Braiding
A method of applying a braided cover to a core comprises braiding a plurality of tows around the core from a plurality of bobbins. One or more properties of the tow on a respective bobbin vary along the length of the tow.
1. A method of applying a braided cover to a core, the method comprising:
braiding a plurality of tows around the core from a plurality of bobbins to form the braided cover,
wherein one or more properties of the tow on a respective bobbin varies along the length of the tow;
wherein the core is the core of a propeller blade and the number of fibres in the tow, the tow diameter or the linear weight of the tow decreases towards a tip region of the core;
wherein the variation of the one or more properties of the tow on a respective bobbin along the length of the tow has the result that the properties of the braided cover are tailored to a particular position on the core and there is no excess braided cover along the length of the propeller core.
2. A method as claimed in claim 1 , wherein the tow is formed by joining fiber with different diameters together to vary a diameter of the tow.
3. A method of claim 1 , wherein the tow is formed by joining fibres with different materials.
4. A method of claim 1 , wherein the tow comprises tow sections having different properties and the tow sections are joined together by one or more of thermal bonding, knotting or winding.
5. A method of claim 1 , wherein a position or nature of a variation in properties of a tow on a first bobbin is different from a position or nature of a variation in properties of a tow on a second bobbin.
6. A method as claimed in claim 5 , wherein the position or nature of the variation in properties of tows deposited in one direction is different from a variation in position and/or nature in properties of tows deposited in another direction.
7. A method as claimed in claim 5 , wherein the variation in properties of tows on different bobbins is staggered such that the properties of the deposited braided cover transition gradually from one property to another.
8. A method of claim 1 , wherein the properties of the tow are adapted to the position of deposition of the tow on the core.
9. A method as claimed in claim 1 wherein the variation of the diameter of the tow on a respective bobbin along the length of the tow has the result that the need to cut the braiding in the tip region of the core is avoided.
10. A method as claimed in claim 1 wherein the properties of each tow are chosen such that there is a close fit of the braiding along the length of the propeller core.
11. A method as claimed in claim 10 , wherein the core is a variable perimeter core, and wherein the core has along its length a base region, a mid span region, and a tip region,
wherein in the base region of the core one or more of the tow diameter, the number of fibres in the tow or the linear weight of the tow in the braided cover are relatively low compared to the mid span region,
wherein in the mid span region of the core where the perimeter of the core is larger than the perimeter of the core in the base region one or more of the tow diameter, the number of fibres in the tow or the linear weight of the tow in the braided cover is increased relative to the base region, and
wherein in the tip region of the core where the perimeter is smaller than the perimeter of the core in the mid span region one or more of the tow diameter, the number of fibres in the tow or the linear weight of the tow is decreased relative to the mid span region.