Background of the Invention
This invention relates to pneumatic tires and more particularly
to a novel carcass structure specifically for use in aircraft tires.
An aircraft tire is subjected to extreme operating conditions
which include very high internal pressure, high speeds in excess of 300 kilometers
per hour, and very high deflections. During taxing and takeoff, the deflection may
be more than 30%, and on landing 45% deflection or more occur under impact conditions.
These extreme pressures, loads and deflections put the sidewall between the shoulder
of the tire and the bead through severe tests. The high pressure and loads place
the ply cords under severe tensile loads. The cords in the plies, particularly in
the lower sidewall area, are frequently mechanically fatigued due to high heat buildup
near the beads while the aircraft is taxing or during takeoff.
In the prior art, it has been conventional to increase
the number of plies of the tire to increase rigidity and to decrease deformation
under load. Also, much work has been directed to reinforcing the ply turnup portion
of tires to improve durability.
US-A- 5,105,865 by Togashi et al
, describes these conventional solutions and proposes that the durability
of the tire can be improved by avoiding bending deformations of the ply surfaces.
The patent describes a tire curvature that permits an increase in durability to
be achieved with no increase in weight.
US-A- 4,029,137 by Robert Suydam
teaches that an improvement in durability can be achieved by a novel wrapping
of the ply structure about the beads. This invention also improves durability without
GB-A- 2 087 806 to Kaisha
, a bias aircraft tire is disclosed wherein cords of the carcass plies
are spaced further apart to achieve improved durability.
In addition to the normal loading conditions of aircraft
tires, military aircraft, in particular naval airships, often are required to land
on the decks of aircraft carriers. The landings are routinely harsh and rapid due
to the shortened landing area. To stop the aircraft, an arrestor cable is employed.
The nose wheel or main landing gear wheel of the aircraft impacts this 4,127 cm
(1-5/8 inch) diameter arrestor cable on landings and can severely damage the tire.
On the F/A-18E/F naval aircraft the main tire can see a camber angle of 10.2°.
This means that one sidewall will take the initial impact at about five times the
normal rated load. This pinches the impacted sidewall severely which can result
in cut or damaged carcass plies. Repeated landings result in cumulative damage.
To extend the life of the main tire additional full width carcass plies have been
used; however, this imposes a weight penalty. A novel approach to improve sidewall
durability while enabling a reduction in overall tire weight was disclosed in
. In that patent sidewall cord reinforced inserts were used to replace
full plies yet provide additional sidewall bruise resistance and increased durability
of the tire carcass.
Advances in ply strength and the use of these inserts has
resulted in sufficiently strong carcasses. The carcasses has become so strong that
on the main landing gear of the F/A 18E/F naval fighter aircraft testing evidenced
that the bead cores were being sufficiently stressed that the bead cores would fail
prior to the crown reinforcement during burst test. This prior art tire is depicted
in Figures 1 and 2. As illustrated the tire had originally 12 plies and three bead
cores of equal size and construction. A more robust carcass construction was requested
and it was discovered that the conventional three bead core design became a limiting
factor wherein the beads would fail prior to the crown of the carcass during tire
burst test. As a general rule, a tire engineer tries to design the tire such that
tires fail in the crown area when subjected to burst testing.
It must be appreciated that the rim and the tire's beads
are confined to a limited amount of space. Accordingly, the simple addition of carcass
plies means that the bead shape or configuration must be adjusted while still allowing
for a proper fit to the rim. Ideally as tire designers improve the tires durability
they strive hard to insure the rim design can remain unchanged. New rim designs
are very costly and generally limit the use of improved tire designs to next generation
vehicles or aircrafts.
discloses a bias aircraft tire according to the preamble of claim 1.
discloses an aircraft tire with three bead cores having a round cross
sectional shape. The wires are not arranged in rows and columns.
discloses a tire for a motor scraper having three beads cores with a substantially
rectangular construction. Again, the wires are not arranged in rows and columns.
It was an object of the present invention to design the
tire to fit on the prior art rim while still improving the bead strength and the
overall carcass strength. It was a further object of the invention to design an
aircraft tire having three bead cores in each bead portion with substantially much
greater strength than conventional prior art tires they were to replace.
Summary of the Invention
An improved bias aircraft tire has a carcass reinforced
by six or more ply pairs. the six or more ply pairs extend from one bead portion
through a crown portion to an opposite bead portion. Each bead portion has three
bead cores, a first heel bead core, a middle bead core and a third toe bead core.
