Patent Application
20170130585
This invention relates generally to airfoil protective leading edge guards and in particular to fan blade leading edge guards with energy absorbing properties.
Fan blades and other structures used in turbine engine applications are susceptible to foreign object impact damage, for example during bird ingestion events. Blades made of composite materials such as graphite fiber reinforced epoxy are attractive due to their high overall specific strength and stiffness. However, graphite composites are particularly prone to brittle fracture and delamination during foreign object impacts due to their low ductility. Blade leading edges, trailing edges, and tips are particularly sensitive because of the generally lower thickness in these areas and the well-known susceptibility of laminated composites to free edge delamination. In addition blade geometry and high rotational speeds relative to aircraft speeds cause ingested objects to strike the blade near the leading edge.
Metallic guards bonded to the leading edges of composite fan blades are known to provide impact damage protection.
One problem with prior art leading edge guards is that they are generally both thin and made of high-density alloys. These requirements make manufacture of leading edge guards difficult with conventional methods such as machining or hot creep forming.
Another problem with prior art fan blade leading edge guards is that they often have complex shapes which are complex and expensive to manufacture.
At least one of the above-noted problems is addressed by an airfoil incorporating an edge guard with energy absorbing elements disposed therein.
According to one aspect of the technology described herein, an edge guard apparatus for an airfoil includes: a body having a nose with spaced-apart first and second wings extending therefrom, the body defining a cavity between the first and second wings; and an energy absorbing structure disposed in the cavity.
According to another aspect of the technology described herein, an airfoil apparatus includes: an airfoil having convex and concave sides extending between a leading edge and a trailing edge; a body having a nose with spaced-apart first and second wings extending therefrom, the body defining, in cooperation with the leading edge of the airfoil, a cavity; and an energy absorbing structure disposed in the cavity.
The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:
Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,
The fan blade 10 may be made from one or more metal alloys, or from a nonmetallic material, such as a composite system with an epoxy matrix and carbon fiber reinforcement.
The airfoil 12 has a leading edge guard 30 attached to the leading edge 22. The leading edge guard 30 helps provide the fan blade 10 with additional impact resistance, erosion resistance and improved resistance of the composite structure to delamination. In particular, the leading edge guard 30 has energy absorbing properties.
As best seen in
Interior surfaces of the nose 36 and wings 38 and 40 collectively define an interior surface 42 of the body 32. The shape and dimensions of the interior surface 42 are selected to closely fit the exterior of the airfoil 12, and to define a cavity 44 in cooperation with the leading edge 22 of the airfoil 12.
The body 32 may be made from a metal alloy of the desired composition. One non-limiting example of an alloy suitable for construction of the body 32 is a nickel-based alloy commercially available as INCONEL 718 or IN718.
The body 32 may be made, for example, starting from flat sheet stock 46, as shown in
The energy absorbing structure 34 is disposed in the cavity 44. As used herein, the term “energy absorbing” refers to any structure configured to reduce a peak impact force by dissipating the impact energy and/or converting it to another form of energy (such as thermal energy). Nonlimiting examples of energy absorbing materials include solid materials with viscous properties, and cellular structures of otherwise rigid elastic materials such as metals, for example configurations similar to a honeycomb. For purposes of comparison, in general, a monolithic, nonporous metallic structure would not be considered “energy absorbing”.
In the illustrated example, the energy absorbing structure 34 comprises a plurality of tubes 52 packed into the cavity 44. The long axes of the tubes 52 run generally in the spanwise direction of the airfoil 12, that is, from root 18 to tip 20. It will be understood that the airfoil 12 may incorporate features such as “twist”, i.e. successive airfoil sections rotated relative to each other, or “bow”, i.e. a non-linear airfoil stacking axis. The tubes 52 may incorporate curvature as necessary follow the path of any non-linear shaping of the airfoil 12.
The tubes 52 may be of varying diameters and wall thicknesses to efficiently pack into the cavity 44 and to provide a preferred combination of energy absorption capability and low weight.
The tubes 52 may be made from various materials, such as metal alloys, polymers, ceramics, or composites of those materials. For example, the tubes 52 may be made by a conventional hot extrusion process. A non-limiting example of an alloy suitable for construction of the tubes 52 is a nickel-based alloy commercially available as INCONEL 718 or IN718.
The tubes 52 may be disposed in direct contact with each other, or they may be spaced apart. They may be bonded to each other, for example using a welding or brazing process. Any voids between tubes 52 may be left open, or may be filled with a material such as an adhesive. The tubes 52 may be assembled as a single pack or bundle and then mated to the airfoil 12 along with the body 36.
The number and distribution of tubes 52 may vary over the span of the airfoil 12. For example, in the example shown in
Optionally, the leading edge guard 30 or portions thereof may be part of a single unitary, one-piece, or monolithic component, and may be manufactured using a manufacturing process which involves layer-by-layer construction or additive fabrication (as opposed to material removal as with conventional machining processes). Such processes may be referred to as “rapid manufacturing processes” and/or “additive manufacturing processes,” with the term “additive manufacturing process” being the term used herein to refer generally to such processes. Additive manufacturing processes include, but are not limited to: Direct Metal Laser Melting (DMLM), Laser Net Shape Manufacturing (LNSM), electron beam sintering, Selective Laser Sintering (SLS), 3D printing, such as by inkjets and laserjets, Sterolithography (SLS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), and Direct Metal Deposition (DMD).
The apparatus described herein has several advantages over prior art leading edge guards. It uses a simple wrap for the external leading edge surface, combined with an energy absorbing structure inserted for added stiffness and increased impact capability. This configuration will reduce part cost in that the external skin can be formed from general sheet stock and the insert tubes can be simple hot formed thin wall tubes. The increased overall stiffness of the leading edge guard 30 (as compared to a prior art solid leading edge guard) may allow for overall thinning of the airfoil 12, resulting in increased airfoil aerodynamic efficiency.
The foregoing has described an airfoil with a leading edge guard. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying potential points of novelty, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
