Title:
PROTECTOR FOR A LEADING EDGE OF AN AIRFOIL
Kind Code:
A1


Abstract:
A protector for the leading edge of a rotor blade to provide enhanced erosion protection thereof. In an embodiment, the protector includes an energy absorption member attached to the rotor blade by a first adhesive bond layer and an erosion resistant member attached to the energy absorption member by a second adhesive bond layer. The erosion resistant member is operative to protect the leading edge of the rotor blade from erosion due to impacts from particulate matter, such as sand and rain. The energy absorption member is operative to absorb and disburse energy from impacts to the erosion protection member so that forces from the impacts are diminished or not transferred to the rotor blade. In another embodiment, the erosion resistant member is coated with a diamond film. As the diamond film is harder than sand, excellent resistance to wear from particulate matter and impacts rain is obtained. Other advantages provided by use of the diamond film include: 1) an ultra-smooth surface that reduces drag on the rotor blade whereby flight performance may be improved, and 2) by being ultra-smooth and chemically inert de-icing equipment may not be needed.



Inventors:
Barbee, Brent W. (Stanfield, NC, US)
Hough, Andrew E. (Mint Hill, NC, US)
Application Number:
12/503070
Publication Date:
01/14/2010
Filing Date:
07/14/2009
Primary Class:
International Classes:
F01D5/14
View Patent Images:
Related US Applications:



Primary Examiner:
JAGODA, AARON H
Attorney, Agent or Firm:
EVERMAN LAW FIRM, PA (9111 Woodhall Lake Drive, Waxhaw, NC, 28173, US)
Claims:
That which is claimed is:

1. A protector for an airfoil, comprising: an energy absorption member; a first adhesive bond layer attached to said energy absorption member wherein said first adhesive bond layer is adapted for attaching said protector to a leading edge of said airfoil and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; wherein environmental impact forces against said erosion resistant member are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

2. The protector in accordance with claim 1, wherein said airfoil is a helicopter rotor blade.

3. The protector in accordance with claim 1 wherein said protector generally forms a C-shape when applied to said leading edge.

4. The protector in accordance with claim 1 wherein said energy absorption member is not exposed to the environment when applied to said leading edge.

5. The protector in accordance with claim 1 wherein said energy absorption member covers trailing edges of said energy absorption member and extends to said airfoil.

6. The protector in accordance with claim 1 wherein said second adhesive bond layer has a bonding strength between said energy absorption member and said erosion resistant which is greater than said bonding strength between said rotor blade and said energy absorption member.

7. The protector in accordance with claim 6 wherein said second adhesive bond layer is formed of a permanent adhesive.

8. The protector in accordance with claim 6 wherein said first adhesive bond layer is a double-coated polyester substrate film.

9. A airfoil having a protector, comprising: a rotor blade having a leading edge; an energy absorption member; a first adhesive bond layer attaching said energy absorption member to said leading edge and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; wherein environmental impact forces against said erosion resistant member are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

10. The protector in accordance with claim 9 wherein said protector generally forms a C-shape when applied to said leading edge.

11. The protector in accordance with claim 9 wherein said energy absorption member is not exposed to the environment when applied to said leading edge.

12. The protector in accordance with claim 9 wherein said energy absorption member covers trailing edges of said energy absorption member and extends to said airfoil.

13. The protector in accordance with claim 9 wherein said second adhesive bond layer has a bonding strength between said energy absorption member and said erosion resistant which is greater than said bonding strength between said rotor blade and said energy absorption member.

14. A protector for an airfoil, comprising: an energy absorption member; a first adhesive bond layer attached to said energy absorption member wherein said first adhesive bond layer is adapted for attaching said protector to a leading edge of said airfoil and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; a diamond film layer attached to a major surface of said erosion resistant member; wherein environmental impact forces against said diamond film are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

15. The protector in accordance with claim 14 wherein said diamond film layer has a hardness of at least 18 GPa.

16. The protector in accordance with claim 14 wherein said diamond film layer has a hardness of between 18 GPa and 90 GPa.

17. The protector in accordance with claim 14 wherein said diamond film layer has an average root mean square surface roughness of less than 5.00 nm.

18. The protector in accordance with claim 14 wherein said diamond film layer has an average root mean square surface roughness of less than 2.00 nm.

19. The protector in accordance with claim 14 wherein said diamond film layer has a thickness has a thickness of 40 mils or less.

20. The protector in accordance with claim 14 wherein said diamond film layer has a thickness has a thickness within the range of 0.5 mils and 20 mils.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/080,673, filed Jul. 14, 2008, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to airfoils and, more particularly, to devices for protecting the leading edge of a helicopter rotor blade against impacts and erosion.

