AIRBUS A319/20/21 RUDDER CONTROL

[AIRBUS58]

WHY DOES THE RUDDER PEDALS SEND A SIGNAL TO THE ELAC,S ?

I KNOW ONE ANSWER TO CONTROL THE NOSE WHEEL STEERING.

WHAT OTHER REASON ,CAN YOU HELP

[SimJock]

for Rudder Trim via the Artificial feel unit ?

[ColdnFoggy]

Guess it needs a signal for turn coordination.

[AIRBUS58]

Thanks for the replys.

I know the rudder moves, when the rudder trim switch is activated ,and the rudder padels get feed back .If the movement of the pedals now input to the ELACS WHICH THE DO AS A MATTER OF COURSE what does the elacs do with this signal?

When the a/c is on the ground ,moving the padels input to the rudder and input to the nose wheel steering . Steering input is electrical and rudder input is mechanical. The electrical input is to the ELAC 1/2 for steering to the BSCU .

In flight if you put an input with the rudder padel and at the same time operate the side stick, you have turn cordination with the sidestick ELACS to FACS to the rudder .. .With this scenario ruddder padels has priority . .over the sidestick logic.

Am I right in saying then that the signal from the rudder pedals through the ELACS stops dual inputs to the rudder??

[Zeke]

AIRBUS58,

The rudder pedals are connected to the ELACS, and they in turn are connected to the FACs which electrically drive the servo jacks. One FAC is active at a time. The other FAC serves as a backup. As the primary computer, the ELAC computes the turn coordination and yaw damping orders. The signals are sent to the FACs. The FACs control hydraulic yaw damper actuators that position the rudder servojacks.

The FACs also limit the rudder travel based upon the aircrafts speed, if the FACs fail you get full rudder when the flaps are deployed.

The rudder pedals are also manually connected to the rudder servojacks by good old cables so you have manual backup control if the computers go offline and you still have at least one of the hydraulic systems.

The artificial feel unit provides feedback to the rudder pedals and moves the pedals when rudder trim is applied. The rudder pedals do not move in response to turn coordination or yaw damping action.

Zeke

[AIRBUS58]

Thanks zeke.

Are you saying then that the rudder pedals can move the rudder in two ways.

1 rudder pedals ELACS to FAC 1 yaw damper summing point rudder servo jacks. .2 rudder manual input summing point servo jacks.

[AIRBUS58]

To Zeke

Does that mean there are two inputs into the rudder at the same time .

If it does who has priorty ?

The Mehanical input will input into the summing unit happens ,is it that the electrical input through the yawdamper actuators happens along side the mechanical?

[Zeke]

Airbus58,

The inputs can be summed into the rudder.

The manual rudder control, ie rudder inputs are machanically activated by the cables, the automatic controls, ie turn co-ordination and yaw damper are electrical through the ELACs/FACs.

If you were to have an engine failure and step on the beta bar you are using manual control over the rudder, count the seconds as you wind in the rudder trim, and engage the autopilot. Then the yaw control is electrical with the autopilot trimming the rudder.

Zeke

[AIRBUS58]

zeke

When the rudder padel move a signal is sent to the ELACs . one reason is the nose wheel steering . The question is , is it only for steering .

You are correct in explaining the engine out scenario.

I believe the rudder padels only input to the rudder mechanicly not electrically through the elacs.. .The summing point is the clever mechanism which recieves inputs from the rudder trim,rudder pedals and yawdampers .

[Zeke]

Airbus58,

The ELACs receive sigals from the rudder pedals, autopilot, and sidesticks.

The ELACs then generate NWS commands and yaw commands.The yaw commands can be to balance a turn, yaw damper, rudder trim, which can be summed with mechanical rudder input.

The ELACs send commands to the FACs. The FACs also receive commands from the rudder trim and autopilot. The FACs the control the rudder limit, turn coordination, yaw damping, and rudder trim.

http://www.airplanepanelmaster.com/gallery/Images/A318-321/027.jpg

Z

[ 14 February 2002: Message edited by: Zeke ]</p>

[AIRBUS58]

Thanks Zeke, Its more clear in my mind now.. .Where did you get the schematic from ???

[N2]

Airbus58

This summing point or "Differential Mechanism" is an interesting unit whose net output is via a push pull rod that exits out of the stab compartment and travels up the rear spar face of the fin. Vertical motion from the differential mechanism is converted into horizontal motion through a bellcrank, one for each of the 3 rudder PCU's. Another rod from the bellcrank attaches to the PCU spool valve, movement of which ports hyd fluid to the head or rod side of the actuator.

Rudder travel limitation is simply done by restricting the vertical travel of the push pull rod on the backside of the fin thereby limiting PCU input.

To get back to the differential mechanism, it can receive simultaneously mechanical rudder peddle input(cable loop) and yaw damp actuator input (through the rudder peddle transducer -&gt; FAC). In manual flight it is constantly balancing out these two inputs finding a null point resulting in the net push pull rod output as mentioned above.

There is a little bit more involved of course, but I think this cuts to the chase.

N2

[spannersatcx]

Zeke if you right click on an image and select properties it will give you the url of where the image is on the net, in this case <a href="http://www.airplanepanelmaster.com/gallery/Images/A318-321/027.jpg" target="_blank">http://www.airplanepanelmast er.com/gallery/Images/A318-321/027.jpg</a> <img src="smile.gif" border="0">