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