Patent Publication Number: US-2017370375-A1

Title: Fan blade filler

Description:
FIELD 
     The present disclosure relates to gas turbine engines, and, more specifically, to a rotor or fan blade assembly. 
     BACKGROUND 
     A gas turbine engine typically includes a fan section, a compressor section, a combustor section, and a turbine section. A fan section may drive air along a bypass flowpath while a compressor section may drive air along a core flowpath. In general, during operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases flow through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads. The compressor section typically includes low pressure and high pressure compressors, and the turbine section includes low pressure and high pressure turbines. 
     The fan section, compressor section, and turbine section typically include a series of rotor systems. Rotor systems typically include a disk and a plurality of circumferentially spaced blades, such as fan blades. A fan blade may be formed with hollow portions in the blade body to reduce weight of the blade. The hollow portions of a fan blade may contain filler materials. Filler material and fan blade surfaces may be relatively smooth, and bonding the filler material to the fan blade may be difficult. Porous mesh fabric, or scrim, which is used for bonding the filler material to the fan blade, may be difficult to manufacture and apply to non-planar surfaces. Scrim fabrics may tend to fray and may increase manufacturing costs, particularly as the complexity of filler material and fan blade surfaces increases. Small pieces of scrim may be difficult to accurately place, particularly on non-planar surfaces, and may shift when heat and pressure is applied during bonding. 
     SUMMARY 
     A blade filler for fan blade of a gas turbine engine is described herein, in accordance with various embodiments. A fan blade of a gas turbine engine may include a blade body having an inner surface defining a cavity in the blade body. A blade filler may be disposed in the cavity. The blade filler may include a bump integrally formed on a first surface of the blade filler. 
     In various embodiments, an adhesive may be formed on the first surface of the blade filler. The first surface of the blade filler may be bonded to the inner surface of the blade body. The first surface of the blade filler may comprise a non-planar surface. The bump may have a height between 0.20 mm (0.008 inches) to 0.30 mm (0.012 inches). A blade cover may be disposed over the blade filler and the cavity. The first surface of the blade filler may be bonded to the blade cover. 
     A fan section of a gas turbine engine is also provided. The fan section may include a blade assembly configured to rotate about an axis of a gas turbine engine. The blade assembly may include a blade body having an inner surface defining a cavity in the blade body. A blade filler may be disposed in the cavity. The blade filler may include a bump integrally formed on a first surface of the blade filler. 
     In various embodiments, an adhesive may be formed on the first surface of the blade filler. The first surface of the blade filler may be bonded to the inner surface of the blade body. The first surface of the blade filler may comprise a non-planar surface. The bump may have a height between 0.20 mm (0.008 inches) to 0.30 mm (0.012 inches). The bump may form a clearance between the first surface of the blade filler and the inner surface of the blade body. A material of the blade filler may comprise a closed cell polyurethane foam. A blade cover may be disposed over the blade filler and the cavity. The first surface of the blade filler may be bonded to the blade cover. 
     A method for forming a fan blade is also provided. The method may include the steps of forming a blade body having an inner surface defining a cavity, forming a blade filler having a first surface with an integral bump, disposing the blade filler in the cavity, and bonding the first surface of the blade filler to a fan blade component. 
     In various embodiments, the method may further include the step of applying an adhesive to at least one of the fan blade component or the first surface of the blade filler. The fan blade component may include at least one of the blade body or a blade cover. The method may further include the step of forming the blade filler further comprises at least one of compression molding or injection molding the blade filler and the integral bump. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the figures, wherein like numerals denote like elements. 
         FIG. 1  illustrates a cross-sectional view of an exemplary gas turbine engine, in accordance with various embodiments; 
         FIG. 2  illustrates a fragmentary perspective view of a fan section of a gas turbine engine, in accordance with various embodiments; 
         FIG. 3  illustrates an expanded view of a fan blade including a blade filler and a blade cover, in accordance with various embodiments; 
         FIG. 4A  illustrates a front view of a blade filler with integral bumps, in accordance with various embodiments; and 
         FIG. 4B  illustrates a perspective view of a blade filler with integral bumps, in accordance with various embodiments; 
         FIG. 5  illustrates a cross-sectional view of a portion of a fan blade including a blade filler, in accordance with various embodiments; and 
         FIG. 6  illustrates a method of forming a fan blade including a blade filler, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. 
     The detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical, chemical, and mechanical changes may be made without departing from the spirit and scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected, or the like may include permanent, removable, temporary, partial, full, and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. Cross hatching lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     As used herein, “aft” refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine engine. As used herein, “forward” refers to the direction associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion. 
