# What is the minimum bank angle that an older aircraft like the Cessna 172 can apply in a coordinated turn?

Suppose the weather conditions are favorable and there are no significant winds. The Cessna with a speed of 200km/h starts a coordinated turn with a bank angle of 0.1°

The turning radius of this trajectory would be 180km. (a circular perimeter of 1130Km)

Would it be feasible to apply and hold such a small bank angle to draw such a circle?

When I say feasible, I mean that if there is a possibility that an old aircraft may set a bank angle as small or less than 0.1° in its controls.

• why do you think it would not be feasible? (usefullness aside) – Federico Dec 29 '20 at 15:02
• Just draw the circle on your sectional chart and fly it, keeping the ball centered. Your average bank angle will be 0.1 degrees. – quiet flyer Dec 29 '20 at 15:05
• This would be entirely theoretical. In reality you will have to compensate your turn for winds aloft so sometimes you would have a much higher bank angle to "draw" a circle on a map. – Ron Beyer Dec 29 '20 at 15:14
• When I say feasible, I mean that if there is a possibility that an old aircraft may set a bank angle as small or less than 0.1 ° in its controls. – El péndulo de Moisés Dec 29 '20 at 15:35
• Case in point. There are 10° & 20° marks on my Attitude Indicator. At my aircraft’s airspeed, I can guess through calculations and know through trial and error to place my bank indicator just a hair past the halfway point of the marks to affect a standard rate turn. But, I can not rely on that alone. I have to cross check that with a clock and a Directional Gyro (compass if necessary). And, that is with modern avionics. – Dean F. Dec 29 '20 at 19:23

No, it is not feasible. It is not feasible to sustain 1 degree of bank, let alone one tenth of that. There is no angle of bank indicator that precise, and even if there were it is not possible to maintain that level of accuracy for such an extended period of time.

For an example, ask yourself this: is it "feasible" for you to hold your fingertip exactly .001" from the tip of your nose for 2 hours? (Maintaining an air gap, not using a feeler gauge...) Of course not. It is not realistic to expect that kind of accuracy and inevitably you would sometimes touch.

However, you can reasonably meet the intent of keeping your finger fairly close. Or of flying a fairly precise arcing ground track if that is your goal.

For another example, assuming you have a driver's license and drive on high speed interstate highways, pay attention the next time you are on a gently arcing curve and see how much your steering wheel actually moves to hold the road. It doesn't. Not perceptibly. Not at 60MPH on a very gradual bend in the road. You simply hold it steady and make miniscule adjustments to stay in your lane.

Same thing in an airplane. You cannot hardly even detect one degree of angle of bank, you simply make fine and continuous adjustments to maintain track. (And sometimes a degree or two of bank is needed just to keep a straight course!)

As it has been pointed out, you are looking at this backwards: It is very easy to fly an arcing path, but you wouldn't do it in the manner you suggest.

• Yes. Humans, and probably most other animals, usually don't maintain precise anything. They work by feedback, constantly correcting position &c. It's the same as maintaining say a 10% bank angle: you constantly apply minor corrections. – jamesqf Dec 29 '20 at 17:10
• @jamesqf . . . . the difference being that 10deg + or - 1deg is still 9deg to 11deg but 0.1deg + or - 1deg is +1.1deg to -0.9deg and -0.9 means you're banked and turning in the opposite direction. – skipper44 Dec 29 '20 at 18:30
• Thanks for answering. I have heard that even in conditions where there are no crosswind components in straight and level flight, commercial aircraft must constantly move the nose 1 ° or 2 ° to the right and left. This is also done by banking to make small coordinated turns or only with the tail rudder? And what is the purpose of this maneuver? – El péndulo de Moisés Dec 29 '20 at 22:45
• If you try to drive a car or ride a bike in a straight line you will need to make small adjustments, right? You cannot just freeze things and expect it to track perfectly straight. Or move the steering wheel once and hold it steady, expecting to perfectly track a curve in the road with no additional corrections needed. Why do you think it would be any different in an airplane? – Michael Hall Dec 29 '20 at 23:18
• There are many differences in the physics of a car moving on a road and in the physics of an airplane moving through the air mass but I agree that corrections are necessary. I just wanted to know if this type of correction had a specific name and what would happen in practice if this horizontal movement of the nose is avoided for a certain time (obviously in ideal atmospheric conditions). So, assuming these constant corrections were unavoidable, I suppose that would be another reason why it would be unfeasible to sustain a 1 ° bank angle for long, even without considerable crosswind components – El péndulo de Moisés Dec 30 '20 at 1:19