Serious question for a QFI

[FCSoverride]

I think.... momentum is mass x velocity. Velocity is a vector, thus momentum is a vector too, i.e. it has both magnitude and direction.

What this means is that, even at constant "speed" momentum changes around the loop (it swings around with the aircraft's velocity). Newton said roughly that "the rate of change of momentum is directly proportional to the applied force and takes place in the direction of that force".

To loop the loop, we need an extra bit of force perpendicular to the momentum vector to unbalance the forces on the aeroplane, i.e. to accelerate the aircraft mass towards the centre of the loop. This is produced by pulling back on the stick to increase angle of attack, increasing the lift generated by the wings, whilst maintaining airspeed with the throttle.