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domi.ga
Topic Author
Posts: 34
Joined: Mon Aug 13, 2001 4:57 pm

Stopping An Airplane

Mon Aug 13, 2001 5:07 pm

Hi...

I've got a general question about airplanes. What does a pilot have to do to stop a plane using the wheelbrakes. Are there special pedals for the brakes in the cockpit? Or does he use the rudder-pedals. If so: Is it necessary to put pressure to both pedals simultaniously, because I think, if one uses the left pedal, only the left wheels are decelerated?

Excuse my ignorance .....

Thanks

Dominic

 
Guest

RE: Stopping An Airplane

Mon Aug 13, 2001 5:08 pm

I was wondering the same thing(s).
 
cdfmxtech
Posts: 1319
Joined: Wed Jul 05, 2000 11:37 am

RE: Stopping An Airplane

Mon Aug 13, 2001 5:20 pm

The rudder-pedals are also the brake pedals. The brake pedals are the foward tip of the pedals. The left pedal controls the left brakes and the right controls the right brakes.
 
air2gxs
Posts: 1443
Joined: Mon Jun 18, 2001 1:29 pm

RE: Stopping An Airplane

Mon Aug 13, 2001 5:23 pm

Just like little airplanes, toe brakes. And yes, if you apply only one side, you will get only one side of the brakes. This is called differential braking.
 
KCLE
Posts: 673
Joined: Fri Feb 23, 2001 11:03 am

RE: Stopping An Airplane

Tue Aug 14, 2001 2:38 am

Or, if you need to stop in a hurry, just put the parking brake on.
 
boeingmd82
Posts: 232
Joined: Thu Jun 21, 2001 11:14 am

RE: Stopping An Airplane

Tue Aug 14, 2001 6:01 am

All these responses are true, yes, you can stop an airliner by using the toe brakes, but it's not usually done that way. I guess to truly answer your question, there are several technologies that most modern jetliners use to bring themselves to a stop.

Rathern than manually stepping on the brakes, most airlines use the autobraking systems in their jets at touchdown. This system insures that there is equal brake pressure when it is critical. A system of lift dumpers on the wings and thrust reversers are used to further slow the A/C. When the A/C is at a manageable speed, the Captain will use the toe brakes. But it all depends on the operating procedures of the airline.
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Stopping An Airplane

Tue Aug 14, 2001 6:59 am

INSERT ADDITIONAL TECHNICAL INFORMATION HERE.....................

This seemed like a good time to talk about the anti-skid system. In essense the anti-skid system available on large jets and turboprops bleed brake pressure off the system when the wheels are in danger of seizing due to over braking or slippery conditions. This prevents damage to the tires and helps maintain control. It's really alot like the ABS brake system available on modern cars.

The automatic braking system mentioned earlier applies brakes to the force (percentage) selected, up to 100% without seizing the wheels as well.



 
IMissPiedmont
Posts: 6199
Joined: Wed May 23, 2001 12:58 pm

RE: Stopping An Airplane

Tue Aug 14, 2001 12:32 pm

On a modern airliner stopping on a runway, as has been mentioned, is done by the autobrake system. However while taxiing, manual braking is employed. Ever wonder how these aircraft turn so nicely into the gate or onto the taxiway/runway? Lock up the right main and they pivot very properly to the right. Of course you rarely lock a brake entirely. You plan the turn to avoid excessive tire scrubbing.
The day you stop learning is the day you should die.
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: Stopping An Airplane

Tue Aug 14, 2001 1:12 pm

Then there is the "spoilers" on the Cessna.... Pop the doors and slam on the brakes. Talk about stopping on a dime. We stopped one in a little around 200 feet one time doing that.  Big grin
Chicks dig winglets.
 
Notar520AC
Posts: 1517
Joined: Sat Jul 21, 2001 6:53 am

RE: Stopping An Airplane

Wed Aug 15, 2001 9:49 am

In helicopters we don't need brakes.
BMW - The Ultimate Driving Machine
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: Stopping An Airplane

Wed Aug 15, 2001 10:52 pm

Notar520AC,

Depends on the Helicopter......
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

RE: Stopping An Airplane

Wed Aug 15, 2001 11:03 pm

Just one more tiny little question:
How do parking brakes work in an airliner? Is there an additional braking mechanism that stays active even when hydraulic pressure goes down? I´ve watched the ground crew using blocks; So what´s the deal here?  Smile
 
cv640
Posts: 843
Joined: Wed Aug 30, 2000 8:10 pm

RE: Stopping An Airplane

Thu Aug 16, 2001 12:15 am

Parking brakes usually work by trapping hydraulic pressure to keep the brakes applied. The problem with this system is that it usually bleeds off and without chocks it can release the brakes and then it would be free to roll away. Had a Saab badily banged up when mechanics forgot to chock a plane they had been working on. Incidentally they were checking problems with the parking brake, HA, guess they were able to duplicate that one.
 
