Method for reducing tip rub loading

1. A method for reducing tip rub loads in an airfoil comprising the steps of:

selecting a location of contact between the airfoil and a static structure to include at least part of a tip portion of the airfoil;

selecting a location on the airfoil for incorporating a tip-cutter, the location including a leading edge of the airfoil that is separated from a trailing edge of the airfoil in a chord-wise direction of the airfoil;

selecting a tip-cutter profile for the tip-cutter; and

incorporating the tip-cutter on the selected location on the airfoil such that the tip-cutter profile comprises an arcuate portion on the leading edge and a flat portion on the leading edge between the arcuate portion and the tip portion of the airfoil, the arcuate portion defining a recess in the leading edge that extends in the chord-wise direction toward the trailing edge of the airfoil, the flat portion defining a cutter-angle with the leading edge that extends in the chord-wise direction toward the trailing edge of the airfoil, wherein the tip-cutter is capable of removing a portion of the static structure during a tip rub such that tip rub loads are facilitated to be reduced.

2. A method according to claim 1 wherein the static structure is an abradable material.

3. A method according to claim 1 wherein the incorporating step comprises forming the cutter-angle to be an angle of two to five degrees.

4. A method according to claim 1 wherein the incorporating step comprises forming the arcuate and flat portions to be contiguous with each other.

5. A method according to claim 1 wherein the incorporating step comprises forming the recess of the arcuate portion to extend into the airfoil to a depth of up to 0.050 inch.

6. A method according to claim 1 wherein the step of incorporating the tip-cutter comprises machining the tip-cutter profile on the leading edge of the airfoil.

7. A method according to claim 1 further comprising the step of selecting a tip-grinder.

8. A method according to claim 7 further comprising bonding the tip-grinder to the airfoil.

9. A method according to claim 8 wherein the bonding step comprises brazing.

10. A method according to claim 1 further comprising forming the airfoil to have a concave edge and a convex edge that are separated from each other at the tip portion, and forming the tip portion to have a tip-rake profile so that the concave edge is closer to the static structure than the convex edge during a tip rub to facilitate reducing loading induced to the airfoil during tip rubs.

11. A method according to claim 10 wherein the tip-rake profile is incorporated on the airfoil by machining.

12. A method for assembling a rotor assembly, said method comprising the steps of:

providing a rotor blade including a first sidewall, a second sidewall, where the first and second sidewalls are connected at a leading edge and a trailing edge that are separated from each other in a chord-wise direction of the blade and the first and second sidewalls extend in span from a root portion to a tip portion of the blade;

removing blade material from a portion of the tip portion to form a tip-cutter having a tip-cutter profile that comprises an arcuate portion on the leading edge and a flat portion on the leading edge between the arcuate portion and the tip portion of the airfoil, the arcuate portion defining a recess in the leading edge that extends in the chord-wise direction toward the trailing edge of the airfoil, the flat portion defining a cutter-angle with the leading edge that extends in the chord-wise direction toward the trailing edge of the airfoil; and

coupling the rotor blade to a rotor hub such that during tip rubs the tip-cutter machines an abradable material to facilitate reducing radial loading induced to the blade during tip rubs.

13. A method according to claim 12 wherein the removing step comprises forming the cutter-angle to be an angle of two to five degrees.

14. A method according to claim 12 wherein the removing step comprises forming the arcuate and flat portions to be contiguous with each other.

15. A method according to claim 12 further comprising the step of bonding a tip-grinder to the rotor blade.

16. A method according to claim 15 wherein the step of bonding comprises brazing.

17. A method according to claim 12 further comprising forming the airfoil to have a concave edge and a convex edge that are separated from each other at the tip portion, and forming the tip portion to have a tip-rake profile so that the concave edge is closer to the static structure than the convex edge during a tip rub to facilitate reducing loading induced to the blade during tip rubs.

18. A method according to claim 17 wherein the tip-rake profile is incorporated on the rotor blade by machining.

19. A method for assembling a rotor assembly, said method comprising the steps of:

providing a blade assembly including an airfoil and a metal leading edge (MLE) coupled to at least a portion of said airfoil;

removing material from a portion of the MLE to form a tip-cutter having a cutter-profile; and

coupling the blade assembly to a rotor hub such that during tip rubs the tip-cutter machines an abradable material to facilitate reducing radial loading induced to the blade assembly during tip rubs.

20. A method according to claim 19 further comprising the step of providing a tip-grinder located on a tip portion of the blade assembly, said tip-grinder capable of removing a portion of an abradable material during a tip rub.

21. A method according to claim 19 further comprising the step of providing a tip-rake located on at least a part of a tip portion of the blade assembly, said tip-rake having a rake-profile that facilitates reducing loading induced in the blade assembly during a tip rub.