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Do the pilots flying sidestick aircraft with fly-by-wire control systems, such as the Airbus A320, use the rudder pedals while in the air? Or does sidestick input affect both the rudder and the ailerons?

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The rudder pedals are not usually used in flight, even with the autopilot off.

The rudder on the Airbus A320 can be controlled via a mechanical connection to the rudder pedals in the flight deck, but also electrically via the fly-by-wire mechanism. The following graphic shows an overview of the rudder control:

A320 Rudder Control
(Airbus A320 FCOM - Flight Controls - Description)

As you can see the sidestick input goes to the ELAC (ELevator Aileron Computer) and from there a Yaw Order is sent to the FAC (Flight Augmentation Computer). This will then be passed on to the rudder via the Yaw Damper Servo Actuator.

Electrical Rudder Control

The yaw damping and turn coordination functions are automatic. The ELACs compute yaw orders for coordinating turns and damping yaw oscillations, and transmit them to the FACs.

Mechanical Rudder Control

The pilots can use conventional rudder pedals to control the rudder.

(Airbus A320 FCOM - Flight Controls - Description)

Since the yaw damping and turn coordination are fully automatic, there is usually no need for the pilot to use the rudder pedals in flight. There are however some situations, where manual rudder input via the pedals is required:

  1. Takeoff Roll: The rudder pedals move both the rudder and the nose wheel steering (NWS, see "NWS ORDER" in graphic above) on the ground to maintain directional control during takeoff and landing. After initiating the takeoff roll, the pilot flying (PF) will use the rudder pedals to control the aircraft:

    The PF should use pedals to keep the aircraft straight. The nosewheel steering authority decreases at a pre-determined rate as the groundspeed increases (no more efficiency at 130 kt) and the rudder becomes more effective.

    (Airbus A320 FCTM - Normal Operations - Takeoff)

  2. Landing: When landing the aircraft in a crosswind the direction in which the aircraft points is not aligned with the runway. To align the aircraft before touchdown (called de-crab), the PF needs to apply rudder input via the pedals during the flare:

    During the flare, rudder should be applied as required to align the aircraft with the runway heading. Any tendency to drift downwind should be counteracted by an appropriate lateral (roll) input on the sidestick.

    (Airbus A320 FCTM - Normal Operations - Landing)

    This is the only time (for normal operations) where the rudder pedals are actually used in flight.

  3. Engine Failure: After an engine failure the asymmetric thrust of the remaining engine needs to be overcome with the rudder. For an engine failure during the takeoff (but after V1), this needs to be done manually with the rudder pedals:

    On the ground: Rudder is used conventionally to maintain the aircraft on the runway centreline. [...]

    When safely airborne: [...] Since the lateral normal law does not command the full needed rudder surface deflection, the pilot will have to adjust conventionally the rudder pedals to center the beta target. [...]

    (Airbus A320 FCTM - Abnormal Operations - Operating Techniques)

    Once the aircraft has accelerated, the rudder is trimmed and no pedal input is required any more.

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  • $\begingroup$ "For an engine failure during the takeoff (but after V1), this needs to be done manually with the rudder pedals" Would this not also be required in the event of an engine failure before V1 in order to maintain the centerline until the remaining engine can spool down and/or reverse thrust deployed? For example, this video shows an A330 engine failure before V1 and you can almost immediately see hard rudder deflection to counter the asymmetric thrust and push the nose back toward the centerline. $\endgroup$ – reirab Oct 2 '20 at 17:13
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    $\begingroup$ @reirab Sure, the manual rudder input is also required before V1, but as you say, once the other engine has spooled down this would fall under point 1 (Takeoff Roll). I only specifically mentioned the case after V1 because you would still need manual pedal input in the air, which is what OP was asking about. $\endgroup$ – Bianfable Oct 2 '20 at 17:17
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Side stick or no, once airborne, you never touch the rudder pedals in any airliner when flying except during landing where independent rudder inputs are used to keep the airplane lined up during the flare. The yaw damper takes care of rudder coordination for normal flying; that is, in addition to controlling yaw excursions, it compensates for adverse yaw for you. The other main use of the pedals is for asymmetric thrust conditions from engine failures.

You use rudder on takeoff for nosewheel steering control, and you keep your feet on the pedals during the initial part of the departure in case an engine quits, but you never actually make any inputs while flying outside of landing, and I used to just put my feet on the floor after the departure to avoid applying pedal without realizing it during hand maneuvering, putting my feet back on the pedals on final.

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Sidestick input does NOT control both the yaw and roll axes. Pilots of sidestick aircraft still use the rudder pedals to control yaw and they use the sidestick for roll. This allows them to perform crosswind landings and sideslips in addition to coordinated turns.

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    $\begingroup$ As far as coordinated turns, you are right in the case of side-stick aircraft that do not employ a fly-by-wire system like a Cirrus. John K and Bianfable have pointed out that the computer does a lot more work for you in newer Airliners. $\endgroup$ – Dean F. Oct 1 '20 at 18:47
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    $\begingroup$ I wouldn't necessarily say "newer". I don't think you'll find any large swept wing aircraft without yaw dampers, dutch roll issues being inherent to the configuration, so even in a jet from the 60s you wouldn't be using rudder to fly and let the YD do it. In the very early days of autopilots, they were 3 channel with the AP running rudder as well (like the B-17). Jets went with standalone YDs because that active yaw control function is needed all the time not just when AP is engaged. $\endgroup$ – John K Oct 2 '20 at 15:25
  • $\begingroup$ @JohnK -- about the only jet I can think of that wouldn't have been that way back then were the early KC-135s, because they had no YD to start with $\endgroup$ – UnrecognizedFallingObject Oct 3 '20 at 2:51
  • $\begingroup$ Also no lift dumpers! There was a PBS documentary called Boomer And The Crew Dogs about a KC135 squadron in Plattsburg NY video.pbswisconsin.org/video/… and I remember a great clip of a KC doing touch and goes, with shots zoomed on the gear, and they would do gentle hops and skips once or twice on some landings, there being no landing spoilers. I wonder if the 707/KC had a sufficiently mild dutch roll mode to get away with no YD. On a lot of jets, perhaps most, it's quite dangerous. $\endgroup$ – John K Oct 3 '20 at 2:58

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