Reversers
Using Autobrakes in either MIN or MED position on a normal landing:
Weight 255 tons
Brakes on at 130 kts
Sea level
ISA (15'C)
No reverse thrust
Brake energy released 23 million ft lbs
Cooling time 1h 10min
However if one would use full reverse until 100 to 80kts and then use autobrakes in either MIN or MED with same conditions as above:
Brake eneregy releases 8 million ft lbs
No cooling time required
On a B747 after Anti-Skid touchdown protection releases with Autobrakes selected, brakes will provide full deceleration with no modulation until reverse thrust comes available (Approx 3 to 4 sec) and modulation of brake input starts. It is this high weight, high speed combination that causes most heating as well as wear and tear of brake units and tires.
One needs to understand that reversers are most effective at high speeds where brakes are at their best al lower speeds. This goes for any airplane.
A brake unit, wheel and tire combination can cost between 100 000 and 300000 USD x 16. Smart use of reverse and brakes can save company millions per year.
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