     In various embodiments and with reference to  FIG. 1 , a gas turbine engine  20  is provided. Gas turbine engine  20  may be a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines may include, for example, an augmentor section among other systems or features. In operation, fan section  22  can drive coolant (e.g., air) along a bypass flow-path B while compressor section  24  can drive coolant along a core flow-path C for compression and communication into combustor section  26  then expansion through turbine section  28 . Although depicted as a turbofan gas turbine engine  20  herein, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. 
     Gas turbine engine  20  may generally comprise a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure  36  or engine case via several bearing systems  38 ,  38 - 1 , and  38 - 2 . Engine central longitudinal axis A-A′ is oriented in the z direction on the provided xyz axis. It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, including for example, bearing system  38 , bearing system  38 - 1 , and bearing system  38 - 2 . 
     Low speed spool  30  may generally comprise an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . Inner shaft  40  may be connected to fan  42  through a geared architecture  48  that can drive fan  42  at a lower speed than low speed spool  30 . Geared architecture  48  may comprise a gear assembly  60  enclosed within a gear housing  62 . Gear assembly  60  couples inner shaft  40  to a rotating fan structure. High speed spool  32  may comprise an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  may be located between high pressure compressor  52  and high pressure turbine  54 . A mid-turbine frame  57  of engine static structure  36  may be located generally between high pressure turbine  54  and low pressure turbine  46 . Mid-turbine frame  57  may support one or more bearing systems  38  in turbine section  28 . Inner shaft  40  and outer shaft  50  may be concentric and rotate via bearing systems  38  about the engine central longitudinal axis A-A′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The core airflow C may be compressed by low pressure compressor  44  then high pressure compressor  52 , mixed and burned with fuel in combustor  56 , then expanded over high pressure turbine  54  and low pressure turbine  46 . Turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     Gas turbine engine  20  may be, for example, a high-bypass ratio geared aircraft engine. In various embodiments, the bypass ratio of gas turbine engine  20  may be greater than about six (6). In various embodiments, the bypass ratio of gas turbine engine  20  may be greater than ten (10). In various embodiments, geared architecture  48  may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. Geared architecture  48  may have a gear reduction ratio of greater than about 2.3 and low pressure turbine  46  may have a pressure ratio that is greater than about five (5). In various embodiments, the bypass ratio of gas turbine engine  20  is greater than about ten (10:1). In various embodiments, the diameter of fan  42  may be significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  may have a pressure ratio that is greater than about five (5:1). Low pressure turbine  46  pressure ratio may be measured prior to inlet of low pressure turbine  46  as related to the pressure at the outlet of low pressure turbine  46  prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other gas turbine engines including direct drive turbofans. A gas turbine engine may comprise an industrial gas turbine (IGT) or a geared aircraft engine, such as a geared turbofan, or non-geared aircraft engine, such as a turbofan, or may comprise any gas turbine engine as desired. 
     In a turbofan engine, lighter components generally lead to more efficient performance. If less energy is expended moving internal engine parts, more energy is available for useful work. At the same time, the components themselves must be strong enough to withstand forces typical for the operating environment and performance envelope. Combining parts having both high strength and low density greatly restricts material choices and increases costs. The fan section  22 , the compressor section  24  and the turbine section  28  may each comprise rotor systems including blade assemblies having one or more sets of rotating blades, which may rotate about engine central longitudinal axis A-A′. In blade assemblies, hollow blades including filler material advantageously reduce the weight associated with the larger blades. 
     With reference to  FIGS. 1 and 2 , a perspective view of a blade assembly  100  of a fan  42  from fan section  22  is shown, with certain components removed, in accordance with various embodiments. Blade assembly  100  may comprise a plurality of rotating blades or fan blades  102  (or airfoil, rotor blade, etc.) extending radially outward from disk  104 , which may be configured to rotate about engine central longitudinal axis A-A′. Disk  104  may be centered on the rotational axis of gas turbine engine  20  with a plurality of fan blades  102  attached to the disk  104  and spaced apart in the circumferential or tangential direction. Fan blade  102  may include a hub end or root  124  attached to the disk  104  and a radially outer edge or tip  126  located radially outward from the root  124 . Fan blade  102  may include a leading edge  106  opposite to trailing edge  108 . Fan blade  102  may further include a blade body  110  between a leading edge  106  and a trailing edge  108  of fan blade  102 . The leading edge  106  and trailing edge  108  may extend from root  124  to tip  126  of fan blade  102 , with root  124  being located radially inward with respect to blade body  110  and tip  126  being located radially outward with respect to blade body  110 . Fan blade  102  may further include a generally concave pressure side and a generally convex suction side joined together at the respective leading edge  106  and trailing edge  108 . Fan blade  102  may be curved and twisted relative to, for example, a plane extending radially from the disk  104 , in terms of the fan blade  102  overall geometry. For example, fan blade  102  may curve into or out of the xy plane, the xz plane, and/or the zy plane, and for example, may twist relative to the x axis, y axis and/or z axis. It will be noted that fan blades for gas turbine engines may be provided in the variety of sizes, shapes and geometries. The fan blades designated by element number  102  in  FIGS. 2-5  are examples and this disclosure is not limited to the specific fan blades disclosed herein. Further, the disclosed fan blade designs may be adapted for use in other types of jet engines, propellers, rotors, etc. 
