Carbon Brakes
Join Date: Feb 2000
Location: U.S.A.
Posts: 54
Likes: 0
Received 0 Likes
on
0 Posts
Carbon brakes also get more efficient the hotter they get, and don't get as hot in any event. Downside is that the wear more if you use them like you do steel brakes, upside is that if used correctly they will outlast steel brakes and continue to provide full braking capability even when worn to almost nothing, whereas steel brakes get dramatically worse as they wear.
Dear forum readers
Carbon brakes represent an advance in brake technology. Carbon has properties that make it highly desirable as an heat absorber.
Its high specific heat reduces brake weight. High thermal conductivity ensures that heat transfer, throughout the disk stack is more uniform and occurs at a faster rate.
Comparation
---------------------Steel---Carbon
Density(lb/in3)______0.283___0.061
Specific heat________0.130___0.310 Btu/lbºF
Thermal Conductivity___24____100 Btu/h.ft2ºF
Temperature Limit ºF__2100___4000
Another aspect to compare is the relative strenght at high temperatures. Although specific strenght (tensile strenght divided by density) is higher for steel, carbon can retain its strenght at high temperature. After 1200 ºF carbon specific strenght exceeds steel.
This property yields a brake heat sink whose operating temperature is limited by the temperature limits of the surrounding structure. This is important in a RTO.
Regarding economic factors. Carbon brakes weight 40% less than brakes with conventional steel rotors and linings which means greater efficiency and ability to carry a heavier payload. The carbon brakes that can be selected for the B767-300 save around 300 pounds per aircraft.
Carbon brakes are more expensive to produce, the process to produce a carbon disk is very complex and can take several months. As far as I know only 2 companies in the world manufacture carbon disks and supply the brake manufacturers (BFGoodrich,Messier ,etc)
Regarding maintenance costs, carbon brake will make 3 times more landings than steel brakes. So more spares should be purchased for steel brakes, however the repair cost (brake heat pack refurbishment) is much greater for carbon.
As an example in a fleet with B737 with steel brakes and A319 with carbon brakes (only option)with similar type of operation. Steel brakes normally last 700 landings and carbon brakes 2100 landings.
However the CPBL (Cost per brake landing) could be ~3 USD for steel and ~10 USD for carbon.
Regards
Carbon brakes represent an advance in brake technology. Carbon has properties that make it highly desirable as an heat absorber.
Its high specific heat reduces brake weight. High thermal conductivity ensures that heat transfer, throughout the disk stack is more uniform and occurs at a faster rate.
Comparation
---------------------Steel---Carbon
Density(lb/in3)______0.283___0.061
Specific heat________0.130___0.310 Btu/lbºF
Thermal Conductivity___24____100 Btu/h.ft2ºF
Temperature Limit ºF__2100___4000
Another aspect to compare is the relative strenght at high temperatures. Although specific strenght (tensile strenght divided by density) is higher for steel, carbon can retain its strenght at high temperature. After 1200 ºF carbon specific strenght exceeds steel.
This property yields a brake heat sink whose operating temperature is limited by the temperature limits of the surrounding structure. This is important in a RTO.
Regarding economic factors. Carbon brakes weight 40% less than brakes with conventional steel rotors and linings which means greater efficiency and ability to carry a heavier payload. The carbon brakes that can be selected for the B767-300 save around 300 pounds per aircraft.
Carbon brakes are more expensive to produce, the process to produce a carbon disk is very complex and can take several months. As far as I know only 2 companies in the world manufacture carbon disks and supply the brake manufacturers (BFGoodrich,Messier ,etc)
Regarding maintenance costs, carbon brake will make 3 times more landings than steel brakes. So more spares should be purchased for steel brakes, however the repair cost (brake heat pack refurbishment) is much greater for carbon.
As an example in a fleet with B737 with steel brakes and A319 with carbon brakes (only option)with similar type of operation. Steel brakes normally last 700 landings and carbon brakes 2100 landings.
However the CPBL (Cost per brake landing) could be ~3 USD for steel and ~10 USD for carbon.
