Patent Application
20110116906
This invention relates to protecting airfoil components from foreign object damage and, more particularly, an indicator that alerts an operator to wear.
Airfoil components are used in various types of aircraft for propeller blades and other engine components, such as vanes and blades. The airfoil components are typically located within an air stream that may include foreign objects such as sand, ice, water droplets, stones, birds, or other debris. The foreign objects strike the airfoil component, particularly a leading edge of the airfoil component. Airfoil components that are made of polymer composites may be particularly vulnerable to erosion and damage caused by the foreign objects because of the relatively soft nature of a polymer composite, although airfoil components made of other types of material are also vulnerable.
To protect a body of the airfoil component, a protective sheath may be mounted to the leading edge. The protective sheath is typically made from a hard material that can withstand cracking, fracture, chipping, and breaking from impact with the foreign objects.
The protective sheaths of some airfoil components, especially those with composite airfoil bodies, include plates made of high strength material (e.g., titanium plates) secured to the suction and pressure sides of the airfoil body. The plates form a first sheath about a portion of the airfoil. The plates strengthen the airfoil and slow erosion of the airfoil body. A second sheath made of another material (e.g., nickel) covers a portion of the plates to prevent the plates from peeling away from the airfoil body and to slow erosion. The second sheath has a more complex geometry than the first sheath. Forming the second sheath of another material desirably reduces costs and manufacturing complexity as is known. The second sheath wears during operation. Sufficient wear can expose the first sheath.
An example airfoil assembly includes an airfoil body extending between a leading edge, a trailing edge, a suction side, and a pressure side. The assembly further includes a first protective sheath, an indicator sheath, and a second protective sheath. The first protective sheath has an outer side and an inner side that forms a cavity for receiving at least a portion of the airfoil body. The inner side is bonded to the leading edge of the airfoil body. A portion of the indicator sheath is positioned forward the first sheath relative to the leading edge of the airfoil. A portion of the second protective sheath is positioned forward the indicator sheath relative to the leading edge of the airfoil.
An example indicator sheath for an airfoil assembly has an outer side and an inner side. The outer side is configured to be received within a first protective sheath. The inner side forms a cavity for receiving at least a leading edge portion of a second protective sheath.
An example airfoil assembly wear indicating method includes providing an airfoil body that extends between a leading edge, a trailing edge, a suction side, and a pressure side with an indicator sheath. The indicator sheath is secured between a first protective sheath and a second protective sheath near the leading edge of the airfoil body. The first sheath has an inner side that forms a cavity for receiving at least a portion of the airfoil body. The inner side is bonded to the leading edge of the airfoil. At least a portion of the indicator sheath is positioned forward the first protective sheath relative to the leading edge of the airfoil. At least a portion of the second protective sheath is positioned forward the indicator sheath relative to the leading edge of the airfoil.
These and other features of the example disclosure can be best understood from the following specification and drawings, the following of which is a brief description:
The airfoil assembly 20 includes a protective sheath 34, which may also be referred to as a first sheath. The sheath 34 is bonded to the leading edge 24 of the airfoil body 22 for protecting the underlying airfoil body 22 from foreign body impact, such as debris within the air flow 32 or a bird strike. As an example, the airfoil body 22 may be formed of a composite material (as illustrated in the cutaway section) that may be less resistant to impact than metallic airfoils. The composite may include a polymer matrix 23a and reinforcement fibers 23b distributed through the matrix. The polymer matrix 23a and reinforcement fibers 23b may be any suitable types of materials for the intended end use, such as epoxy polymer and graphite fibers.
In the illustrated example, the sheath 34 includes an outer side 36 and an inner side 38 that forms a cavity 40 for receiving at least a portion of the airfoil body 22. The inner side 38 is bonded to at least the leading edge 24 of the airfoil body 22, and in the illustrated example, also portions of the suction side 28 and pressure side 30.
The sheath 34 is formed from a titanium-based metallic material. The titanium material may be relatively pure titanium or a titanium alloy. The titanium-based metallic material is relatively ductile and serves to absorb energy from the impact of any foreign objects on the airfoil assembly 20. An adhesive 42 bonds the inner side 38 of the sheath 34 and the airfoil body 22 together. For instance, the adhesive 42 may be a polymer adhesive, such as an epoxy. Other examples of the adhesive 42 include film adhesives, such as 3M2214, 3MAF111, EA9346.5, EA9628.
The example sheath 34 includes a first plate 44a bonded on the suction side 28 of the airfoil body 22 and a second plate 44b bonded on the pressure side 30. Initially, the first and second plates 44a and 44b are separate and distinct pieces that are then assembled onto the airfoil body 22 using the adhesive 42.
In this case, the first and second plates 44a and 44b meet at a nose 46 of the sheath 34 and form a seam 48 where the first plate 44a is bonded directly to the second plate 44b. The adhesive 42 may also be used to bond the first and second plates 44a and 44b together at the seam 48. Alternatively, the first and second plates 44a and 44b may be metallurgically bonded at the seam 48, such as through diffusion bonding or welding in a known manner.