boeingmd82
Posts: 232
Joined: Thu Jun 21, 2001 11:14 am

RE: Stopping An Airplane

Thu Aug 16, 2001 5:37 am

Hmm, I noticed a previous post about making an AIRLINER make a sharp turn by "locking" up one brake? I'm not sure about other jets, but on the B737 series, there's a nose wheel tiller that allows sharp turns and differential braking is not authorized for this type of maneuver. Most other aircraft that I've studied have the same type of system.
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

CV640

Thu Aug 16, 2001 11:08 am

I thought it might be something like this; Just wondering if they might have come up with a better solution. Apparently not...  Wink/being sarcastic

Thanks for the info!  Smile
 
Mr.BA
Posts: 3310
Joined: Sun Sep 24, 2000 12:26 pm

RE: CV640

Thu Aug 16, 2001 4:35 pm

Hey everyone,

I wonder is it usual for a pilot to increase power on one engine and put the other to idle when it is turning? For example, if he has to turn left, he increases power on the right and decreases power on the left.

Thanks
alvin
Boeing747 万岁!
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: Stopping An Airplane

Fri Aug 17, 2001 12:50 am

Yep... as opposed to differential braking, that is called differential thrust. It is reccomended as it increases brake life.
Chicks dig winglets.
 
musang
Posts: 818
Joined: Sun Apr 08, 2001 4:11 am

RE: Stopping An Airplane

Fri Aug 17, 2001 3:15 am

A couple of points re. the above posts.

Making a tight turn by locking up a brake would be generally considered inconsiderate treatment of the aircraft! obviously it scrubs the tyres, but also imposes a twisting force on the main gear leg. The leg will of course be built to withstand this, but long term wear will ensue. A pre-production Concorde once wrecked a main gear leg at Bahrain by turning too tightly, I'm led to believe.

On the 146 the nose gear breaks free of the steering mechanism and castors freely when turned beyond 70 degrees. It can be re-connected simply by forcing it back into the +- 70 degree range. So we would be wary of using differential thrust or brakes to assist the turn when turning tightly.

Happened to me once lining up on 28 at Zurich, it swung about 30 degress through centreline before I got it stopped (I couldn't just stamp on the brakes!) and I'm sure the other 146 crews waiting on the parallel taxiway knew exactly what was going on! I brought it back into submission with assymetric or differential thrust and brake, thats the only way, and is quite easy anyway. Won't make that mistake again. I now make a point of using the outside brake when turning, if needed. BAe/Avro don't recommend the use of differential thrust except when essential on slippery surfaces.

In general terms, on landing, aerodynamic braking is most useful at higher speeds, wheel braking at lower speeds. So for max stopping performance, reverse, spoilers and airbrakes just after touchdown, and minimal braking. (Holding the nose off the ground increases the frontal area and is very effective, but its also considered "hot-dogging" and would surely be the mark of a cowboy!)

As speed decreases, aero. braking diminishes in effectiveness, which is why most carriers procedures require reversers to be stowed by about 60 knots. Much lower than that and they risk ingesting debris blown up from the ground, but even at max reverse thrust, they're much less effective than wheel brakes at low speeds.

You sometimes see aircraft taxiing with a reverser deployed. This is not so much braking, its more a case of negating the idle thrust. Many aircraft, once rolling, will continue accelerating to the point where you have to use the brakes to slow to a safer taxiing speed. Remove some of the thrust and its not such an issue.

The correct braking technique for aircraft from Cessna 150s to 747s is to let the speed rise to the point where you think its fast enough, then slow to a walking pace, then let it accelerate again. A BA F/O once told me each brake application on the taxiways costs about £10 on a 777. The thing to avoid is riding the brakes, this wears them out faster, and heats them up short term.

Anti skid is usually an ON/OFF system, but Autobraking usually has several settings. I believe Boeings typically have a knob with OFF, and settings 1 to 4. There would not be an occasion in normal ops to switch the anti skid off. Like a car system, it will extract much more effort out of the brakes than a human can, and adjusts for the conditions. With anti skid off, there would be considerably more rubber left on runways than there already is.

Air brakes have a seperate lever, usually on the captain's side of the centre console, left of the thrust levers.

Reverse thrust is selected and modulated by levers protruding forward from the thrust levers. So when the thrust levers are back to idle, the reverse levers are in an easily accessible position. Engines have to be at idle to select reverse, then can be spooled up. Some types place a limit on RPM in reverse, some don't.

Brakes heat up at a rate which varies exponentially with speed, so its best to use them sparingly at high speed, increasingly as you slow down. Depending on whether they're carbon or steel, they lose effectiveness with temperature.

Air brakes of the fuselage mounted type (146 or F-28) are also more effective the faster you go. They're hardly noticeable at approach speeds. Wing mounted air brakes, however, certainly slow you down, but by virtue of their location, destroy large quantities of lift, so there is a much more dramatic effect.

Anyway, dinner's ready.

Regards - Musang

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