Will the tiller be seperate to the rudder pedals.

[Blake H]

When I move the rudder pedals on my PSX sim will there be 7 degrees each side of movement on the gear? When I move the tiller in PSX will there be 70 degrees each side, 2 pot input?

Is there an output I can run to a dc motor in the tiller, this is to show position of the gear and to be able to check the rudder movement without the gear moving by holding the dc motor in place.  

The position of the tiller is the true position of the gear. If you move the rudder pedals without holding the tiller you will see the tiller position can move up to 7 degrees each side. If the gear is uplocked the tiller will be in the centre position.

[John H Watson]

When I move the rudder pedals on my PSX sim will there be 7 degees of movement on the gear? When I move the tiller in PSX will there be 70 degrees, 2 pot input?

Under ideal circumstances, 150 degrees tiller movement results in 70 degrees  nosewheel movement.

The position of the tiller is the true position of the gear.

Speculation or fact?

If you move the rudder pedals without holding the tiller you will see the tiller position can move up to 7 degrees each side.

If 150 degree tiller movement results in 70 degrees nosewheel steering, and rudder pedal nosewheel steering results in 7degrees (1/10th the movement), wouldn't the tiller move 1/10th of 150 degrees? (i.e. 15 degrees)

If the gear is uplocked the tiller will be in the centre position.

Can you move the tiller in this condition?

Question: If the Rudder Trim controls move the rudder 8/10ths of full rudder travel, how much nosewheel steering will you get from Rudder Trim (given that the Rudder Trim moves the rudder pedals)?  :mrgreen:

Rgds
JHW

[Blake H]

I have edit first post "each side of center". Sorry misunderstood the technical manual.
 :roll:

From what I have seen from the tiller movement.

I am most sure there is a delay from tiller movement to the nose gear repositions (how long is a piece of string). If you read the manual you can see that it says "Shows steering direction". This is placarded on the tiller. 70 total each side. If you move the rudder you should get 7 degrees from center each side.

Rudder trim I though it repositions to a neutral position making the rudder central in flight, if needed. The pot for the tiller is unchanged and the repositioning of the rudder would have to be a different pot. Tiller also always overrides rudder input to check freedom of controls (rudder). Must be a very bent a/c, taking-off, landing and taxiing around with rudder trim not centered  :mrgreen:

When you land, you land with center rudder trim. As a pilot you re-center more and more as power is bleed off and only re-apply in the go-around or missed approach if you have too. You also don't take-off asymmetric.

I think the only way to replicate the true movement in PSX of the tiller and rudder pedals are 1 pot for tiller, 1 pot for rudder control, 1 pot for rudder pedal steering and tiller always has command over the rudder pedal steering. 1 output for nose gear position to a dc motor on the tiller. This is to show position of gear.

Guys, I am trying to get the best suggestions for usage of PSX to make as real as possible. Hoping for hardware and software suggestions with this post. But feel free to add in technical 747-400 posts

Blake

Ps I disregarded main wheel steering for simplified understanding. The software should take into account main wheel steering.

[John H Watson]

Blake, the Boeing 744 Maintenance Manual says the tiller provides maximum steering angle when the tiller is 150 degrees from (spring-loaded) centre. i.e. Total tiller angle = 300 degrees.

My other comment on steering directness was not relating to system lag, nor steering actuator geometry, but the fact that steering input doesn't always equate to steering, both at high speeds and at dead stop. Lack of friction is the cause of the former, too much friction is the cause of the latter.

Rgds
JHW

P.S. My Rudder Trim example was just a mental exercise with an added safety precaution. In theory, Rudder Trim input may affect steering at even slower speeds.

[Blake H]

Hi John,

300 total, I thought it was 70 + 70, 140 degrees. I thought 150 was total on tiller. 300 is better suits a pots. I won't have to gear the pot.

So are you saying the steering tiller position is not always the position of the gear. Do you have any known boeing wording related to this happening. Reference?

Do you think if you had a dc motor driving the tiller to a close related postion of the gear this would be a better device then a spring loaded centering. I think that the dc motor with a hydraulic strut (damping) would have a better feel and have steering control more like the 744. I have found spring loaded centering make the sim nasty to steer. Unless you can think of another option I was hoping to get a post related to a better system control. People still like taxiing sims from the gate.  The one pot rudder and gear control in mfs is not working for taxi.  