2. Description of the Related Art

Helicopter rotor assemblies and, in particular, rotor blades are subjected to a variety of operational forces such as, for example, aerodynamic, inertial, and centrifugal. In particular, rotor blades must be designed to accommodate various dynamic loads such as bending loads, both flapwise (out-of-plane) and chordwise (in-plane), axial loads (centrifugal), and torsional loads (pitch). Such dynamic loads subject the rotor blade to varying degrees of stresses and strains.

Conventional rotor blades may be capable of maintenance-free operation for up to several thousand hours in ideal environmental conditions. Practically, however, helicopters are operated in a wide variety of environmental conditions which negatively affect their rotor blades. For example, rain and environments having abrasive particulate matter such as sand negatively affects rotor blades through erosion wear and impact forces; dramatically reducing the rotor blades operational life. Erosion wear and impacts are of particular concern at the outboard end of the rotor blades due to the higher rotational velocities thereof (the rotational speed at a given span point of the rotor blade is directly proportional to the radial distance from the rotor hub in exponential relationship) whereat the relative impact velocities of rain and/or sand particles are significantly higher.

Experience has shown that rain impinging upon the leading edges of rotating rotor blades cause erosion wear of the leading edges. Additionally, impact forces due to the mass of the rain drops are transferred into the rotor blades which can damage the intrinsic de-icing system and bond lines of the blade spars.

Environmental conditions having particulate matter, such as sand, present a different set of problems for rotor blades. Sand typically does not have as great of a mass as rain, however, it is extremely abrasive and quickly erodes the rotor blades leading edges.

Several different techniques have been explored to increase the erosion resistance of the leading edges of helicopter rotor blades. One technique used by the Sikorsky Aircraft Division of United Technologies Corporation has been the incorporation of ductile metal leading edge caps as an integral part of the rotor blade. More specifically, nickel and/or titanium leading edge caps are shaped to a leading edge configuration by electroforming and adhesively bonded to the outboard end of the substrate, e.g., composite comprising the rotor blade. These leading edge caps provide good wear resistance against rain impacts encountered during helicopter flight operations, but are subject to quick erosion as a result of particulate impacts, typically in the form of sand, and provide little benefit against energy transfer from large particle impacts, e.g., impact forces due to rain.

Moreover, as experience in Desert Storm revealed, nickel and titanium leading edge caps experienced undesired erosion wear when subjected to operations in a sand particle environment such as a desert. Not only were the leading edge caps subjected to rapid erosion wear as a result of forward flight through sand storms, but also as a result of hover operations, e.g., take-offs and landings, due to particulate sand motion caused by rotor blade vortices, i.e., downwash. Sand erosion wear of the nickel leading edge caps quickly leads to the need to replace such caps to maintain desired flight characteristics of the rotor blades. However, inasmuch as the nickel leading edge caps comprise an integral part of the rotor blade, i.e., such caps are adhesively bonded to the composite infrastructure, replacement of the eroded nickel edge caps is not a field level repair. Rather, eroded rotor blades are removed from the helicopter and the nickel leading edge caps thereof replaced at an OEM or depot level maintenance facility. Such repair is expensive and results in significant downtime for the affected helicopter.

In an effort to reduce erosion wear of the nickel leading edge caps due to particle impacts, it is known to apply a sacrificial material to the leading edges of rotor blades. Typically, the sacrificial material is an elastomeric material such as polyurethane. While an elastomeric sacrificial coating does not provide erosion resistance characteristics of a ductile metal such as nickel, i.e., erosion occurs at a much higher rate, an elastomeric sacrificial coating does provide some advantages. First, the elastomeric sacrificial coating may be applied to the leading edge of a rotor blade as a tape. As such, a worn elastomeric sacrificial coating may be routinely replaced at the field level by stripping off the worn tape and replacing it with new tape, thereby significantly reducing helicopter downtime. Further, the cost of elastomeric sacrificial tape coatings is significantly less than nickel leading edge caps. Moreover, erosion wear of elastomeric sacrificial tapes is readily observable through visual inspection.

