edge) without actually having to extend the wingspan. This is important
as wings with a higher aspect ratio provide longer range at cruising speed. One study found that
while lengthening wings could reduce drag, the addition of winglets caused a 35% reduction of
drag and was shown to be the best method for achieving enhanced performance associated with
drag reduction.
Figure 3: ’Illustration of airflow with and without a winglet”.
There are even some slight environmental benefits to the use of winglets on an airplane wing.
Boeing states that winglets can account for a 6.5 percent reduction in noise levels on takeoff and
a 4.5 percent reduction in nitrogen dioxide emissions on a flight of 2,000 nmi. If used on all
aircraft, the addition of winglets could have a substantial environmental impact. Table 1 shows
how new planes equipped with winglets could save fuel, which means making less emission.
Table 1: Fuel savings on aircrafts with blended winglets.(www.boeing.com)
As described, a winglet is the curved tip of an airplane wing (pictured in Fig. 1). It is
produced by smoothly curving the tip of a wing into the desired shape that will increase
efficiency and speed. The winglet is made of the same materials as the rest of the wing, usually
aluminum because of its lightness and strength. Manufacturers have to carefully consider the
wing’s aspect ratio and fully-loaded weight to determine the optimal length of the wing with the
winglet. Planes that do not have winglets can have them added. This is done by removing the
desired amount of the end of the wing (determined by length and aspect ratio calculations) and
attaching the new piece with winglet to the existing wing. The material quality of a winglet
determines it’s endurance, strength, flexibility and weight. Therefore advances in material
science field also affects the aviation industry in terms of designing components with much more
durability and environmental benefits. Figure 4 shows the structure and composites of a blended
winglet used widely by Boeing.
Figure 4: Structure of a blended winglet.(www.boeing.com/aeromagazine)
Winglets were not popular on aircraft before the late 1970s. In 1976, because of the
energy crisis that raised fuel prices, Richard Whitcomb, a NASA aerodynamicist, published a
paper that compared a wing with a winglet to the same wing with an extension to increase its
span. Whitcomb found that winglets reduced the drag by about 20 percent and doubled the
improvement in lift-to-drag ratio, as compared to the other extended wing. His development of
the winglet was an important contribution to the science of aerodynamics. Boeing now offers
blended winglets (standard upward-swept extensions) as standard features of its Boeing Business
Jet and as optional on the 737-800 commercial planes. According to Boeing, these winglets
“allow an airplane to extend its range, carry as much as 6,000 lb more payload from takeofflimited airports, and save on fuel.” Winglets can even be retrofitted to older airplanes and have a
minimal effect on in-service maintenance of the plane, and the design allows for a wide range of
structural repairs.
There are a few different types of winglets that are now prominent in the industry. The
Hoerner winglet is named after a pioneer in the field. It is a drooping down wing tip commonly
seen on glider aircraft, instead of a curved up tip. This focuses the airflow or vortex away from
the top of the wing and reduces downward pressure, a very important benefit for gliders. The
blended winglet is the more commonly seen winglet on commercial airplanes, and is the
traditional upward raised tip that has been discussed above. Other new designs include the
Scimitar Winglet, which looks like a “Y” at the tip of the wing. The Scimitar Winglet can further
reduce drag (compared to blended winglet) by 2.5-3%. This results in additional fuel savings. As
winglets become standard on all aircraft, like everything else, the technology will continuously
develop and new designs will emerge. Figure 5 is an example for the ‘Y- tip of’ a Scimitar
winglet.
Figure 5 A Scimitar winglet.
As
discussed in Brian
Clancy’s Airfinance journal article, the competition in the cargo industry is high and any savings
a company can make translate to an advantage. Winglets, whether included on newer fleet
purchases or retrofitted to older aircraft, can make a huge difference in fuel savings, range, and
payload increases. More cargo means more profit, especially when you can save fuel on the trip.
As recently as three months ago, United Airlines decided to order a retrofit of a the Scimitar
Winglet on their fleet of 737-900ER. Aviation Partners Boeing says they expect the planes to be
able to increase their range by 60 nmi and save as much as 57,000 gallons of fuel per year while
carrying an additional 3,300 lbs of luggage. The benefits of winglets are obvious for a company
of this magnitude and a fleet of 76 aircraft.
Clearly, winglets are a very simple, yet fundamental, change to wing design that has had
a huge impact on the use of airplanes, as passenger planes or cargo planes. The retrofit of
winglets to older aircraft can provide immediate improvements in fuel efficiency, range, and
payload with other benefits to the environment. As new planes are designed and produced, new
winglet designs, such as the Scimitar Winglet that United adopted, will continue to improve
performance and push the aviation industry forward. Since the introduction of winglets in the
1970s they have become more and more popular in airplane design and will continue to be
implemented in the long term. In an industry made up of complex technology and engineering,
from computers and electronics to navigation and GPS, the simple benefits of a mechanical piece
like the winglet can be easily overlooked. Yet the benefits are nothing short of outstanding, as
evidenced by the increased range, payload, and fuel efficiency that the United Boeing 737900ER fleet expects with the retrofit of the Scimitar Winglet. The improvement of this
technology is certain, and the aviation industry as a whole will benefit.
Works Cited
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