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.
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.
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.
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.
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.
tread compound is formulated to resist wear, abrasion, cutting, cracking and
heat buildup. It prolongs the life of the casing by protecting the underlying
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
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.
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
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.
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.
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
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.
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.
UNIQUE TO THE RADIAL TIRE
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.