Quote:

---

how an airplane turn during taxiing, i have come to know that the wheels are not connected with the control surface. my friend who is a commercial pilot told me that small airplanes line cessena and beech airplanes use rudder controls, how does it work? he also said that heavy airplanes like 737, 747's using something called differential braking, how does it work?

---

Hey blackcat,

Differential braking is when you brake 1 wheel and not the other. The airplane has 2 brake pedals...the one operated by the right foot controls the right main gear assembly. The one operated by the left foot controls the left wheels. So stepping on the right brake makes the plane turn right and vice-versa. At higher speeds when there's still aerodynamic authority for the rudder to work, the rudder can be used to steer as well.

Aircraft also have nosewheel steering. Smaller ones may be operated by the rudder pedals. In larger aircraft, there is often a 'tiller' which looks like a small steering wheel in the cockpit.

Drew

--------------------
When eating an elephant take one bite at a time.
-- Gen. C. Abrams

Post Extras:      

Quote:

---

...Differential braking is when you brake 1 wheel and not the other. The airplane has 2 brake pedals...the one operated by the right foot controls the right main gear assembly. The one operated by the left foot controls the left wheels. So stepping on the right brake makes the plane turn right and vice-versa. At higher speeds when there's still aerodynamic authority for the rudder to work, the rudder can be used to steer as well.
Drew

---

Hey Drew,

I'm assuming the wheel brakes never get used until the taxi speed drops to a predetermined level, right? I would think it would be kind of tricky to try to apply equivalent braking pressures on both sides with the individual pedals. Right after the nosewheel touches down, they solely rely on the airbrakes and the thrust reversers to slow the plane down, is this correct?

I'm not that positive about this cause I've seen pictures of a jetliners brakes and they use multiplates which obviously is for dissipating the great amounts of heat generated during high speed braking--something that won't be needed if the brakes were indeed for low speed braking only.


Post Extras:      

Quote:

---

how an airplane turn during taxiing, i have come to know that the wheels are not connected with the control surface. my friend who is a commercial pilot told me that small airplanes line cessena and beech airplanes use rudder controls, how does it work? he also said that heavy airplanes like 737, 747's using something called differential braking, how does it work?

---

Hi, BC,

As usual, Drew has given a correct and detailed answer.

I just wanted to add that differential braking is something that has been in use in other applications for a great number of years. It has been used in farm equipment, earth-moving equipment (bulldozers, backhoes, etc) and military tanks and other heavy equipment.

The process, just as Drew described in the airplane, is both simple and very effective. If the brakes are applied to one wheel, that wheel can be made to stop turning at all. Since the other wheel (or tracks) is still rotating, the whole vehicle can be made to "turn on a dime." It can easily rotate 180-degrees and be facing the direction that it came from and be on a direct parallel path with the original direction of travel. Very handy for most farm work or grading/leveling an area.

A tank can immediately reverse directions and run while it's cannon can continue firing at whatever it found and is retreating from.

An additional note about modern tanks: During the Gulf war and the current efforts in the Middle East, the workhorse tank of the U.S. forces has been the Abraham M1A1. In addition to differential braking it also has individual throttle controls for each side. It is being slowly replaced by the newer M1A2.

--------------------
If you do not wish to gain knowledge and happen to sleep alone, you have a fool for a bedmate.

Post Extras:      

Quote:

---

Hey Drew,

I'm assuming the wheel brakes never get used until the taxi speed drops to a predetermined level, right? I would think it would be kind of tricky to try to apply equivalent braking pressures on both sides with the individual pedals. Right after the nosewheel touches down, they solely rely on the airbrakes and the thrust reversers to slow the plane down, is this correct?

I'm not that positive about this cause I've seen pictures of a jetliners brakes and they use multiplates which obviously is for dissipating the great amounts of heat generated during high speed braking--something that won't be needed if the brakes were indeed for low speed braking only.

---

You're right, the brakes normally aren't applied until the airplane goes below a certain speed, but that's in normal operation.

In emergency situations they *can* be applied at decision speed during a rejected takeoff. I remember a particularly impressive documentary about a test they performed on a 777. The aircraft had to come to a complete stop under maximum takeoff weight from decision speed using only the brakes. Then they had to wait 5 minutes before the fire trucks came to cool the brakes to make sure the wheels don't catch fire (every one of them deflated in that time).

Drew

--------------------
If the ends don't justify the means, then what does?
-- Robert Moses

Post Extras:      

Quote:

---

Hi, BC,

As usual, Drew has given a correct and detailed answer.

I just wanted to add that differential braking is something that has been in use in other applications for a great number of years. It has been used in farm equipment, earth-moving equipment (bulldozers, backhoes, etc) and military tanks and other heavy equipment.

The process, just as Drew described in the airplane, is both simple and very effective. If the brakes are applied to one wheel, that wheel can be made to stop turning at all. Since the other wheel (or tracks) is still rotating, the whole vehicle can be made to "turn on a dime." It can easily rotate 180-degrees and be facing the direction that it came from and be on a direct parallel path with the original direction of travel. Very handy for most farm work or grading/leveling an area.

A tank can immediately reverse directions and run while it's cannon can continue firing at whatever it found and is retreating from.

An additional note about modern tanks: During the Gulf war and the current efforts in the Middle East, the workhorse tank of the U.S. forces has been the Abraham M1A1. In addition to differential braking it also has individual throttle controls for each side. It is being slowly replaced by the newer M1A2.

---

Two black handles on the grey shafts in the middle. Left and right track drives on a Cat Excavator

-dave








--------------------
You're drunk again!
No, I'm just exhausted 'cause I've been up all night drinking.

Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam.


Post Extras:      

Quote:

---

what's a cat excavator?

---

You know, when your cat chases a mouse underground and gets stuck? Thats what you use to get him out.







or







Caterpillar is a manufacturer of Construction Equipment - Dozers, Loaders, Compactors, Excavators, etc. They are commony refered to as "Cat" for short. You can even see the CAT logo on the boom in this picture of an Excavator

-dave







--------------------
You're drunk again!
No, I'm just exhausted 'cause I've been up all night drinking.

Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam.


Edited by Phonedave (05/23/06 02:23 PM)

Post Extras:      

Quote:

---

..differential braking is something that has been in use in other applications for a great number of years. It has been used in farm equipment, earth-moving equipment (bulldozers, backhoes, etc) and military tanks and other heavy equipment....

---

...but is more commonly referred to as skid-to-steer or skid steering when applied to those more earthbound types of vehicles....

--------------------
Unpleasant truth of the day - You're unique, but that doesn't make you special.

Post Extras: