Angle of bank
Tried to make some diagrams but they didn't paste.
To clarify a few bits on angle of bank. I don’t know how to get some scientific / mathematical notations into this post so will make up some of my own.
Angle of bank (AOB) doesn’t in itself place any stress on the aircraft. G (G) does. As a simplified explanation imagine that the wings are trying to clap above the aircraft but we fasten the wings such that they can’t do that. The wings try to move up but can’t and the fuselage lifts under the wings. In level flight Lift (L)= Weight (W) and the load factor G = 1. In order to maintain level flight as AOB is applied the vertical factor of the L vector will be < W which always acts vertically therefore L has to be increased to ensure that the vertical factor of L will be = W. 60 AOB needs 2G for level flight.
Up to 60 AOB the slope or curve of G required for level flight is quite shallow but once we get beyond 60 AOB the curve, and therefore G, increases quite markedly.
The formula is cosAOB = 1/G so if max allowed G is 2.5 cosAOB = 1/2.5 and then for max G in level flight maxAOB = 66.5 degrees. Lockheed placed a G limit on aircraft then an artificial AOB limit of 60 AOB ensuring max G required for level flight is 2G and aircraft doesn’t need to be overstressed to maintain level flight.
You will notice that level flight keeps being mentioned. This is the only parameter used for AOB and G fatigue calculations. If you don’t want to maintain level you can bank to any angle, pull any G less than 2G and descend actally applying less stress on aircraft than doing a 60AOB level turn. (AOB and G required for level flight is completely independent of weight or speed so applies to all aircraft at all speeds)
Lockheed set an AOB limit and a limit is a limit but exceeding that limit at less than the aircraft G limit isn’t in itself placing undue or extra stress on the aircraft (assuming that rudder input is co-ordinated to balance turn).