Patent Description:
Gas turbine engines can include a fan for propulsion air and to cool components. The fan also delivers air into a core engine where it is compressed. The compressed air is then delivered into a combustion section, where it is mixed with fuel and ignited. The combustion gas expands downstream over and drives turbine blades. Static vanes are positioned adjacent to the turbine blades to control the flow of the products of combustion. The fan typically includes an array of fan blades having dovetails that are mounted in slots of a fan hub.

<CIT> relates to a strong, lightweight rotor for turbomachines such as axial-flow compressors and turbines, and a multistage axial-flow compressor having a lightweight titanium drum rotor and blades mounted by a clevis and pin arrangement. <CIT> also relates to the use of very high tensile strength fibrous composite wrap to reinforce the metal rotor drum against the very high centrifugal forces exerted upon it, principally by the blades, but also by the structure of the drum itself, wherein the structure is such that the force exerted by the blades is delivered against the interior of the rotor drum, whereas the reinforcing ring is disposed about the exterior of the rotor immediately adjacent the point of application of the centrifugal forces from the blade roots.

<CIT> relates to a turbomachine rotor of the type comprising a disc having a plurality of annular ribs which extend outwards from the periphery of said disc and which define a plurality of annular grooves, a plurality of blades, regularly disposed at the periphery of said disc and extending radially outward, each blade comprising a notched foot so as to define heels each of which lodges in a corresponding groove on said disc, and means for fixing said blades to the disc.

<CIT> relates to an aircraft propeller system of the unducted fan type including a plurality of propeller blades which are respectively fastened to a rotor, rotate about an axis of rotation and also rotate about a pitch axis, wherein each blade is fastened to the rotor by a hinge which has a pivot axis to reduce the effective stiffness of each blade, the pivot axis being non-parallel to the axis of rotation.

According to the present invention, there is provided a rotor assembly for a gas turbine engine as claimed in claim <NUM>.

Some embodiments of the present invention are claimed in the dependent claims.

<FIG> illustrates a rotor assembly <NUM> for a gas turbine engine according to an example. The rotor assembly <NUM> can be incorporated into the fan section <NUM> or the compressor section <NUM> of the engine <NUM> of <FIG>, for example. However, it should to be understood that other parts of the gas turbine engine <NUM> and other systems may benefit from the teachings disclosed herein. In some examples, the rotor assembly <NUM> is incorporated into a multi-stage fan section of a direct drive or geared engine architecture.

The rotor assembly <NUM> includes a rotatable hub <NUM> mechanically attached or otherwise mounted to a fan shaft <NUM>. The fan shaft <NUM> is rotatable about longitudinal axis X. The fan shaft <NUM> can be rotatably coupled to the low pressure turbine <NUM> (<FIG>), for example. The rotatable hub <NUM> includes a main body 62A that extends along the longitudinal axis X. The longitudinal axis X can be parallel to or collinearly with the engine longitudinal axis A of <FIG>, for example. As illustrated by <FIG>, the hub <NUM> includes an array of annular flanges 62B that extend about an outer periphery 62C of the main body 62A. The annular flanges 62B define an array of annular channels 62D along the longitudinal axis X.

An array of airfoils <NUM> are circumferentially distributed about the outer periphery 62C of the rotatable hub <NUM>. Referring to <FIG>, with continued reference to <FIG>, one of the airfoils <NUM> mounted to the hub <NUM> is shown for illustrative purposes. The airfoil <NUM> includes an airfoil section 66A extending from a root section 66B. The airfoil section 66A extends between a leading edge LE and a trailing edge TE in a chordwise direction C, and extends in a radial direction R between the root section 66B and a tip portion 66C to provide an aerodynamic surface. The tip portion 66C defines a terminal end or radially outermost extent of the airfoil <NUM> to establish a clearance gap with fan case <NUM> (<FIG>). The airfoil section 66A defines a pressure side P (<FIG>) and a suction side S separated in a thickness direction T. The root section 66B is dimensioned to be received in each of the annular channels 62D.

