Aircraft tire having an improved bead

1. An aircraft tire, the inflation pressure of which is greater than 12 bar, comprising a crown, two sidewalls and two beads, a carcass reinforcement anchored in the two beads, and a crown reinforcement, wherein the carcass reinforcement comprises at least two circumferential alignments of first reinforcing threads of high elasticity modulus, and wherein means of anchoring said first reinforcing threads within each bead comprise windings of second reinforcing threads oriented circumferentially and axially bordering said circumferential alignments of said first reinforcing threads, said first reinforcing threads and said second reinforcing threads being separated by a layer of rubber mix of very high elasticity modulus.

2. An aircraft tire according to claim 1 , wherein each circumferential alignment of said first reinforcing threads is, within each bead, bordered axially inwardly and axially outwardly by said windings of second reinforcing threads oriented circumferentially.

3. An aircraft tire according to claim 1 , wherein the second reinforcing threads have a modulus greater than that of the first reinforcing threads.

4. An aircraft tire according to claim 1 , wherein said second reinforcing threads of said anchoring means are formed of reinforcing threads selected from among the group consisting of carbon, tungsten, high-modulus aramid and steel reinforcing threads.

5. An aircraft tire according to claim 4 , wherein said second reinforcing threads of said anchoring means are formed of monofilaments of steel.

6. An aircraft tire according to claim 5 , wherein the diameter of said steel monofilaments is between 0.7 and 1.3 mm.

7. An aircraft tire according to claim 1 , wherein, where ER 1 is the total of the rigidities of extension of the windings of second reinforcing threads arranged axially inwardly relative to the, carcass reinforcement and where ΣR Σ is the total of the rigidities of extension of the windings of second reinforcing threads arranged axially on either side of the carcass reinforcement:

0.6

≤

∑

R

I

∑

R

E

≤

1.5

.

8. An aircraft tire according to claim 7 , wherein:

0.7

≤

∑

R

I

∑

R

E

≤

1.3

.

9. Aircraft tire according to claim 1 , wherein, the outer surface of each beads comprises a seat, a frustoconical wall of substantially radial orientation located radially inwardly adjacent to a wall section in the shape of an arc of a circle EF of center C, and all of the windings of second reinforcing threads are arranged at a radial distance from the tire rotation axis A less than or equal to the locus of a straight line CD passing through the center C and the bead and forming an angle of +45 ±5 degrees relative to the axis A of the tire.

10. An aircraft tire according to claim 1 , wherein, each of said beads has an outer surface intended to come into contact with a corresponding surface of the seat and of the hook of a rim on which the time is to be mounted, and wherein, after mounting of the tire on said rim and inflation of said tire, the contact zone between said outer surface of said bead and said rim extends at least as far as a point B of the hook of maximum radius R 1 .

11. An aircraft tire according to claim 10 , wherein φ is the diameter of the circumference of the outer surface of the bead intended to come to bear against the circumference of the hook of the rim of maximum radius R 1 , and:

φ=2( R j −ε)

with ε being between 0.5 and 2 mm.

12. An aircraft tire according to claim 1 , wherein said first reinforcing threads of the carcass reinforcement form forward and return paths arranged adjacently, with, at the level of each bead, loops connecting one forward path to one return path each time.

13. An aircraft tire according to claim 1 , wherein said crown reinforcement comprises at least one working block with at least two plies of reinforcing threads which are parallel within each ply, oriented substantially circumferentially and of high elasticity modulus.

14. An aircraft tire according to claim 13 , wherein, said crown comprises a central zone and two lateral zones, and said at least one working block further comprises two layers of reinforcement elements of high elasticity modulus, oriented substantially circumferentially, arranged axially on either side of the median plane of the tire in the lateral zones of said crown.

15. An aircraft tire according to claim 14 , wherein said two layers of said at least one working block are arranged radially beneath said at least two plies of circumferentially oriented reinforcing threads of said at least one working block.

16. An aircraft tire according to claim 13 , wherein said at least one working block further comprises two additional plies of reinforcing threads parallel to each other within each ply and crossed from one ply to the next, forming with the circumferential direction an angle of between 5 °and 35°, said reinforcing threads having a high elasticity modulus.

17. An aircraft tire according to claim 13 , wherein said crown reinforcement furthermore comprises, arranged radially externally relative to said at least one working block, a protective ply extending axially beyond the axial width of said plies of reinforcing threads of high elasticity modulus.

18. An aircraft tire according to claim 1 , wherein the reinforcing threads of high elasticity modulus have a secant modulus of extension greater than 1000 cN/tex.

19. An aircraft tire according to claim 18 , wherein the reinforcing threads of high elasticity modulus are formed of aromatic polyamide.

20. An aircraft tire according to claim 1 , wherein the layer of rubber mix of very high elasticity modulus has a secant modulus of extension at 10% deformation greater than 20 MPa.

21. An aircraft tire according to claim 20 , wherein said secant modulus of extension at 10% deformation is greater than 30 MPa.

22. An aircraft tire according to claim 1 , wherein the layer of rubber mix of very high elasticity modulus has a Shore A hardness of greater than 70.