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Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 12:02 PM

I was on a flying trip a while ago that necessitated several legs to the journey and I noticed on one landing that it seemed like the pilot had the nose wheel fully braked before the nose wheel actually hit the ground and when the nose wheel did hit the ground it caused a huge jarring to the nose wheel assembly as if the nose wheel was fully locked when the nose wheel hit the ground.

So what happened in sequence seemed to be normal, ie, the rear wheels touched down and I can't remember for sure because there was nothing noteworthy at that time to pay much attention, but I don't remember feeling any braking action being applied to the rear wheels at that time, and I'm only guessing here, but wouldn't it be a little risky to apply braking to the rear wheels before the nose wheel is on the ground because wouldn't that slam the nose wheel into the ground at an unnecessary loading, and by the way, the nose wheel did not seem to be slammed into the ground by any braking action on the rear wheels and that's another part of my question.

But what happened next is the cause of my question.

When the nose wheel did hit the ground it felt exactly as if the front wheel brake was already fully applied, so it felt like the front wheel was not free to rotate when it hit the ground and that caused a massive jarring and shuddering at the front end and it felt like the pilot realized straight away what was wrong and released the front wheel brake so the wheel could then roll, and then when it was rolling, then it was fine to apply all the brakes in the normal way.

So it made me wonder, are passenger planes fitted with separate front and rear wheel braking abilities like on a motor cycle or do they have combined front and rear wheel braking like in a car?

I don't remember for sure but I think it was a 777 I was on at the time.

If the front and rear wheel brakes are indeed separate, as it appears they could be on the basis of what I perceived that day, then isn't there a way for the plane to override the pilot if he's applying the front wheel brake before the front wheel hits the ground on landings?

Or do they have that override system and it just failed that day?

Or, do they have a joined up brake system for the front and rear wheels and my perception that the rear wheels were not being braked before the front wheel hit the ground was wrong so then that too could account for the front wheel being locked when the front wheel hit the ground?

I would guess that rear wheel braking before the front hit the ground could be risky in case there was an imbalance between left and right braking that could cause some slewing to one side or the other and without the front on the ground at that time it would seem you have less control and less ability to correct by steering the front away from the side that the plane was veering towards.

I'm maybe guessing too much here, only being used to motorcycles and cars and having no experience at all in aircraft control but it did make me wonder what was going on that day.

I'm assuming the makers overbuild their structures to take into account some exuberant flying techniques but how many times can they handle that kind of abuse to the front wheel structure, not to mention the locked front wheel would be trying to tear the front wheel structure entirely off the chassis at those sort of speeds and with that sort of loading?

On another aircraft control matter, I've noticed that some passenger planes on braking when landing have a severe front end slew that causes the plane to veer from side to side at the front while under braking.

I guess that could be caused by the runway having grooves like you get on the highways from heavy traffic or it could be a design problem or a maintenance problem or maybe it's not even seen as a problem?

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Guru

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#1

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 12:12 PM

to further confuse you....pay extra attention on the reverse thrust on landinghttp://www.youtube.com/watch?v=gRfKTjOk6Xg

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#2

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 12:48 PM

I am pretty sure reverse thrust would come before mechanical braking.

Hitting the ground with the wheels locked would be...

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#3

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 1:14 PM

The brake pedal is attached to the top of the rudder pedal on each side.

You can push the rudder pedals without actuating the brakes to turn the plane in flight. Pushing one side brake pedal is how many aircraft are steered on the ground. Some have wheel steering, too.

To the best of my knowledge front gear is not braked.

What you felt was the application of the main gear brakes after the nose wheel touched down. That's how it's supposed to work.

Reverse thrust doesn't shake the plane like hard braking would.

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#4
In reply to #3

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 1:43 PM

One more comment. Busy airports want planes off the runway ASAP. You are not allowed to clear an aircraft for takeoff until the previous plane has cleared the runway.

So depending where the turnouts are located, relative to the plane's touchdown point, the pilot may stand a little harder on the brakes to get off the runway sooner.

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#5

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 2:49 PM

What you felt is known as a controlled crash,and not a "greased landing" As Lyn stated, aircraft only have brakes on the main gear, which are controlled individually by pressing on the top of the rudder pedals and as Lyn said, the aircraft can be steered by using the main gear brakes only and why the brakes are separate from each other. And all commercial aircraft anti-skid protection, (that's where the automotive industry got their ideas from). Press the left rudder pedal and the plane turns left, press the right and it turns right. All commercial aircraft have nose wheel steering, but no brakes on them. The nose gear is not built strong enough to handle the extra stress of additional braking of the nose wheel.

The shutter and shaking you feel during the landing roll-out is due to the massive amount of weight moving at an extremely fast speed and trying to stop it in a very short distance. I think Sir Isaac Newton had something to say about this.

The smoke you see when a plane touches down at landing is not from the brakes, but from "wheel spin-up" when touching down. As a pilot, you do not want spinning wheels after take-off due to gyroscopic effect, causing the plane not wanting to maneuver, so the main gear brakes are applied after lift-off and the nose wheel will usually have some kind of skid pad in the gear well to stop it.

There has been a lot of research done to spin the wheels up as the aircraft comes in for the landing to reduce flat spotting the tires and burning out wheel bearings but nothing very successful, too expensive, initial tire costs and the extra weight penalty isn't cost effective.

