Mr Spaceman
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Boeing-747 Rudder Question?

Thu Jul 25, 2002 3:30 am

Hi guys.

In the photo below you can clearly see that the nosegear tires are lined up with the runway while the aircraft's rudder is fully deflected....which leads me to think that there's no conection between the cockpit's "tiller wheel" for nosegear steering and the rudder. (unlike small GA airplanes).

My questions to you are....Are the tiller wheel and rudder peddals completely seperated from each other? If so, during the takeoff roll, at what speed does the pilot flying (in this case a 747), switch from his hands to his feet while tracking the centerline?


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Chris  Smile
"Just a minute while I re-invent myself"
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 3:42 am

The rudder pedals usually have a very limited authority over the nose gear, full deflection of the pedals giving only a few degrees of deflection of the nose gear. Otherwise it would be way too sensitive during the take off roll. I've tried controlling the take-off roll using the tiller when fooling around in the simulator and it is not easy.

/Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Mr Spaceman
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RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 4:11 am

Hi Fred. Thanks for your reply.

Do you have an idea of what speed the pilot would switch from the tiller to his rudder peddals during the takeoff roll? I suspect that the ruder of a 747 probably has authority for directional steering during a ground roll, at around 80 knots. However, I really don't have a clue.

I always see 767's wagging their rudder quite a bit during the begining of it's T/O roll, while the nosegear is tracking dead straight. (especially during a stiff crosswind). So, like you said, the rudder peddals and tiller must act seperatly...to a point.

Chris  Smile
"Just a minute while I re-invent myself"
 
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RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 4:35 am

Hello Spaceman -
The nose wheel steering is connected through the rudder pedals, however with a "reduced" steering authority. PanAm airplanes, did not have that feature (I was PanAm until their bankruptcy 1991), the rudder pedal steering capability was removed... and with that airline you steered the airplane exclusively with the tillers until the "80 knots" call on takeoff roll...
With rudder pedal steering, you dont handle the tiller on takeoff, all steering is done through the rudder pedals. The tiller is only used at "taxi speeds" when required... some taxiing can be achieved with the rudder pedals as well... unless tight turns are required.
Suggestion, in a simulator, dont use a tiller... unless you "play taxi"... once lined up on a runway, use rudder pedals only... I found that applicable to all simulators I have flown... (707 727 and 747...), simulators are oversensitive on the yaw axis...
(s) Skipper
 
FDXmech
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RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 4:38 am

On non fly-by wire aircraft, the steering tiller and rudder pedals are not completely segregated systems.

Generally speaking:

In flight mode the rudder pedals declutch from from nose steering system.

On the ground moving the rudder pedals will backdrive the steering tiller as the nose gear turns.

It is possible on the ground to steer the a/c with the tiller and restrain the rudder pedals. This done on some a/c to test the yaw damp system.
You're only as good as your last departure.
 
Mr Spaceman
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RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 4:51 am

Hello B747skipper.

Thank you for your information. When I mentioned that I suspected a 747's rudder would have authority around 80 knots, I was taking a wild guess, and you let me know that "80" is a call during the takeoff roll.......cool  Big thumbs up That makes me feel good inside because even though I don't fly airliners, I sure learn a lot about what makes them tick from you guys. I can't Thank you pro's enough for teaching me. It is not taken for granted.

Chris  Smile
"Just a minute while I re-invent myself"
 
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RE: Boeing-747 Rudder Question?

Thu Jul 25, 2002 3:54 pm

Thanks Spaceman -
You see, the nosewheel steering has very little "effectiveness" to keep an airplane on centerline, should an engine fail (particularly outboard engines), the steering would be TOTALLY unable to compensate for the yaw... There is actually very little "weight" applied on a nose wheel, it is as "effective" as a piece of wet Kleenex tissue  Wink/being sarcastic
I personally feel the rudder fairly responsive as early as some 50-60 kts on take off rolls and able to compensate for keeping that centerline... The 80 kts call with PanAm (with no nosewheel steering on rudder pedals) was the call for "hands off" the tiller, and also to compare pilot/copilot airspeed indications.
That 80 kts call is also a reminder to flight engineers that engine power must be established by then... Should they need to adjust further, the "max EPR" is no longer the correct setting, it has to be "go around EPR" thereafter... and finally for the 747 models I presently fly, is the time I put the autothrottles "on" since we have FFRATS unlike PanAm dinosaurs...
(s) Skipper
 
FredT
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Joined: Thu Feb 07, 2002 9:51 pm

RE: Boeing-747 Rudder Question?

Fri Jul 26, 2002 12:59 am

B747skipper,
the part about the simulators often being more sensitive in yaw is interesting. Which simulators have you noticed this in? How does older simulators compare with the newer ones in this respect?

Are there any other common discrepancies between simulators and the real thing that you can think of? Working on the tech side, I've had a bit of simulator time but naturally nothing but engine runups in real aircraft. They won't let me borrow any aircraft to go travelling over the weekends, the bahstids...  Big grin

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
Guest

RE: Boeing-747 Rudder Question?

Fri Jul 26, 2002 5:36 am

Dear FredT -
I spend a lot of time in simulators besides flying the line... and I personally think that the "yaw" stability (or instability) is somewhat amplified - this I believe is because of the "visual" (picture) seems to exagerate the amount of yaw imputs, such as on a "runway" for a takeoff or landing exercise...
I have flown 707, 727, and DC8s as well, their simulators had about the same problem - visual "amplification" of yaw inputs...
xxx
Realize that simulators are an excellent training device, and obviously making them a little more "unstable" than the real aircraft helps to improve a trainee's ability to control an aircraft... All pilots, will tell you that the "airplane" - the real one, is much easier than the simulator...
xxx
The old simulators of course were not so good, but realize that I fly 747s which are "old airplanes" and the simulators I use are very old... although such simulators are often improved... I sometimes use a 737 simulator, an aircraft I am not qualified in, to do "instrument work" with some pilots or, to see how good a pilot applicant is at flying - for selection... That 737 simulator is outstanding and I like to fly it myself occasionally...
xxx
Being in operations and training management of my airline, I sometimes get invited in simulators of newer airplanes (to try to convince me that we need this new kind of aircraft)... The 747-400 simulator I flew is outstanding, but this is a much newer simulator...
(s) Skipper

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