AIRCRAFT TIRE CONSTRUCTION

 An aircraft must withstand a wide range of operational conditions. When on the ground, it must support the weight of the aircraft. During taxi, it must provide a stable, cushioned ride while resisting heat generation, abrasion and wear. At take-off, the tire structure must be able to endure not only the aircraft load but also the forces generated at high angular velocities. Landing requires the tire to absorb impact shocks while also transmitting high dynamic braking loads to the ground. All of this must be accomplished while providing a long, dependable, reliable, service life.

These extreme demands require a tire which is highly engineered and precisely manufactured. For this reason, tires are designed as a composite of various rubber, fabric and steel products. Each of the components serves a very specific function in the performance of the tire.

To meet the aircraft demands of today and tomorrow, tire manufacturers design and produce two different and distinct tire constructions, the conventional cross‑ply or BIAS tire and the RADIAL tire. Both nomenclatures describe the angular direction of the carcass plies.

 While many of the components of bias and radial tires have the same terminology, the carcass ply angles are not the only difference between a bias constructed tire and a radial constructed tire. The technologies utilized are quite different involving different design parameters, compounds, and materials.

THE TREAD refers to the crown area of the tire in contact with the ground. Most Michelin tires are designed with circumferential grooves molded into the tread area. These provide a mechanism to channel water from between the tire and runway surface which helps to improve ground adhesion.

 The tread compound is formulated to resist wear, abrasion, cutting, cracking and heat buildup. It prolongs the life of the casing by protecting the underlying carcass plies.

THE UNDERTREAD is a layer of specially formulated rubber designed to enhance the bonding between the tread reinforcement/protector plies and the carcass body. For those tires designed to be retreaded, this rubber layer will be of sufficient thickness to act as the interface for buffing the old tread assembly, as well as the liaison with the new retread products.

A CARCASS PLY consists of fabric cords sandwiched between two layers of rubber. Today, the most common fabric cord is nylon. The carcass body itself is made from multiple layers of carcass plies, each one adding to the strength and load bearing capability of the tire. The carcass plies are anchored by wrapping them around bead wires, thus forming  the ply turn ups.

FOR BIAS constructed tires, the carcass plies are laid at angles between 30' and 60* to the centerline or direction of rotation of the tire. Succeeding plies are laid with cord angles opposite to each other, to provide balanced carcass strength.

FOR RADIAL constructed tires, each carcass ply is laid at an angle approximately 90' to the centerline or direction of rotation of the tire. Each successive layer is laid at a similar angle. Radial constructed tires of the same size have a fewer number of plies than do tires of a bias construction, because the radial cord direction is aligned with the burst pressure radial force allowing for optimized construction.

THE BEADS or bead wires anchor the tire to the wheel. They are fabricated from steel wires layered together and can be embedded with rubber to form a bundle. The bundle is then wrapped with rubber coated fabric for reinforcement. Depending on the size and design application, BIAS tires are constructed with 2 to 6 bead bundles (1 to 3 per side). By contrast, RADIAL constructed tires have 2 bead bundles (1 on each side) regardless of tire size.

CHAFER STRIPS are strips of protective fabric or rubber laid over the outer carcass plies in the bead area of the tire. Their purpose is to protect the carcass plies from   damage when mounting or demounting and to reduce the effects of wear and chafing between the wheel and the tire bead.

THE LINER in tubeless tires is a layer of rubber specially compounded to resist the permeation of nitrogen and moisture through to the carcass. It is vulcanized to the inside of the tire and extends from bead to bead. It replaces the inner tube common to tube type tires. In tube type tires, a different, thinner liner material is used to protect the carcass plies from moisture and tube chafing, but is generally insufficient to maintain air retention.

THE SIDEWALL is a layer of rubber covering the outside of the carcass plies. Its purpose is to protect the cord plies. in addition, the sidewall rubber contains anti­oxidants. They are slowly released over time to protect the tire from ultraviolet and ozone attack, which cause rubber cracking.  

PRODUCTS UNIQUE TO THE BIAS TIRE

The tread reinforcing ply consists of single or multiple layers of a special nylon fabric and rubber laid midway beneath the tread grooves and top carcass ply. These plies help to strengthen and stabilize the crown area, by reducing tread distortion under load, and to increase high speed stability. They also offer a resistance to tread puncture and cutting and help to protect the carcass body. 

Fabric tread (not shown) is a unique development for application on high speed military aircraft. Multiple plies of nylon cord are layered throughout the tread stock, reducing rubber distortion under load and high speeds, thus reducing heat normally generated by flexing. The laminates also control the formation of high speed "standing waves." Improved resistance to cuts and punctures is also a benefit of this type of construction.

Spiral Wrap (not shown) is technique used with retreaded tires. individual textile cords are layed within the replacement tread rubber as it is applied to the tire casing. Cords are oriented to the top 1/2 ‑1/3 of the skid and are free to "float." Because of their circumferential orientation, the textile cords provide added resistance to the cutting and tearing action associated with chevron cutting.

 

PRODUCTS UNIQUE TO THE RADIAL TIRE

The protector ply is placed in the crown area just below the tread rubber. It provides cut resistance protection to the underlying belts and carcass plies.

 

CHINE TIRES

 The "chine" tire is a nose wheel tire designed to deflect water and slush to the side and away from intakes on aft­-fuselage mounted jet engines.

 It consists of a flared upper sidewall protrusion which deflects the spray pattern of water or slush displaced by the tire's contact with the runway. A tire can have a single chine (one sidewall flared) for dual nose wheel tire configurations or double chines (both sidewalls flared) for single nose wheel tire configurations.

 The chine tire is now in use as standard equipment on many commercial jets. It is fully retreadable and may be used on any aircraft provided adequate clearance is available.