Question

An airplane is doing a loop de loop. Where is G-force the strongest?

Answer 1

For a loop de loop, The centrifugal force due to rotaion always in the outward direction of loop. But the force due to gravity is always in downward direction. So the net force in lowest point of the loop de loop is addition of centrifugal force and gravity force. But in heighest point the net force is the difference between centrifugal and gravity force.

So, at the lowest point of loop de loop the G-force will be maximum.