Originally Posted by HarryC

The physics of a loop is interesting.

Assume a perfectly circular loop.

If load at the bottom is 3G, 1G of that is normal gravity, so the loop itself is causing 2G. If the speed was constant all the way around, the load would be 3G at the bottom and 1G over the top, because the loop is causing 2G and inverted you have to deduct, not add the 1g of gravity. To make the wing pull 1G, the plane is already trimmed to fly at that, so the elevator would be at neutral over the top of the loop.

But keeping a perfectly constant speed is near impossible.
Let’s see what happens if the speed at the top of the loop is half what it is at the bottom of the loop, remember we are keeping the plane going around a perfect circle.
Again 3G at the bottom, of which 2G is the loop and 1G is gravity. The G load of the loop part is velocity squared/radius. For a perfect circle the radius is fixed, so G load varies with the square of the speed. Since the speed at the top is 1/2, the G load is 1/4 what it was at the bottom. 1/4 of 2G is 1/2G, so at the top, the loop part causes 1/2G load, but it is inverted so deduct the 1G due to gravity, and the G load is minus 1/2G.

So in a perfectly circular loop which has 3G at the bottom and where speed over the top is half what it was at the bottom, the G load varies between plus 3G at the bottom and minus 1/2G at the top.

To get minus 1/2G the elevator needs to be pushed forward.

The actual numbers for your model will depend on initial G load, how much speed is kept or lost, but the point you can see is that it is perfectly possible for G to go negative over the top of a genuinely circular loop. It also shows you why most loops are not circular, because people are still pulling back over the top, when they should be pushing forward!

Another factor of loops is that on a prop driven plane, the rudder is only trimmed at one speed and throttle setting, a change in either will cause the plane to yaw. With the way our props rotate, high power and low speed causes a yaw to the left, so right rudder is required to stay straight. Loops involve high power and low speed so some right rudder will be required as soon as speed starts to reduce and will reach a peak at the slowest part of the loop.

Someone said ailerons reverse if supersonic, not true, if it were true it would make it near impossible for people to fly supersonic planes!