The rotor assembly <NUM> includes an array of platforms <NUM> that are separate and distinct from the airfoils <NUM>. The platforms <NUM> are situated between and abut against adjacent pairs of airfoils <NUM> to define an inner boundary of a gas path along the rotor assembly <NUM>, as illustrated in <FIG>. The platforms <NUM> can be mechanically attached and releasably secured to the hub <NUM> with one or more fasteners, for example. <FIG> illustrates one of the platforms <NUM> abutting against the airfoil section 66A of adjacent airfoils <NUM>.

<FIG> illustrates an exploded, cutaway view of portions of the rotor assembly <NUM>. <FIG> illustrates a side view of one of the airfoils <NUM> secured to the hub <NUM>. The rotor assembly <NUM> includes a plurality of retention pins <NUM> for securing the airfoils <NUM> to the hub <NUM> (see <FIG>). Each of the platforms <NUM> can abut the adjacent airfoils <NUM> at a position radially outward of the retention pins <NUM>, as illustrated by <FIG>.

Each of the retention pins <NUM> is dimensioned to extend through the root section 66B of a respective one of the airfoils <NUM> and to extend through each of the flanges 62B to mechanically attach the root section 66B of the respective airfoil <NUM> to the hub <NUM>, as illustrated by <FIG> and <FIG>. The retention pins <NUM> react to centrifugal loads in response to rotation of the airfoils <NUM>. The hub <NUM> can include at least three annular flanges 62B, such as five flanges 62B as shown, that are axially spaced apart relative to the longitudinal axis X to support a length of each of the retention pins <NUM>. However, fewer or more than five flanges 62B can be utilized with the teachings herein. Utilizing three or more flanges 62B can provide relatively greater surface contact area and support along a length each retention pin <NUM>, which can reduce bending and improve durability of the retention pin <NUM>.

The airfoil <NUM> can be a hybrid airfoil including metallic and composite portions. Referring to <FIG>, with continuing reference to <FIG>, the airfoil <NUM> includes a metallic sheath <NUM> that at least partially receives and protects a composite core <NUM>. In some examples, substantially all of the aerodynamic surfaces of the airfoil <NUM> are defined by the sheath <NUM>. The sheath <NUM> can be dimensioned to terminate radially inward prior to the root section 66B such that the sheath <NUM> is spaced apart from the respective retention pin(s) <NUM>, as illustrated by <FIG>. The sheath <NUM> includes a first skin 72A and a second skin 72B. The first and second skins 72A, 72B are joined together to define an external surface contour of the airfoil <NUM> including the pressure and suction sides P, S of the airfoil section 66A.

The core <NUM> includes one or more ligaments <NUM> that define portions of the airfoil and root sections 66A, 66B. The ligament <NUM> can define radially outermost extent or tip of the tip portion 66C, as illustrated by <FIG>. In other examples, the ligaments <NUM> terminate prior to the tip of the airfoil section 66A. In the illustrative example of <FIG>, the core <NUM> includes two separate and distinct ligaments 76A, 76B spaced apart from each other as illustrated in <FIG> and <FIG>. The core <NUM> can include fewer or more than two ligaments <NUM>, such as three to ten ligaments <NUM>. The ligaments 76A, 76B extend outwardly from the root section 66B towards the tip portion 66C of the airfoil section 66A, as illustrated by <FIG>, <FIG>.

The sheath <NUM> defines one or more internal channels 72C, 72D to receive the core <NUM>. In the illustrated example of <FIG>, the sheath <NUM> includes at least one rib <NUM> defined by the first skin 72A that extends in the radial direction R to bound the adjacent channels 72C, 72D. The ligaments 76A, 76B are received in respective internal channels 72C, 72D such that the skins 72A, 72B at least partially surround the core <NUM> and sandwich the ligaments 76A, 76B therebetween, as illustrated by <FIG>. The ligaments 76A, 76B receive the common retention pin <NUM> such that the common retention pin <NUM> is slideably received through at least three, or each, of annular flanges 62B. The common retention pin <NUM> is dimensioned to extend through each and every one of the interface portions <NUM> of the respective airfoil <NUM> to mechanically attach or otherwise secure the airfoil <NUM> to the hub <NUM>.

