Why do plane wings flex?

The question window-seat passengers ask most: “Why is the wing moving?” The answer is in the design itself.

Flexibility is a feature

Airliner wings are made to flex on purpose. Like a tree bending in the wind and springing back, a flexing wing smooths out ripples in the air and passes less of them to the cabin. A completely rigid wing would pass every small bump straight through.

In flight the wing lifts

On the ground the wingtips droop a little. Once airborne, lift starts carrying the wing and the tips curve upward. On long-range wide-body aircraft especially, the curve is clearly visible from the window.

It's tested

Before a new aircraft type enters service, its wings are bent on the ground under loads far greater than anything expected in flight. These tests are part of the standard process of manufacturers and aviation authorities.

In turbulence

In light turbulence you may see the wingtip rise and dip a little. That shows the wing doing exactly its job: absorbing the bump by flexing. If looking out makes you tense, turn your eyes to the cabin, a book or a screen; if it helps, watch the wing's calm rhythm.