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?
$\begingroup$ "the bank tends to roll back to level, remain where it is or continue to steepen. " That sounds more like a stability definition. There is neutral, positive, and negative stability. Is it at all possible you are mixing up steepness with stability? They both start with "st" :) $\endgroup$– Andreas LauschkeAug 4, 2015 at 21:00
$\begingroup$ No I'm not mixing anything up. Read the accepted answer. $\endgroup$– ryan1618Aug 5, 2015 at 11:50
$\begingroup$ OK, all right then! $\endgroup$– Andreas LauschkeAug 5, 2015 at 12:44
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).
$\begingroup$ Radius and bank angle are related only if you include speed, which is not in the original question. $\endgroup$– rbpAug 5, 2015 at 2:48
$\begingroup$ Oops! The point I was making is that there are many different definitions. Also what might be considered steep in one aircraft type might not be in another. The UK CAA tend to have three bank angles that interest them: 15 degrees, 30 degrees and 60 degrees. 15 being related to slow flight, 30 the max. for turns in the circuit and 60 the max. for normal category aircraft although they mention these angles many times in their docs. $\endgroup$ Aug 5, 2015 at 10:19