Why Wings Flex — and Why That's a Good Thing
2 min read
The short answer
Wings are designed to bend, like a shock absorber. Flexing soaks up the energy of bumpy air, so you feel less of it. In testing, wings bend far beyond anything they'll ever meet in flight — the movement you see is a sign of strength.
Flexible Wings Are Stronger Wings
Watching the wings bend during turbulence is one of the most common triggers for flight anxiety. It looks wrong, as if something might break. In fact, it's one of the clearest signs that the plane is working exactly as designed.
Why Wings Are Built to Bend
A completely stiff wing would pass every bump straight into the cabin — and on to you. It would also be heavier and more likely to crack under extreme loads, because stiff things snap instead of absorbing energy.
A flexible wing works like a shock absorber. When a gust pushes up on it, the wing bends upwards and soaks up the energy. When the gust passes, it springs back. You feel only a fraction of the force.
How Far Can Wings Bend?
In testing, the Boeing 787's wings flexed about 25 feet (7.6 metres) upward, under 150% of the strongest forces the plane is ever expected to meet. That's far beyond anything they'll ever meet in flight.
In normal flight, even in strong turbulence, the wings bend only a small fraction of that. What you see from your window is a tiny movement compared with what the wing can handle.
Built Stronger Than Needed
FAA safety rules require the structure to take 1.5 times the biggest load it's ever expected to meet. It must hold that load for at least three seconds. Manufacturers test well beyond this before a plane is approved.
Wings are among the strongest parts of the plane.
How the Wings Are Joined
The wings aren't simply bolted to the sides of the cabin. They're joined to each other through a very strong centre wing box, which runs across the plane beneath the cabin floor. Together, the wings and the box work like one long, strong beam. The body of the plane is built around it.
Modern Materials
Newer planes like the Boeing 787 and Airbus A350 have wings made largely of carbon fibre. For its weight, it's stronger than steel, it resists wear well, and it flexes naturally. That lets engineers build wings that are lighter, stronger and more flexible than older metal ones.
What to Think When You See the Wings Move
Instead of "the wings are going to break," try: "the wings are soaking up the bumps for me." Every flex you see is the plane doing its job, shielding you from the full force of the air.
Sources
- FAA, 14 CFR 25.305 — Strength and deformation: https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25/subpart-C/subject-group-ECFRea44cbb3048b817/section-25.305
- Boeing, 787 Dreamliner Wing Flex Test: https://www.boeing.com/commercial/787family/background.page
- Boeing, Boeing Completes Ultimate-Load Wing Test on 787 (March 2010) — wings flexed upward about 25 feet at 150% of the most extreme expected forces: https://boeing.mediaroom.com/2010-03-28-Boeing-Completes-Ultimate-Load-Wing-Test-on-787
- Airbus (2017), New centre wing box design holds great promise for future aircraft (the part that supports and stiffens the wings): https://www.airbus.com/en/newsroom/news/2017-01-airbus-new-centre-wing-box-design-holds-great-promise-for-future-aircraft
- Wikipedia, Wingbox (the wing structure continues through the body as the centre wing box): https://en.wikipedia.org/wiki/Wingbox