Referring to <FIG>, with continued reference to <FIG> and <FIG>, each of one of the ligaments <NUM> includes at least one interface portion <NUM> in the root section 66B. <FIG> illustrates ligament <NUM> with the first and second skin 72A, 72B removed. <FIG> illustrates the core <NUM> and skins 72A, 72B in an assembled position, with the interface portion <NUM> defining portions of the root section 66B. The interface portion <NUM> includes a wrapping mandrel <NUM> and a bushing <NUM> mechanically attached to the mandrel <NUM> with an adhesive, for example. The bushing <NUM> is dimensioned to slideably receive one of the retention pins <NUM> (<FIG>). The mandrel <NUM> tapers from the bushing <NUM> to define a teardrop profile, as illustrated by <FIG>.

In the illustrative example of <FIG> and <FIG>, each of the ligaments <NUM> defines at least one slot <NUM> in the root section 66B to define first and second root portions 83A, 83B received in the annular channels 62D on opposed sides of the respective flange 62B such that the root portions 83A, 83B are interdigitated with the flanges 62B. The slots <NUM> can decrease bending of the retention pins <NUM> by decreasing a distance between adjacent flanges 62B and increase contact area and support along a length of the retention pin <NUM>, which can reduce contact stresses and wear.

Each ligament <NUM> can include a plurality of interface portions <NUM> (indicated as 78A, 78B) received in root portions 83A, 83B, respectively. The interface portions 78A, 78B of each ligament 76A, 76B receive a common retention pin <NUM> to mechanically attach or otherwise secure the ligaments 76A, 76B to the hub <NUM>. The root section 66B defines at least one bore <NUM> dimensioned to receive a retention pin <NUM>. In the illustrated example of <FIG>, each bore <NUM> is defined by a respective bushing <NUM>.

Various materials can be utilized for the sheath <NUM> and composite core <NUM>. In some examples, the first and second skins 72A, 72B comprise a metallic material such as titanium, stainless steel, nickel, a relatively ductile material such as aluminum, or another metal or metal alloy, and the core <NUM> comprises carbon or carbon fibers, such as a ceramic matrix composite (CMC). In examples, the sheath <NUM> defines a first weight, the composite core <NUM> defines a second weight, and a ratio of the first weight to the second weight is at least <NUM>:<NUM> such that at least <NUM>% of the weight of the airfoil <NUM> is made of a metallic material. The metal or metal alloy can provide relatively greater strength and durability under operating conditions of the engine and can provide relatively greater impact resistance to reduce damage from foreign object debris (FOD). The composite material can be relatively strong and lightweight, but may not be as ductile as metallic materials, for example. The hybrid construction of airfoils <NUM> can reduce an overall weight of the rotor assembly <NUM>.

In the illustrative example of <FIG>, each of the ligaments <NUM> includes at least one composite layer <NUM>. Each composite layer <NUM> can be fabricated to loop around the interface portion <NUM> and retention pin <NUM> (when in an installed position) such that opposed end portions 80A, 80B of the respective layer <NUM> are joined together along the airfoil portion 66A. The composite layers <NUM> can be dimensioned to define a substantially solid core <NUM>, such that substantially all of a volume of the internal cavities 72C, 72D of the sheath <NUM> are occupied by a composite material comprising carbon. In the illustrated example of <FIG>, the composite layers <NUM> include a first composite layer 80C and a second composite layer 80D between the first layer 80C and an outer periphery of the interface portion <NUM>. The composite layers 80C and 80D can be fabricated to each loop around the interface portion <NUM> and the retention pin <NUM>.

