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Topic: Rookie Questions On Nose Gear Steering
Username: PHX787
Posted 2013-01-01 13:52:08 and read 3854 times.

Hey guys, I have a few questions about how the steering works for an aircraft while taxiing.

1) when a fly by wire a/c for Boeing, such as a 777, is taxiing, what controls the nose gear and what prevents the nose gear controls and the supercritical controls from interfering?
2) what about a pre-fly by wire Boeing aircraft in the same conditions?
3) how about airbus aircraft? How does the side stick control the nose wheel and what differentiates the controls? Is there something else that works with the nose wheels?
4) how about old airplanes, such as the DC-3, who had two wheels in front?
5) How are errors such as the B6 incident in LAX prevented but how did that actually occur?


Sorry for all the questions but its something that really drives my curiosity.


PHX787

Topic: RE: Rookie Questions On Nose Gear Steering
Username: CaptCufflinks
Posted 2013-01-01 14:06:54 and read 3839 times.

Hi there,

The majority of modern airline aircraft, including the big Airbus and Boeing birds are controlled by a tiller which is like a mini steering wheel. It is normally in the 'arm space', available to the Captain's left hand and the FO's right hand. This applies to both all of the airliners, irrespective of their autoflight systems, or indeed, lack of them.

You can see the tiller in this photo:

http://www.airliners.net/photo/Emira...d=39cca169d09de42e29ddc97e8d7b9965

Look at the FO's side, to the right of his sidestick and beneath the electronic flight bag on his side.

I can't think of any major aircraft where the control column, side stick or yoke have a control on the nose wheel.

Smaller aircraft are controlled, on the ground, by the rudder pedals - simply push left or right and press your toes forward to use the brakes.

Older aircraft had two forms of steering as far as I'm aware (I don't know enough about them to be completely honest with you):

1) Rudder pedal steering, as with smaller aircraft as discussed above

2) Differential braking - IE, depress the brakes on the left hand side to turn left and the right brakes to turn right. Use both sets of brakes simultaneously to stop in a straight(ish) line.

Hope this helps,

Josh

Topic: RE: Rookie Questions On Nose Gear Steering
Username: LimaFoxTango
Posted 2013-01-01 16:59:21 and read 3737 times.

Quoting CaptCufflinks (Reply 1):
I can't think of any major aircraft where the control column, side stick or yoke have a control on the nose wheel.

There's at least one.


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Topic: RE: Rookie Questions On Nose Gear Steering
Username: fr8mech
Posted 2013-01-01 17:48:06 and read 3701 times.

Quoting CaptCufflinks (Reply 1):
1) Rudder pedal steering,

Modern aircraft also have rudder pedal steering. The pedals have less range of motion than the tiller, but provide directional control at higher speeds (to maintain runway centerline) until the rudder gains aerodynamic authority.

The B744 provides 7 degrees on either side of center through rudder pedal steering.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: ANITIX87
Posted 2013-01-01 19:28:58 and read 3643 times.

Quoting fr8mech (Reply 3):
The B744 provides 7 degrees on either side of center through rudder pedal steering.

Does this mean the center gear is constantly turning (I don't mean spinning, I mean "steering") inside the wheel well when retracted, or is there a mechanism disabling the pedals once the gear comes up (or when rudder authority takes over)?

TIS

[Edited 2013-01-01 19:29:23]

Topic: RE: Rookie Questions On Nose Gear Steering
Username: fr8mech
Posted 2013-01-01 20:38:35 and read 3605 times.

Quoting ANITIX87 (Reply 4):
Does this mean the center gear is constantly turning (I don't mean spinning, I mean "steering") inside the wheel well when retracted, or is there a mechanism disabling the pedals once the gear comes up (or when rudder authority takes over)?

Nose gear steering is disabled and/or inhibited when the strut extends. I'm not sure of the exact means this is done on the B744, but several other aircraft have used a disconnect valve that is actuated by strut extension.

