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Brakes? JetBlue Flight 271 (diverted)  
User currently offlineRyanAirB737 From United States of America, joined May 2004, 37 posts, RR: 0
Posted (2 years 3 months 2 weeks 5 days 19 hours ago) and read 6519 times:

Hopefully this is the correct subforum. I usually post in "Civil Aviation", but I have technical questions at the end.

I had some nervewrecking moments last night. I followed my parents' flight on FlightAware for the entire hour or so out of interest. I tried listening to air traffic control but could not find the right channel (I am a newb). Halfway through the flight, I saw that it had changed course to LGB, instead of BUR. This flight had already been quite delayed due to a large delay of the incoming JFK-LAS flight. I thought the diversion was because the flight was delayed past noise abatement at BUR or closing.

My mom texted me while at 8,000 feet or so (according to the site) saying that a "brake" warning light was on and the crew would potentially need a longer runway. I didn't think it was anything major because these things seem to happen all the time, so I was happy the crew was being extra cautious. I had assumed it was the speedbrakes, which correct me if I am wrong, are the flaps that come up off the wings after landing.

Unfortunately, most of the passengers did not see it the same way. LGB was practically closed, so everyone was stuck on the plane for about an hour, and once they were off the plane, there was nobody to guide them out or give them any update on how they were going to get to BUR. While this may be unacceptable, I am much more grateful that the plane landed. Apparently the scene was quite ugly with people yelling at the captain and flight crew and calling them "cowards" (ironic). I am sure this scene plays out several times a day. I don't know how flight crews can deal with it!

So after my long rant, some questions:

1. What could this "brake" light usually refer to given the need for a longer runway? Speedbrakes? Thrust reversers? Spoilers? People were said to be assuming it was the thrust reversers.

2. What happens when a jet lands without working reverse thrust? My understanding is that the speed combined with other braking systems would likely damage the tires, potentially collapse the landing gear, and in the worst case go off the runway.

3. Why not land at LAX which has even longer runways, is operational at 10pm, and has more mechanics to inspect?

30 replies: All unread, showing first 25:
 
User currently offlinevikkyvik From United States of America, joined Jul 2003, 10331 posts, RR: 26
Reply 1, posted (2 years 3 months 2 weeks 5 days 15 hours ago) and read 6421 times:

Quoting RyanAirB737 (Thread starter):
1. What could this "brake" light usually refer to given the need for a longer runway? Speedbrakes? Thrust reversers? Spoilers? People were said to be assuming it was the thrust reversers.

Speedbrakes and spoilers are usually the same panels (not on all airplanes, but on most airliners). In flight they're typically referred to as speedbrakes (or flight spoilers), and only deploy partway. After touchdown, they deploy all the way and are generally called spoilers (as a primary function is to "spoil" the lift being generated, thereby transferring more weight onto the wheels and allowing better braking).

Quoting RyanAirB737 (Thread starter):
2. What happens when a jet lands without working reverse thrust? My understanding is that the speed combined with other braking systems would likely damage the tires, potentially collapse the landing gear, and in the worst case go off the runway.

Nah, generally nothing nearly so serious. Many airplanes/flights can be cleared to fly without operational thrust reversers. Landing distances are usually calculated without taking into account thrust reversers anyway (not necessarily true for contaminated runways, a.k.a. wet or icy).

Thrust reversers DO enable better energy management; they allow less usage of the brakes, which can extend brake life and also prevent the brakes from heating up too much. But airliners are more than capable of landing and slowing down perfectly normally without functional thrust reversers. The A380, for example, only has reversers on two of its four engines.

Quoting RyanAirB737 (Thread starter):

3. Why not land at LAX which has even longer runways, is operational at 10pm, and has more mechanics to inspect?

My guess would simply be that Jetblue has a hub at LGB, meaning they'll have a better ability to correct the issue there. And LGB's 10,000 foot runway is plenty, though if they were landing from the southeast, they have about 8000' available for landing. Still plenty to get a passenger airliner stopped at typical landing weights.

All that said, I don't know what sort of landing penalties airliners garner for inoperational spoilers. Wheel braking ability would be reduced, but you'd still have the thrust reversers to help out at higher speeds.