     With reference to  FIG. 3 , a fan blade  102  for a gas turbine is shown in additional detail, in accordance with various embodiments. In various embodiments, fan blade  102  may include a blade body  110  fabricated from titanium, titanium alloy, aluminum, aluminum alloy, composite material or other suitable structural materials. To reduce the weight of fan blade  102 , one or more cavities  130  may be formed through blade body  110 . Cavities  130  may be formed by removing material from a surface of blade body  110 , such as by machining, milling, electrochemical machining (ECM), electrical discharge machining (EDM) or other suitable process. Cavities  130  are shown in  FIG. 3  as being formed in a surface of blade body  110 , which may be a suction surface or a pressure surface of fan blade  102 . An inner surface  132  of blade body  110  may define a cavity  130 . A plurality of cavities  130  may further be defined by stiffening walls or ribs  134 . Cavities  130  may comprise a plurality of pockets or channels separated by ribs  134 . Thus, ribs  134  may be formed on internal surface  132  of blade body  110  and may define cavities  130 . Ribs  134  may reinforce fan blade  102  and may allow the outer surfaces of fan blade  102  to be made thinner, thus saving weight. The particular design of ribs  134  may depend on several factors but may typically be directed toward balancing weight reduction and manufacturing costs. 
     In various embodiments, cavities  130  may be filled wholly or partially with a blade filler  140 . The blade filler  140  may be a structural filler material that may be bonded to blade body  110  to form a part of the fan blade  102 . A plurality of pre-formed strips or pieces of a blade filler  140  may each be sized to fit within one of the plurality of cavities  130 . Blade filler  140  may at least partially fill one or more cavities  130  between adjacent ribs  134 . In various embodiments, blade filler  140  may include a plurality of bumps  142  formed integrally on one or more surfaces of blade filler  140 . 
     In various embodiments, a blade cover  150  may be placed over cavities  130  to form an aerodynamic flow surface over cavities  130 . In various embodiments, blade cover  150  may be fabricated from titanium, titanium alloy, aluminum, aluminum alloy, composite material or other suitable structural materials. In various embodiments, blade filler  140  may be glued, bonded, or otherwise coupled to blade body  110  and/or blade cover  150 . Referring momentarily to  FIG. 5  and with continued reference to  FIG. 3 , an adhesive  160  may be used to bond the blade filler  140  with bumps  142  to inner surface  132  of blade body  110 , ribs  134 , and/or blade cover  150 . 
     Referring again to  FIG. 3 , blade filler  140  may conform to the inner surface  132  of blade body  110  and to an inner surface of blade cover  150 . Blade filler  140  may prevent inward distortion (i.e., inward toward cavity  130 ) of the surfaces of blade body  110  and blade cover  150  and may increase the ability of the fan blade  102  to carry shear load. Blade filler  140  may provide additional surface area to which the blade cover  150  can contact, mate, and/or bond. In various embodiments, blade filler  140  may comprise a geometry that is complementary to the geometry of cavities  130 . Although the blade body  110 , cavities  130 , ribs  134 , blade filler  140  and blade cover  150  of fan blade  102  are shown as having certain relative dimensions, such dimensions are only exemplary and other relative dimensions are possible. 
     With reference to  FIG. 4A , a blade filler including bumps is shown, in accordance with various embodiments. Blade filler  140  may include a low density filler or another lightweight material, such as a foam. Blade filler  140  may comprise a material having a lower density than, for example, the material of blade body  110 . In various embodiments, blade filler  140  may comprise a polymer foam, such as polyethylene or polyurethane foam, a metallic foam, such as aluminum foam, or other suitable materials. Blade filler  140  may comprise, for example, a closed cell foam, such as closed cell polyurethane foam. 
