Aircraft Wheels and Tyres

Types of Aircraft Tyres

Aircraft tyres are classified by their construction and whether they use an inner tube. The main types are:

• Tubeless tyres: Common on modern commercial aircraft, these rely on a perfect seal between tyre and wheel.
• Tubed tyres: Use an inner tube to hold the inflation gas, often found on older or smaller aircraft.
• Diagonal (cross-ply) tyres: Feature plies laid at alternating angles, offering robustness and resistance to side loads.
• Radial (circumferential bias) tyres: Plies run perpendicular to the direction of travel, providing better heat dissipation and longer tread life.

Tyre Construction and Markings

• Ply rating: Indicates the tyre's strength, not the actual number of plies, but its load-carrying capability compared to a standard reference.
• Tread: The patterned surface that contacts the runway, designed for water dispersion and grip. Circumferential grooves are typical for paved runways, while block treads suit rough fields.
• Tyre creep: The slight movement of the tyre around the wheel under heavy braking, monitored by alignment marks.
• Retread (cover): Process of replacing the worn tread to extend tyre life, provided the casing remains sound.

Wheel Assemblies

Aircraft wheels are typically split-hub designs, allowing easy tyre changes. Precision seals ensure gas-tightness for tubeless tyres, while knurled flanges on tubed wheels help prevent tyre slippage.

Tyre Checks and Damage

Pre-flight inspection should focus on:

• Cuts and damages: Deep cuts, especially those exposing the carcass or wider than half a rib, require tyre replacement.
• Flat spots: Indicate locked brakes or skidding; severe cases can compromise tyre integrity.
• Bulges or blisters: Suggest internal ply separation and demand immediate replacement.
• Tread separation: Exposes the underlying structure and is a serious hazard.

Tyre Failure and Safety Features

• Thermal/fusible plugs: Fitted in wheel hubs, these melt at high temperatures (from brake overheating), allowing controlled tyre deflation to prevent explosive bursts.
• Tyre speed limits: Exceeding rated speeds can lead to structural failure. Aircraft performance may be limited by tyre speed, especially at high weights or density altitudes.

Wear Patterns

• Over-inflation: Wears the crown (centre) of the tread.
• Under-inflation: Wears the shoulders (edges) due to excessive flexing.

Tyre Markings Explained

Tyre sidewalls display size, ply rating, speed rating, and sometimes retread status, all critical for correct selection and operation.