While the use of elastomeric sacrificial tape extends the useful life of the nickel leading edge caps with respect to sand particle erosion, the maintenance cycle for replacement of worn elastomeric sacrificial tape makes the use of such tape a less than optimal solution. Additionally, sand particles may become embedded in the tape thereby adding mass and surface roughness to the leading edge which can affect rotor blade balance and flight performance. Still another deficiency is that hydrolysis can occur when elastomeric tape is subjected to rain impacts, ultimately causing chucks of the elastomeric tape to break-off. Another disadvantage is that the mass of the elastomeric tape can cause the tape to debond from the rotor blade during flight. Furthermore, due to the mass of the elastromeric tape, its application may require time-consuming tracking and balancing of the rotors blades. These problems may be acerbated due to inconsistent application of the tape to the rotor blade and uneven distribution of mass throughout the elastomeric tape. Under the aforementioned conditions, the useful erosion protection lifetime of elastomeric sacrificial tape is significantly reduced.

Another approach to improve erosion wear of nickel leading edge caps of rotor blades is taught in U.S. Pat. No. 5,542,820 to Eaton et al. The Eaton patent discloses an engineered ceramic component that includes an outer ceramic member and a strain isolator member that is sandwiched between ceramic member and the leading edge of the rotor blade. The hardness of the ceramic member provides superior erosion resistance against sand particles, as compared to elastomeric tape.

Notwithstanding the advantages stated in the Eaton et al. patent, ceramics have inherent disadvantages. One downside is that ceramics may be brittle whereby microfractures develop under the stress and strain due to rotor blade flexure that occurs during flight operations. In an attempt to protect the ceramic member, Eaton et al. utilizes a strain isolator member to minimize stress and strain transfer between the rotor blade infrastructure and the ceramic member. As performance of the stress isolator is critical to the useful life of the ceramic member, its construction may be limited to a narrow range of suitable fabrications which adds complexity, mass and bulk to the engineered ceramic component. Another disadvantage of the Eaton et al. patent is that the ceramic member acts as an insulator such that de-icing must be performed by a cartridge heater which must be repaired or replaced at the OEM level, as opposed to de-icing by resistant heating which may be repaired or replaced at the field level. Still another disadvantage is that the ceramic member, being rigid, must to be preformed prior to being applied to the leading edge of a rotor blade, thereby eliminating the ability to form and apply the engineered ceramic component at field level.

A need in the art exists to provide enhanced erosion wear protection for the leading edge of helicopter main and tail rotor blades. Such erosion wear protection should be effective in both rain and particulate matter environments, i.e., significantly reduce erosion wear rate of, and impact forces to, rotor blades. Such erosion wear protection should be able to accommodate the stressed environment of a helicopter rotor blade, i.e., the torsional, flapwise, and chordwise bending loads experienced by a rotor blade during flight operations. Moreover, such erosion wear protection should have minimal mass so that additional tracking and balancing of the rotor blades is minimized or not required, and have a minimal coefficient of drag so that flight performance is not adversely affected. Furthermore, such erosion wear protection should eliminate or reduce the need for de-icing. Still further, such erosion wear protection should be capable of being applied and replaced at the field level.

BRIEF SUMMARY OF THE INVENTION

To achieve the foregoing and other objects, the present invention, as embodied and broadly described herein, provides various embodiments of a protector for protecting the leading edge of a helicopter rotor blade from erosion and impact forces.

In an embodiment, the protector includes an energy absorption member attached to the rotor blade by a first adhesive bond layer and an erosion resistant member attached to the energy absorption member by a second adhesive bond layer. The erosion resistant member is operative to protect the leading edge of the rotor blade from erosion due to impacts from particulate matter, such as rocks, sand, and rain. The energy absorption member is operative to absorb energy from impacts against the erosion protection member so that forces from the impacts are diminished or not transferred to the rotor blade. In another embodiment, the erosion resistant member includes a substrate coated with a diamond film. As the diamond film is harder than sand, excellent wear resistance against particulate matter and rain impacts is obtained. Other advantages provided by use of the diamond film include: 1) an ultra-smooth surface reduces drag on the rotor blade whereby flight performance may be improved, and 2) by being ultra-smooth and chemically inert de-icing equipment may not be needed.

In the broadest sense, the invented protector for an airfoil comprises an energy absorption member; a first adhesive bond layer for bonding said energy absorption member to a rotor blade; an erosion resistant member; a second adhesive bond layer for bonding said erosion resistant member to said energy absorption member; and wherein the energy absorption member is disposed between the rotor blade and the erosion resistant member.

