Why nosewheel tiller?

[PolarMoosE]

Wouldn't it be better if the rudder pedals steered the aircraft?

PolarMoosE

[stagger]

I'm not a professional pilot so I could very well be wrong about this but...

Surely one important reason is that you need separate control of the rudder and nosewheel when landing in a crosswind. Specifically, when you need to use the rudder to kick the a/c straight after a crabbed approach but you still need the nosewheel pointing straight down the rwy when you touch down.

[PolarMoosE]

Yes, but that could be controlled automatically couldn't it? Once the aircraft touches the ground nosewheel steering is gradually fed in.

Do airliners actually use the nosewheel for centerline guidance at > 100 kt? I think they use the rudder once it becomes effective.

Martin

[ft]

The steering tiller is capable of turning the nose wheel quite a lot, 70 degrees on the B744, for taxiing. If the pedals were to be able to do this, the pedal travel for the few degrees of deflection needed on takeoff and landing would be next to none, making it nearly impossible to guide the a/c down the runway with any kind of precision.

Anyone know any other reasons?

Cheers,
/ft

[PolarMoosE]

Today's aircraft know when they're taking off don't they? Once the throttles are set to takeoff thrust, the rudder electronics switch to 'takeoff' or 'landing' mode. This way, the whole travel of the pedals equals maybe 10 deg.

Martin

[BIK_116.80]

Consider the Fairchild Metroliner and Merlin series of aircraft (SA226/SA227).

These aircraft have hydraulically powered, electrically controlled nose wheel steering capable of operation between 63 degrees left and 63 degrees right. Pilot inputs to the nose wheel steering include an on-off switch, a park switch, and the rudder pedals.

When the on-off switch is on, the pilot and co-pilot rudder pedals control the nose wheel steering, but full rudder pedal deflection can only call for a maximum of 10 degrees nose wheel deflection. This arrangement works well for normal taxing and for take offs and landings.

When the on-off switch is on, and the pilot holds down a push-on, momentary action park mode switch for a period of 12 seconds the maximum nose-wheel deflection is progressivly increased from 10 degrees to 63 degrees. This mode allows very tight turns and acurate parking, but would be far too sensitive for take-offs and landings. When the park mode switch is released the maximum nose wheel deflection is progessively reduced from 63 degrees to 10 degrees over a 12 second period.

Interestingly, on the SA226TC Metro II (which is 60 ft 6 inches long, but has a wing span of only 40 ft 6 inches) with 63 degrees nose wheel steering it is quite possible during a very tight turn to miss an obstacle with the wing tip, but clobber it with the tail. Its happened before, and no doubt will happen again.

[Moonbeam Purple]

PolarMoosE

On the 744 the steering tiller is mainly used for taxiing and the line up. The tiller is able to turn the nosewheel up to 70 degrees in either direction.

For the take off roll, we use the rudder pedals, which are able to turn the rudder up to 7 degrees in either direction.

Further more during sharp turns on the ground(nose wheel steering angle exeeds 20 degrees), the body gear steering is activated when ground speed decreases through 15 knots. When speed increases through 20 knots, the body gear steering is deactivated, and the body gear is centered as well.

RGRDS

MP

[QAVION]

"Yes, but that could be controlled automatically couldn't it? Once the aircraft touches the ground nosewheel steering is gradually fed in."

That's all I need... another bl**dy computer to fix :rolleyes:

Anyone heard of the KISS principle?

747-400 Avionics-fixer,
Q.

[FLUFFY SHOES]

"For the take off roll, we use the rudder pedals, which are able to turn the rudder up to 7 degrees in either direction."

Sorry to be exacting, but the 400 rudder fine steering system provides up to 7 degrees nosewheel steering with rudder pedal deflection - not 7 degrees of rudder.

[spannersatcx]

The 747/744 has landing rollout control, an automatic function that alledgidly would guide the a/c down the centre line of the runway, it is obviously dependant on localiser accuracy, and a/c system fully operational. Once the a/c speed reduces below 80kts rudder pedal steering is available to deflect nosewheels as previously stated.

[V2Climb]

Some aircraft take of with the yaw damper in all the way from the start of the roll. Some other means of steering is needed ie: a nosewheel tiller.(BAE 146 for example)

[take ECAM action]

For what its worth on the A319/320/321 family the rudder pedals have 6 degrees of authority upto 40kts reducing to 0 degrees at 130kts, whereas the hand wheels have 75 degrees upto 20kts reducing to 0 degrees at 70kts. They are also capable of CAT 3B approaches with rollout guidance (ie automatic steering on the landing roll)

[BIK_116.80]

V2Climb, there is no reason why an aircraft can not take-off with yaw damper(s) engaged and still have pilot inputs to the hydraulic nose-wheel steering via the rudder pedals. This is in fact exactly how things are done on most FAR25 aircraft. Yaw damper rudder inputs are not an input to the rudder artificial feel units on any aircraft I know about.

