Why Airplane Tires Are Made of Conductive Rubber
Airplane tires play a crucial role in the landing system of an aircraft. Unlike cars and trucks, airplanes cannot land on the belly of their fuselage. Instead, they rely on inflated tires that can withstand the weight of the aircraft and the friction created on the runway. While airplane tires may appear similar to their automotive counterparts, they are made of a special type of rubber known as conductive rubber. In this article, we will explore the reasons behind the use of conductive rubber in airplane tires and delve into the design and construction of these essential components.
What is Conductive Rubber?
Conductive rubber is an elastic rubber-based material designed specifically to conduct electricity. It is also known as conductive elastomer, as it allows electricity to flow through it with minimal restriction. Conductive rubber is any type of rubber-based material that facilitates the easy flow of electricity. It possesses excellent conductivity, which is a measure of how well electricity can flow through a material or object.
The Importance of Conductive-Rubber Tires in Airplanes
Airplanes employ tires made of conductive rubber to neutralize electricity. During takeoffs and landings, the friction between an airplane’s tires and the runway can generate static electricity. This build-up of electricity poses a risk to the aircraft’s electronic components, which are highly sensitive to electrical discharge. Without proper protection, stray electrical charges can damage these components and lead to their failure.
Conductive rubber tires prevent the accumulation of electricity by allowing it to flow through the tires and dissipate to the ground. While conductive rubber facilitates the flow of electricity, it effectively prevents the buildup of static electricity within the tires. This unique property of conductive rubber ensures that the friction-created electricity does not accumulate in the airplane’s tires, thus safeguarding the aircraft’s electronic systems.
The Design and Construction of Aircraft Tires
Aircraft tires are meticulously designed and constructed to withstand the immense forces they encounter during takeoffs, landings, and taxiing. They must bear the weight of the aircraft, endure high speeds, and provide stability in various weather conditions. The design and construction of aircraft tires involve a combination of materials and technologies aimed at maximizing performance and safety.
Tire Construction Materials
Aircraft tires are composed of several materials, including rubber, nylon, cord, and steel. These materials are combined through a vulcanization process, which chemically converts polymers into durable materials by introducing crosslinks. The resulting structure of the tire provides the necessary strength, elasticity, and stability required for its operation.
Ply Rating and Tire Types
The term “ply rating” is used to indicate an index to the load rating of the tire. Years ago when
tires were made from cotton cords, “ply rating” did indicate the actual number of plies in the carcass. With the
development of higher- strength fibres such as nylon, fewer plies are needed to give an equivalent strength.
Therefore, the definition of the term “ply rating” (actual number of cotton plies) has been replaced to mean an
index of carcass strength or a load carrying capacity.
Bias-Ply Tires: Bias-ply tires consist of layers of rubber running diagonally to each other. They are known for their strength and are commonly used in aircraft due to their ability to withstand high loads. These tires often incorporate Inter Tread Reinforcing Fabric (ITF), which enhances stability, protects the casing plies, and acts as wear indicators.
Radial Ply Tires: Radial ply tires have layers that run radially from the center line of the tire. These tires are lighter in weight compared to bias-ply tires but offer less strength. They are commonly used in aircraft where weight reduction is a priority.
Tread Reinforcing Ply
Tread reinforcing plies are one or more layers of fabric that help strengthen and stabilize the tread
area for high-speed operation. It also serves as a reference for the buffing process in retreadable
tires
Aircraft Tire Conductivity
Tires dissipate some static electricity in service but this conductivity will change with the cleanliness of
the tire surface, atmospheric conditions and runway surface. Since this discharge rate is variable and
not very controllable, the tire cannot be counted on to dissipate static electricity. If there is any
question about static charge build-up, the aircraft must be grounded by mechanical means (during
maintenance or parking position).
Construction of tire
Comparing, in particular, the LOAD and SPEED ratings of same sized Aircraft tires and other road
vehicle tires, the aircraft tire carries up to approximately six times than the other road vehicle tire. The
aircraft tire also is designed to travel over twice as fast for the same size.
Components of Aircraft Tires
Aircraft tires are comprised of several components, each serving a specific purpose in supporting the tire’s functionality and durability.
1. Tread: The tread is a specially formulated composite rubber designed to resist wear, cutting, chunking, and heat build-up. It features circumferential grooves that disperse water on wet runways, reducing the risk of hydroplaning and improving traction.
2. Shoulder: The tire shoulder is the portion of the tread between the tread center and the tire sidewall. It provides support and protection to both the sidewall and the tread, allowing the tire to maintain its form during cornering maneuvers.
3. Casing: The casing plies form the foundation strength of the tire. They consist of layers of fabric coated with high modulus of elasticity rubber, enhancing the tire’s elastic strength. These casing plies are wrapped around the beads to ensure proper fitting.
4. Beads: Beads are bundles of high-tensile steel wires that attach the tire to the rim and create an airtight seal. Each strand of wire is coated in rubber compound and wound into coils of the correct diameter for the tire size.
5. Chafers: Chafers are made of tough nylon material and are fitted around the bead clinch area to resist chafing damage to the tire and rim flange caused by repetitive rubbing.
6. Sidewall: The sidewall of the tire is the area between the shoulder and the bead. It is covered with specially formulated rubber treated with anti-oxidants to protect the casing from weathering, cuts, and flexing.
7. Inner Tread: Tubeless tires have an inner tread, a layer of rubber bonded to the inside of the first casing ply from bead to bead. This layer resists the permeation of nitrogen and moisture into the casing.
8. Under Tread: The under tread is a layer of rubber designed to improve the adhesion between the tread and the casing plies.
Air Pressure in Aircraft Tires
The durability and performance of aircraft tires are heavily reliant on the air pressure within them. The tires of an aircraft are inflated to high pressures, typically around 200 psi (pounds per square inch), which is approximately six times higher than the pressure used in car tires. This high pressure provides the necessary strength for the tires to withstand high-speed landings and support the weight of the aircraft.
To enhance tire performance and longevity, many aircraft now use dry nitrogen instead of compressed air for inflation. Dry nitrogen offers several advantages, including better pressure stability, reduced oxidation of tire components, and minimal moisture content compared to compressed air.
Proper tire inflation is essential to maintain tire health and prevent damage. Overinflation can lead to uneven tread wear, reduced traction, and increased stress on the wheel assemblies. Underinflation is even more detrimental, causing excessive heating, tread wear, and potential tire failure. It is crucial to regularly check tire pressure using a gauge and ensure that tires are inflated to the correct pressure.
Changes in temperature can also affect tire pressure. For every five to six degrees Fahrenheit change in temperature, there is approximately a one-percent change in tire pressure. This should be taken into consideration when operating aircraft in extreme temperature conditions to ensure tire pressures are maintained within the required range.
Protecting Aircraft Tires
To prolong the lifespan of aircraft tires and ensure their optimal performance, proper care and maintenance are essential. Tires should be kept clean and free from oil, hydraulic fluids, grease, tar, and solvents, as these substances can deteriorate the rubber. Additionally, exposure to sunlight and extreme weather conditions can impact tire longevity. Using protective covers when aircraft are parked outside can help shield tires from these environmental factors.
Conclusion
Aircraft tires made of conductive rubber are a vital component of an aircraft’s landing system. The use of conductive rubber helps neutralize static electricity generated during takeoffs and landings, protecting the aircraft’s sensitive electronic components. The design and construction of aircraft tires involve a combination of materials and technologies to withstand the tremendous forces they encounter. By understanding the importance of tire design, proper inflation, and regular maintenance, the longevity and performance of aircraft tires can be maximized, ensuring safe and reliable aircraft operations.