Composite aerofoil structure with a cutting edge tip portion

1. An aerofoil structure for a gas turbine engine, the aerofoil structure comprising:

a carbon composite aerofoil portion; and

a tip portion, the tip portion comprising:

a tip surface configured to face a corresponding casing structure, the tip portion further comprising a ridge line cutting edge extending along at least a portion of the tip surface, wherein the tip surface comprises a first surface and a second surface provided on a first side and a second side, respectively of the ridge line cutting edge,

wherein, at the ridge line cutting edge, the first surface is angled at a first angle with respect to a radial axis of the aerofoil structure and the second surface is angled at a second angle with respect to the radial axis of the aerofoil structure so that the ridge line cutting edge is defined by an intersection of the first and second surfaces,

wherein the ridge line cutting edge and the first and second surfaces define a roof-top shaped cross-section,

the roof-top shaped cross-section having a total angle at the ridge line cutting edge which is the sum of the first angle and the second angle, and

wherein the ridge line cutting edge follows a camber line of the aerofoil structure at the tip surface and is configured to cut into the casing structure during an interaction between the aerofoil structure and casing structure.

2. An aerofoil structure as claimed in claim 1 , wherein the ridge line cutting edge is parallel to the camber line of the aerofoil structure at the tip surface.

3. An aerofoil structure as claimed in claim 1 , wherein the first and second angles are equal.

4. An aerofoil structure as claimed in claim 1 , wherein the first angle is different from the second angle.

5. An aerofoil structure as claimed in claim 1 , wherein one or both of the first and second surfaces are convex.

6. An aerofoil structure as claimed in claim 1 , wherein one or both of the first and second surfaces are concave.

7. An aerofoil structure as claimed in claim 1 , wherein one or both of the first and second surfaces comprise one or more cutting edges provided on a surface thereon.

8. An aerofoil structure as claimed in claim 1 , wherein an angle between one of the first and second surfaces and a tangent to a radial axis of the aerofoil structure is greater than or equal to a maximum anticipated lean angle of the aerofoil structure relative to the radial axis occurring outside a normal mode of operation for the aerofoil structure.

9. An aerofoil structure as claimed in claim 1 , wherein the tip portion further comprises a further ridge line extending along at least a portion of the tip surface.

10. An aerofoil structure as claimed in claim 1 , wherein the aerofoil structure further comprises a coating provided over the ridge line cutting edge.

11. An aerofoil structure as claimed in claim 10 , wherein the coating extends over the tip surface.

12. An aerofoil structure as claimed in claim 11 , wherein the coating extends over and beyond the tip surface.

13. An aerofoil structure as claimed in claim 10 , wherein the coating comprises embedded abrasive particles selected from the group consisting of: Cubic Boron Nitride (CBN), Zirconia, and combinations thereof.

14. An aerofoil structure as claimed in claim 1 , wherein the aerofoil structure comprises a metallic tip portion.

15. The aerofoil structure as claimed in claim 1 , wherein the aerofoil structure is a first aerofoil structure of a gas turbine engine.

16. A compressor fan blade or a turbine blade of a gas turbine engine comprising:

an aerofoil structure having:

a carbon composite aerofoil portion; and

a tip portion, the tip portion comprising:

a tip surface configured to face a corresponding casing structure, the tip portion further comprising a ridge line cutting edge extending along at least a portion of the tip surface, wherein the tip surface comprises a first surface and a second surface provided on a first side and a second side respectively, of the ridge line cutting edge,

wherein, at the ridge line cutting edge, the first surface is angled at a first angle with respect to a radial axis of the aerofoil structure and the second surface is angled at a second angle with respect to the radial axis of the aerofoil structure so that the ridge line cutting edge is defined by an intersection of the first and second surfaces,

wherein the ridge line cutting edge and the first and second surfaces define a roof-top shaped cross-section,

the roof-top shaped cross-section having a total angle at the ridge line cutting edge, which is the sum of the first angle and the second angle; and

wherein the ridge line cutting edge follows a camber line of the aerofoil structure at the tip surface.

17. A fan blade for a gas turbine engine, comprising:

an aerofoil structure comprising a carbon composite aerofoil portion; and

a tip portion comprising a tip surface arranged to face a corresponding casing structure, the tip surface comprising:

a first tip surface and a second tip surface, both being angled with respect to one another at an intersection between them to form a ridge line cutting edge extending along at least a portion of the tip surface,

wherein the ridge line cutting edge and the first and second tip surfaces define a roof-top shaped cross-section,

wherein, at the ridge line cutting edge, the first tip surface is angled at a first angle with respect to a radial axis of the aerofoil structure and the second tip surface is angled at a second angle with respect to the radial axis of the aerofoil structure, the roof-top shaped cross-section having a total angle which is the sum of the first angle and the second angle; and

wherein the ridge line cutting edge follows a camber line of the aerofoil structure at the tip surface and is configured to cut into the casing structure during an interaction between the fan blade and the casing structure.