Regards
None but a blockhead
Join Date: Nov 1999
Location: London, UK
Posts: 535
Likes: 0
Received 0 Likes
on
0 Posts
Out of interest, how do you make a carbon disc for a brake? I know roughly how you make carbon fibre by torturing some poor long chain polymer, but can you do that for discs?
R
R
Join Date: Jun 2000
Location: CYTZ
Posts: 169
Likes: 0
Received 0 Likes
on
0 Posts
I vaguely recall an earlier thread where it was mentioned that carbon brakes reduces the need for T/R, so the reduced engine wear can offset some (but not nearly all) of the higher cost per landing. Forget the exact subject of the thread (it was about a year ago) but it had something to do with some carriers changing their standard ops to land without T/R.
Join Date: Jul 2000
Location: A one horse town...
Posts: 248
Likes: 0
Received 0 Likes
on
0 Posts
Can anyone describe how higher temperatures improve the wear on carbon brakes?
I believe that one of the contributing factors in the QF1 accident at BKK was a company policy that encouraged crews to use higher touchdown speeds to get better wear out of the carbon brakes. So how does this work?
Thanks in advance, Dave.
I believe that one of the contributing factors in the QF1 accident at BKK was a company policy that encouraged crews to use higher touchdown speeds to get better wear out of the carbon brakes. So how does this work?
Thanks in advance, Dave.
Squawk 8888
The T/R versus carbon brakes scenario is that of using Autobrake for landing. If you use Autobrake, the unit senses total retardation, so if T/R is used the brakes will be modulated to achieve the selected retardation. Carbon brakes do not react well to modulation - they are much better at having one constant application being held. This gets them up to temperature quickly and reduces the wear. Soooooo.. Reverse idle and medium Autobrake works well and costs less.
The T/R versus carbon brakes scenario is that of using Autobrake for landing. If you use Autobrake, the unit senses total retardation, so if T/R is used the brakes will be modulated to achieve the selected retardation. Carbon brakes do not react well to modulation - they are much better at having one constant application being held. This gets them up to temperature quickly and reduces the wear. Soooooo.. Reverse idle and medium Autobrake works well and costs less.
Join Date: May 2001
Posts: 39
Likes: 0
Received 0 Likes
on
0 Posts
I was told that carbon brakes wear exactly the same for each application, wether it be an RTO or a gentle press. So you might as well give them a proper thrashing! Beware that nosewheel if you have medium autobrake and a high nose attitude - it don't arf thump!!
Join Date: Jun 2001
Posts: 324
Likes: 0
Received 0 Likes
on
0 Posts
Dave I - not quite!
The touchdown speed is the same, but no reverse is used on landing, so that the brakes do all the work and thus heat up to quite a temperature. As stated elsewhere on this thread, carbon brakes are more efficient at higher temperatures.
This SOP is not confined to QF, many airlines use it these days because the manufacturers recommend it. Some airlines have gone half way and use idle reverse only - in all cases though it's captain's discretion - if he thinks that particular landing merits the use of full reverse (eg short/wet runways)then he's free to do so.
The touchdown speed is the same, but no reverse is used on landing, so that the brakes do all the work and thus heat up to quite a temperature. As stated elsewhere on this thread, carbon brakes are more efficient at higher temperatures.
This SOP is not confined to QF, many airlines use it these days because the manufacturers recommend it. Some airlines have gone half way and use idle reverse only - in all cases though it's captain's discretion - if he thinks that particular landing merits the use of full reverse (eg short/wet runways)then he's free to do so.
Join Date: Jan 2000
Location: USA
Posts: 167
Likes: 0
Received 0 Likes
on
0 Posts
Yak Hunt, The BF Goodrich publication, plus the representative said that most of the wear on carbon brakes is done on the first flight of the day during taxi out. Additionaly if the brakes are not heated up during landing eg to 300-400deg, the wear is still significant. Don't think I would worry to much about the nose gear "thumping down" vs getting a tail by holding the nose gear off.