How can I be an admiral without my cap??!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 2, posted (2 years 3 months 2 weeks 5 days 14 hours ago) and read 6371 times:

Quoting RyanAirB737 (Thread starter):
1. What could this "brake" light usually refer to given the need for a longer runway? Speedbrakes? Thrust reversers? Spoilers? People were said to be assuming it was the thrust reversers.

My first thought with "brake light" would be that they were referring to the wheel brakes. Each wheel has multiple disks and so forth so in that case it would probably just be a partial failure. And quite possibly just an indication error.

Quoting RyanAirB737 (Thread starter):
2. What happens when a jet lands without working reverse thrust? My understanding is that the speed combined with other braking systems would likely damage the tires, potentially collapse the landing gear, and in the worst case go off the runway.

As vikkyvik says, planes land without reverse all the time. And lots of landings are on idle reverse only. With a few exceptions, reverse cannot be used in performance calculations. The stopping distance is calculated on wheel braking only. However if you don't have spoilers the aircraft won't settle onto the runway as positively so braking takes longer.

I think this idea that tires blow and so forth may be based on videos of rejected take-off tests, where tires do blow. Yes, if you reject a take-off at max speed and use max braking, you will most probably blow some tires and potentially damage stuff. However you would most certainly not collapse the gear. Maximum braking is almost never used. As SlamClick famously put it, if you use max braking, probably the last thing you would see as a pilot before the aircraft was engulfed in a cloud of smoke is the paint sliding off the front of the aircraft.

Quoting RyanAirB737 (Thread starter):
Unfortunately, most of the passengers did not see it the same way. LGB was practically closed, so everyone was stuck on the plane for about an hour, and once they were off the plane, there was nobody to guide them out or give them any update on how they were going to get to BUR. While this may be unacceptable, I am much more grateful that the plane landed. Apparently the scene was quite ugly with people yelling at the captain and flight crew and calling them "cowards" (ironic). I am sure this scene plays out several times a day. I don't know how flight crews can deal with it!

Ah, the grateful and informed public. I think flight crews learn to ignore the general public since the vast majority of people understand practically nothing about aviation. I'm not a pilot but I cringe on a regular basis about common misconceptions.

[Edited 2012-08-30 17:26:02]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineRyanAirB737 From United States of America, joined May 2004, 37 posts, RR: 0
Reply 3, posted (2 years 3 months 2 weeks 5 days 13 hours ago) and read 6351 times:

Wow! Thanks for the great responses! I was totally out of the loop about the role of thrust reversers! My assumption was that they were the main braking force on landing.

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 4, posted (2 years 3 months 2 weeks 5 days 13 hours ago) and read 6346 times:

Quoting RyanAirB737 (Reply 3):
Wow! Thanks for the great responses! I was totally out of the loop about the role of thrust reversers! My assumption was that they were the main braking force on landing.

Reversers account for less than a third of stopping power. Also they decrease in effectiveness with decreased speed.

BTW unlike the moronic name callers on the flight, you seek information. Kudos.

Found SlamClick's post in my "SlamClick's Greatest Hits" note.

Now as to the original question (disregaring the "THOUSAND TONS" of fuel which is more than a 747 would hold if the filler cap was on top the tail) I think I can put some realistic numbers to it. Using actual weight and balance documents from the last time/place I flew the 737:

72000 lbs BOW of the heaviest 737-300 in the fleet sample I have.
10380 winter weight of 60 passengers
1410 bags of 60 pax at the 23.5 lbs per in use at the time
6400 lbs landing fuel includes alternate at 100 nm away and :45 IFR reserve fuel
90190 landing gross weight of my sample Boeing

For 90K landing weight at Flaps 40 I get VREF of 116 knots. That means stall speed of 89.2 knots. So if I want to do a STOL landing I think I can do the last 200' or so at 1.1 VSO or 98 knots approach speed.

Add to that, automatic ground spoilers that are going to kill the lift upon wheel spin-up, thrust reversers that no one has said I cannot use, and the mind-boggling multi-disc, multi-puck, anti-skid protected brakes and I'm beginning to think that the last thing I'd see before sliding to stop in a cloud of tire and brake smoke is my own paint job sliding off the nose of the airplane.