In an embodiment, the invented protector for an airfoil, comprises an energy absorption member; a first adhesive bond layer attached to said energy absorption member wherein said first adhesive bond layer is adapted for attaching said protector to a leading edge of said airfoil and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; wherein environmental impact forces against said erosion resistant member are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

In an embodiment, the invented protector is applied to an airfoil and comprises a rotor blade having a leading edge; an energy absorption member; a first adhesive bond layer attaching said energy absorption member to said leading edge and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; wherein environmental impact forces against said erosion resistant member are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

In an embodiment, the invented protector is a protector for an airfoil, comprising an energy absorption member; a first adhesive bond layer attached to said energy absorption member wherein said first adhesive bond layer is adapted for attaching said protector to a leading edge of said airfoil and having a bonding strength between said energy absorption member and said airfoil such that said protector is manually removable from said leading edge; an erosion resistant member forming the outer surface of said protector and providing erosion resistance against environmental effects, wherein said erosion resistant member is made of a metal or alloy; a second adhesive bond layer sandwiched between said energy absorption member and said erosion resistant member, wherein said adhesive bond layer bonds said erosion resistant member to said energy absorption member; a diamond film layer attached to a major surface of said erosion resistant member; wherein environmental impact forces against said diamond film are at least partially dissipated by said energy absorption member prior to being transferred to said airfoil; and wherein said protector has a flexibility whereby it can be manually pressed against said leading edge and conformed to a contour of said leading edge.

BRIEF DESCRIPTION OF THE DRAWINGS

The above described and other features, aspects, and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawings, wherein:

FIG. 1A is a top plan view of an exemplary main rotor blade for a helicopter;

FIG. 1B is a cross-sectional view of the main rotor blade of FIG. 1A taken along line 1B-1B thereof;

FIG. 1C is an enlarged top plan view of the replaceable anhedral tip portion of the main rotor blade of FIG. 1A;

FIG. 1D is a partial perspective view of a leading edge sheath for the main rotor blade of FIG. 1A;

FIG. 2 is a cross-sectional view of a protector for the leading edge of a helicopter rotor blade wherein the protector includes an outer erosion resistant member and an energy absorption member disposed between the erosion resistant member and a rotor blade, in accordance with an exemplary embodiment of the present invention;

FIG. 3 is a cross-sectional view of a protector for the leading edge of a helicopter rotor blade similar to that of FIG. 2, but wherein the protector further includes a diamond film layer deposited on the outer surface of the erosion resistant member, in accordance with an exemplary embodiment of the present invention; and

FIG. 4 is a cross-sectional view of a protector similar to that of FIG. 2, but wherein the erosion resistant member further includes a transition portion for enclosing the remaining components of the protector from exposure to the environment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be considered as limited to the embodiments set forth herein. These exemplary embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference characters identify corresponding or similar elements throughout the several figures.

The present invention is a protector for the leading edge of an airfoil, e.g. a helicopter rotor blade, to reduce the transfer of impact forces and enhance erosion resistance thereof. To appreciate the advantages of the present invention over conventional practices, a detailed review of a helicopter rotor blade applied with prior art leading edge protection is hereinafter presented.

Referring now to the drawings, FIGS. 1A-1D illustrate an exemplary main rotor blade 100. The main rotor blade 100 comprises an inboard segment 102 configured for mounting the main rotor blade 100 to the helicopter rotor hub assembly (not shown), an intermediate segment 104, and a replaceable tip segment 106 (reference numeral 105 in FIG. 1A identifies the demarcation between the outboard end of the intermediate segment 104 and the replaceable tip segment 106). The inboard, intermediate, and tip segments 102, 104, 106 in combination define the span of the main rotor blade 100. The main rotor blade 100 has a leading edge 108 and a trailing edge 110, which in combination define the chord of the main rotor blade 100.

The inboard and intermediate segments 102, 104 of the main rotor blade 100 are fabricated from upper and lower composite skins 112, 114 that define the upper and lower aerodynamic surfaces of the main rotor blade 100, respectively; a honeycomb core 116; a prefabricated composite or metallic (e.g. titanium) spar 118 that functions as the primary structural member of the main rotor blade 100, reacting the torsional, bending, shear, and centrifugal dynamic loads developed in the rotor blade 100 during operation of the helicopter; one or more counterweights 120 adhesively bonded to the composite spar 118 to statically and dynamically balance the main rotor blade 100; and a leading-edge sheath 122, as shown in FIG. 1B. Adjustable trim tabs 124 extend rearwardly from the trailing edge 110.

The composite skins 112, 114 are prefabricated components formed from several plies of prepreg composite material of a type know to those skilled in the art, e.g., woven fiberglass material embedded in a suitable resin matrix. The upper and lower skins 112, 114 are bonded to the honeycomb core 116. The honeycomb core 116 is fabricated of material of a type typically used in aerospace applications, e.g., NOMEX®, and functions as a low weight, structural stiffening member between the upper and lower composite skins 112, 114. The upper and lower composite skins 112, 114, the honeycomb core 116, the spar 118, and the counterweights 120 in combination define a main rotor blade subassembly.

