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Whenever any object follows a circular path, there is always a centripetal force which is provided by something.

However, in the case of a glider making a loop in air, what provides the centripetal force?

This is the picture that made me think of this question:

enter image description here

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The ailerons do it. – DumpsterDoofus Apr 23 '14 at 16:28
up vote 6 down vote accepted

There is indeed a centripetal force acting on the glider as it moves through its loop. The size of the force depends on the mass of the glider, the speed of the glider and the radius of the circle the glider is following at the moment.

There are two sources for this force:

  1. The component of the force of gravity acting towards the center of the circle. This is negative in the lower half of the loop, and positive in the second half.

  2. The lift from the airflow over the wings of the glider. The pilot varies this force by adjusting the controls to maintain the desired path during the loop. This lift cancels the outward component of the force of gravity during the bottom portions of the loop, and combines with gravity during the top half of the loop.

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