Anti-Skid Aircraft Braking Systems
Whether you are driving a motorbike, Formula 1 car, or aircraft, one of the things that are you most reliant upon is the braking system. The basic principle of an aircraft braking system is to absorb energy from the moving system in order to slow the moving vehicle down. A key component of most braking systems is the anti-skid system. Skidding is sliding across a surface with little-to-no control. Skidding is often associated with the phrase ‘locked up’, which is in reference to the wheels of the vehicle. In most circumstances skidding in an automobile isn’t a desirable occurrence. In Formula 1 it could lose a race, on an aircraft it could result in an aircraft sliding off a runway.
Anti-skid systems are fitted on all large aircraft. Every anti-skid system includes a set of wheel sensors, valves, and a control unit. The wheel sensors are located on each individual wheel, anti-skid valves are attached to the wheels, and a control unit is usually found amongst the avionics of the aircraft. Each of these components work together in what is an autonomous anti-skid braking system. There are two key functions of an anti-skid system; firstly, the system detects when skidding may occur, secondly, the system works to mitigate the slipping and bring the aircraft under control.
When the wheels of the braking system stop spinning or are not spinning fast enough, the anti-skid mechanism kicks in. The hydraulic brake system is interrupted as pressure is removed from the brakes and rerouted via the hydraulic return line. Change in the brake hydraulic system allow the wheel speed to increase. Maximum brake efficiency is when the wheels are decelerating at maximum speed while avoiding the risk of skidding. Aircraft rely on the braking system and the anti-skid systems to safely slow the aircraft during taxiing and landing.
Since a pilot can’t sense when an aircraft’s wheels are about to lock up, the anti-brake system needs to be more or less self-functioning. Wheel speed sensors convert the physical spinning motion of the wheels into electronic signals that are received in the control unit. Unusually fast wheel deceleration is an early indicator that the brakes may lock up, possibly causing the aircraft to skid. The wheel speed sensor is pre-programmed with a set deceleration rate for desired aircraft braking. If the rate is surpassed, the sensor sends a signal to the control unit which, in turn, reduces the hydraulic pressure on the brake via the brake control valves. The anti-skid system must be turned on via a switch in the cockpit. During the landing process, pilots trigger the anti-skid system into working as they push down on the rudder brake pedals following touch-down.
Certain runway conditions make the possibility of skidding more likely. Wet weather such as snow and rain can lead to aquaplaning (where a layer of water builds between the wheel and the runway surface) making anti-skids systems all the more important. Not only does the anti-skid system help the pilot maintain control, the system also saves the aircraft wheels from incurring any exterior damage such as deflation, break-up, or reverted rubber skids, all of which are costly and could jeopardize the airworthiness of the aircraft. Routine checks and maintenance of the anti-skid systems should be carried out.
- charles price
- Posted on August 28, 2019 aviation
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