In the illustrated example, the first and second plates 44a and 44b each include a wall thickness 50 that tapers from the nose 46 to rearward ends 52a and 52b of the respective first and second plates 44a and 44b. The taper of the sheath 34 facilitates energy transfer between the sheath 34 and the airfoil body 22.
The example airfoil assembly 20 additionally includes another protective sheath 60, which may also be referred to as a second sheath. The sheath 60 is bonded to a portion of the outer side 36 of the sheath 34. The sheath 60 may be formed of a nickel-based metallic material and further facilitates protecting the underlying airfoil body 22. For instance, the sheath 34 that is formed from the titanium-based metallic material provides ductility that absorbs energy from an impact on the airfoil assembly 20 and the sheath 60, which is not as ductile as the material of the sheath 34, provides a relatively high hardness that protects from erosion. The sheath 60 also protects against the first plate 44a separating from the second plates 44b due to the location of the sheath 60 relative to the seam 48. Given this description, one of ordinary skill in the art will recognize other types of materials for use as the sheath 60 to meet their particular needs. Example materials include nickel-cobalt alloys, stainless steel, Inconel, Waspaloy, Hastelloy, etc. As can be appreciated, the sheath 60 is geometrically more complex than the sheath 34.
The sheath 60 includes a nose 62 and rearward ends 64a and 64b. In this case, a wall thickness 66 of the sheath 60 tapers between the nose 62 and the rearward ends 64a and 64b in order to facilitate aerodynamics of the airfoil assembly 20 and transfer of energy between the sheath 60, the sheath 34, and the airfoil body 22.
The sheath 60 may be formed using any suitable process, such as electroforming, and then assembled onto the airfoil assembly 20. For instance, the sheath 60 may be pre-fabricated as a separate and distinct piece and then bonded to the outer side 36 of the sheath 34. In this regard, the airfoil assembly 20 may include another adhesive 142 between an inner surface 68 of the sheath 60 and the outer side 36 of the sheath 34. In some examples, the adhesive 142 may be a polymeric adhesive, such as epoxy, that is the same as the adhesive 42. In another example, the adhesive 142 is different than the adhesive 42.
In this disclosure, like reference numerals designate like elements where appropriate, and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding original elements.
The example airfoil assembly 20 additionally includes an indicator sheath 72 positioned forward the sheath 34 relative to the leading edge 24. An inner side 76 of the indicator sheath 72 is adhesively bonded to a portion of the outer side 36 of the sheath 34. More specifically, the indicator sheath 72 is adhesively bonded near the seam 48. The sheath 60 covers, and is adhesively bonded to, an outer side 80 of the indicator sheath 72.
Referring to
A thickness 88 of the indicator sheath 72 and other dimensions (e.g., length) can be adjusted to provide the desired visual cue. In one example, the indicator sheath 72 is tapered such that more of the indicator sheath 72 is exposed as the distance 84 of the worn area increases.
In the illustrated example, the airfoil body 22 may be considered to be a wide chord length airfoil that may be associated with a relatively large component, such as a propeller, helicopter rotor blade, or fan blade of a gas turbine engine. In this regard, the sheath 34 may be designed to cover a relatively large surface area of the suction side 28 and the pressure side 30. For instance, the coverage may be represented in terms of an amount of area that is covered by the sheath 34 in comparison to an amount of area that is not covered by the sheath 34. In one example, the ratio of the surface area covered to the surface area not covered may be about 0.1-1. In other examples, the coverage may be represented by a length of the sheath 34 in comparison to a chord length of the airfoil body 22.
The nose 246 of the sheath 234 is somewhat elongated in comparison to the nose 46 of the prior examples. In this case, the nose 246 extends forward relative to the notches 270a and 270b and terminates at a tip 74. Each of the first and second plates 244a and 244b tapers between the respective notches 270a and 270b and the tip 74. That is, each plate 244a and 244b becomes progressively thinner toward the tip 74. The exemplary shape facilitates absorbing energy from an impact on the leading edge 224 of the airfoil assembly 220. For instance, the elongated nose 246 provides additional titanium-based metallic material for absorbing more energy of the impact.
In this example, the indicator sheath 272 extends away from the airfoil body 222 past the tip 74 toward the tip 262. Sufficient wear of the tip 262 exposes the indicator sheath 272. As can be appreciated, wear exposes the indicator sheath 272 before the sheath 234 is exposed due to wear.
The indicator sheath 372 extends away from the airfoil body 322 past the tip 374 toward the tip 362. Wearing of the tip 362 exposes the indicator sheath 372 prior to the sheath 334.
As may be appreciated, utilizing separate and distinct plates in the illustrated examples to form the respective sheaths 34, 234, and 334 facilitates providing a low cost assembly that is relatively easy to construct. For instance, the plates may be individually manufactured to the designed shape and then assembled on to the airfoil body. In contrast, forming the sheaths from a single, monolithic piece of titanium material may be difficult to manufacture and would significantly increase the cost of the airfoil assembly.
In this example, the rearward ends 464a and 464b of the metal sheet stock 96 are not tapered. The airfoil body 422 includes notched areas 100 that receive the rearward ends 464a and 464b. In another example (not shown) the rearward ends 464a and 464b are machined to tapers prior to securing the sheath 460 and the indicator sheath 472 to the sheath 446.
Although a preferred embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