The leading edge sheath 122, which is illustrated in greater detail in FIG. 1D, is a prefabricated hybrid component fabricated from composite materials and conventional abrasive-resistant materials as known in the art. The sheath 122 has a generally C-shaped configuration that defines the leading edge 108 of the main rotor blade 100 from the inboard end of the inboard segment 102 to the outboard end of the intermediate segment 104 (FIG. 1A). The sheath 122 comprises one or more plies 130 of prepreg composite material, e.g., woven fiberglass material embedded in a suitable resin matrix that defines the inner mold line (IML) of the leading edge sheath 122, a first protector abrasion strip 132, and a second protector abrasion strip 134. For the described exemplary embodiment of the main rotor blade 100, only an outboard portion of the leading edge sheath 122, i.e., corresponding to the outboard end of the intermediate segment 104, includes the first and second abrasion strips 132, 134 inasmuch as it is the outboard portion of the main rotor blade 100 that experiences the bulk of abrasion effects (velocity effects are proportional to the span station of the main rotor blade 100 in exponential relationship). The first abrasion strip 132 is fabricated from titanium and the second abrasion strip 134 is fabricated from nickel for the exemplary embodiment of the leading edge sheath 122. The titanium strip 132 with the nickel strip 134 overlay is adhesively bonded to the prepreg composite plies 130 to form the leading edge sheath 122. Exposed segments 130ES of the prepreg composite plies 130 facilitate adhesive bonding of the leading edge sheath 122 in combination with the main rotor blade subassembly to form the main rotor blade 100. The leading edge sheath 122 is removable at the OEM level to facilitate replacement thereof. The leading edge sheath 122, and in particular the titanium strip 132 and the nickel strip 134 overlays, provides abrasion protection for the leading edge 108 of the main rotor blade 100. The leading edge sheath 122 also provides control of airfoil tolerances of the main rotor blade 100.

The replaceable tip segment 106 of the described embodiment of the main rotor blade 100 has a configuration that comprises a rearward sweep, taper, and anhedral which in coactive combination are operative to produce an increase in lift distribution over the span of the main rotor blade 100. Such a tip configuration redirects the tip trailing edge vortex and displaces such vortex so that it produces minimal interference on the trailing main rotor blade. The replaceable tip segment 106 comprises upper and lower composite skins bonded in combination with the honeycomb core. With reference to FIG. 1C, a recess 140 is formed in the honeycomb core of the replaceable tip segment 106, the recess 140 having dimensions slightly greater than the external dimensions of the spar 118. An adhesive material such as epoxy film adhesive is applied to the walls defining the recess 140 and the spar 118 so that the replaceable tip segment 106 is bonded to the intermediate segment 104. In addition, fasteners 142, e.g., threaded fasteners, may be used to secure the replaceable tip segment 106 in combination with the intermediate segment 104. The tip segment 106 is removable at the depot level for repair or replacement thereof.

The described exemplary embodiment of the main rotor blade 100 further includes a composite tip cap 144, e.g., graphite fibers embedded in a resin matrix, that is secured in combination with the outboard end of the replaceable tip segment 106 by means of fasteners 146. Alternatively, the tip cap 144 may be fabricated from a metallic material such as titanium. The tip cap 144 is removable at the field level, which minimizes the time and costs associated with replacement thereof. The replaceable tip segment 106 includes an abrasion strip 150 and the composite tip cap 144 includes an abrasion strip 152. The abrasion strips 150, 152 in combination define the leading edge of the replaceable tip segment 106. For the described embodiment, the abrasion strips 150, 152 are formed from nickel.

The abrasion strips 134, 150, 152 provide good wear resistance against water droplet, e.g., rain, impacts at the speeds encountered during helicopter flight operations, but are subject to erosion as a result of particulate impacts, typically in the form of sand.

Depending upon the erosion wear rate(s) of the abrasion strips 134, 150, 152, replacement procedures (and, concomitantly, helicopter downtime) for the abrasion strips 134, 150, 152 range from relatively simple to relatively complex (and regardless of the complexity, replacement of abrasion strips 134, 150, 152 drives up the helicopter operating costs). For example, replacement of the tip cap abrasion strip 152 is relatively simple since it has been designed for field level replacement while replacement of the abrasion strip 134 of the intermediate segment 104 is relatively complex since it must be accomplished at the OEM's facility (replacement of the abrasion strip 150 of the replaceable tip segment 106 is intermediate in complexity since it can be accomplished at the depot level).