I have a brake energy chart at hand. It is a "web of death" grid chart with skewed lines and I don't want to blow my whole day staring at that but I believe that I could start at the end with ultimate energy absorbtion (roll the fire trucks) and at the beginning with my weight and solve to the middle to find my runway length required. That is not what these charts are for, but I think I could do it and give the actual feet of runway that would be used up. I just don't want to take the time but I'm pretty sure it will support my claim.

Also, as stated in reply #2, second line, it would require a precise approach and landing and would absolutely not be "normal." but I'd bet my life that I could get it stopped between the first brick and the last brick of a 2400' runway.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBreninTW From Taiwan, joined Jul 2006, 1719 posts, RR: 1
Reply 5, posted (2 years 3 months 2 weeks 5 days 11 hours ago) and read 6298 times:

Quoting Starlionblue (Reply 4):

And here is the original thread that story came from: Can A 737 Land On A 2,400 Ft Runway? (by Mozart Feb 9 2005 in Tech Ops)



I'm tired of the A vs. B sniping. Neither make planes that shed wings randomly!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 6, posted (2 years 3 months 2 weeks 5 days 11 hours ago) and read 6276 times:

Quoting BreninTW (Reply 5):
Quoting Starlionblue (Reply 4):

And here is the original thread that story came from: Can A 737 Land On A 2,400 Ft Runway? (by Mozart Feb 9 2005 in Tech Ops)

A classic thread.

EDIT: Darnit. Now I've spent 20 minutes re-reading it. So much for productivity this morning...

[Edited 2012-08-30 20:00:43]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (2 years 3 months 2 weeks 5 days 8 hours ago) and read 6229 times:

Quoting RyanAirB737 (Thread starter):
1. What could this "brake" light usually refer to given the need for a longer runway? Speedbrakes? Thrust reversers? Spoilers? People were said to be assuming it was the thrust reversers.

It should refer to the wheel brakes. It may, depending on the aircraft, refer to the spoilers but that would be odd. There is no way that a light labelled "brakes" would apply to thrust reversers.

Quoting RyanAirB737 (Thread starter):
2. What happens when a jet lands without working reverse thrust? My understanding is that the speed combined with other braking systems would likely damage the tires, potentially collapse the landing gear, and in the worst case go off the runway.

The brakes get hotter. That's it. Assuming that the landing is done per normal procedures, it will not damage the tires, collapse the gear, or send the airplane off the runway.

Of the three, collapsing the gear is the least likely. Gear is almost impossible to collapse once it's down; there are several over-center locks that stick the gear down as long as the crew don't move the gear handle to "Up". It's far more likely for the gear to separate (to protect the wing from structural overload) than for it to collapse. The only time you're likely to have a gear collapse is if the gear downlocks don't function properly, which is annunciated to the crew and has nothing to do with the brake system.

Tom.


User currently offlineTristarsteve From Sweden, joined Nov 2005, 4066 posts, RR: 33
Reply 8, posted (2 years 3 months 2 weeks 5 days 4 hours ago) and read 6182 times:

Quoting RyanAirB737 (Thread starter):
that a "brake" warning light was on and the crew would potentially need a longer runway.

Didn't work out what aircraft type we are on,
but on the B737 there are two brake lights in front of the pilots. An Autobrake Inop light, and an Antiskid Inop light. They are connected, if antiskid is inop, there are no autobrakes. So if the pilot is talking about a brakes light, it must be the antiskid light. This means that antiskid is inop. You use manual braking, and use it carefully, and the aircraft stops, but you use more runway. I assume that from their charts they can see that BUR runway was a bit limiting, so went for a longer runway. They could have landed at BUR, but the brakes might have locked, and the tyres deflated.
There is no spoilers inop light. There is a Auto Ground Spoiler inop light, but you must arm the spoilers first, and this is done on final approach. But this would not cause diversion.

By the way antiskid inop is only a problem in the wet. Your car did not have antiskid until 10 years ago. My Polo has no antiskid, and stops just fine, but I have to pump the brake pedal in the rain. Aircraft are the same. In the rain, use the brakes lightly and pump the pedals.

A320 and other jets are exactly the same, but don't always have lights. They have messages on a screen instead.


User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 9, posted (2 years 3 months 2 weeks 5 days 2 hours ago) and read 6155 times:

Quoting RyanAirB737 (Thread starter):
Apparently the scene was quite ugly with people yelling at the captain and flight crew and calling them "cowards" (ironic)

In Aviation its always safety first.....and often the ignorent critisize the ones that take a decision when things turn out ok.
the crew know their job & the decision is taken based on the situation at hand.