To really get an understanding of flight, I would suggest that you go to your local airport and find a flight school that offers an introductory flight. the could be money well spent and who knows, you could get hooked on flying too.

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#6

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 3:20 PM

Also, "on braking when landing have a severe front end slew" One of two reasons for slewing, 1) the pilot has one leg shorter than the other, thus applying uneven brake pressure, or 2) landing in a cross wind and the plane is trying to "weather vane"

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#7
In reply to #6

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 3:56 PM

Crabbing, but the pilot isn't supposed to touch down until the plane is squared to the runway.

Crosswind landing - Wikipedia, the free encyclopedia

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#8
In reply to #7

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 4:18 PM

Ah, there's an exception to just about every rule...

https://www.youtube.com/watch?v=TCUHQ_-l6Qg

Video is a Boeing B52 crab landing. There may be other aircraft with this capability, the B52 is the only one I know of.

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#9

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 4:23 PM

As others have implied but not stated I don't believe that the front landing gear brakes were actually applied at touchdown. Most likely the puff of smoke you saw was the wheel coming up to speed when contact was made with the runway. Then again most landings are not all that jarring. If the wheel was actually locked from debris or another failure mode then the tire might have been ripped off of the rim. A tire failure might have caused some emergency vehicle response if just to clean up the debris before another plane tried to use the runway.

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#10
In reply to #7

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 5:17 PM

I was referring to an aircraft trying to weather vane after touch down and roll out after de-crabbing in a cross wind component. Crabbing is usually referred to the alignment of the aircraft nose relative to the line of flight. I know you already know this.

And depending on how big of a sail your vertical stabilizer is, and the cross wind component is at the time, the aircraft will want to weather vane during ground handling. Have a good one, my friend.

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#11
In reply to #9

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 5:21 PM

Or something like this? The nose wheel self-centering failed.

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#12
In reply to #4

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 5:41 PM

Actually, flights following another takeoff depend more on how fast the jetwash from the previous flight dissipates.

Jetwash turbulence can cause an aircraft to lose lift.

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#13

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 5:55 PM

I think not, but most of my knowledge is based on fast military jets. There is no front wheel brakes on those aircraft and to the best of my knowledge I know of no commercial passenger jets that do have nose wheel brakes.

I do know the brakes for the Boeing airliners use differential toe brakes on the rudder pedals. Each pedal (left & right) controls the left and right sides of the aircraft independently. That is probably an industry standard.

There would be no way to bias or differentiate the braking performance between the nose gear and the main gear wheels, and as such, that is why the nose gear wheels have no brakes at all.

The toe brakes only operate the left and right landing gears.

What you felt was probably due to a slight nose up attitude when the jet contacted the runway and the nose dropped a little harder than normal.

Also, tires are not rotating when the plane lands, so you get a skidding effect as the tires first make contact.

Typically, brakes are not activated until the plane is wheels down and already rolling on the tarmac.

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#14
In reply to #12

Re: Do passenger aircraft have separate brake systems on the front and rear wheels?

07/16/2014 6:17 PM

Yes, two minutes for aircraft smaller than the type aircraft that just departed.

This thread concerns landing aircraft and that was what I was referring to when discussing braking of the landing aircraft to get off the runway.

Landing separation is governed by distance, not time.

None the less, only one aircraft is allowed on an active runway at any one time, unless the a departing aircraft is allowed to "taxi into position and hold" while the landing aircraft rolls out and turns off or departing traffic completes its takeoff and is at least one, or two, minutes out, depending on relative size.

At least, that's the way I remember it.

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#15
In reply to #9

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 7:01 PM

I stated that front wheels don't have brakes.

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#16
In reply to #15

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/16/2014 10:03 PM

I thought we both did. But there has been aircraft with nose wheel brakes, B-727 had nose wheel brakes, but was found ineffective and unreliable, so they were removed. The Saab Gripens also uses nose wheel brakes and so did the Messerschmitt Me 262, but nose wheel brakes are not common on commercial aircraft.

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#17

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/17/2014 9:38 AM

I would like to thank everyone who replied, I appreciate your willingness to respond and your help in clearing that up, I never imagined that nose wheels would not have a brake but looking at how fragile they appear compared to the rears then it makes perfect sense that they don't.

I loved all the videos and the explanations, thanks again.

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#18

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

07/19/2014 1:59 AM

I seem to remember reading a flight engineers book for a Boeing jet (not sure which one) and it specifically stated that in theory the captain could land the plane with the brakes fully applied before touch down. My memory is not what it was so it could have been for a different type of aircraft that I read about. If the brakes were fully on at touch down it would jar the landing gear but this would gradually (perhaps over milliseconds) be dissipated as the wheels started to roll. I think this same (or similar)question was once asked in Play Boy magazine in the mid sixties. If anyone can debunk this idea I wish they would as I have some trouble believing it myself.

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#19

Re: Do Passenger Aircraft Have Separate Brake Systems on the Front and Rear Wheels?

08/25/2014 11:59 AM

I know of no fixed wing aircraft that has brakes on the nose wheel. In fact the nose wheel isn't considered a "landing gear" at all, by most pilots. All it really does is keep the nose off the ground and allows one to steer while on the ground. most Aerobus aircraft have and use (as prescribed by the company) auto braking, and now SWAL is also required to use it on their 37s.

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