Braided composite spar

1. A braided composite spar or preform for a braided composite spar, comprising:

a plurality of tubular plies of braided fibres,

wherein the spar or preform extends lengthwise from a first end to a second end, and the spar or preform has a tapered portion in which each ply has a height which reduces and a width which increases as the ply extends toward the second end, and

wherein each ply in the tapered portion has a circumference which reduces as the ply extends toward the second end.

2. The spar or preform of claim 1 , wherein each ply in the tapered portion has a circumference which reduces continuously as the ply extends toward the second end.

3. The spar or preform of claim 1 , wherein each ply in the tapered portion comprises forward and aft webs joined by upper and lower caps, and wherein for each ply in the tapered portion a height of the webs reduces and a width of the caps increases as the ply extends toward the second end.

4. The spar or preform of claim 1 , wherein each ply in the tapered portion has a height which reduces continuously as the ply extends toward the second end.

5. The spar or preform of claim 1 , wherein each ply in the tapered portion has a width which increases continuously as the ply extends toward the second end.

6. A winglet comprising a composite spar according to claim 1 , wherein the composite spar comprises forward and aft webs joined by upper and lower caps, and the winglet comprises an upper skin joined to the upper cap of the composite spar and a lower skin joined to the lower cap of the composite spar.

7. An aircraft wing comprising a main wing element with a tip; and a winglet according to claim 6 attached to the tip of the main wing element.

8. The wing of claim 7 wherein the composite spar is canted up or down relative to the main wing element.

9. The wing of claim 7 wherein the composite spar is swept forward or aft relative to the main wing element.

10. The wing of claim 7 wherein the main wing element comprises a main wing spar, and the composite spar of the winglet has an inboard portion which overlaps with the main wing spar and is attached to the main wing spar by fasteners.

11. A method of manufacturing a preform for a composite spar according to claim 1 , the method comprising:

forming the preform on a mandrel, wherein the mandrel extends lengthwise from a first end to a second end and the mandrel has a tapered portion in which the tapered portion has a height which reduces and a width which increases as the tapered portion extends toward the second end, and

wherein the tapered portion has a circumference which reduces as the tapered portion extends toward the second end.

12. The method of claim 11 wherein each ply is formed by feeding a first set of fibres from a first set of bobbins onto the mandrel;

rotating the mandrel and/or the first set of bobbins to generate a clockwise relative rotation between the first set of bobbins and the mandrel;

feeding a second set of fibres from a second set of bobbins onto the mandrel;

rotating the mandrel and/or the second set of bobbins to generate an anti-clockwise relative rotation between the second set of bobbins and the mandrel; and

traversing the bobbins and/or the mandrel to generate a relative motion between the bobbins and the mandrel so that the first and second sets of fibres are wound onto the mandrel and become intertwined to form a braided structure.

13. A mandrel for manufacturing a preform for a composite spar according to claim 1 , wherein the mandrel extends lengthwise from a first end to a second end, and

the mandrel has a tapered portion in which the tapered portion has a height which reduces and a width which increases as the tapered portion extends toward the second end, and

wherein the tapered portion has a circumference which reduces as the tapered portion extends toward the second end.