Aircraft brakes turn the kinetic energy of a landing airplane into thermal energy so the aircraft can slow safely on the runway. Large jets use carbon multi-disc brakes because they can absorb enormous heat while keeping weight lower than many steel brake designs. Antiskid systems help the tires keep rolling instead of locking, which improves directional control and shortens stopping distance on many runway surfaces.
Understanding these systems is important for pilots, engineers, and technicians because braking performance affects every landing and rejected takeoff.
Key Facts
- Braking converts kinetic energy into heat: KE = 1/2 mv^2.
- Stopping distance depends strongly on speed because kinetic energy increases with v^2.
- Braking force at the tire is limited by friction: Fmax = μN.
- Antiskid reduces brake pressure when wheel speed drops too quickly, helping prevent a locked wheel.
- Autobrake systems command a selected deceleration level after touchdown or during a rejected takeoff.
- Brake temperature rises when more energy is absorbed, and overheated brakes can reduce braking effectiveness or damage components.
Vocabulary
- Carbon multi-disc brake
- A brake assembly using alternating rotating and stationary carbon discs to create friction and absorb high amounts of heat.
- Antiskid system
- An aircraft braking control system that monitors wheel speed and adjusts brake pressure to help prevent wheel lockup.
- Autobrake
- A system that automatically applies wheel brakes to achieve a selected deceleration after landing or during a rejected takeoff.
- Torque tube
- A structural part in the brake assembly that supports stationary brake discs and carries braking torque into the landing gear.
- Brake fade
- A reduction in braking effectiveness caused by excessive heat, material limits, or changes in friction behavior.
Common Mistakes to Avoid
- Assuming more pedal force always means shorter stopping, because tire friction has a limit and locked wheels can slide with less control.
- Ignoring the v^2 in kinetic energy, because doubling landing speed gives four times as much energy for the brakes to absorb.
- Thinking antiskid removes the need for pilot judgment, because runway contamination, tire condition, and aircraft weight still affect stopping distance.
- Treating brake heat as only a comfort issue, because excessive temperature can cause wear, fuse plug release, brake fade, or maintenance limits.
Practice Questions
- 1 A 70000 kg aircraft lands at 70 m/s. Estimate its kinetic energy using KE = 1/2 mv^2.
- 2 If the maximum braking friction coefficient is 0.40 and the aircraft weight on the braked wheels is 600000 N, what is the maximum braking force using Fmax = μN?
- 3 Explain why an antiskid system usually improves stopping and steering compared with a locked-wheel skid on the runway.