The Brake light probably seems to be an INOP A/S system,thus the decision to go in for a longer runway.
T/R is not the primary braking/decelaration medium,there are brakes & Speedbrakes too.



Think of the brighter side!
User currently offlinespchamp1 From United States of America, joined Apr 2010, 87 posts, RR: 0
Reply 10, posted (2 years 3 months 1 week 6 days 18 hours ago) and read 5691 times:

Quoting RyanAirB737 (Thread starter):
Unfortunately, most of the passengers did not see it the same way. LGB was practically closed, so everyone was stuck on the plane for about an hour, and once they were off the plane, there was nobody to guide them out or give them any update on how they were going to get to BUR. While this may be unacceptable, I am much more grateful that the plane landed. Apparently the scene was quite ugly with people yelling at the captain and flight crew and calling them "cowards" (ironic). I am sure this scene plays out several times a day. I don't know how flight crews can deal with it!

Let me just chime in if I may. I am a jetBlue crewmember who works in Long Beach and did in fact happen to be working the night this diversion came in.

One of the reasons for diverting to LGB was in fact due to the longer runway, the second reason is that LGB is a MX base for jetBlue as well. LGB also has additional a/c that could be used to continue the flight if the one that diverted needed to be taken out of service.

While I personally did not assist with that aircraft, the story is that our local MX team boarded the aircraft to correct the FAULT message and within about 20-30 minutes resolved the issue and cleared it with our MX Control department. The aircraft was at time continue on over to BUR. The flight crew for reasons unknown to me called "Fatigue", I assume they did this due to the extensive delays they had throughout the day, but that is pure speculation on my part.

At the time the flight crew called fatigue, we did not have buses or transportation arranged because there no indication that it would terminate in LGB.


User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 11, posted (2 years 3 months 1 week 5 days 18 hours ago) and read 5537 times:

Quoting spchamp1 (Reply 10):
The aircraft was at time continue on over to BUR. The flight crew for reasons unknown to me called "Fatigue",

Was this because they were not satisfied with the rectification OR just tired.



Think of the brighter side!
User currently offlineDocLightning From United States of America, joined Nov 2005, 20334 posts, RR: 59
Reply 12, posted (2 years 3 months 1 week 5 days 16 hours ago) and read 5508 times:

Quoting Starlionblue (Reply 2):
My first thought with "brake light" would be that they were referring to the wheel brakes. Each wheel has multiple disks and so forth so in that case it would probably just be a partial failure. And quite possibly just an indication error.

Does each individual wheel have multiple disks? That seems complicated.

Also, how are the brake hydraulics split up? I'd be shocked if all brakes are on the same hydraulic circuit. Is it that some proportion of the wheels on each bogie are connected to each circuit?


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17172 posts, RR: 66
Reply 13, posted (2 years 3 months 1 week 5 days 15 hours ago) and read 5492 times:

Quoting DocLightning (Reply 12):
Does each individual wheel have multiple disks? That seems complicated.

Yepp. Multiple discs.

http://img.photobucket.com/albums/v174/jkrusat/DSC03516-1.jpg

Quoting DocLightning (Reply 12):
Also, how are the brake hydraulics split up? I'd be shocked if all brakes are on the same hydraulic circuit. Is it that some proportion of the wheels on each bogie are connected to each circuit?

Pretty sure you are right. To tired to research right now.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinebond007 From United States of America, joined Mar 2005, 5451 posts, RR: 8
Reply 14, posted (2 years 3 months 1 week 5 days 14 hours ago) and read 5481 times:

Quoting Starlionblue (Reply 4):
Reversers account for less than a third of stopping power. Also they decrease in effectiveness with decreased speed.

On a dry runway, it's actually almost negligible for most airliners, at less than 5% at max manual braking. Now this 100ft might be the difference you need of course!

On contaminated runways of course it's a different story, and could provide a couple of thousand feet extra stopping distance.

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineTristarsteve From Sweden, joined Nov 2005, 4066 posts, RR: 33
Reply 15, posted (2 years 3 months 1 week 5 days 2 hours ago) and read 5391 times:

Quoting DocLightning (Reply 12):
how are the brake hydraulics split up? I'd be shocked if all brakes are on the same hydraulic circuit.