Respectfully, I am not saying I don't believe your comment I just want to have a reference down the track for 744. If I don't end up taking note I will forget what I have learnt and how to apply to my sim.

Do you know of any other downloadable technical manuals online? I have 744 vol 4 technical manual cathay pacific. 744 AFM.

Blake  

[John H Watson]

So are you saying the steering tiller position is not always the position of the gear. Do you have any known boeing wording related to this happening. Reference?

No direct reference, only experience.

All maintenance nosewheel steering checks mentioned in the maintenance manuals are done with the nose torsion link disconnected. i.e. the link between the steering mechanism (just under the Runway Turnoff Lights) and the nosewheel axle is disconnected. Ref Airplane Maintenance Manual 32-50-00 (etc).

Perhaps some of my esteemed Airframe colleagues know of other procedures, perhaps using turntables to reduce the friction between the tyres and the tarmac.

Rgds
JHW

P.S. Note that the nosewheels are castered (like office chairs) to assist centering when the aircraft is moving. This may affect the behaviour of the steering when the aircraft is motionless.

[Jeroen Hoppenbrouwers]

Terminology... "castered". You mean that the axle is not vertically under the pivot axis, but typically aft of it, so that the wheel swings with the lateral forces and aims in the direction it is being pushed?

[Blake H]

Ok, this is a castor senario that would make sense. I want to know what the tiller to nose wheel position indicator when hydraulic psi is directed to steering. I am relating to words I know from the metroliner Ive flown. We have a button at 80 kts we disengage this makes a castor situation on t/off. But the 744 to my understanding always has psi going to it unless towed or loss or hydraulic psi? Is there a ON/OFF maybe a castor switch in the nose wheel well?

[John H Watson]

@ Jeroen

100% correct :mrgreen:

[Blake H]

I beat your reply :roll:

[dutch57]

Hi guy`s,

Nose gear steering on the B744, 2 ways to steer the nose gear, steering tiller and rudder pedals.

Steering tiller give a left or right movement of the nose gear in proportion to tiller movement  max 70deg left or right , ruddr pedel steering only availeble on ground and for max 7 deg left or right when using rudder pedals rudder wil move as wel.
Rudder pedal steering is connected with tiller steering by means of 2 electric actuators. With no steering input the wheels are centered by hyd pressure in both sides of the steering cilinders , and centering is done via de wheel axcle ofset from the strut.

Steering is automaticly locked out during lift-off by means of a mecanical system, works with nose gear movement.
Centering the wheels is than done by 2 centering cams inside the nose gear strut.

Hope this shows some lite in the system,

Sincerly,
Bob

[John H Watson]

Thanks for the feedback, Bob.

Do you think the centering cams would work even if the tiller was full left/right during takeoff?

That reminds me. I was thinking about something a year or two ago ...

If you lost nose strut pressure during flight (and, say, the aircraft had a nose up attitude), would the strut compress (via gravity)? What angle does the gear sit in the nosewheel normally?
I'm wondering what would happen to the interconnect mechanism. Would the interconnect mechanism re-engage? Maybe you could fly with the tiller in this strange scenario  :mrgreen:

By the way, I realise that the nosewheel steering uses "gear down" hydraulic pressure, so you still wouldn't be able to turn the nosewheel (Haven't thought about the Body Gear Steering yet).

Rudder pedal steering is connected with tiller steering by means of 2 electric actuators.

I believe it needs two actuators to disconnect, but only one actuator to connect.

Regards
JHW

[dutch57]

Hi John,

I think if you have the tiller full left or right during the T/O run, you will turn and loose your nose gear depending on the speed. The rudder pedal is just for that a little control during the highspeeds.

The strut can/will compress if pressure is lost during flight, one reason is that the wheels are pushed into the spinbrakes and the gear sits at a slight angle wheels up, so the weight of the wheels can push the strut in.
The interconnect mechanism is connected to the fiixed strut, not the piston(with the wheels) as we call it.

And the design is such that a compressed strut will extend out of the wheel well without causing damage.

There are 2 steering actuator and they work via the nose gear squat switches and work in parralel, monitored by a contol unit so if one fails you get and eicas status msg pedal steering.