The layers <NUM> can include various fiber constructions to define the core <NUM>. For example, the first layer 80C can define a first fiber construction, and the second layer 80D can define a second fiber construction that differs from the first fiber construction. The first fiber construction can include one or more uni-tape plies or a fabric, and the second fiber construction can include at least one ply of a three-dimensional weave of fibers as illustrated by layer <NUM>-<NUM> of <FIG>, for example. It should be appreciated that uni-tape plies include a plurality of fibers oriented in the same direction ("uni-directional), and fabric includes woven or interlaced fibers, each known in the art. In examples, each of the first and second fiber constructions includes a plurality of carbon fibers. However, other materials can be utilized for each of the fiber constructions, including fiberglass, Kevlar®, a ceramic such as Nextel™, a polyethylene such as Spectra®, and/or a combination of fibers.

Other fiber constructions can be utilized to construct each of the layers <NUM>, including any of the layers <NUM>-<NUM> to <NUM>-<NUM> of <FIG> illustrates a layer <NUM>-<NUM> defined by a plurality of braided yarns. <FIG> illustrates a layer <NUM>-<NUM> defined by a two-dimensional woven fabric. <FIG> illustrates a layer <NUM>-<NUM> defined by a non-crimp fabric. <FIG> illustrates a layer <NUM>-<NUM> defined by a tri-axial braided fabric. Other example fiber constructions include biaxial braids and plain or satin weaves.

The rotor assembly <NUM> can be constructed and assembled as follows. The ligaments 76A, 76B of core <NUM> are situated in the respective internal channels 72C, 72D defined by the sheath <NUM> such that the ligaments 76A, 76B are spaced apart along the root section 66B by one of the annular flanges 62B and abut against opposed sides of rib <NUM>, as illustrated by <FIG>, <FIG> and <FIG>.

In some examples, the ligaments 76A, 76B are directly bonded or otherwise mechanically attached to the surfaces of the internal channels 72C, 72D. Example bonding materials can include polymeric adhesives such as epoxies, resins such as polyurethane and other adhesives curable at room temperature or elevated temperatures. The polymeric adhesives can be relatively flexible such that ligaments <NUM> are moveable relative to surfaces of the internal channels 72C, 72D to provide damping during engine operation. In the illustrated example of <FIG>, the core <NUM> includes a plurality of stand-offs or detents <NUM> that are distributed along surfaces of the ligaments <NUM>. The detents <NUM> are dimensioned and arranged to space apart the ligaments <NUM> from adjacent surfaces of the internal channels 72C, 72D. Example geometries of the detents <NUM> can include conical, hemispherical, pyramidal and complex geometries. The detents <NUM> can be uniformly or non-uniformly distributed. The detents <NUM> can be formed from a fiberglass fabric or scrim having raised protrusions made of rubber or resin that can be fully cured or co-cured with the ligaments <NUM>, for example.

The second skin 72B is placed against the first skin 72A to define an external surface contour of the airfoil <NUM>, as illustrated by <FIG> and <FIG>. The skins 72A, 72B can be welded, brazed, riveted or otherwise mechanically attached to each other, and form a "closed loop" around the ligaments <NUM>.

The detents <NUM> can define relatively large bondline gaps between the ligaments <NUM> and the surfaces of the internal channels 72C, 72D, and a relatively flexible, weaker adhesive can be utilized to attach the sheath <NUM> to the ligaments <NUM>. The relatively large bondline gaps established by the detents <NUM> can improve flow of resin or adhesive such as polyurethane and reducing formation of dry areas. In examples, the detents <NUM> are dimensioned to establish bondline gap of at least a <NUM> inches (<NUM>), or more narrowly between <NUM> and <NUM> inches (<NUM> and <NUM>). The relatively large bondline gap can accommodate manufacturing tolerances between the sheath <NUM> and core <NUM>, can ensure proper positioning during final cure and can ensure proper bond thickness. The relatively large bondline gap allows the metal and composite materials to thermally expand, which can reduce a likelihood of generating discontinuity stresses. The gaps and detents <NUM> can also protect the composite from thermal degradation during welding or brazing of the skins 72A, 72B to each other.

