In aviation we often refer to the bank of a turn as shallow, medium or steep. I remember reading somewhere that the definition is not universal as to how many degrees it is, but it has to do with the airplane and whether the bank tends to roll back to level, remain where it is or continue to steepen. Does anyone know if this is a correct definition or have any references to share?
I don't know if this is only definition out there, but according to the FAA's Airplane Flying Handbook:
Shallow turns are those in which the bank (less than approximately 20°) is so shallow that the inherent lateral stability of the airplane is acting to level the wings unless some aileron is applied to maintain the bank.
Medium turns are those resulting from a degree of bank (approximately 20° to 45°) at which the air- plane remains at a constant bank.
Steep turns are those resulting from a degree of bank (45° or more) at which the “overbanking tendency” of an airplane overcomes stability, and the bank increases unless aileron is applied to prevent it.
Also very closely related is the turning radius, which also depends on the speed. For example, a Rate 1 turn is defined as a turn that changes the aircraft heading 3 degrees per second, so it takes 2 minutes (120 seconds) to turn a full 360 degree circle.
If you are in an ultralight, doing 50 knots, you need approx. 50 / 10 = 5 + 7, or 12 degrees of bank to achieve a full circle in 2 minutes.
If you are in a 747 flying at 180 knots, you need 180 /10 = 18 + 7, or 25 degrees of bank to achieve a full circle in 2 minutes.
Both turns might be classed as "shallow" (although on that definition I would hate to do a steep turn in a 747).