Body gear steering is armed by a pos switch in the cable system from the nose gear steering and activates by more than 20 deg steering, also you need to be on the ground wheel speed less than 15 knots(signal from bscu) and iru ground speed less than 40knots

Hope this helps a bit,

Sincerly
Bob

[John H Watson]

I think if you have the tiller full left or right during the T/O run, you will turn and loose your nose gear depending on the speed. The rudder pedal is just for that a little

Thanks, Bob. I saw some photos of a 744 landing with what appeared to be full turn. In this case, the nosewheel just skids (this happens even if pilots take turns to the gate too quickly. The gear seems to be strong enough to take this punishment. This is why I was thinking of the scenario where the wheels were hard left/right.

The strut can/will compress if pressure is lost during flight

After I posted my question, I found a nice pic in some old training notes showing gear position. I see that the aircraft doesn't need to be climbing. There is already a significant angle on the strut (wheels high).

The interconnect mechanism is connected to the fixed strut, not the piston(with the wheels) as we call it.

Not sure I understand. I was referring to the fact that if the strut does compress a lot (if strut pressure is lost) the nose gear air/ground prox sensors will trigger ground mode and the interconnect mechanism will reconnect. The centering cams would also disengage because of the decompressed strut. If hydraulics somehow could get to the nosewheel with the gear up, then wouldn't all the steering elements work normally?
I notice that the steering torsion link is close to the top of the wheelwell. I wonder if this would restrict the movement of the wheels and cylinder.

There are 2 steering actuator and they work via the nose gear squat switches and work in parallel, monitored by a contol unit so if one fails you get and eicas status msg pedal steering.

Understood, but the design allows for the system to engage rudder pedal nosewheel steering if one fails, but not to disengage if one is inop.

Body gear steering is armed by a pos switch in the cable system from the nose gear steering and activates by more than 20 deg steering, also you need to be on the ground wheel speed less than 15 knots(signal from bscu) and iru ground speed less than 40knots

Most maintenance tows are carried out with the IRUs turned off. Do you know if the body gear steering still operates with the IRUs off?

Thanks,
Regards
JHW

[dutch57]

John,

During towing body gear steering is disarmed we do not use it.

Whit the nose gear in a turn at landing, yes it is possible as you say but if the gear touches hard you loose it.

The pedal steering is connected to the cable system of the nose gear steering tiller, the interconnect for nose gear steering is a function of gear down or gear up, mechanism is located just aft if swivel point from the nose gear strut.

sincerly Bob

[John H Watson]

During towing body gear steering is disarmed we do not use it.

Do you mean you disarm the body gear steering by pulling the CB or by the fact that the IRUs are turned off? Even during towing, the steering cables backdrive the tiller, so I assume the Command Transducer still senses the >20 degree angle on the nosegear (and activates body gear steering).

If the IRUs are aligned and the CBs are set, I see no reason why it can't be used normally during towing.

However, I'm more interested in abnormal situations. The wiring schematics tend to be over-simplified in places. It's not 100% clear what happens if all the IRUs are OFF.

Regards
JHW

[John H Watson]

Here's a nice shot of the body gear steering in action

http://www.airliners.net/photo/172630/L/

[John H Watson]

High speed turnoff attempt.... or gear malfunction? :mrgreen:


http://www.airliners.net/photo/Qantas/Boeing-747-338/0021016/L/

(See rudder)

[dutch57]

John,

Nice pictures , specially the QF one , wonder what was going on?

Towing is done with a nose gear steering by-pass pin which you put into the summing lever on the nose gear steering control valve, with this when turning with a towtruck hyd fluid can by-pass to both sides of the steering cylinders.

The feedback does give the input for arming but the irs is off so no valid signal to the BSCU where the arming cicuit is made/controlled. And YES with iru`s alligened and  a valid speed signal less 40kn and wheel speed less 20kn with hyd system 1 under pressure bodygear steering will work during towing.

If the iru`s are off you will not have a valid speed signal so the BSCU has no speed info for the arming cicuit and circuit will not arm.

Also if you have no hyd system 1 pressure you can arm the bodygear steering system, but it will not steer no valid hyd pressure sensed by the hyd control unit of the body gear steering system.

sincerly Bob

[John H Watson]

Nice pictures , specially the QF one , wonder what was going on?

Since the rudder is opposite to the steering, it's not the pilot trying to do a high speed turnoff. I believe it was a malfunction of the nosewheel steering.

This is why I had doubts the nosewheel would break off if it was fully turned at high speed. Because the nosewheel slides at high speeds, the force on the nosewheel is limited.

Maybe a bad tug driver would have greater effect  :mrgreen:

Rgds
JHW