For example, a resin or adhesive such as polyurethane can be injected into gaps or spaces established by the detents <NUM> between the ligaments <NUM> and the surfaces of the internal channels 72C, 72D. In some examples, a relatively weak and/or soft adhesive such as polyurethane is injected into the spaces. Utilization of relatively soft adhesives such as polyurethane can isolate and segregate the disparate thermal expansion between metallic sheath <NUM> and composite core <NUM>, provide structural damping, isolate the delicate inner fibers of the composite core <NUM> from relatively extreme welding temperatures during attachment of the second skin 72B to the first skin 72A, and enables the ductile sheath <NUM> to yield during a bird strike or other FOD event, which can reduce a likelihood of degradation of the relatively brittle inner fibers of the composite core <NUM>.

The composite layers <NUM> can be simultaneously cured and bonded to each other with the injected resin, which may be referred to as "co-bonding" or "co-curing". In other examples, the composite layers <NUM> can be pre-formed or pre-impregnated with resin prior to placement in the internal channels 72C, 72D. The composite core <NUM> is cured in an oven, autoclave or by other conventional methods, with the ligaments <NUM> bonded to the sheath <NUM>, as illustrated by <FIG>.

The airfoils <NUM> are moved in a direction D1 (<FIG>) toward the outer periphery 62C of the hub <NUM>. A respective retention pin <NUM> is slideably received through each bushing <NUM> of the interface portions <NUM> and each of the flanges 62B to mechanically attach the ligaments <NUM> to the flanges 62B. The platforms <NUM> are then moved into abutment against respective pairs of airfoils <NUM> at a position radially outward of the flanges 62B to limit circumferential movement of the airfoil sections 66A, as illustrated by <FIG>.

Mechanically attaching the airfoils <NUM> with retention pins <NUM> can allow the airfoil <NUM> to flex and twist, which can reduce a likelihood of damage caused by FOD impacts by allowing the airfoil <NUM> to bend away from the impacts. The rotor assembly <NUM> also enables relatively thinner airfoils which can improve aerodynamic efficiency.

<FIG> illustrate an airfoil <NUM> according to another example. 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. A first skin 172A of sheath <NUM> defines internal channels 172C, 172D. The internal channels 172C, 172D are adjacent to each other and are bounded by a pair of opposing ribs <NUM>. The ribs <NUM> can extend in a radial direction R, for example, and are spaced apart along an internal gap 172F that interconnects the internal cavities 172C, 172D. The internal gap 172F can be spaced apart from the radial innermost and outermost ends of the first skin 172A of the sheath <NUM>. Composite core <NUM> includes a ligament bridge <NUM> that interconnects an adjacent pair of ligaments <NUM> at a location radially outward of a common pin <NUM> (shown in dashed lines in <FIG> for illustrative purposes). The ligament bridge <NUM> can be made of any of the materials disclosed herein, such as a composite material.

The ligament bridge <NUM> is dimensioned to be received within the gap 172F. The ligament bridge <NUM> interconnects the adjacent pair of ligaments <NUM> in a position along the airfoil section 166A when in the installed position. During operation, the core <NUM> may move in a direction D2 (<FIG>) relative to the sheath <NUM>, which can correspond to the radial direction R, for example. The ligament bridge <NUM> is dimensioned to abut against the opposing ribs <NUM> of the sheath <NUM> in response to movement in direction D2 to react blade pull and bound radial movement of the core <NUM> relative to the sheath <NUM>. The ligament bridge <NUM> serves as a fail-safe by trapping the ligaments <NUM> to reduce a likelihood of liberation of the ligaments <NUM> which may otherwise occur due to failure of the bond between the sheath <NUM> and ligaments <NUM>.