The 146 does not have rudder pedal control inputs to the nose wheel steering for the same reason that it has so many other unique features...because it is english.

[Bellerophon]

BIK_116.80

Good post, but you finish with …because it is english…

BAe’s other four engined jet with unique features does have rudder pedal control input to the nosewheel steering, allowing ±10° nosewheel travel, compared to ±60° nosewheel travel available from the handwheel.

Electrically controlled, hydraulically operated, autostabilization system engaged from start of taxy out……works like a dream. http://www.pprune.org/ubb/NonCGI/cool.gif

[This message has been edited by Bellerophon (edited 06 February 2001).]

[411A]

BIK_116.60
<....are not on any aircraft that I know about.>
The early models of the Boeing 707 (B707-100 and -300 nonfan series), and the yaw damper on these aircraft had to switched OFF for takeoff and landing.
Before your time perhaps?

[mustafagander]

BIK etc
The Saab 340 also has Y/D off for T/O and LDG.
As a general rule (for oldies at least) series Y/D must be off at low alt and airspeed since they move the rudder pedals and can reduce rudder authority e.g. B707

[411A]

Mustafagander--
Actually, it is the "parallel" yaw dampers that should be switched OFF for takeoff and landings, series remain ON at all times (at least on the B707). Hibred types, like the L1011, series for all flight ops except at A/L track where it switches to parallel for runway alignment. Recently delivered a TriStar on its last flight before being parted-out. Even though it had not had a gold-wire check in years, the Approach/Land
function worked perfectly with centerline displacement of no more than about six feet.

[Moonbeam Purple]

FLUFFY SHOES

Of course - You're absolutely correct. Don't know what went through my mind! :)

Rgrds

MP

[BIK_116.80]

411A, yes afraid you are right, mate. The intricacies of early pure-jet 707s are a little before my time. Are you suggesting that some early 707s had yaw dampers in parallel with the rudder pedals such that the rudder pedals moved with the yaw damper?

And, mustafagander, can you enlighten us as to why it is that the Saab 340 yaw damper must be off for take-off? Is it because the yaw damper provides inputs to a rudder artificial feel unit or for some other reason?

[411A]

BIK_116.80
Yes indeed, on the early B707 aircraft with a parallel yaw damper, the rudder pedals moved with the inputs from the yaw damper unit. It was normally switched OFF at 1000 feet AGL before landing and ON after flap retraction on takeoff. If it was a gusty day, these early aircraft were a real handful due to their dutch-roll tendencies. They were rather ah....unstable, to say the least.

[BIK_116.80]

Ok then, 411A, do early 707s have artificial feel units on the rudder pedals, or simply rely on aerodynamic control surface feedback? I am aware that they have hydraulic rudder boost, but aren' the rudder pedals also mechanically connected to the rudder on 707s?

[mustafagander]

411A
Thanks for the correction re series/parallel Y/D. Oops, its been a while.... http://www.pprune.org/ubb/NonCGI/redface.gif

BIK etc
The glib answer re Saab Y/D off for t/o and ldg is "because the AFM says so". As I understand it, the Y/D is off close to the ground because it inputs rudder in the event of an engine failure - you can see the potential failure modes!!!!
About the B707 rudder feel, on the -300 there was a "Q bellows" in the fin to adjust the feel for airspeed. The -100 was simply a dog's breakfast in the rudder - the JT3C powered series had no power rudder, but with the JT3D fan series, power rudder was a must (12,000lb vs 18,000lb thrust). How this was achieved depended on degrees of rudder displacement and varied from no power to full power. All I can remember was that it was a bloody nightmare to rig. I'm fairly sure that the B707-300 had artificial feel on the rudder. The rest of the system is for another thread I think!! It's been a hell of a long time since I was an airframe LAME on the B707. ;)

[411A]

BIK_116.80
Mustafagander has it right on the money. Q bellows provided artificial feel and yes, the rudder was connected by bellcranks and cables as well. Once rigged correctly, it gave little trouble. If however, the rudder boost was switched OFF during a three engine go-around, the aircraft required LOTS of airspeed. Vmca (boost ON)= 120 knots, boost OFF= 180 knots. The rudder boost was switched OFF on just such a maneuver during a TWA training flight years ago by an FAA inspector in the obs seat and the aircraft rolled over on its back and crashed, killing everyone. After the investigation, the FAA bought TWA a brand NEW 707. The 707 also had a system for aileron assist using aerodynamic balance panels. Wonderful old bird, it was a delight to fly, especially the later -320B advanced models.

