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Modern aircraft have yaw damper systems installed. Is there any difference between the two big manufacturers on yaw damper systems, such as the location, etc.?

I have to do some research on this topic and haven't found any answers yet.

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  • $\begingroup$ Interestingly, early on, autopilot systems like the Sperry C1 system used on the B-17 bomber were three axis with the A/P running the rudder to coordinate turns. 2 channel autopilots with a separate yaw damping system came along later due to the need for full time active yaw damping on swept wing jets when dutch roll issues came to the fore. The system doesn't care what the AP is doing so much, it just does whatever it has to do to resist yaw excursions and keep the ball centered, AP on or not. $\endgroup$ – John K Sep 10 '20 at 18:49
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The difference is more between conventional flight controls vs. fly-by-wire rather than Airbus vs. Boeing.

Both Airbus and Boeing used separate yaw dampers in their non fly-by-wire aircraft, which applied their commands with separate actuators to the rudder control servos, without feedback to the mechanically linked rudder pedals in the flight deck. The exact details will differ for every aircraft of course, but the general design is quite similar. Consider e.g. the Airbus A310 and the Boeing 747:

Airbus A310:

The rudder is controlled by 3 actuators, which are commanded by a single cable run from the rudder pedals. Rudder artificial feel is provided by a spring-loaded rod.

Additional inputs to the rudder come from:

  • the rudder trim, and
  • the 2 yaw dampers.

[...]

The yaw damper ensures the following functions:

  • dutch roll damping
  • turn coordination which becomes active if sufficient control wheel deflection is applied [...]
  • yaw compensation in case of engine failure, provided the AP is engaged in CMD with SRS (takeoff) or GO AROUND mode annunciated on FMA.

Yaw damper command is transmitted to the rudder but there is no deflection feedback sent to the rudder pedals.

A310 Rudder Logic

(Airbus A310 FCOM - Flight Controls - Rudder Control)

Boeing 747-400:

Yaw Dampers

Two independent yaw damper systems operate continously in flight to improve airplane directional stability and provide turn coordination. The upper and lower yaw damper actuators are powered by hydraulic systems 3 and 2 respectively. Yaw damper inputs do not result in rudder pedal motion.

747-400 Rudder Logic

(Boeing 747-400 FCOMv2 9.20.9 - Flight Controls - System Description)


On the other hand, fly-by-wire aircraft usually integrate the yaw damper logic into the fly-by-wire commands sent to the actuators. Consider e.g. the Airbus A320 and the Boeing 777:

Airbus A320:

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.

Rudder Actuation

Three independent hydraulic servojacks, operating in parallel, actuate the rudder. In automatic operation (yaw damping, turn coordination) a green servo actuator drives all three servojacks. A yellow servo actuator remains synchronized and takes over if there is a failure.

There is no feedback to the rudder pedals from the yaw damping and turn coordination functions.

A320 Rudder Logic

(Airbus A320 FCOM - Flight Controls - Description)

Boeing 777:

The yaw control law contains the usual functionality employed on other Boeing jetliners, such as the yaw damper and rudder ratio changer (which compensates a rudder command as a function of airspeed). However, the 777 FBW rudder control system has no separate actuators, linkages, and wiring for these functions, as have been used in previous airplane models. Rather, the command for these functions are calculated in the PFCs and included as part of the normal rudder command to the main rudder actuators. This reduces weight, complexity, maintenance, and spares required to be stocked.

(Boeing B-777: Fly-By-Wire Flight Controls 11.8.2 - Yaw Control)

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