NorthstarBoy
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Nosewheel Steering Question

Mon Jul 02, 2012 10:38 am

I got to thinking today about the few PPL discovery rides I took as a teenager years ago and how hard it was to keep the nose wheel aligned to the center line in order to keep the airplane from sliding off into the ditch as it buzzes down the runway and wants to gradually drift left or right of center.

Assuming that the same phenomena happens in the big jets, how do the pilots prevent it?
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tdscanuck
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 11:04 am

Quoting NorthstarBoy (Thread starter):
Assuming that the same phenomena happens in the big jets, how do the pilots prevent it?

Well, jets don't have asymmetric thrust the way that small GA aircraft do and their time constant is long (i.e. they don't react particularly quickly) so the problem isn't as bad. However, the nosewheel on big jets is hooked into the rudder pedals just like on what you flew. Gentle pressure on the pedals is all you need to keep on centerline.

Tom.
 
ALTF4
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 2:48 pm

Quoting tdscanuck (Reply 1):

How does the tiller fit into that? I've heard (could be wrong) that on planes with a tiller, the PNF provides steering during the takeoff run until the rudder authority comes in? Depends on the plane, I assume.
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BoeingGuy
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 3:12 pm

Quoting ALTF4 (Reply 2):
Quoting tdscanuck (Reply 1):

How does the tiller fit into that? I've heard (could be wrong) that on planes with a tiller, the PNF provides steering during the takeoff run until the rudder authority comes in? Depends on the plane, I assume.

The tiller controls nosewheel steering at all times. Tom was referring to the rudder pedals also giving about 15 degrees (I forget the exact number) of nosewheel steering on the ground. That's enough to make minor adjustments during landing and takeoff roll, but not enough for sharp turns during taxi. This alleviates the pilots from having to hold the tiller during takeoff and landing. They do use the tiller during taxi, of course.

On Boeing airplanes the procedure is to use the tiller until the airplane is lined up with the runway. Then the PF uses the rudder pedals to steer during takeoff roll. As mentioned, the rudder pedals control both the nosewheel and rudder so at that point it doesn't matter whether they've reached the rudder authority speed. The PM (Pilot Monitoring) never touches the tiller. (Boeing no longer uses the term PNF - Pilot Not Flying, but rather calls it PM now).

Right side tillers are baseline on the 777 and 787, but optional on other models. Thus for a 767 without the F/O tiller, for example, only the Captain steers during taxi. If the F/O is making the takeoff then the Captain lines the airplane up with the runway and then the F/O takes over steering with the rudder pedals. If the Captain chooses to RTO then he/she takes back steering control with the rudder pedals if the F/O was making the takeoff.

Some airlines' SOP were that only the Captain can taxi at any time, even on the 777 which has a F/O tiller. CO was one example AFAIK.
 
yeelep
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 5:28 pm

Quoting tdscanuck (Reply 1):
However, the nosewheel on big jets is hooked into the rudder pedals just like on what you flew.

I think its likely the planes he flew on did not have nosewheel steering, instead relying on differential braking to steer until the rudder became effective.

To give an idea of the difference between rudder pedal and tiller steering. A 737 has tiller steering of 78° L/R and 7° L/R pedal steering.
 
atct
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 6:10 pm

Quoting NorthstarBoy (Thread starter):
Assuming that the same phenomena happens in the big jets, how do the pilots prevent it?

Experience and time. With time on a certain model of aircraft it becomes as if the airplane is an extension of your body. I have no problem taxiing the super cub in strong winds and keeping it on center line, nor the king air. Now throw me into my buddies twin commander and im like a pinball between the edges constantly jerking the brakes (Twin Commander's have a very odd rudder / nosehweel / brake linkage system) yet he can do it smooth as silk with no problems. It all comes with time and experience!

Clint
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ALTF4
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 6:39 pm

Quoting BoeingGuy (Reply 3):

Wow, thanks for the detailed response.
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tdscanuck
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 7:06 pm

Quoting ALTF4 (Reply 2):
I've heard (could be wrong) that on planes with a tiller, the PNF provides steering during the takeoff run until the rudder authority comes in? Depends on the plane, I assume.

You definitely don't do that on a Boeing; you may on other types but I'm not sure. If I was PF on a Boeing and the PM touched the tiller during takeoff roll I'd be strongly tempted to abort below V1 because he's never supposed to do that and he'd better have a damn good reason. Also, I wouldn't see him do it so it would look, to the PF, like an uncommanded nosewheel motion.

Quoting BoeingGuy (Reply 3):
Tom was referring to the rudder pedals also giving about 15 degrees (I forget the exact number) of nosewheel steering on the ground.

Total swing is 14 for most Puget Sound heritage Boeings (+/- 7 like yeelep said). The bigger jets are +/- 70 (as opposed to 78 on the 737).

Quoting yeelep (Reply 4):
I think its likely the planes he flew on did not have nosewheel steering, instead relying on differential braking to steer until the rudder became effective.

That capability is present but you don't use it during takeoff roll (unless you're already aborting the takeoff) because you don't want the brakes on while you're trying to gain speed.

Tom.
 