Now, by center gear, if you mean the sterrable body gear, those only come into play when the nose gear sterrs over 21(?)degrees on either side of center. On the old airplane, the flight crew switched body gear steering off at take-off, I'm sure ts completely automatic on the -400 and -800.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: B747FE
Posted 2013-01-01 20:44:09 and read 3602 times.

Quoting ANITIX87 (Reply 4):
Does this mean the center gear is constantly turning

I assume you meant Body Gear. Is not.
BG steering is active (provided other conditions are also met) only after the nose wheels are commanded beyond 20 degrees, rudder pedal steering provides only 7 degrees.
Steering system, nose & body, is only active on the ground.

Regards,
B747FE.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: B747FE
Posted 2013-01-01 20:52:47 and read 3596 times.

Sorry fr8mech I didn't see your post before sending mine.

Quoting fr8mech (Reply 5):
On the old airplane, the flight crew switched body gear steering off at take-off, I'm sure ts completely automatic on the -400 and -800.

Correct.
After lining up and once the aeroplane reaches taxi speed on the classics. Accelerating through 20 knots on the -400.
No idea the -8.

B747FE.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: FlyDeltaJets
Posted 2013-01-02 01:03:03 and read 3510 times.

How far do the mains turn on the 747, I neve knew that they could turn as well. When I push back 744's in tight areas I just see the tires do a lot of flexing but never "turning".

Topic: RE: Rookie Questions On Nose Gear Steering
Username: fr8mech
Posted 2013-01-02 01:36:58 and read 3494 times.

Quoting FlyDeltaJets (Reply 8):
How far do the mains turn on the 747, I neve knew that they could turn as well. When I push back 744's in tight areas I just see the tires do a lot of flexing but never "turning".

13 degrees is what sticks in my head.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: ANITIX87
Posted 2013-01-02 11:29:46 and read 3391 times.

Quoting fr8mech (Reply 5):
Nose gear steering is disabled and/or inhibited when the strut extends. I'm not sure of the exact means this is done on the B744, but several other aircraft have used a disconnect valve that is actuated by strut extension.

I meant nose gear, yes. Oversight on my part to call it the "center" gear.

What if there is a severe crosswind, and the PIC is on the pedals up through rotation. Once nose-wheel steering is disabled witht the strut's extension, does the gear auto-center before being retracted?

TIS

Topic: RE: Rookie Questions On Nose Gear Steering
Username: KC135Hydraulics
Posted 2013-01-02 14:13:00 and read 3288 times.

Quoting fr8mech (Reply 3):
Modern aircraft also have rudder pedal steering. The pedals have less range of motion than the tiller, but provide directional control at higher speeds (to maintain runway centerline) until the rudder gains aerodynamic authority.

How recent is modern? The KC-135 has rudder pedal steering as well and that's a '50s design. The rudder pedals give about 8° maximum steering. When using the steering tiller, it can override any input that the rudder pedals are giving on steering because the way it is rigged, it provides more leverage to the cables than the pedals provide.

Once airborne, we have a steering disconnect valve that shuts off hydraulic pressure to the steering metering valve. As the strut rotates and retracts, it disengages a spring-loaded plunger which shuts off hydraulic pressure to the nosewheel steering metering valve.

There is also a linear actuator (electrical) that engages or disengages rudder pedal steering input to the metering valve in flight. When the main gear safety switch shows air mode (aka weight on wheels switch) an electrical actuator is engaged which moves a quadrant that disengages input. When the safety switch shows ground mode, the linear actuator repositions the linkages and allows the rudder pedals to steer the nosewheels again.

I could go on all day. If you want to know about C-17 steering, I got that covered too!

Topic: RE: Rookie Questions On Nose Gear Steering
Username: B6JFKH81
Posted 2013-01-02 14:37:35 and read 3277 times.

Quoting PHX787 (Thread starter):
5) How are errors such as the B6 incident in LAX prevented but how did that actually occur?