Each bead core has one or more ply pairs wrapped around and extending radially upwardly
relative to the bead core.
The three bead cores in each bead portion are each of a
substantially rectangular cross-section having a semi-rounded radially innermost
portion. Each of the three bead cores have lateral rows and vertical columns of
bead wires. Wherein, the middle bead core has at least one row or one column less
of bead wires than the first heel bead core.
Each bead core has an inside diameter d. The middle bead
core has a diameter dm less than the diameter dh, first heel
The toe bead core has one or more row or column than the
middle bead core. The toe bead core has an inside diameter dT equal to
or greater than the diameter dm of the middle bead core minus the differences
in the diameter dH of the first bead heel less the diameter dM
of the middle bead core or dt ≥ dm, - (dh
In the preferred embodiment tire the pair of carcass plies
equal 7. The heel bead core has 12 rows and 8 columns of wire totaling 96 wires
when viewed in cross-section. The toe bead core is the same construction as the
heel also having a 12 x 8, 96 wire construction. The middle bead core has an 11
x 8 construction with 88 wires.
In the preferred tire of a size 32X11.5-15, the inside
diameter dh equals 39,878 cm (15.70 inches), dm equals 39,726
cm (15.64 inches), and dt equals 39,472 cm (15.54 inches) thus satisfying
the relationship wherein the middle bead core has a smaller diameter than the heel
bead core while the toe bead core dt is greater than or equal to dm--
(dh- dm). As in the preferred tire dt ≥
39,624 cm (15.60 inches) - [39,878 - 39,624 cm (15.70 - 15.60 inches)] or dt
= 39,472 cm (15.54 inches) which is greater than 39,37 cm (15.50 inches).
Description of the Drawings
- Figure 1 is a cross-sectional view of the prior art tire of
- Figure 2 is an enlarged cross-sectional view illustrating one-half of the prior
art tire of Figure 1.
- Figure 3 is a cross-sectional view illustrating the improved aircraft tire made
in accordance with the present invention;
- Figure 4 is a further enlarged cross-sectional view illustrating one side or
half of a tire made in accordance with the present invention;
"Apex" means a non-reinforced elastomer positioned radially
above a bead core.
"Aspect ratio" of the tire means the ratio of its section
height (SH) to its section width (SW) multiplied by 100% for expression as a percentage.
"Axial" and "axially" means lines or directions that are
parallel to the axis of rotation of the tire.
"Bead" means that part of the tire comprising an annular
tensile member wrapped by ply cords and shaped, with or without other reinforcement
elements such as flippers, chippers, apexes, toe guards and chafers, to fit the
"Belt or breaker reinforcing structure" means at least
two layers of plies of parallel cords, woven or unwoven, underlying the tread, unanchored
to the bead, and having both left and right cord angles in the range from 17 degrees
to 33 degrees with respect to the equatorial plane of the tire.
"Bias ply tire" means a tire having a carcass with reinforcing
cords in the carcass ply extending diagonally across the tire from bead core to
bead core at about a 25°-50° angle with respect to the equatorial plane
of the tire. Cords run at opposite angles in alternate layers.
"Carcass" means the tire structure apart from the belt
structure, tread, undertread, and sidewall rubber over the plies, but including
"Circumferential" means lines or directions extending along
the perimeter of the surface of the annular tread perpendicular to the axial direction.
"Chafers" refers to narrow strips of material placed around
the outside of the bead to protect cord plies from the rim, distribute flexing above
the rim, and to seal the tire.
"Chippers" mean a reinforcement structure located in the
bead portion of the tire.
"Cord" means one of the reinforcement strands of which
the plies in the tire are comprised.
"Equatorial plane (EP)" means the plane perpendicular to
the tire's axis of rotation and passing through the center of its tread.
"Flipper" means a reinforced fabric wrapped about the bead
core and apex.
"Footprint" means the contact patch or area of contact
of the tire tread with a flat surface at zero speed and under normal load and pressure.
"Innerliner" means the layer or layers of elastomer or
other material that form the inside surface of a tubeless tire and that contain
the inflating fluid within the tire.
"Net-to-gross ratio" means the ratio of the tire tread
rubber that makes contact with the road surface while in the footprint, divided
by the area of the tread in the footprint, including non-contacting portions such
"Nominal rim diameter" means the average diameter of the
rim flange at the location where the bead portion of the tire seats.
