Why when a plane is in flight, the wingtip goes up?

Flex of the wing structure by the action of the lift created by that wing -

When airplane is parked, no lift, so the wing bends down because of its weight -

The longer the wings are, the more the bending is noticeable -

ALL airplanes wings bend... some very little indeed -

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Wings have to be a little flexible so that they don't break under stress of rough air and air currents. It's the suspension system of the aircraft while in flight. In the air, the wings support the entire weight of the aircraft. Positive air pressure on the underside of the wing and negative (actually less positive) air pressure on the upper surface of the wing causes it to flex upward. It's almost like the airplane wing is being sucked upwards and the fuselage is being brought downwards by gravity.

The B52 bomber had a wing flex of -10 degrees on the ground to +22 degrees when airborne - a 32 foot difference. Longer wing spans have more flex. A small single engine, fixed gear Cessna has no measurable wing flex.

JetDoc is in part suitable. the reason of the bent wingtips is so they might greater healthy greater passenger planes on plane distributors. it particularly is a trick they discovered from WWII. it particularly is glaring that in case you may take a deliver nearer to Europe or Asia, it does not value as plenty for a airplane value ticket.

Well, that is because the wing is supporting the entire weight of the airplane! When the airplane takes off, the weight is transferred from wheels to the wing, and the flex you see is because of that. The wings are designed to support the weight of the airplane (and more) and can flex to surprisingly high angles.

Gravity pulls them down on the ground. When in flight, high pressure under the wing and low above, cause it to curve up. Thy are somewhat flexible.