Some good info here:

http://www.ntsb.gov/aviationquery/br...927X01540&ntsbno=LAX05IA312&akey=1

Basically B6 modified all a/c within a particular s/n range that had a certain style NLG on it after the incident happen, been discussed on here many, many times. I remember those mod days here at the hangar, we were able to pump out 1 - 2 planes a night on average, I think there were like 80 a/c that had to be done.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: BoeingGuy
Posted 2013-01-02 15:19:46 and read 3252 times.

Quoting CaptCufflinks (Reply 1):
The majority of modern airline aircraft, including the big Airbus and Boeing birds are controlled by a tiller which is like a mini steering wheel.

The 747, 757, 767 and 777 have tillers. The 707, 727, 737 and 787 have something that more resembles a quarter of a steering wheel. I think Airbus airplanes have the latter, but without one of the sides (in other words, a steering wheel basically shaped like an upside down "L").

First Officer side tillers are baseline on the 777 and 787; and optional on the 737, 747 (not sure about the -8 though), 757 and 767. The 787 steering is fly-by-wire. The 777 steering is cable driven, but most of the rest of the flight controls are FBW. Other non fly-by-wire airplanes have cable driven steering like the rest of their flight controls.

Quoting fr8mech (Reply 3):
The B744 provides 7 degrees on either side of center through rudder pedal steering.

It's about the same for all Boeing models. I think the 787 is 8 degrees, but all are in the same ballpark. The tiller or steering wheel will mechanically override the rudder pedals. In other words, if doing a flight controls check during taxi, the captain will hold the tiller while pushing the rudder pedals to keep the nosewheel gear from steering back and forth. The 787 actually has a switch on the steer wheel to disconnect the steering from the rudder pedals for this reason, since it's FBW.

I hope this helps.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: B6JFKH81
Posted 2013-01-02 16:18:44 and read 3227 times.

Quoting BoeingGuy (Reply 13):
I think Airbus airplanes have the latter, but without one of the sides (in other words, a steering wheel basically shaped like an upside down "L").

Pretty much, yeah:


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Topic: RE: Rookie Questions On Nose Gear Steering
Username: fr8mech
Posted 2013-01-02 19:10:07 and read 3176 times.

Quoting ANITIX87 (Reply 10):
Once nose-wheel steering is disabled witht the strut's extension, does the gear auto-center before being retracted?

There is a centering cam in the strut that forces the nose gear to center itself, absent hydraulic pressure.

Quoting KC135Hydraulics (Reply 11):
How recent is modern?

Not sure exactly why I wrote "modern". I've worked on and taxied some pretty non-modern aircraft that had rudder pedal steering.

Topic: RE: Rookie Questions On Nose Gear Steering
Username: rwessel
Posted 2013-01-02 20:46:34 and read 3154 times.

To address the OP's #4, tail draggers get steered by all off the same mechanism as trikes. Some aircraft have a free swiveling tail wheel, and steering is through differential braking or thrust application (the latter obviously only possible in a multi-engine aircraft), and some have steerable tail wheels, usually attached to the rudder petals. For an example, take a look about a third of the way down this page:

http://members.eaa.org/home/homebuil...4Tail%20Wheel%20Installations.html

OTOH, most tail wheels are not retractable, so that tends to simplify things a bit.

Quoting ANITIX87 (Reply 4):
Does this mean the center gear is constantly turning (I don't mean spinning, I mean "steering") inside the wheel well when retracted, or is there a mechanism disabling the pedals once the gear comes up (or when rudder authority takes over)?

As mentioned elsewhere, no. And some aircraft go through considerable contortions stowing the gear - in A320s, for example, it's actually turned 90 degrees before being stowed, leading to great showers of sparks on landing when the mechanism fails to straighten out the nose gear before landing.

Quoting FlyDeltaJets (Reply 8):
How far do the mains turn on the 747, I neve knew that they could turn as well.

On the 747s, only the body gears steer, the wing mounted ones do not. The 777 takes a slightly different approach, and only the last axle on each main bogie steers.


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