"Normal inflation pressure" refers to the specific design
inflation pressure and load assigned by the appropriate standards organization for
the service condition for the tire.
"Normal load" refers to the specific design inflation pressure
and load assigned by the appropriate standards organization for the service condition
for the tire.
"Ply" means a continuous layer of rubber-coated parallel
"Radial" and "radially" means directions radially toward
or away from the axis of rotation of the tire.
"Radial-ply tire" means a belted or circumferentially-restricted
pneumatic tire in which the ply cords which extend from bead to bead are laid at
cord angles between 65° and 90° with respect to the equatorial plane of
"Section height" (SH) means the radial distance from the
nominal rim diameter to the outer diameter of the tire at its equatorial plane.
Detailed Description of the Invention
With reference to Fig. 3, there is illustrated a tire 10
which in the specific embodiment illustrated is a size 32x11.5-15 tire. The tire
has a 81.3 cm (32 inch) maximum inflated outside diameter and the maximum width
of the inflated tire in axial directions is 29.2 cm (11.5 inches) and the tire has
a nominal bead diameter of 38.1 cm (15 inches).
The tire 10 includes a ground engaging circumferentially
extending tread portion 12, a pair of sidewalls 14,16 extending radially inwardly
from the axially outer edges of the tread portion and terminating at their radial
extremities in a pair of bead portions 18,20. The sidewalls 14,16 each have an upper
portion 14A,16A in the shoulder region of the tire radially inward of the tread
and radially outward of the maximum section width of the tire, and a lower portion
14B,16B radially inward of the maximum section width of the tire. A cord reinforced
carcass structure 22 extends circumferentially about the tire and from bead portion
18 to bead portion 20.
The particular embodiment of the cord reinforcing structure
22 includes seven pairs of plies of tire cord fabric 36,37,38,39,40, 41 and 42.
Each pair of plies has one of its plies extending at one bias angle with respect
to the equatorial plane or circumferential center line of the tire, and the other
ply at the same angle but extending in the opposite direction with respect to the
equatorial plane. The angle that the cords in the individual carcass plies make
with respect to the equatorial plane decreases progressively from an angle of about
34° in the radially inner pair of plies 36 to 30° in the radially outer
pair of plies 41.
Also included in the carcass structure is a pair of tread
breaker plies 44 extending circumferentially about the carcass and generally from
one edge of the tread portion 12 to the axially opposite edge of the tread portion
12. The angle of the cords in the tread breaker plies with respect to the equatorial
plane is approximately 26°. The material of the cords in all of the plies in
the carcass structure 22 is nylon although any suitable material or combination
of materials can be utilized. It is believed preferable that the cords be a textile
material. Further, while specific angles have been specified for the carcass and
tread plies, these angles can be varied within the normal range of bias ply aircraft
tires. For example, the angles of the carcass plies could be from 25° to 45°
while the angle of the tread breaker plies can be from about 20° to 45°
for a bias ply aircraft tire.
Interposed between the tread breaker plies 44 and the carcass
plies is a cushion gum layer 19.
The bead portions 18,20 each include three annular inextensible
bead cores 50,52 and 54.
Two pairs of carcass plies 36 and 37 extend radially inwardly
of the tire adjacent to the axially inner side of the axially inner bead core 50.
The respective end portions 36a and 37a are turned axially outwardly about bead
core 50 and ply ends 37a are turned radially outwardly about bead core 50 while
ply end 36a turns radially outwardly about bead core 54.
Carcass plies 38 similarly extend radially inwardly adjacent
to the axially inner side of the central or middle bead core 52 and have their end
portions 38a turned radially outwardly of the bead core 52.
Carcass plies 39 extend radially inwardly about the axially
outer side of the middle bead core 52 and the ply ends 39a are turned axially inwardly
adjacent the radially inner sides of the inextensible bead cores 50 and 52. Since
the pairs of carcass plies 39 are wrapped about two sides of the bead core 52 as
they progress radially inwardly from the tread 12, the tensile loading of these
plies caused by inflation pressure and loading on the tire are supported by bead
The axially outer bead core 54 has two pairs of carcass
plies 40,42 extending radially inwardly adjacent the axially inner side of the bead
core and has its ends 40a,42a turned axially outwardly adjacent the radially inner
side of the bead core. The turnup ends 40a turns radially outwardly adjacent the
turnup ends 42a which are adjacent and turnup around axially outer side of the bead
Carcass plies 41 extend radially inwardly interposed between
the turnup ends 36a and the axially outer side of the bead core 54. The carcass
ply end portions 41a each turn axially inwardly adjacent the radially inner side
of bead core 54 extending inwardly to the radially inner side of bead core 50. The
end 41a is interposed between the bead cores 50,52 and 54's radially inner sides
and the end 36a. The ends 36a terminate in the lower sidewall area at a point radially
inwardly of the point 62 of maximum section width of the inflated tire.
