alwaysontherun
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Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 5:54 pm

Hi,

in my own limited experience of flying, I always notice smaller aircraft swaying a bit from one side to the other while taxiing, and a bit more during take off or landing runs.
Obviously not thát much, but you always end up correcting a bit left, right, left etc etc.

Looking at commercial aircraft however, they seem to move rock-steady.
My question therefore is:

Does a pilot need a lot of "footwork" during high speed "driving"?
Is he constantly correcting by pushing the pedals in quite a lot, or are bigger aircraft very steady once lined up properly?

Certain aircraft have a special steering wheel, but that is for tight maneuvering only, correct?
The brakes are always applied by stepping on the top part of the pedal, is that on any airliner?

Any inside would be appreciated!

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bri2k1
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 6:55 pm

Many small single-engine planes use bungee-cord steering. The rudder pedals are connected to the nose gear with elastic cords, so it does take some back-and-forth, especially over bumps or on a sideways-sloping surface, to taxi straight. Other small aircraft don't have a steerable nose gear at all; it just casters in the direction the plane is taxiing, and steering is accomplished using differential braking. These types can be more challenging to keep straight at low speeds with significant crosswind, such as at the beginning of the takeoff roll.

The crosswind component can vary significantly along a taxiway or while rolling down the runway due to ground clutter, such as buildings, obstructing part of a crosswind but allowing it to pass through open spaces. Airliners are much heavier, and so it takes a stronger wind or greater bump or slope to deflect their path while taxiing due to their greater momentum even at slower speeds.

The steering tiller when so equipped is used to provide a greater range of motion, such as 70 degrees to either side of center, of the nose gear. The rudder pedals typically provide much less, such as 7 degrees to either side of center. At high speeds, such tight turns are unnecessary and unsafe, and so the rudder pedals are used exclusively. This is also because the control surfaces, such as the rudder, have more effectiveness at higher speeds.

There will always be some exception to everything, but all of the types (small and large aircraft alike) with which I'm familiar have braking controls integrated into the upper portion of the rudder pedals, with a separate actuator somewhere for a parking brake control.

It is generally considered poor airmanship to taxi erratically. Keeping taxi speeds to a slow and safe level where adequate and smooth control is possible by the pilot taxiing is prudent.

[Edited 2010-01-14 10:56:48 by bri2k1]
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Goldenshield
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 7:35 pm



Quoting Bri2k1 (Reply 1):
It is generally considered poor airmanship to taxi erratically.

I've seen many student pilots on their first lesson nearly crash a 152 into a wall by slamming on the rudder and associated brake. Granted, it's their first day, but if they can drive a car, they would know not to correct by going hard-over.
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KELPkid
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 7:39 pm

Also, in a taildragger, your forward visibility is rather limited, and to see where you are going, sometimes it is necessary to do "S-turns" on the taxiway...I've even seen DC-3's doing this while taxiing  Wink
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DiamondFlyer
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 8:05 pm



Quoting Bri2k1 (Reply 1):
There will always be some exception to everything, but all of the types (small and large aircraft alike) with which I'm familiar have braking controls integrated into the upper portion of the rudder pedals, with a separate actuator somewhere for a parking brake control.

Some of the older tailwheel aircraft (and perhaps new) have a rather odd brake control setup. The brake pedals are actually on the lower half of the rudder pedals, making it quite confusing if you aren't sure. Quite fun I got in one, as I couldn't figure it out very quickly. After a few minutes of taxing, it seems to get better. One big thing it to make sure your heels are off the pedals during a landing.

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Jetlagged
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 8:37 pm

The big difference is the much greater inertia of a large airliner compared to a light aircraft.

Quoting DiamondFlyer (Reply 4):
Some of the older tailwheel aircraft (and perhaps new) have a rather odd brake control setup. The brake pedals are actually on the lower half of the rudder pedals, making it quite confusing if you aren't sure. Quite fun I got in one, as I couldn't figure it out very quickly. After a few minutes of taxing, it seems to get better. One big thing it to make sure your heels are off the pedals during a landing.

