Patent Application
20130064676
Titanium alloys and organic matrix composite are the benchmark classes of materials for fan and compressor blades in commercial airline engines. One reason for the materials being so broadly adopted is that regulations require an engine in commercial service to be capable of ingesting various sizes and quantities of birds while allowing for continued operation or safe and orderly shutdown of that engine. Another reason is that the blades must resist cracking from nicks and dents caused by small debris such as sand, hail and rain. Engines with titanium fan blades as well as certain reinforced fiber composite fan blades are the predominant configurations that currently meet these criteria.
While titanium blades are relatively strong and light in weight, composite blades may offer sufficient strength and a significant weight savings over titanium. However, composite blades do not scale well to smaller engine applications and currently, the costs are several times those of comparably sized titanium blades. Both titanium and fiber composite raw materials are also expensive to process. These blades often require expensive specialized equipment to process the material into an aerodynamic shape that maintains strength while keeping weight to a minimum. Further, due to their relatively low strain tolerance, portions of composite blades require a greater thickness than otherwise equivalent metal blades to meet certain requirements, for example, bird strike requirements. Greater blade thickness reduces fan efficiency and offsets a significant portion of weight savings from using composite materials.
A method of forming an airfoil includes forming a metal portion of the airfoil including a tip, a leading edge, a trailing edge, a pressure side and a suction side; forming a plurality of grooves into one side of the airfoil; and filling the plurality of grooves with composite material.
A fan blade includes a metallic airfoil with a leading edge and a trailing edge separated in a chordwise direction, a root and a tip separated in a spanwise direction, and a suction face and a pressure face separated in a thickness direction; and one or more grooves in one of the faces of the airfoil, wherein at least a portion of the one or more grooves filled with composite materials.
An example dual-spool turbofan engine is depicted in
In a turbofan engine, lighter components generally lead to more efficient performance. The components must also be strong enough to withstand forces typical for the operating environment and performance envelope. Safety considerations based on the frequency and/or severity of possible failure will often dictate that the engine components also be able to withstand certain atypical, yet foreseeable events as well. Because stronger components are often heavier and/or more expensive, a balance must be struck between efficiency, safety, and cost. The current invention uses a mix of high strength metallic components as well as light-weight composite materials to achieve this balance of efficiency, safety and cost and improve blade performance in relation to other characteristics, such as tuning, damping, and dimensional stability and repeatability.
One or more composite filled grooves 48 are located on suction side 44 of airfoil 34 in this embodiment. Metallic parts of blade 30 can be titanium (including titanium alloys), aluminum (including aluminum alloys) and/or any other suitable metal. Grooves 48 can be machined into airfoil 34 suction side 44 towards pressure side 46. Composite material can consist of filler materials, such as chopped fibers, a braided rope, tape, other materials or a combination of materials cured with resin. Filler materials can be dry and have resin added or can be pre-impregnated with resin. Additionally, composite materials can be mechanically locked into grooves 48 (see
Composite filled grooves 48 act with metal portions of blade 30 to define airfoil 34. Replacing parts of metallic blade 30 with composite filled grooves 48, decreases weight of blade 30 while still maintaining sufficient strength to resist impacts. Additionally, the placement and design of grooves can improve blade resistance to aero-mechanical vibrations known as flutter, affect tuning of the blade, change structural properties such as strength and stiffness, and improve dimensional stability and repeatability.
Blade 30 has a natural frequency. If that frequency corresponds to certain engine operating conditions, blade 30 can be subject to aero-mechanical vibrations called flutter. Flutter can lead to large amounts of strain on blade 30, which can eventually result in blade 30 cracking and possible total blade 30 failure. To minimize flutter, composite filled grooves 48 can be added in selected areas of blade 30, affecting the tuning of the natural frequency to avoid frequencies corresponding to engine states used most often, such as idle or cruise. Composite filled grooves 48 can also affect blade 30 stiffness to further resist vibrations and flutter.
Dimensional stability and repeatability can be improved through blade 30 with composite filled grooves 48 due to use of mostly metal in blade 30. The surface profile of fully composite blades can be difficult to control and repeat in manufacture due to the process of forming and curing the composite. Forming root 42, tip 44, leading edge 36, trailing edge 38 and pressure side of blade 30 of metal limits the more difficult composite to a much smaller area (only composite in grooves 48). This results in a more stable and repeatable blade 30.
Composite materials can consist of resin cured with filler materials such as chopped fiber, tows, ropes, tapes, other materials or a combination of materials depending on blade requirements. The filler material can be dry and then be injected with resin or can be pre-impregnated with resin. Composite material can be formed in grooves 48 by placing the filler materials in grooves, adding resin (if filler material is not pre-impregnated) and curing.
The addition of composite filled grooves 48 to airfoils and tailoring the spacing, size, and shape of those grooves 48 allows for a lighter-weight blade with improvements in resistance to flutter, strength and stiffness. The varying of groove 48 characteristics and size allows for metal blade with composite filled grooves to be useful in many different situations. The size and spacing of composite filled grooves 48 can be varied according to blade size and type, engine size and type, desired blade characteristics and many other factors. Additionally, by shaping grooves 48′ to mechanically lock in composite materials, blade 30 retains much of the durability of blades made of a single material. The use of composite materials in grooves 48 and/or in cover ply 50 can also eliminate the need for erosion coatings needed to protect metal blades from erosion.
Forming airfoil tip, leading edge, trailing edge and pressure side of metal (step 62) can be done by machining titanium or another metal to form airfoil dimensions desired.
Forming airfoil suction side of metal with a plurality of grooves (step 62) can be done by machining grooves into suction side of airfoil. In alternative embodiments, grooves could be machined into pressure side of airfoil. Number of grooves and groove spacing, size and shape can be determined based on airfoil, blade and engine requirements and desired blade characteristics. Grooves can be shaped to have a negative draft at the opening on suction side for mechanical locking of composite material in grooves (see
Filling at least a portion of grooves with composite materials (step 66) can be done using filler material such as chopped fiber, tows, ropes, tapes, other materials or a combination of materials depending on blade requirements. The filler material is then cured with resin to form the composite material. The filler material can be dry and then be injected with resin or can be pre-impregnated with resin. If a cover ply is used, the cover play can be attached to composite material in grooves by interlocking fibers.
Curing the composite material (step 68) can be done in a variety of different ways and at different temperatures, depending on the composite filler materials and resin used to fill grooves. Curing ensures that the composite material sets properly with the airfoil to result in a high-strength, light-weight airfoil.
The filling and curing of composite materials in grooves (steps 66 and 68) allows for the use of composite materials without the challenges of forming entire airfoil surfaces of composite materials. Grooves 48 act as a type of mold, resulting in the need to only control the forming of one surface of the composite material.
In summary, forming composite filled grooves into a metal airfoil results in a high-strength, light weight blade that is adaptable to a variety of different requirements and desires. The use of metal through much of the airfoil ensures that airfoil 34 retains much of the strength of fully metal airfoils, and the addition of composite filled grooves 48 reduces the overall weight of blade 30. The ability to tailor the size, shape, location and spacing of grooves allows for the use of blade 30 in a variety of different engines and situations. Grooves can be tailored to increase or decrease strength or stiffness in particular areas and adjust tuning of the blade to resist flutter or vary other blade properties as desired. Additionally, the use of composite materials can eliminate the need for erosion coatings on the side of blade where composite filled grooves 48 are located.
As noted above, while composite filled grooves are shown to be located on suction side of airfoil, in alternative embodiments grooves could be located on pressure side of airfoil. Grooves shown in
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