     In various embodiments, blade filler  140  may include one or more bumps  142  formed on one or more surfaces of blade filler  140 , such as a first surface  144  of blade filler  140 . First surface  144  may comprise a bonding surface of blade filler  140 . A bump  142  may comprise raised feature such as a bump or a ridge formed on or integrated onto first surface  144  of blade filler  140 . One or more surfaces of blade filler  140  may not include bumps  142 , such as a second surface  146  of blade filler  140 . Second surface  146  may comprise a non-bonding surface of blade filler  140 . Blade filler  140  may comprise various non-planar surfaces, wherein a non-planar surface may be a surface that is not flat. As such, a non-bonding surface, such as second surface  146  of blade filler  140 , may be a portion or extension of a bonding surface, such as a first surface  144  with bumps  142 . As illustrated in  FIG. 4A , second surface  146  without bumps  142  may include edge surfaces of a piece of blade filler  140  adjacent to first surface  144  with bumps  142 . It will be understood that various bonding surfaces and non-bonding surfaces of blade filler  140  may include bumps  142 . 
     In various embodiments, bumps  142  may be integrally formed with blade filler  140 . As used herein, the term “integrated” or “integral” may include forming one, single continuous piece. Bumps  142  may, for example, be molded with blade filler  140 , or machined into first surface  144 , depending on the blade filler  140  fabrication method. Blade filler  140  and bumps  142  may be made from moldable materials. The material of blade filler  140  with bumps  142  may be compression molded using an autoclave or injection molded by injecting material into a mold. Blade filler  140  and bumps  142  may be formed by a subtractive manufacturing process such as casting, forging, milling, grinding, machining, and the like. Blade filler  140  and bumps  142  may also be formed by additive manufacturing. 
     In various embodiments, a base of bumps  142  may have a width or radius R of about 2 millimeters (0.08 inches), wherein “about” in this context only means+/−1 millimeter (mm) (0.04 inches). Radius R of bumps  142  may be between 1.52 mm (0.06 inches) to 2.54 mm (0.10 inches), and further between 1.78 mm (0.07 inches) to 2.29 mm (0.09 inches). Bumps  142  may include various shapes, such as semi-spherical, dome, pyramid, conical or other geometric shape. Bumps  142  are illustrated in  FIG. 4A  as having a round base shape, however it will be understood that a base of each bump may be round, oval, triangular, rectangular, or other shape. A density of bumps  142  across first surface  144  may vary, i.e., a distance between adjacent bumps  142  may be various distances, and may depend on a size and shape of the surface, material type, adhesive type and/or other design considerations. Bumps  142  may or may not be uniformly spaced apart, such that portions of first surface  144  may have a greater density of bumps  142  than other portions of first surface  144 . For example, bumps  142  may be spaced apart by less than 2.54 mm (0.10 inches) to 10 mm (0.39 inches), by less than 20 mm (0.79 inches), or may be spaced apart by less than or greater than 25.4 mm (1 inch). 
     With reference to  FIG. 4B , a blade filler with integral bumps is shown, in accordance with various embodiments. As discussed, bumps  142  may be formed on a bonding surface, such as first surface  144 , of blade filler  140 . Non-bonding surfaces of blade filler  140 , such as second surface  146 , may or may not include bumps  142 . A third surface  148  of blade filler  140 , which may be opposite to first surface  144 , may comprise a non-bonding surface of blade filler  140  and may or may not include bumps  142 . Each of bumps  142  may generally have a uniform height and may generally follow a contour of first surface  144 , such that blade filler  140  with bumps  142  fits the shape of its corresponding cavity  130  in blade body  110  (see  FIG. 3 ). Bumps  142  may increase a surface area of first surface  144 , thereby improving bonding first surface  144 . In various embodiments, bumps  142  may have a semi-spherical or dome-shaped geometry, or other shape. A shape of bumps  142  may allow blade filler  140  to be molded and subsequently removed from the mold more easily. By incorporating the bumps  142  or surface features of blade filler  140  into a mold, the cost of assembling fan blade  102  with blade filler  140  may be reduced. 
     With reference to  FIG. 5 , a cross-sectional view of a portion of a blade filler  140  having bumps  142  is shown bonded to a surface of a fan blade component, in accordance with various embodiments. Blade filler  140  may be bonded to a fan blade component  180 , which may be blade body  110  or blade cover  150 . First surface  144  of blade filler  140  with bumps  142  may be bonded to a bonding surface  182  of the fan blade component  180 . The bonding surface  182  of the fan blade component  180  may comprise an inner surface  132  of a cavity  130  of blade body  110 . In various embodiments, blade filler  140  may be bonded to fan blade component  180  by an adhesive  160 . Adhesive  160  may include a urethane-based adhesive, polyurethane-based adhesive, epoxy-based adhesive, epoxy film, rubber adhesive or other suitable adhesive. Adhesive  160  may be applied to first surface  144  of blade filler  140  or to the bonding surface  182  of fan blade component  180 . Heat and pressure may be applied to cure adhesive  160  to bond blade filler  140  to fan blade component  180 . 
