Winglets and Flight
Date: Fall 2011
How do winglets effect flight performance on an airplane?
NASA's Richard T. Whitcomb invented winglets in the early 1970s to increase the efficiency of airplane wings. Winglets function by reducing induced drag. Induced drag is an ever-present side effect of lift. If you have lift, you have induced drag. One particular source of this induced drag is wingtip vortices. A wing that is producing lift has higher pressure air below and lower pressure air above. Some of that higher pressure air wraps up around the tip of the wing to the top surface, creating a rotational flow to the air. The result is a trailing vortex of air coming from each wingtip. This vortex transfers energy to the atmosphere and takes away energy from the aircraft, resulting in increased drag and lower efficiency. The winglet helps by preventing some of the air below the wing from wrapping around to the top. The vertical (or near vertical) winglet provides an aerodynamic side load that acts to prevent the vortex from forming. Whitcomb found that an optimally designed winglet of a certain height can potentially provide twice the reduction in drag than a wing that is simply extended the same amount.
John C. Strong
Winglets on an airplane reduce turbulence at the wing tip, resulting in
less drag, a little more lift and most importantly, better fuel economy.
On an aircraft wing the wing tip area is the most inefficient area of the
wing. When in motion the aircraft wing creates a higher pressure below a
wing as compared to the area over the wing. This difference creates lift.
However, some of the air from below the wing escapes over the wing tip
diminishing the difference in pressure between the upper and lower areas and
therefore reducing the lift. The winglets and droop wing tips are an
attempt to reduce the amount of air moving around the wing tip and increase
the efficiency of the wing.
If you visualize this motion of the air over the wing tip and project it
through space as the aircraft flies, you will understand the origin of wing
tip vortices. The vortices can become quite strong behind large, heavy
When an airplane flies, the air on the top of the wing is at a lower
pressure than the air under the wing, producing lift, and allowing
the plane to fly. At the outer end of the wing, however, the
effectiveness of the wing is reduced because the high pressure air
under the wing flows around the wing tip to the lower pressure area
on the top. this is what produces the spinning air that trails
behind the wing tips that are know as wing tip vortices. Sometimes
you can see them. Google the term wing tip vortices to see pictures
of what they look like. Anyway, the process of making these
vortices produces drag on the airplane. It takes energy to start
the vortex spinning, and it comes from the passage of the plane
through the air.
Winglets get in the way of the air coming around the wing tip. They
are angled such that the air flows over the winglet at a specific
angle, producing lift on the winglet in the same way that the wing
itself produces lift. Because the winglet is at an angle, some of
this lift is in the forward direction, and gives the plane a little
bit of an extra push forward. In this way, the winglets recover
some of the energy that would otherwise be wasted as drag making the vortices.
Depending on the airplane, winglets can extend the range that can be
flown on a single tank of fuel by about 3 to 12 percent, which can
make a big difference in an airline's fuel bill over the life of the plane.
Wings have higher air-pressure underneath and lower pressure over the top.
the air is moving from front to back too fast to try to go around the front or back edge of the wing.
But it does start a move to go around the end tip of the wing.
It does not get very far before it passes to the rear edge and is gone,
but still, that means the air underneath is thrust away from the body
and the air on top is pulled towards the tail.
So behind the plane, air on top and on bottom are moving in opposite directions,
so they make little tornados extending backwards from each wing tip.
Not making these vortices would save energy and be safer for following planes.
Winglets push back in the direction opposite against each vortex,
so there is less vortex trailing behind each wing tip.
You might think of them as barrier-walls at the end of the wing,
so the air under the wing cannot escape around the wing-tips to the top,
trying not to do its job of holding up the heavy weight of the plane.
The real improvement is in the left-behind air well behind the airplane,
but the general idea is about right.
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Update: June 2012