One short term solution to the erosion problem that extends the time between replacements for the various abrasion strips 134, 150, 152, is the application of an elastomer such as polyurethane as an overlay, e.g., tape, on the abrasion strips 134, 150, 152. The elastomeric overlay functions as a sacrificial covering for the abrasion strips 134, 150, 152. The elastomeric overlay does not provide the same degree of erosion resistance as the abrasion strips 134, 150, 152, but such elastomeric overlays are readily replaceable in the field by stripping away the old tape and applying new tape. Moreover, the erosion capability of the elastomeric overlay may be readily determined by routine visual inspection.

While elastomeric-coated abrasion strips 134, 150, 152 provide the main rotorblade 100 with a significant degree of protection against the abrading effects of sand and water, these abrasion strips 134, 150, 152 are still susceptible to the eroding effects of a hostile environment of sand and/or water over a period of time. In addition to the effects of impacting sand on the life of the abrasion strips 134, 150, 152, three erosion mechanisms also occurs due to the impact of water droplets on the abrasion strips 134, 150, 152: (1) the water hammer effect; (2) the jet effect; and (3) the ram effect.

The water hammer effect is the primary water erosion mechanism affecting the structural integrity of the leading edge 108 of the main rotor blade 100, defining the force (in terms of pressure) exerted against the leading edge 108 of the main rotor blade 100 as a result of the initial impact of the water droplet there-against. The jet effect defines the shearing force exerted against the leading edge 108 of the main rotor blade 100 as a result of the high velocity, low angle water jet created by the collapse of the impacting water droplet. This waterjet action is particularly effective at removing surface asperities and opening cracks in the substrate surface. Finally, the ram effect defines the kinetic energy exerted against the leading edge 108 of the main rotor blade 100 as a result of the mass of the water droplet. A better appreciation of the erosion effects as a result of water droplet impacts, the concomitant need to mitigate the erosion effects of sand particulate impacts, and the desire to be able to apply and replace leading edge protection at the field level led to the invented leading edge protector described hereinafter.

A cross-sectional view of an exemplary embodiment of a protector 10 for the leading edge of a helicopter rotor blade is illustrated in FIG. 2, in accordance with the present invention. The protector 10 enhances erosion and impact resistance of an airfoil 11 (e.g. rotor blade) against both water droplets and particulate matter.

The protector 10 comprises an aerodynamic erosion resistant member 12, an energy absorption member 14, a first adhesive bond layer 16 for bonding the energy absorption member 14 to the rotor blade 11, and a second adhesive bond layer 18 for bonding the erosion resistant member 12 to the energy absorption member 14. In combination, the rotor blade 100 and protector 10 define the aerodynamic configuration of the leading edge of the rotor blade/protector system. The protector 10 is applied where desired along the span of the rotor blade 100.

In the preferred embodiment, the protector 10 obviates in need for abrasion strips 134, 150, 152 (FIGS. 1A-1D) as known in the prior art. That is, the protector 10 may be directly bonded, by means of the first adhesive bond layer 16, to the composite plies that form the leading edge sheath of a rotor blade 11.

As one skilled in the art will appreciate, the protector 10 may alternatively be used in combination rotor blades having one or more abrasion strips or with other types of erosion protection devices (collectively “known device”) by attaching the protector 10 over the outer surface of the known device. As with the preferred embodiment, attachment is achieved by means of the first adhesive bond layer 16.

As those skilled in the art will also appreciate, the present invention may be used with a variety of airfoils and mechanical devices having leading edges that are subject to the effects of environmental impacts and erosion. For example, the invention has utility with any configuration of helicopter rotor blades, leading edges of fixed wing aircraft and leading edges of turbine blades.

The erosion resistant member 12 may be formed of metal such as steel, chromium alloy, more preferably titanium, and most preferably nickel, or an alloy of the same. In a less preferred embodiment, the erosion resistant member 12 may be formed as a composite of carbon fiber or polyester, or as a metal and composition combination.

The erosion resistant member 12 is positioned on the outer surface of the energy absorption member 14 with the second adhesive bond layer 18 sandwiched there-between. The erosion resistant member 12 forms the outer surface of the protector 10 and provides a hard outer layer which provides erosion resistance against water droplets and particulate matter. The erosion resistant member 12 is desirably thin so as to minimize its mass and sufficiently flexible to allow for the protector 10 to be applied to the leading edge of the rotor blade 17 in a fashion like tape wherein the protector 10 is unrolled over the area to be protected then pressed into shape against contour of the rotor blade 17.

