Rotor blade erosion protection system

1. A rotor blade comprising:

a root end;

a tip end;

a skin member defining an airfoil surface, the airfoil surface having a leading edge surface, an upper airfoil surface, and a lower airfoil surface; and

a cermet coating exterior to the skin member, the cermet coating being configured to protect the rotor blade against erosion during operation;

wherein the cermet coating is tapered spanwise along the leading edge surface.

2. The rotor blade according to claim 1 , wherein the cermet coating is tapered along a chordwise direction.

3. The rotor blade according to claim 1 , wherein the cermet coating is tapered along a chordwise direction, such that a thickness of the cermet coating decreases as the distance from an apex of the leading edge surface increases, along the chordwise direction.

4. The rotor blade according to claim 1 , wherein the cermet coating comprises approximately 80-90% tungsten carbide and 10-20% cobalt.

5. The rotor blade according to claim 1 , wherein the cermet coating comprises approximately 80-90% tungsten carbide and 10-20% nickel.

6. The rotor blade according to claim 1 , wherein a first thickness of the cermet coating near an apex of the leading edge surface is approximately five times a second thickness near the upper airfoil surface.

7. The rotor blade according to claim 1 , wherein the cermet coating is applied on the upper airfoil surface at a greater chordwise distance from an apex of the leading surface as compared to the cermet coating applied on the lower airfoil surface.

8. The rotor blade according to claim 1 , wherein the cermet coating is configured to visually detectable wear band upon an erosive wearing through a layer of the cermet coating.

9. A method of selectively applying an erosion protective coating on an airfoil surface, the method comprising:

developing a map of an erosion coating pattern, comprising:

calculating a predicted erosive wear rate about the airfoil surface;

mapping the predicted erosive wear rate onto an erosion surface model, the erosion surface model being a representation of the airfoil surface;

transforming the mapped predicted erosive wear rate into the map of the erosion coating pattern, the map being dependent in part upon the predicted erosive wear rate and a desired life of the erosion protective coating;

applying the erosion protective coating on the airfoil surface.

10. The method according to claim 9 , wherein the step of calculating the predicted erosive wear rate about the airfoil surface includes using test data from a test rotor blade to calculate the predicted erosive wear rate.

11. The method according to claim 9 , wherein the step of calculating the predicted erosive wear rate about the airfoil surface includes using actual erosion data from an actual rotor blade to calculate the predicted erosive wear rate.

12. The method according to claim 9 , wherein the step of calculating the predicted erosive wear rate about the airfoil surface includes at least one of the following:

a rotor twist;

a rotor speed data;

an airfoil surface data; and

a rotor diameter data.

13. The method according to claim 9 , wherein the step of mapping the predicted erosive wear rate onto the erosion surface model includes using a three-dimensional graphic model.

14. The method according to claim 9 , wherein the step of applying the erosion protective coating on the airfoil surface includes spraying a cermet material onto the airfoil surface.

15. The method according to claim 14 , wherein the cermet material comprises tungsten carbide and nickel.

16. The method according to claim 9 , wherein the step of applying the erosion protective coating on the airfoil surface includes using a spray machine, the spray machine being programmable.

17. A method of selectively applying an erosion protective coating on an airfoil surface, the method comprising:

developing an erosion surface model of the airfoil surface, the erosion surface model representing a measurement of an existing surface geometry of the airfoil surface;

developing a map of an erosion coating pattern, the erosion coating pattern being an indicative of a requisite footprint and thickness pattern of the erosion protecting coating suitable for enduring a certain amount of operation time; and

applying the erosion protective coating to the airfoil surface so as to build the erosion protective coating between the existing surface geometry to coating levels dictated by the map of the erosion coating pattern.

18. The method according to claim 17 , wherein the step of developing the erosion surface model of the airfoil surface includes measuring any surface damage on the airfoil surface.

19. The method according to claim 17 , wherein the airfoil surface is the outer surface of a rotor blade.