<FIG> illustrate an airfoil <NUM> according to yet another example. Airfoil <NUM> includes at least one shroud <NUM> that extends outwardly from pressure and suction sides P, S of airfoil section 266A at a position radially outward of platforms <NUM> (shown in dashed lines in <FIG> for illustrative purposes). The shroud <NUM> defines an external surface contour and can be utilized to tune mode(s) of the airfoil <NUM> by changing boundary constraints. The shroud <NUM> can be made of a composite or metallic material, including any of the materials disclosed herein, or can be made of an injection molded plastic having a plastic core and a thin metallic coating, for example. The airfoil <NUM> can include a second shroud <NUM>' (shown in dashed lines) to provide a dual shroud architecture, with shroud <NUM> arranged to divide airfoil between bypass and core flow paths B, C (<FIG>) and shroud <NUM>' for reducing a flutter condition of the airfoil <NUM>, for example.

The shroud <NUM> includes first and second shroud portions 286A, 286B secured to the opposing pressure and suction sides P, S. The shroud portions 286A, 286B can be joined together with one or more inserts fasteners F that extend through the airfoil section 266A. The fasteners F can be baked into the ligaments <NUM>, for example, and can be frangible to release in response to a load on either of the shroud portions 286A, 286B exceeding a predefined threshold. It should be appreciated that other techniques can be utilized to mechanically attach or otherwise secure the shroud portions 286A, 286B to the airfoil <NUM>, such as by an adhesive, welding or integrally forming the skins 272A, 272B with the respective shroud portions 286A, 286B. In some examples, the airfoil <NUM> includes only one of the shroud portions 286A, 286B such that the shroud <NUM> is on only one side of the airfoil section 266A or is otherwise unsymmetrical.

<FIG> illustrate a rotor assembly <NUM> according to another example. Each annular channel 362D of hub <NUM> is dimensioned to receive a composite reinforcement member <NUM>. Each reinforcement member <NUM> can have an annular geometry and is dimensioned to extend about the outer periphery 362C of the hub <NUM> and to be received within a respective channel 362D.

As illustrated by <FIG> and <FIG>, each reinforcement member <NUM> can be situated radially between the outer periphery 362C of the hub <NUM> and the retention pins <NUM>. An outer diameter of the reinforcement member <NUM> can be positioned radially inward of an innermost portion of each of the ligaments <NUM> of core <NUM> such that each reinforcement member <NUM> is situated radially between the outer periphery 362C and the respective ligament <NUM>. The retention pins <NUM> can be positioned radially outboard of the reinforcement members <NUM> with respect to the longitudinal axis X.

Each reinforcement member <NUM> can include at least one composite layer LL that is formed to extend around the outer periphery 362C of the hub <NUM>. Referring to <FIG>, with continued reference to <FIG>, the reinforcement member <NUM> can have a plurality of composite layers LL. Each layer LL can include any of the composite materials and fiber constructions disclosed herein, including carbon and CMC materials. For example, the reinforcement member <NUM> can be a carbon tape <NUM> having uni-directional fibers and that is continuously wound around the outer periphery 362C of the hub <NUM> two or more times to define the composite layers LL, such as a total of five layers LL. It should be understood that the reinforcement member <NUM> can have fewer or more than five layers LL. The tape <NUM> can be a dry form and impregnated or injected with an epoxy or resin after formation along the hub, and then cured to fabricate the reinforcement member <NUM>, for example, which can reduce creep.

The reinforcement member <NUM> can be constructed relative to a dimension of the hub <NUM> to reinforce the hub <NUM> during engine operation. For example, the reinforcement member <NUM> can define a first thickness T1. The hub <NUM> can define a second thickness T2 along the outer periphery 362C that defines a respective one of the channels 362B. In some examples, the second thickness T2 is less than the first thickness T1. For example, a ratio of thickness T2 to thickness T1 can be less than <NUM>:<NUM>, or more narrowly less than <NUM>:<NUM> or <NUM>:<NUM>, for at least some, or each, of the reinforcement members <NUM>. The reinforcement members <NUM> reinforce or support the hub <NUM> along the outer periphery 362C to react centrifugal forces and carry relatively high hoop loads during engine operation, and can reduce an overall weight of the hub <NUM>, for example.