For the purposes of this invention, end portions shall
be those portions of a carcass ply pairs that wraps about or extends radially outwardly
from a bead core. If the end portions terminate short of the point 62 of maximum
axial width of the tire, it is not considered working portions of the plies since
it does not exert a significant radially outwardly directed pull on the bead core.
A bead core that absorbs a major radially outwardly directed pull of the carcass
plies is an active or working bead core, and for purposes of this invention is a
bead core bounded on any axial side and a radially inner side by the working portions
of the carcass plies. The working portions of the carcass plies is that portion
of the plies extending from a bead on one side of the tire to the opposite side's
bead, and for purposes of this invention the working portion of the carcass plies
is called the ply side; the non-working portion is the turn-up or end portions of
Referring to Figs. 4 of the embodiment illustrated, there
is shown the group of structural components employed in the tires.
Radially above each bead core 50,52,54 is an elastomeric
apex 57. Wrapped about each bead core and axially adjacent each apex is a flipper
55. Wrapped about the entire bead structure is a chafer 56. The chafer 56 extends
radially inwardly from an axially outer end toward the bead heel 59, turns axially
inwardly extending to the bead toe 58 where the chafer 56 turns radially outwardly
to an axially inner end. In the embodiment as illustrated, the air chamber formed
by the tire is surrounded by a generally air impervious innerliner 17 extending
from bead to bead.
As illustrated in Figs. 3 and 4, a reinforcement insert
90 is radially outward of the pair of plies 40,41. As shown, the inserts 90 are
positioned on the radially outer side of the plies and extend from adjacent or slightly
above the bead cores radially and axially outwardly to a radially outer end below
the tread 12 in the upper sidewall 14A,16A region between the carcass 22 and the
In the best mode of practicing the invention, the reinforcement
inserts 90 consist of a pair of cord reinforced members 91,92. The cords in the
reinforced members 91,92 are at bias angles relative to the circumferential center
line, the cord angle of one member of a pair being equal to but opposite in orientation
relative to the cords of the adjacent member of the same pair.
It is believed preferable that the insert cords have a
tensile elongation at break substantially similar to the nylon cord of the plies.
For that reason, the cords in the preferred embodiment were made of nylon. Alternatively,
the cords could be any other suitable textile type material.
It is believed that the reinforcement insert 90 could be
fabricated from an elastomeric material having fiber reinforced materials.
In the preferred embodiment the reinforcement insert 90
extends circumferentially around the tire 10 on both sides. The purpose of the reinforcement
insert 90 is to increase the carcass 22 lower to upper sidewall impact durability
with a corresponding decrease in weight when compared to conventional bias ply aircraft
tires. The carcass impact strength is increased by locating impact absorbing reinforcement
inserts 90 in the sidewalls 14,16.
In a first use of the invention as illustrated in Fig.
1, the inserts 90 were fabric plies 91,92 having the same green angle as the adjacent
full casing plies. The insert fabric plies 91,92 were located in the tire 10 in
pairs, one fabric member 91 oriented at an angle left and one fabric member 92 at
an equal angle right. One such two-ply fabric insert 90 was located adjacent the
axially outer side of the bead core 54 and extended radially outwardly to the upper
sidewall portion 16A. The inserts 90 were located radially outward of the full band
plies and had the radially inner ends purposely terminated such that the insert
ends did not extend around the bottom of the bead 54.
Although one set of inserts 90 per tire side was contemplated
in the early evaluation of this invention, it was determined that one set on each
side was sufficient in the application being evaluated. One, two, three or four
sets of inserts 90 per tire side can be used, depending on how much additional carcass
impact strength is required.
Although the inserts 90 were used having pairs of bias
angled cord reinforced members 91,92, it is believed that the cord reinforced members
91,92 can be individually used. Also in the above description, the cord reinforced
members had bias angles in the same range as the carcass plies. Alternatively, higher
angles up to 90° could be used.
