7
$\begingroup$

In a typical car steering wheel if you release it while the car is in motion, it will return to its center, neutral position.

What's the corresponding situation in an airplane? Is a yoke self centering? Or does it stay put until corrected by the pilot inputs? Let's stick to non autopilot modes to simplify the basic behavior.

The forces on the control surfaces ought to be high when deflected from their default position, right? So I'm assuming that offers a restoring torque? E.g. with the rudder if you take your feet off the pedals then it centers, I think.

Some additional points:

  1. As a simplified case what happens on the ground when the aircraft is stationary. If I deflect the control surfaces to their extreme position & release the yoke would they all return to the neutral position? Is the restoring force gravity or spring loading?

  2. The answers on the other question seem to focus on ailerons but what about elevators?

  3. Does the rudder typically self center with more alacrity than the other surfaces? Why?

$\endgroup$
  • 3
    $\begingroup$ This depends on the roll stability of the airplane. For many there will be a correcting force below some bank angle and a diverging force above some bank angle with a neutral regime between. $\endgroup$ – casey Jul 22 '15 at 19:25
  • 1
    $\begingroup$ @Simon: Indeed. It looks a duplicate. What's the right protocol to close my question? Just to delete it? $\endgroup$ – curious_cat Jul 22 '15 at 19:57
  • 2
    $\begingroup$ Several folks will stop by and vote to close. It is usually considered a Good Thing™ at SE to leave the newly duplicate questions as a sign-post to the 'original' - if you didn't find the original, odds are good others won't either. This is one more opportunity for someone to find it instead of asking yet another duplicate. $\endgroup$ – FreeMan Jul 22 '15 at 20:15
  • 5
    $\begingroup$ @curious_cat: It may not be a duplicate. There are two things: whether the stick centres itself (yes, it does, for suitable, and relatively complicated, definition of centre) and whether the aircraft returns to flying straight (no, it does not). That suggested duplicate question addresses the later only. The former would still make a good question with potentially quite long answer detailing the definition of centre and what it means. $\endgroup$ – Jan Hudec Jul 22 '15 at 20:28
  • $\begingroup$ @JanHudec: Great. You are right. I am looking forward to some good answers about this. $\endgroup$ – curious_cat Jul 23 '15 at 4:39
2
$\begingroup$

With respect to "centering", a yoke only "centers" itself in the equilibrium point where forces on both ailerons and on both top and bottom of the elevator/stabilator are equal. That said, I wouldn't want to let the yoke "center and fly itself" as the forces on the control surfaces can be equal even when the aircraft is not straight and level. If not enough power is applied the plane will pitch down and "center" as you say, and if too much power is applied the plane will pitch up and then "center". As for roll, I find that in light aircraft (Cirrus excluded as the side stick has a spring mechanism) you don't usually want to leave the yoke out of hand as slight wind and light wind shear will cause the airplane to roll somewhat. So - short answer is - yes, it will "center" eventually but you might not like the attitude the plane is in when it's done, much of this depending on power setting and gusts/shear aloft/turbulence. As for autopilot, a roll and pitch (2-axis) autopilot actually continually applies force to the controls to keep the airplane level or turning as commanded, and at a constant altitude or climb/descent/airspeed as commanded, so I wouldn't say the controls really "center" when on autopilot either. Cheers!

As a bit more of an explanation, a "nice" airplane (one with positive aerodynamic stability) with the appropriate power setting should re-enter and maintain straight and level flight if the controls are disturbed and the yoke is released (but I've always had to input a little roll to keep the wings level). Check out the following picture from the FAA Pilot's Handbook of Aeronautical Knowledge Page 4-14:

PHAK 4-14

Notice that the orange line eventually gets more and more flat. You can expect that in a Cessna 172 or something of the like... not in a more aggressive plan like aerobatic planes and fighter jets - you'll see something a little more like the green or red line. You can read more in Chapter 4 of the FAA PHAK (link here).

$\endgroup$
  • 1
    $\begingroup$ By your explanation, gliders should self-center, but I can tell you from experience, gliders are no better than airplanes. $\endgroup$ – rbp Jul 30 '15 at 9:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.