Prepare to be shocked.
Normal braking is all brakes from a single hyd system.
Then there is Alternate brakes from a separate hyd system
Then emergency brakes from an accumulator.

On a Boeing (not 787) there is one set of brake pistons. The normal and alternate brake lines meet in the wheel well at a shuttle valve, and one line goes down to the brake.
On an Airbus there are two sets of pistons on the brake, one for normal, and one for alt.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (2 years 3 months 1 week 4 days 23 hours ago) and read 5376 times:

Quoting DocLightning (Reply 12):
Does each individual wheel have multiple disks? That seems complicated.

It's not very complicated. The brake consists of layers of plates. Each plate is splined on either the inside or outside edge (they alternate). There are groves in the axle and the wheel. Half the plates with the splines on the inside edges engage the grooves on the axle. The other half with the splines on the outside edge engage the groves on the wheel. When the brake pistons (a single assembly on the inboard side) squeeze the whole brake stack together the torque goes from the wheel into half the plates, which rub on the other half of the plates, which are locked to the axle.

There is only one set of "calipers". The only difference is that they're squashing a stack (which looks just like a really thick disc to the calipers) rather than a single disc.

Quoting DocLightning (Reply 12):
Also, how are the brake hydraulics split up? I'd be shocked if all brakes are on the same hydraulic circuit. Is it that some proportion of the wheels on each bogie are connected to each circuit?

On a Boeing, each gear is supplied by two hydraulic circuits (center and one other). At any one time the whole gear is powered by one circuit but it automatically fails over to the other if pressure is lost in the primary. From the anti-skid module to the individual brakes are individual lines so a failure of any one brake only takes out that brake.

The 787 is a totally different animal because the brakes are electric.

Tom.


User currently offlineHAWK21M From India, joined Jan 2001, 31702 posts, RR: 56
Reply 17, posted (2 years 3 months 1 week 4 days 3 hours ago) and read 5277 times:

Quoting tdscanuck (Reply 16):

The 787 is a totally different animal because the brakes are electric.

Pls elaborate.....



Think of the brighter side!
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 18, posted (2 years 3 months 1 week 3 days 12 hours ago) and read 5183 times:

Quoting HAWK21M (Reply 17):
Quoting tdscanuck (Reply 16):

The 787 is a totally different animal because the brakes are electric.

Pls elaborate.....

The brakes aren't hydraulic. Each brake has four electric-motor actuators. It's much easier to switch/reroute/bypass electrical power than hydraulic. The 787 brakes can run off any of the 6 generators, the battery, or the RAT, and they can function happily with a dead actuator on each brake (the other actuators just clamp harder to compensate). Hydraulic brakes don't give you actuator-level control and fail much less gracefully.

Tom.


User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 19, posted (2 years 3 months 1 week 2 days 12 hours ago) and read 5053 times:

Interesting. What would they do in the event of total power loss? (Near impossible, I know, just curious)


The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineDarkSnowyNight From United States of America, joined Jan 2012, 1412 posts, RR: 3
Reply 20, posted (2 years 3 months 1 week 2 days 5 hours ago) and read 5031 times:

Quoting Tristarsteve (Reply 8):

A320 and other jets are exactly the same, but don't always have lights. They have messages on a screen instead.

Right. The A320 has a full page for this which also shows temp & tire PSI. An error msg will show up if the anti-skid becomes an issue, but it is not a "light" per se.



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 21, posted (2 years 3 months 1 week 1 day 23 hours ago) and read 5027 times:

Quoting Fabo (Reply 19):
What would they do in the event of total power loss?

Die.

Seriously...modern aircraft can't function with *total* power loss. Even if certain parts keep working (e.g. direct cable flight controls), the crew would have no instrumentation. With no attitude/airspeed/altitude/thrust display, you're going to be in trouble very quickly. The way they deal with this is to have so many independent power sources that you "never" lose all of them.

For example, on a 787:
-There are two generators on each engine (4 primary generators total).
-There are two generators on the APU
-There is a ram-air turbine
-There is a ships battery

Any one of these is capable of maintaining continued safe flight and landing by themselves (the battery is limited to about 30 minutes, which is enough to get to the ground).

