Aircraft Systems
Chapter 30: Aircraft Wheels, Tyres, and Brakes
Technical General for Aviators — Capt. Pankaj Pahil
30.1 Wheels
Aircraft wheels are typically made of aluminum or magnesium alloy and are designed in two
pieces (split-wheel design) to facilitate tyre changes.
Creep: The tendency of the tyre to rotate slightly around the wheel rim on landing. Creep
marks (a white line on the tyre and wheel) are used to monitor this.
Fusible Plugs: These plugs are fitted in the wheels of transport aircraft. If the brakes
verheat, the core of the plugs melts at a set temperature, allowing the tyre to deflate in a
controlled manner, which prevents a dangerous tyre explosion.
30.2 Tyres
Aircraft tyres are designed to withstand very high loads and speeds. They are typically
inflated with nitrogen because it is inert and does not support combustion.
Construction: Built with multiple layers of fabric (plies) embedded in rubber. The ply
rating is an index of the tyre's strength, not the actual number of plies.
Tread: The tread is often ribbed with circumferential grooves to channel water away and
prevent aquaplaning (when a wedge of water lifts the tyre off the runway surface, causing a
loss of braking and directional control).
Aquaplaning Speed: The minimum speed at which aquaplaning can occur can be estimated
by the formula: Speed (knots) = 9 × √Tyre Pressure (PSI).
30.3 Brakes
Multi-Disc Brakes: Large aircraft use brakes consisting of a stack of alternating rotating
discs (rotors, keyed to the wheel) and stationary discs (stators, keyed to the axle). Hydraulic
pressure from pistons squeezes this stack together, creating immense friction.
Brake Materials: The discs are made of steel or, more commonly on modern aircraft,
carbon-carbon composites. Carbon brakes are lighter, can absorb much more heat, and are
more effective at high temperatures.
Anti-Skid System: Similar to ABS in a car, this system prevents the wheels from locking up
during heavy braking.
Operation: A wheel speed sensor on each wheel detects if a wheel is decelerating too rapidly
(indicating an impending skid). The anti-skid control unit then commands a hydraulic valve
to momentarily release and reapply brake pressure to that wheel, maintaining maximum
braking effectiveness without skidding.
Autobrake System: This system automatically applies the brakes upon landing or during a
rejected takeoff (RTO). The pilot can select a desired deceleration rate (e.g., LOW, MED,
MAX), and the system modulates the brake pressure to achieve it.