Understanding the White Smoke from Aircraft Wheels During Landing

The phenomenon of white smoke emanating from an aircraft's wheels during landing has often caught the attention of curious observers. This article will delve into the scientific explanation behind this intriguing occurrence.

Factors Contributing to White Smoke During Landing

The primary cause of the white smoke observed during an aircraft's landing is the intense heat generated when the tires make contact with the runway. Here, we will explore the main factors contributing to this phenomenon:

Friction

During landing, the wheels of the aircraft rapidly decelerate due to the friction between the tires and the runway. This friction generates a substantial amount of heat. The rapid deceleration causes the tires to grip the runway surface, resulting in wavering between skidding and sliding, which further contributes to heat generation.

Material Composition

Aircraft tires are primarily composed of rubber and other synthetic polymers. These materials are designed to withstand high temperatures but can still produce smoke when heated to abnormal levels. The heat from the friction causes the rubber to break down and vaporize, leading to the appearance of white smoke.

Moisture on the Runway

If the runway is wet or contains moisture, this can interact with the heat generated by the tires. The water vaporizes, creating steam that appears as white smoke. This is particularly noticeable in humid climates or when the aircraft lands in rainy conditions.

Braking Systems

In addition to the friction between the tires and the runway, the aircraft's braking systems also contribute to heat generation. The heat from the brakes can be transferred to the tires, further exacerbating the smoke effect. Modern aircraft often employ antiskid braking systems to prevent the tires from locking up during full braking, which would otherwise produce significant smoke.

How Aircraft Tires Handle the Heat and Stress

The smoke observed during a landing is a normal occurrence and is generally not a cause for concern. However, it is worth noting how the tires are designed to handle the extreme conditions they encounter during landing:

The Consumable Surface Layer

The outer surface of an aircraft tire is intentionally designed to be a consumable layer. This surface wears off with each landing, providing a new layer for the next landing. A typical airliner tire can be recapped 7 to 9 times before being replaced, depending on the total number of landings and the condition of the tire's side wall and load-carrying structure.

No Tire Smoke in General

Unlike other road vehicles, modern aircraft are equipped with sophisticated braking systems that prevent the wheels from locking up. This feature significantly reduces the likelihood of producing visible smoke even during full braking, making the smoke phenomenon less common in aircraft. The tire marks that might be visible are a result of the friction but not necessarily caused by combustion.

In conclusion, the white smoke from aircraft wheels during landing is primarily a result of friction, the inherent properties of the tire materials, and moisture on the runway. It is a natural and normal occurrence, reflecting the immense heat and stress that aircraft tires must endure during the landing process. If you observe this phenomenon, rest assured that it is not a cause for concern.