Total power loss would require independent failure of all the power sources at the same time. The statistical chance of this is less than 1 in a billion per flight hour (and has never happened in service in modern history, as far as I know).

Tom.


User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 22, posted (2 years 3 months 1 week 1 day 15 hours ago) and read 5024 times:

I was thinking total in terms of total on the brakes itself, something like, the cables got cut by a crazy person, or something.

But thanks either way.



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlinerwessel From United States of America, joined Jan 2007, 2411 posts, RR: 2
Reply 23, posted (2 years 3 months 1 week 1 day 13 hours ago) and read 5017 times:
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Quoting Fabo (Reply 22):
I was thinking total in terms of total on the brakes itself, something like, the cables got cut by a crazy person, or something.

They would then be just as useless as hydraulically actuated brakes after the (less redundant) hydraulic lines were cut.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 24, posted (2 years 3 months 1 week 1 day 12 hours ago) and read 5001 times:

Quoting Fabo (Reply 22):
I was thinking total in terms of total on the brakes itself, something like, the cables got cut by a crazy person, or something.

Ah, sorry. Like rwessel said, you'd lose them just like if you cut the hydraulic lines on hydraulic brakes.

The upside is that you'd have to actually sever all the conductors to kill the brakes; you don't need to put much of a hole in a hydraulic line before the flow destroys the line and any ability it has to carry pressure. Electrical wires play much nicer with minor damage than hydraulics.

Another neat features is that the electric brakes don't backdrive...if you depower the brakes while they're set, they stay set. The parking brake is (finally!) actually a parking brake. You don't need an accumulator to maintain pressure and you don't have an accumulator to bleed down with the inevitable internal leakage. This is a double-edged sword though...if you pull the battery on a 787 while the brakes are set, you're stuck where you are until you put in a new battery or manually "hotwire" the brakes to back off the actuators. On the whole, I'd rather a brake stay on than relax though.

Tom.

[Edited 2012-09-10 18:48:00]

User currently offlinerwessel From United States of America, joined Jan 2007, 2411 posts, RR: 2
Reply 25, posted (2 years 3 months 1 week 1 day 10 hours ago) and read 5036 times:
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Quoting tdscanuck (Reply 24):
Another neat features is that the electric brakes don't backdrive...if you depower the brakes while they're set, they stay set. The parking brake is (finally!) actually a parking brake.

Interesting. How does that work? I'm imagining a worm gear or jack screw driving the calipers, or something like that.


User currently offlineDarkSnowyNight From United States of America, joined Jan 2012, 1412 posts, RR: 3
Reply 26, posted (2 years 3 months 1 week 1 day 5 hours ago) and read 5002 times:

Quoting rwessel (Reply 25):

Interesting. How does that work? I'm imagining a worm gear or jack screw driving the calipers, or something like that.

What that be able to give the level of speed & precision required for braking, especially modulated braking and anti-skid protections?

I always thought it was something more along the lines of magnetic repulsion along the width axis of the pad-rotor stack...


Ok, well, looks like I was wrong (maybe, probably) about that too... Here we go.

"One innovative application of the more-electric systems architecture on the 787 is the move from hydraulically actuated brakes to electric. Electric brakes significantly reduce the mechanical complexity of the braking system and eliminate the potential for delays associated with leaking brake hydraulic fluid, leaking valves, and other hydraulic failures. Because its electric brake systems are modular (four independent brake actuators per wheel), the 787 will be able to dispatch with one electric brake actuator (EBA) inoperative per wheel and will have significantly reduced performance penalties compared with dispatch of a hydraulic brake system with a failure present. The EBA is line-replaceable enabling in-situ maintenance of the brakes."

This is from here... http://www.boeing.com/commercial/aer...rticles/qtr_4_06/article_04_3.html

I'm guessing it's just the actuators themselves that are at all different, as the rest of the design does look very familiar. Interestingly, this article goes on to mention that one basically no longer has to disengage the park brake at the stand, as the system will know when the brakes are hot, and relieve pressure to the absolute minimum req'd for parking, as opposed to full force. I'm sure this will add both utility and lifetime to the stacks themselves. Neat times...



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 27, posted (2 years 3 months 1 week 21 hours ago) and read 4971 times:

Quoting rwessel (Reply 25):
Quoting tdscanuck (Reply 24):
Another neat features is that the electric brakes don't backdrive...if you depower the brakes while they're set, they stay set. The parking brake is (finally!) actually a parking brake.

