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.