Landing Gear, Wheels, Tyres and Brakes
Gear configuration and loads
Landing gear absorbs landing and taxi loads through shock absorbers (oleo struts) that convert kinetic energy into heat. A gas (nitrogen) spring supports the aircraft and oil metering dissipates energy. Gear may be fixed or retractable; retraction is hydraulic or electric, with uplocks and downlocks and a sequence that usually closes the doors after retraction. Squat switches detect weight on wheels and inhibit retraction on the ground.
Wheels and tyres
Tyre construction includes tubeless or tube-type, bias or radial. Tyre limits are marked: maximum speed, load rating and pressure. Under-inflation causes sidewall flexing and heat, a major cause of tyre failure; over-inflation reduces footprint and increases wear. Wheel fuse plugs melt at high temperature to release pressure before the tyre bursts. Hydroplaning (aquaplaning) occurs when speed, water depth and tyre pressure combine so the tyre lifts off the runway; higher tyre pressure raises the hydroplaning speed.
Brakes
Brakes may be independent, with anti-skid and auto-brake systems. Anti-skid releases brake pressure when it detects wheel deceleration approaching a skid, maintaining friction near the peak slip ratio. Carbon brakes are common on transports; they are effective when hot but wear with excessive taxi braking. Parking brake uses accumulator pressure. Brake temperature must be monitored after landing to avoid fuse plug melt or fire.
Worked example
If hydroplaning speed is approximately 9 × √(tyre pressure in psi), a tyre at 100 psi gives about 90 knots. Doubling pressure increases hydroplaning speed by about 41% (√2).
Traps
Assuming maximum braking occurs at a fully locked wheel - it does not; peak friction is at a small slip. Also, auto-brake settings (low, medium, high) are selected before landing and affect stopping distance, not the anti-skid function itself.