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Have you ever looked out your plane window and wondered what the hell those little curly
bits at the end of the wing were for? The development of winglets, as we see them today,
started during the 1973 oil crisis. The Arab states put an Oil Embargo on the United States
for providing aid to Isreal during the Yom Kippur War. This caused oil prices to sky
rocket. Forcing engineers to get creative to reduce fuel consumption.
Enter, Richard T. Whitcomb. I could and probably will do an entire video about this guys contribution
to aviation, but let’s focus on his work with the Winglet’s for now. Part of his
inspiration came from birds that curl their wing feathers up while gliding to achieve
more lift. So he got to work testing this theory and found that it worked exactly as
he expected. Let’s take a look at the science. As you probably know from watching my previous
videos, planes fly by developing high pressure air under their wings and low pressure air
above. Fluids will always flow from high pressure regions to low pressure regions and this can
cause some problems at the wing tips. High pressure air from below the wing will bleed
into the low pressure air above, creating mini tornadoes off the tips of the wing. This is
called induced drag and it decreases the lift of the wing and increases the fuel consumption of the plane.
Winglet’s reduce this airflow by reducing the pressure gradient at the tips of the wings,
thus making the vortices much smaller. Their ultimate goal is to create a lift distribution
across the wing in the shape of an ellipse. This minimizes the amount of air that wants
to flow over the wing tips, while maintaining maximum lift. Let’s compare some wing shapes
and their lift distributions to see how this works.
Here are 3 wing shapes. An elliptical, rectangular and triangular wing and their lift distributions
look like this. As you can see the elliptical wing also has an elliptical lift distribution.
This is the ideal. The iconic Spitfire was one of the few mass produced planes in history
to have this shape, as it is difficult and expensive to manufacture.
The rectangular wings lift distribution is quite high at the edges and this leads to
high levels of induced drag, but this is the easiest shape of wing to manufacture and is
mostly used in smaller, cheaper aircraft. Our last wing, a triangular wing has high
lift in the center, which rapidly drops off to the edge. This type of wing has low induced
drag, but its lift distribution is far from ideal.
So the ultimate goal is to tailor the lift across the wing into the shape of an ellipse
to maximize lift and minimize induced drag. Winglets are just one way to do this. Boeings
latest plane the Boeing 787 Dreamliner has done away with winglets in favor a raked wingtip,
which sweeps the tip of the wing backwards. Boeing have said that their raked wingtips
have improved fuel efficiency by 5.5% over the 4.5% for conventional wingtips. You can
learn why this alters the lift distribution by watching my video “Why are plane wings
angled backwards” If you would like to learn more about the
costs of air travel, check out this quick preview for a video Wendover Productions and
I worked on.