In the preferred embodiment the energy absorption member 14 is fabricated of an polymeric, e.g., urethane, polyurethane or other elastomer, and is positioned between and follows the respective contours of the erosion resistant member 12 and the rotor blade 17.

The energy absorption member 14 is operative to absorb and disburse energy from particulate matter and rain impacts to the erosion resistant member 12 in order to reduce or prevent the transfer of forces to the rotor blade 17. When an impact occurs, the erosion resistant member 12 assists to keep the energy absorption member 14 from deforming past its failure point and disburses the impact energy thereby reducing the effect on the rotor blade 17. By doing so, both the erosion resistant member 12 and rotor blade 17 will have longer useful lives before maintenance or replacement is required. For example, the rotor blade's spar lamination lines and any de-icing mechanism intrinsic to the leading edge will be subjected to less strain and impact forces.

Adhesives of the type known to those skilled in the art may be used to form the first and second adhesive bond layers 16, 18 of the protector 10. The adhesives selected for a particular application depend on the compositional characteristics of the leading edge infrastructure of the rotor blade 17, the energy absorption member 14, and the erosion resistant member 12, respectively. The selected adhesive for the second adhesive bond layer 18 should provide a good bond between the energy absorption member 14 and the erosion resistant member 12, whereas the adhesive for the first adhesive bond layer 16 should provide a good bond between the leading edge infrastructure of the rotor blade 17 and the energy absorption member 14.

In a preferred embodiment, the second adhesive layer 18 is formed of a permanent adhesive which strongly bonds together the erosion resistant member 12 and energy absorption member 14; preferably has a dynamic operating temperature range of about −5° C. to 90° C.; has high shear and tensile strength; and has a thickness of less than 20 microns. It is further preferred that the second adhesive layer 18 is resistant to solvents and moisture.

The first adhesive layer 16 is formed of an adhesive having a bonding strength sufficient to maintain the protector 10 in position during operation, while preferably less than that of the second adhesive layer 18 so that the protector 10 may be manually removed from the rotor blade 17 without damaging the rotor blade 17. For example, the first adhesive bond layer 16 maybe a double-coated polyester substrate film having different adhesive properties on each side, wherein a first adhesive adheres to the energy absorption member 14 and a second adhesive having the characteristic of clean removal adheres to the rotor blade 17.

As it will be appreciated by those skilled in the art, the minimal mass of the protector 10 enables the first adhesive bond layer 16 to have a bonding strength sufficient to maintain the protector 10 in place on the rotor blade 17 during flight, yet wherein the protector 10 may be removed from the rotor blade 17 by peeling it there-from by hand. Accordingly, removal of the protector 10 is done at the field level. Although not anticipated for normal operation, there may be operating conditions in which it is desired to utilize a first adhesive bond layer 16 having a bonding strength that requires prying or use of a solvent to facilitate removal of the protector 10 from the rotor blade 17. In such a case, removal of the protector 10 may still be done at the field level, however more care would be needed to during the removal process to ensure to the rotor blade 17 does not inadvertently become damaged.

In the embodiment illustrated by FIG. 2, the erosion resistant member 12 only covers the outer surface of the energy absorption member 14 and not its trailing edges 14a. However, as only a very limited portion of the energy absorption member 14 is subject to direct exposure to the environment, concerns of degradation due to environmental exposure are minimal. Notwithstanding, where it is desired to further minimize the effects of environment exposure, the trailing edges 14a can be treated with an atomized moisture resistant solution, cyanoacrylate product, or other suitable product. Alternatively, the trailing edges 14a maybe enclosed by the erosion resistant member 12, as described below with regards to FIG. 4.

In an embodiment illustrated by FIG. 4, the protector 10b is as described in reference to the embodiment of FIG. 2, which is incorporated herein, except that the energy absorption member 14 is completely covered by the erosion resistant member 12 such that no portion of the energy absorption member 14 is exposed to the environment. That is, the erosion resistant member 12 not only covers the outer surface of the energy absorption member 12, but also extends over the trailing edges 14b of the energy absorption member 14 where it ultimately engages to the rotor blade 17. (Although not shown, it is to be understood that a diamond film layer could also be applied to the erosion resistant member 12 and extend coextensively therewith over the trailing edges 14b of the energy absorption member 12). Optionally, the erosion resistant member 12 may be compression fitted in place to secure bonding at the trailing edge 14b. This protective positioning further obviates potential problems such as erosion, hydrolysis and impregnation of mass, for example sand. Additionally, as the energy absorption member 14 is fully enclosed from the environment, a greater variety of energy absorption members may be suitable. That is, concerns with UV stability, abrasion, hydrolysis, fungus resistance, oxidation and salt fog/spray resistance, are limited.