[quid]

PM-

Most all jets flying today have limited nosewheel steering controlled by rudder pedal inputs.

The tiller has much more "turning" authority than the rudder pedals. It should be used only for taxiing, and shouldn't be used for takeoff or landing.

[Strong Winds]

I know you guys do Big planes, and I hope I will in a very short time from now.
Let me tell you something about the Lears
I´m sure most of you know that they have a little button called steer.
This button basically increases and decreases the amount of degrees the nosewheel moves each side. On takeoff you hold it pressed until you reach 60kt at that speed you release it for 2 reasons.
1) Because now the rudder has enough authority to control the plane directionally and
2) Because if you keep it depressed chances are you´ll lose directional control out of the rwy.

I´ve seen 747 captains use it after touchdown, but very cautiously. I´ve seen 757 pilots using assymetrical thurst to control the plane better. That guy was an ex-C130, that might be the reason, though.

Be safe !! Hands On from TOD PLEASE !!!!

SW.

[BIK_116.80]

Gawd theres some knowledge out there in pprune land. Thanks for the info guys.

But it still sounds to me like my original proposition stands. That "Yaw damper rudder inputs are not an input to the rudder artificial feel units on any aircraft I know about."

So early 707s had yaw dampers in parallel with the rudder pedals - but there was no artificial feel unit since the rudder controls were entirely a manual affair. You say that more recent 707s had a Q-feel unit on the rudder pedals, but was the yaw damper in parallel on these models? Or was it in series?

So the Saab requires the yaw damper to be switched off for take-off and landing - still hasn't got me convinced that its anything to do with yaw damper inputs to an artificial feel unit. (Does the Saab have a powered rudder?? Does the Saab have an artificial feel unit for the rudder pedals??)

So I am still unable to agree with V2Climb's proposition that "Some aircraft take of with the yaw damper in all the way from the start of the roll. Some other means of steering is needed ie: a nosewheel tiller.(BAE 146 for example)"

And, 411A, thanks for the interesting story about the Feds screw up at TWA. I spose you are well aware of the RAAF (Royal Australian Air Force) B707 training crash off the south east coast of Australia about 10 or 12 years ago when the officer in charge (who was sitting on the jump seat) decided to switch off the rudder boost while two engines on the same side were shut down, and while the aircraft was at 5,000 feet over the ocean? The aircraft rolled over and went into the water with a hell of a thud in well under 30 seconds. May all five crew members on board RIP.

[411A]

BIK_116.80
All B707's had yaw dampers and especially the early models were quite unstable in the yaw axis. Earlier models had parallel units, later had series.
Had not heard about the RAAF accident. Nasty business, it has always ammazed me why someone would purposely switch OFF an esential system, especially rudder boost on the 707.
With two engines out on one side, the B707
Vmca (boost ON) 170 knots, (boost OFF) 235 knots. This is for the -320B advanced series.

[BIK_116.80]

So the early 707s had no artificial feel unit (no powered rudder) but the rudder pedals moved with the parallel yaw damper.

And the more recent 707s had a Q-feel system, but the yaw damper was in series and so the rudder pedals did not move with the yaw damper.

So again, I think my proposition that, "Yaw damper rudder inputs are not an input to the rudder artificial feel units on any aircraft I know about." stands.

The RAAF OIC was trying to give the trainees a challenging scenario to deal with for training purposes. I guess he succeeded in that regard, but the trainees never got the chance to use their new found knowledge.

It is interesting that in both the RAAF and the TWA accidents it seems that the OIC and the FAA PIC were on the jump seat and therefore had no way of either :

(1) Knowing what control inputs and with what force were being applied to the rudder pedals; or,

(2) Making their own rudder pedal inputs to correct the rapidly deteriorating situation (and therefore quickly realising that it was not able to be sorted out), but rather were only able to shout words of encouragement from the jump seat.

It also seems that in both cases no crew member chose to switch the rudder boost back on when they realised that things were not going according to plan. Interesting CRM lesson about assertiveness and mindset perhaps?

But oh what a terrible waste all round.

[411A]

Yes, very sad indeed. It is interesting to note that an FAA inspector on a line or training surveillce flight have NO authority to touch any switch or control. Many years ago (on a DC3 would you believe) I left an inspector in StThomas due to his inability to keep his hands to himself. I complained to the ACDO supervising inspector and this misfit was later transferred.

[BIK_116.80]

Well I have heard about a few sleazy captains having problems at their work because they were not able to keep their hands to themselves, but perhaps the FAA thing is a slightly different matter!

[jonno]

With this question on rudder/tiller control of the aircraft is as all the others as far as I am concerned, ie. the less automatics we have in the control of the the aircraft, the better I will like it, manual is much better, and also much, much more reliable!!