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larshjort
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 7:24 pm

Quoting tdscanuck (Reply 7):
You definitely don't do that on a Boeing; you may on other types but I'm not sure. If I was PF on a Boeing and the PM touched the tiller during takeoff roll I'd be strongly tempted to abort below V1 because he's never supposed to do that and he'd better have a damn good reason. Also, I wouldn't see him do it so it would look, to the PF, like an uncommanded nosewheel motion.

How is it done on the 737 and 787? The CRJ is electrically "measured" and hydraulic actuated. An RVDT on the tiller and on one of the rudder pedal quadrants sending signals to the same cbox and then adding the total together.

Quoting tdscanuck (Reply 7):
Total swing is 14 for most Puget Sound heritage Boeings (+/- 7 like yeelep said). The bigger jets are +/- 70 (as opposed to 78 on the 737).

I believe thats the same on the CRJ200 also.

/Lars
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yeelep
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RE: Nosewheel Steering Question

Mon Jul 02, 2012 11:01 pm

737 tiller steering is by cable input/feedback through a summing mechanism to a metering valve which ports hyd. fluid to the steering actuators. The rudder pedal input mechanically connects to the tiller cable run through a quadrant that is engaged by a electrical rotary actuator. The quadrant also provides centering forces using a spring. Wonderful Flintstones technology.
 
BoeingGuy
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 1:01 am

Quoting yeelep (Reply 9):
Wonderful Flintstones technology.

Just like the 1955 style light driven alerting system on the 737. But hey, it works.

The 787 has fly-by-wire nosewheel steering. I believe even the 777 is mechanical.
 
tdscanuck
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 1:51 am

Quoting BoeingGuy (Reply 10):
The 787 has fly-by-wire nosewheel steering. I believe even the 777 is mechanical.

Yep. 787 was the first Boeing to go steer-by-wire, all predecessors are cable-actuation, hydraulic power.

Tom.
 
aklrno
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 6:11 am

Quoting yeelep (Reply 4):
I think its likely the planes he flew on did not have nosewheel steering, instead relying on differential braking to steer until the rudder became effective.

I didn't know that even existed in aircraft. That's how you steer tanks. At least with a tank minor errors usually cause you no harm, but adjacent objects may be in serious trouble.
 
Max Q
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 7:05 am

I stand to be corrected but I believe that nosewheel steering through the rudder pedals is an option on some models of the B747
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larshjort
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 12:44 pm

Quoting aklrno (Reply 12):
I didn't know that even existed in aircraft. That's how you steer tanks. At least with a tank minor errors usually cause you no harm, but adjacent objects may be in serious trouble.

The Cirrus SR20 has a free castering nosewheel, I can't remember how much but it is +90 degrees to each side the hinge point is to the front of the wheel sio it wil self centerif the is no force acting on the fuselage and the brakes isn't applied.

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/Lars
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fuelfool
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 7:28 pm

Quoting yeelep (Reply 4):
I think its likely the planes he flew on did not have nosewheel steering, instead relying on differential braking to steer until the rudder became effective.

The most common trainers have nose wheel steering, i.e. C-172.
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golfradio
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 7:34 pm

Does the nose wheel return to center automatically after using the tiller? Also is there an attitude indicator for the nose wheel (to indicate how many degrees off center)?
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tdscanuck
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 8:06 pm

Quoting golfradio (Reply 16):
Does the nose wheel return to center automatically after using the tiller?

Yes. There's a centering spring and detent. Friction is pretty high so if you just let go it won't go back very quickly though.

Quoting golfradio (Reply 16):
Also is there an attitude indicator for the nose wheel (to indicate how many degrees off center)?

Sort of...the tiller handle is your indicator normally. In an EICAS airplane, if the tiller handle and the actual nosegear position diverge you'll get a caution message.

Tom.
 
BoeingGuy
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 8:40 pm

Quoting tdscanuck (Reply 17):
In an EICAS airplane, if the tiller handle and the actual nosegear position diverge you'll get a caution message.

Actually, I think only the 787 has this. I assume you are referring to the NOSE WHEEL STEERING message. The 777 and 767 do not have those (I didn't look at the 747 FCOM).
 
tdscanuck
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 9:14 pm

Quoting BoeingGuy (Reply 18):
Actually, I think only the 787 has this. I assume you are referring to the NOSE WHEEL STEERING message.

Yep, that's what I was thinking of.

Quoting BoeingGuy (Reply 18):
The 777 and 767 do not have those (I didn't look at the 747 FCOM).

Interesting...since I'm pretty sure they don't have a nosewheel position indicator on the flight deck. What's the equivalent? Or is it sufficiently self-evident? If you move the tiller and the airplane doesn't turn, something is wrong with the steering. One could argue that's a pretty good indicator.

Tom.
 
BoeingGuy
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RE: Nosewheel Steering Question

Tue Jul 03, 2012 10:22 pm

Quoting tdscanuck (Reply 19):
Interesting...since I'm pretty sure they don't have a nosewheel position indicator on the flight deck. What's the equivalent? Or is it sufficiently self-evident? If you move the tiller and the airplane doesn't turn, something is wrong with the steering. One could argue that's a pretty good indicator.

I just checked the 777 FCOM. No discussion or crew messages at all about what happens if the tiller input disagrees from nosewheel position. Remember that it's mechanical on non-787 airplanes. I'm assuming it's considered self-evident as you state. If you have a disagree there is probably some kind of significant mechanical failure.

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