Referring to FIG. 3, in an alternative embodiment, the protect 10a includes and incorporates herein all the elements described in reference to FIG. 2, but wherein the erosion resistant member 12 further acts as a substrate upon which diamond-like film or more preferably a diamond film layer 22 is applied to its outer surface. Not to be construed as limiting, the preferred method for depositing the diamond film 22 onto the substrate is in accordance with the teachings of U.S. Pat. No. 7,306,778, issued Dec. 11, 2007, entitled DIAMOND FILMS AND METHODS OF MAKING DIAMOND FILMS. It is contemplated that other less preferred substrates may also be used, such as for example ceramics.

The diamond film layer 22 produced by the aforementioned preferred method has desirable properties such as hardness greater than sand particles, scratch and wear resistance, high thermal conductivity, thermally stable, chemically inert, ultra-smoothness and a nano-crystalline matrix that is resistant to forming microfractures. For example, the hardness of the diamond film layer 22 and its nano-crystalline matrix provide wear resistance from shape edged particulate matter impacts, for example by sand, and larger impacts such as rain drops. Without limitation, the preferred hardness of the diamond film layer 22 is at least 18 GPa, more preferably between 18 Gpa to 90 GPa, and most preferably between 60 GPa and 90 GPa.

Moreover, as the diamond film layer 22 is chemically inert and ultra-smooth, ice formation on the leading edge of the rotor blade is reduced or does not occur. As a result, de-icing equipment may not be required.

By being ultra-smooth, the diamond film layer 22 improves flight performance by reducing the coefficient of drag of the rotor blade 17, as compared to conventional rotor blades having a leading edge of composite or fitted with abrasion strips. Not to be construed as limiting, the average root mean square surface roughness of the diamond film layer 22 is less than 5.00 nm, more preferably less than 2.00 nm, and most preferably less than 1.50 nm.

The diamond film layer 22 can be made ultra-thin and still provides exceptional wear resistance. For example and without limitation, the preferred thickness of the diamond film layer 22 is of 40 mils or less, and more preferably within the range of 0.5 mils to 20 mils. The distribution of mass through the diamond film layer 22 is very consistent and by being ultra-thin the diamond film layer 22 adds insignificant mass to the rotor blade 17. Additionally, the diamond film layer 22 allows for the remaining components of the protector 10 to have a simple construction so that the protector 10 as a whole is thin and has minimal mass. Where the protector 10 is used in place of prior art abrasion strips, the overall mass of the rotor blade 17 is reduced providing more freedom in rotor blade design.

The various embodiments of the leading edge protector 10, 10a, 10b described herein advantageously have little mass such that tracking and balancing of the rotor blade 17 may be minimized or not required upon application of the protector 10, 10a, 10b. Additionally, less bonding strength is required for the first and second adhesive layers 16, 18 in order to maintain the protector 10 from de-bonding during flight operation. As a result, a broader range of adhesives 16, 18 may be suitable, including those that allow for the protector 10 to be removed from the rotor blade 17 at the field level.

Additionally, each of the described embodiments of the present invention advantageously may be applied at field level. That is, the protector 10, 10a, 10b may be applied to the leading edge of the rotor blade 17 like a tape wherein the protector 10, 10a, 10b is unrolled over the area to be protected then pressed against the leading edge of the rotor blade 17 to match it's C-shape.

A variety of modifications and variations of the present invention are possible in light above teachings. For example, the embodiments of the leading edge protector described hereinabove are utilized in combination with a helicopter main rotor blade. One skilled in the art will appreciate that the protector according to the present invention also has utility for use in combination with helicopter tail rotor blades. Moreover, the protector according to the present invention also has utility for leading edge erosion protection of engine propellers, airplane wing and turbine blades. It is therefore to be understood that, within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described hereinabove. And, specifically, it is to be understood that the use of the terminology “airfoil” in the appended claims encompasses without limitation helicopter rotor blades, tail rotor blades, engine propellers, airplane wings, and turbine blades.

The foregoing provides a detailed description of exemplary embodiments of the present invention. Although embodiments of a protector for a leading edge of an airfoil have been described with reference to preferred embodiments and examples thereof, other embodiments and examples may perform similar functions and/or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the following claims.