Going back even further to the WW2 era, British designed aircraft used a brake lever on the control column. Differential braking was controlled via the position of the rudder bar.
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swiftski
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RE: Pedal To The Metal While "driving" An Aircraft?

Thu Jan 14, 2010 9:27 pm



Quoting Alwaysontherun (Thread starter):
in my own limited experience of flying, I always notice smaller aircraft swaying a bit from one side to the other while taxiing, and a bit more during take off or landing runs.

It's called Slipstream Effect. Single engine aircraft feel a yawing moment to the left when power is increased, which needs to be countered with right rudder. You also get this with multi engine aircraft if they do not have counter rotating props.
 
alwaysontherun
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RE: Pedal To The Metal While "driving" An Aircraft?

Sat Jan 16, 2010 3:45 pm



Quoting KELPkid (Reply 3):
Also, in a taildragger, your forward visibility is rather limited, and to see where you are going, sometimes it is necessary to do "S-turns" on the taxiway...I've even seen DC-3's doing this while taxiing  

Interesting...........never thought of if that way.

Quoting Jetlagged (Reply 5):
The big difference is the much greater inertia of a large airliner compared to a light aircraft.



Quoting Swiftski (Reply 6):
Single engine aircraft feel a yawing moment to the left when power is increased, which needs to be countered with right rudder.

Yes, both very true...........

But my basic question still stands: do pilots have to do a lot of compensating during the take-off roll and / or landing roll?
I know "a lot of" is a pretty vague term, so let me ask it like this: do student-pilots spend many hours just in taxiing (high speed) or is it pretty obvious, just something that comes natural to the average novice?

In the little planes we fly, it took me a while to go straight.......and I was told I am "above average"........whatever that means.
Hence my question........would it be hard for me to control a 747 during the take off roll?

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SEPilot
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RE: Pedal To The Metal While "driving" An Aircraft?

Sat Jan 16, 2010 4:13 pm

Most of my experience is in Cessnas, which have the bungee-cord nosewheel steering. There definitely is a tendency to wander a little bit when starting the takeoff roll, which with experience one instinctively corrects for, Pipers and Mooneys have rigidly connected nosewheel steering, and they are less prone to this behavior, and are easier to taxi precisely. The reason for the bungee cord steering, I presume, is to allow more rudder correction during the takeoff/landing roll while tracking straight. I have not noticed it to be necessary, frankly, and I prefer the rigid connection. The one advantage of the bungee cord system that I do like is that it is used for rudder trim as well, and makes the trim system very simple with no cables to the tail to maintain, and no trim tab necessary.
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DiamondFlyer
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RE: Pedal To The Metal While "driving" An Aircraft?

Sat Jan 16, 2010 5:07 pm



Quoting SEPilot (Reply 8):
Most of my experience is in Cessnas, which have the bungee-cord nosewheel steering. There definitely is a tendency to wander a little bit when starting the takeoff roll, which with experience one instinctively corrects for, Pipers and Mooneys have rigidly connected nosewheel steering, and they are less prone to this behavior, and are easier to taxi precisely. The reason for the bungee cord steering, I presume, is to allow more rudder correction during the takeoff/landing roll while tracking straight. I have not noticed it to be necessary, frankly, and I prefer the rigid connection. The one advantage of the bungee cord system that I do like is that it is used for rudder trim as well, and makes the trim system very simple with no cables to the tail to maintain, and no trim tab necessary.

I'm the other way around. It is much, much easier to keep a Cessna going straight than to keep a Piper going straight. 99 times out of 100, the nose wheel in the Piper's isn't centered perfectly with the steering mechanism, so you get stuck with a little back and forth motion. That said, the easier things to taxi, IMO, are castoring nose wheel types. Once you figure out the right combination of brake to use, they go straight very, very easily.

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