C-17 Rudder

[JohnnyP]

Quick question...

What is the deal with the C-17's rudder always turning in the wrong direction during it's taxi turns?....How is that thing hooked up?

 

[AvroGuy]

Quick question...

What is the deal with the C-17's rudder always turning in the wrong direction during it's taxi turns?....How is that thing hooked up?

that would be called a yaw damper functioning

 

[JungleJett]

that would be called a yaw damper functioning

...on the ground? uhmmmmmm,

 

[AvroGuy]

...on the ground? uhmmmmmm,

Sure, In the E-3 we had two yaw dampers, series and parallel, I forget which one is primary and secondary. At any rate, one of the things to watch for was the yaw indicators during turns on the ground to ensure the rudder was deflecting out of the turn. Hence yaw damping. It was obvious from the exterior also. I am sure other planes that have full time yaw dampers will do the same thing.

 

[JungleJett]

The airplanes I have flown, (Civilian) are restricted from using the YD on the ground.

 

[AvroGuy]

The airplanes I have flown, (Civilian) are restricted from using the YD on the ground.

I know there are some planes that the YD isn't used until flight, but CRJ series, e-3, avro rj-85. On the other hand I thing
EMB-135-145 the YD is engaged after TO

 

[AvroGuy]

da.. it

 

[JungleJett]

I know there are some planes that the YD isn't used until flight, but CRJ series, e-3, avro rj-85. On the other hand I thing
EMB-135-145 the YD is engaged after TO

The ERJ's DO use the YD after TO.

 

[FADECtoBLACK]

I have asked this question several times of IP's and even some Boeing guys and have gotten several different answers - none definitive.

The most common "guess" I've been given says it's the Yaw Damper. One explanation is that the IRU's sense a turn, and the Yaw EFCS logic (if airborne) would be to dampen the movement with opposite rudder. Obviously a turn on the ground occurs over a much smaller radius than one in the air so the rudder responds with full deflection.

The other possible explanation I've been given is that it has to do with some sort of hydraulic lockout built into the system that comes into play when using the tiller to turn the nosewheel as opposed to the rudder pedals. On the ground, tiller inputs override rudder pedal inputs and provide a greater nosewheel angle, but I haven't been given much more detail than that.

Both sound good to me, but I'm not an engineer.

 

[JohnnyP]

.........

Also noticed it seemed to be only one-half of the rudder making the opposite direction turns.....

 

[LIGHTDRIVER]

It is the yaw damper.

 

[tankerswede]

The airplanes I have flown, (Civilian) are restricted from using the YD on the ground.

The smaller aircraft (Beechjet, Excel, etc.) can't use the YD on the ground because it directly and adversely affects the nosewheel steering - if you try to make a left rudder input the YD senses it and tries to push it right. You fight against the YD, for example, if you leave it engaged and land with it on. Or so I'm told...

The bigger airplanes have the YD and nosewheel steering as separate systems so the YD can be engaged on the ground. In the KC-135, for example, it is required to be on for takeoff and landing. You never feel it in the rudder pedals because it is a separate channel on the rudder control and the only way you know it is moving is by looking at the rudder deflection indicator on the panel.

Of course the -135 has a different fly-by-wire than the C-17...the wires are twisted into cables and everything is connected together with them.

 

[FFLSinHI]

Of course the -135 has a different fly-by-wire than the C-17...the wires are twisted into cables and everything is connected together with them.

Great analogy (LMAO)--I never minded that system. It brought me home safe many times. Every time my computer locks up, I can't help but wonder about fly-by-wire. I'll admit that I have become quite fond of boosted flight controls though.