Interesting. How does that work? I'm imagining a worm gear or jack screw driving the calipers, or something like that.

The speed reduction from the motor to the piston jack screw is via a worm gear transmission.

Quoting DarkSnowyNight (Reply 26):
What that be able to give the level of speed & precision required for braking, especially modulated braking and anti-skid protections?

Yes. How would they have certified it otherwise?

Quoting DarkSnowyNight (Reply 26):
I'm guessing it's just the actuators themselves that are at all different, as the rest of the design does look very familiar.

Correct. The brake stack itself is very conventional.

Quoting DarkSnowyNight (Reply 26):
Interestingly, this article goes on to mention that one basically no longer has to disengage the park brake at the stand, as the system will know when the brakes are hot, and relieve pressure to the absolute minimum req'd for parking, as opposed to full force.

Yes. The actuators go to something like 30% force when the parking brakes are set. They automatically ramp up to 100% when the throttles are advanced (until the parking brake is released). They also will "take up" braking as the brakes cool after landing to maintain parking brake force.

Tom.


User currently offlinevikkyvik From United States of America, joined Jul 2003, 10331 posts, RR: 26
Reply 28, posted (2 years 3 months 6 days 17 hours ago) and read 4854 times:

This incident seems a propos to the discussion regarding brakes and electrical power:

http://www.avherald.com/h?article=455c3629&opt=6400

All four generators apparently failed. And without reversers and anit-skid (and, I assume, close to MLW), the aircraft blew most tires upon landing.

Southern Air Accident In Anchorage (by jourdan747 Sep 11 2012 in Civil Aviation)



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User currently offlineDarksnowynight From United States of America, joined Jan 2012, 1412 posts, RR: 3
Reply 29, posted (2 years 3 months 5 days 9 hours ago) and read 4744 times:

Quoting tdscanuck (Reply 27):

Quoting DarkSnowyNight (Reply 26):
What that be able to give the level of speed & precision required for braking, especially modulated braking and anti-skid protections?

Yes. How would they have certified it otherwise?

Right. I don't think I asked the question right.

I meant what I said in the sense of "if this whole method good enough; if not is something else --maybe magnetic repulsion braking-- used to close the stacks," and not so much "I know they put that on, but is it good enough?" I know Boeing & the FAA wouldn't certify a crap solution, lol.

Most of my experience WRT worm gears & jack screws involves things like Stab Trim & Flap Actuators. Though I know it's as much a function of the PSIs of the relevant systems, it's hard for a guy like me to imagine a jack screw or w gear turning fast enough to satisfy anti-skid requirements. That pulsation is pretty quick. Anyway, on reflection, yes, it's hard to imagine something in that design that would militate against that speed, given a fast enough (high enough torque) motor.

Quoting tdscanuck (Reply 27):
They also will "take up" braking as the brakes cool after landing to maintain parking brake force.

While I see no reason not to do this, is it necessary? Seems that if 30% will hold it, no need to exert more pressure. Kinda the same reason I come back off my car's brake at a level stop/intersection. I don't need it; no reason to heat it.



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User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 30, posted (2 years 3 months 4 days 22 hours ago) and read 4682 times:

Quoting Darksnowynight (Reply 29):
Though I know it's as much a function of the PSIs of the relevant systems, it's hard for a guy like me to imagine a jack screw or w gear turning fast enough to satisfy anti-skid requirements. That pulsation is pretty quick.

The key is that, once you've got the slack out of the brake stack, the force-displacement curve is really steep. Very small changes in actuator position result in big changes in clamping force. So the actuators don't have to move very far at all to modulate the brakes. Unlike something like a stab actuator, the active operating range in terms of position is extremely small.

Quoting Darksnowynight (Reply 29):

Quoting tdscanuck (Reply 27):
They also will "take up" braking as the brakes cool after landing to maintain parking brake force.

While I see no reason not to do this, is it necessary?

If you set the parking brakes at 30% force with the brakes hot, you will lose clamping when they cool. The brake stack will shrink and, since the force/displacement relationship is so steep, even a small bit of cooling is enough to significantly drop the braking force. That's why the actuators have to "creep up" to maintain force until the brakes cool down.

Tom.


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