     In various embodiments, bumps  142  formed on first surface  144  may have a height H as measured from first surface  144  to a tip of bump  142  (see  FIG. 5 ) which may further be a bonding surface. Bumps may include a height H of about of about 0.25 mm (0.01 inches), wherein “about” in this context only means+/−0.1 mm (0.004 inches). Height H of bumps  142  may be between 0.025 mm (0.001 inches) and 0.76 mm (0.03 inches), and further between 0.13 mm (0.005 inches) and 0.51 mm (0.02 inches), and further between 0.20 mm (0.008 inches) to 0.30 mm (0.012 inches). 
     A clearance C may be defined between first surface  144  of blade filler  140  and bonding surface  182  of fan blade component  180  by the height H of bumps  142 . Bonding surface  182  of fan blade component  180  may contact bumps  142 , and may not directly contact first surface  144  of blade filler  140 . Bumps  142  provide clearance C for adhesive  160  to fit between fan blade component  180  and blade filler  140 , with adhesive  160  formed around bumps  142 . Thus, adhesive  160  may remain between fan blade component  180  and blade filler  140  during the application of heat and pressure for bonding. The height of the bumps  142  sets the adhesive  160  layer thickness and reduces areas of direct contact between blade filler  140  and the bonding surface  182  of the fan blade component  180  and the pushing out of adhesive  160  during the adhesive cure process. Bumps  142  integrated onto the bonding surfaces of blade filler  140  may eliminate the need for a scrim separator between first surface  144  of blade filler  140  and bonding surface  182  of fan blade component  180 . 
     With reference to  FIG. 6  a method  200  of forming a fan blade  102  including blade filler  140  (of  FIGS. 3-5 ) is shown, in accordance with various embodiments. Method  200  may include the step of forming a blade body defining a cavity (step  202 ), forming a blade filler with an integral bump (step  204 ), applying an adhesive to the blade filler or to the fan blade component (step  206 ), disposing the blade filler in the cavity of the blade body (step  208 ), and bonding the blade filler to the fan blade component (step  210 ). 
     Step  204  may further include machining integral bumps on blade filler  140  or molding integral bumps, such as bumps  142 , with blade filler  140 . Blade filler  140  with bumps  142  may be compression molded using an autoclave or injection molded by injecting material into a mold. A mold may be formed to define outer surfaces of blade filler  140  including bumps  142 . The mold may be a negative of a fan blade component, such as blade filler  140  with bumps  142 . A material may be placed into the mold. Blade filler  140  formed of moldable materials such as polyurethane closed cell foam. The contents of the mold may undergo a curing process. Thus, a blade filler  140  with integral bumps may be formed using a low cost technique. 
     Step  206  may further include applying adhesive  160  to a fan blade component  180 , which may be the blade body  110  and/or the blade cover  150 . Adhesive  160  may be applied to first surface  144  of fan blade filler  140  and around bumps  142  of blade filler  140 . Adhesive  160  may be applied to a bonding surface  182  of the fan blade component  180 . Adhesive  160  may be applied to inner surface  132  of cavity  130  of blade body  110 , and/or to an inner surface of blade cover  150 . 
     Step  208  may further include placing a pre-formed blade filler  140 , with integral bumps pre-formed on a bonding surface of blade filler  140 , into cavity  130  of blade body  110 . 
     Step  210  may further include bonding one or more bonding surfaces of blade filler  140  to a bonding surface  182  of the fan blade component  180 , which may include which may be the blade body  110  and/or the blade cover  150 . A first surface  144  of blade filler  140 , with integral bumps pre-formed on a bonding surface of blade filler  140 , may be bonded to inner surface  132  of cavity  130  of blade body  110 , and/or to an inner surface of blade cover  150 . 
     Benefits and other advantages have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, and any elements that may cause any benefit or advantage to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of A, B, or C” is used in the claims, it is intended that the phrase be interpreted to mean that A alone may be present in an embodiment, B alone may be present in an embodiment, C alone may be present in an embodiment, or that any combination of the elements A, B and C may be present in a single embodiment; for example, A and B, A and C, B and C, or A and B and C. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “various embodiments”, “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element is intended to invoke 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.