Historically, bias ply aircraft tires have been designed
with full width carcass plies, which extend from a bead bundle on one side of the
tire to the bead bundle on the other side of the tire. In order to increase carcass
strength in any one area of the tire, it was common practice to add full width plies
to the carcass. The present invention, by adding fabric or fiber inserts between
the plies and the sidewall of the tire, strengthens only the area requiring the
impact strength increase. Since full plies are not used, there is a substantial
tire weight savings.
An aircraft tire 10 built in accordance with the prior
art invention as shown in Figs. 1 and 2 was tested against standard production aircraft
tires for impact durability. The standard or control tire was size 32x11.5-15 and
the test tire 10 was made of the same materials and of similar construction as the
standard tire, except for the addition of the fabric reinforced insert plies 91,92
on each tire side. The test tire 10, according to the present invention, exhibited
a marked improvement over the impact durability of the standard tire without inserts.
One of the most rigorous requirements of the MacDonald
Douglas F/A-18E/F bias main aircraft tire is for the tire 10 to survive the 4,127
cm (1-5/8") diameter cable load test at more than 5 times rated tire load applied
at a camber angle of 10.2 degrees. This severe test pinches the tire sidewall between
the wheel and the cable on one side of the tire which can result in the cutting
of the carcass plies and if excessive, can cause a failure of the tire structure.
To protect the tire carcass 22 in the sidewall area from
such an operation, two layers of fabric 91,92 starting from the tire shoulder area
16A to just above the bead area 20 were inserted between the tire carcass 22 and
sidewall 16. The two layers 91,92 are of the same material and ply angle as the
carcass plies and are offset 1,27 cm (0.5") to avoid high stress concentration at
the layer edges. The carcass material is 1260/2 nylon.
This original F-18 tire was constructed with six ply pairs
and three identical bead cores having 8 columns and 7 rows of bead wire in each
bundle. The tire had a minimum burst pressure of 8,27 MPa (1200 psi). This prior
art tire experienced some cuts in the rim flange area during severe airframe drop
test and flight test. A higher design standard was requested requiring a minimum
burst pressure of 9,65 MPa (1400 psi).
A modified construction using 14 plies, two sidewall inserts
and 3-9 x 7 bead cores was attempted in a test tire. While the tire performed, the
failure mode was observed to be in the bead core closest the heel. Finite element
analysis confirmed that the bead core adjacent the heel was stressed sufficiently
to cause a tensile break prior to the crown failing.
Analysis of this failure mode lead to the development of
a combination of bead cores wherein the heel bead core had one more row of bead
wire than the middle bead core.
The test tire according to the present invention used a
12 x 8 (96 bead wire) construction at the bead heel core, an 11 x 8 (88 bead wire
construction in the middle, while the bead toe core used a 12 x 8 (96 bead wire
construction). The bead heel core had a 39,878 cm (15.70 inch) inside diameter dh,
the middle core a 39, 624 cm (15.60 inch) inside diameter dm, and a bead
toe core had a 39,472 cm (15.54 inch) inside diameter dt.
Of 14 test tires subjected to a minimum burst pressure
in excess of 9,65 MPa (1400 psi), all 14 test tires burst in the crown area.
Overall bead wire forces in the inventive design are less
than those of the prior art design.
The equivalent stress (von Mises) in the three bead bundles
at 6,55 MPa (950 psi) inflation pressure for the original and the new design were
compared. For the original design as shown in Figures 1 and 2 half of the heel bead
bundle has exceeded the yield point. Whereas, yielding is confined to only a few
bead wires in the new design of Figures 3 and 4.
In metal plasticity, material behaves elastically for stress
levels less than the yield stress, and the plastic flow occurs for a stress level
above the yield stress. The total strain energy density can be decomposed into elastic
and plastic energy densities. During plastic flow, the plastic strain energy accumulates
until the ultimate failure.
The plastic energy density is a measure of permanent deformation
(damage). The total plastic energy density in the new design is much less than the
old design, and this difference increases with increasing tire inflation pressure.
For example, a 6,55 MPa (950 psi) inflation pressure, the plastic energy density
in the original design is ten times that of the new design. That is, the old design
will fail at much lower pressure than the new design. This is consistent with the
The tire design of the present invention is believed to
be far superior than the prior art tire of a similar size using the same rim. Heretofore
it was believed that an overall increase in tire size and rim construction might
be required to meet the much higher loads and abuse the tire will be asked to survive
in the future. The present invention enables the aircraft mainframe not to be changed
to accommodate larger sized tires. This is believed to be a very valuable design