Automotive Engineer: Does an Aircraft have Anti-Skid System?

Welcome to today's blog...

Let's talk about what is an ABS system?

Antilock-Braking system is equipped in the cars to prevent unnecessary locking of the wheels while driving, or under any unwanted situation and on a wet surface. This safety equipment ensures the safety of the vehicle and prevents the vehicle from losing its stability. Even an aircraft has a similar system to prevent the life of passengers and aircrew.

An aircraft possess multiple disc brakes made up of carbon fibres which consist of a stator (rotary part) and a carbon fibre disc on the rotary, as shown in the figure below. This generates the friction in between the two while rotation; thus, the speed is reduced or deacceleration is obtained. The carbon fibre is used over steel brakes due to efficient performance as it posses lower weight and high capability of absorbing energy whereas, the steel brakes are smaller in size and have more wear & tear as compared to carbon fibres. They are cost-effective, lighter weight, longer life and helps in fuel saving.

Braking action also incorporates slip movement in action consider there is 10% slip in a stretch of 20 m, which means the aircraft covers 18 m. Whereas in the case of 100% slip with maximum brake pressure, the wheels will lock, and the tires start to skid. The slipping of tires is defined as the abrasion of tires when in contact with the runway. This condition of sliding/skidding can lead to blow out of tire due to extreme friction between the contact surface (runaway and tires), which might also turn into a loss of aircraft stability.

Therefore, to prevent these unwanted situations, the aircraft is enabled with Anti-Skid System. This system works similar to the ABS system in cars, which prevent the wheels to lock by continuously braking them through electronic control systems. In the aircraft, the wheels are equipped with sensors and hydraulic valves which takes control over this type of unwanted situations. The primary function of the wheel sensor is to ensure whether the wheels have touched down the runway and they are spinning. If not, you cannot apply the brake pressure to prevent the wheels from getting lock before touching the runway. Secondly, the sensor monitors the wheel speed to prevent skidding/sliding. If there is a situation of the wheels are locked the valve release the pressure so that the wheels can spin and then apply the brake pressure to brake the wheels, hence, to switch off the Anti-skid system.

Consider a wet runway the technology of Anti-Skid system will help the aircraft to brake efficiently as the friction coefficient reduces and there is a less braking effect. In general, after an aircraft reaches a speed of about 85 knots (~ 43.7 m/s) the Anti-Skid system automatically switches on because there might be a need to brake an aircraft while taking off due to some technical faults/malfunction.