<FIG> illustrates a gas turbine engine <NUM> including a rotor assembly <NUM> according to another example. Fan section <NUM> delivers a portion of airflow into a core flow path C defined by compressor section <NUM> and another portion of airflow into a bypass flow path B defined by a bypass duct <NUM> of a fan case or nacelle <NUM>. The rotor assembly <NUM> includes retention pins <NUM> (one shown for illustrative purposes) to releasably secure each airfoil <NUM> to the hub <NUM>.

The rotor assembly <NUM> can be driven by shaft <NUM> through geared architecture <NUM>. Geared architecture <NUM> can be an epicyclic gear train such as a planetary or star gear system including a sun gear 448A, intermediate gears 448B (one shown for illustrative purposes) and ring gear 448C. The sun gear 448A is mechanically attached or otherwise secured to the shaft <NUM>. The ring 448C surrounds each intermediate gear 448B and sun gear 448A. Each intermediate gear 448B meshes with the sun gear 448A and ring gear 448C. The geared architecture <NUM> includes a carrier 448D that supports journal bearings 448E (one shown for illustrative purposes) that each carry a respective intermediate gear 448B.

Carrier 448D can be mechanically attached or otherwise fixedly secured to engine static structure <NUM>. Ring gear 448C can be mechanically attached to fan shaft <NUM>, which is mechanically attached to a flange 462B or another portion of the hub <NUM>. In other examples, the shaft <NUM> is directly attached to fan shaft <NUM>' (shown in dashed lines for illustrative purposes), and the geared architecture <NUM> is omitted. The hub <NUM> and fan shaft <NUM> can be mechanically attached with one or more fasteners. Rotation of the shaft <NUM> causes rotation of the hub <NUM> to rotate each airfoil <NUM>.

The engine <NUM> can include at least one bearing assembly <NUM> that supports an outer diameter of the fan shaft <NUM>. Each bearing assembly <NUM> can be mechanically attached and carried by a bearing support <NUM>, which is mechanically attached or otherwise secured to the engine static structure <NUM>.

In the illustrated example of <FIG>, the engine <NUM> includes two bearing assemblies <NUM>-<NUM>, <NUM>-<NUM> that support the fan shaft <NUM> at a location that is axially forward of the geared architecture <NUM> with respect to engine longitudinal axis A. Each bearing assembly <NUM> includes at least one bearing <NUM> and carrier <NUM> that support the fan shaft <NUM> at a position that is radially outward a portion of the geared architecture <NUM> such as the ring gear 448C with respect to the engine longitudinal axis A. Each bearing <NUM> can be a ball bearing, roller bearing or taper bearing, for example. In the illustrated example of <FIG>, at least a portion of the bearing assemblies <NUM>-<NUM>, <NUM>-<NUM> are positioned radially outward of the outer periphery 462C of the hub <NUM> with respect to the engine longitudinal axis A, with bearing assembly <NUM>-<NUM> being an axially forwardmost bearing assembly <NUM> relative to the engine longitudinal axis A. The bearing assemblies <NUM>-<NUM>, <NUM>-<NUM> can be radially aligned or outward of the annular channels 462D with respect to the engine longitudinal axis A.

The arrangement of the rotor assembly <NUM> can be utilized to increase a volume V radially inward of the hub <NUM> and/or fan shaft <NUM>, including positioning bearing assemblies <NUM> at a relatively further distance radially outward from the engine longitudinal axis A. The relatively greater volume V can serve to incorporate different types of bearings and support architectures for the hub <NUM>, for example. A radially outermost portion or tip 466T of airfoil section 466A defines first radius R1, and an outer diameter of the fan shaft <NUM> defines a second radius R2 adjacent to each respective one of the bearing assemblies <NUM>-<NUM>, <NUM>-<NUM> with respect to the engine longitudinal axis A. In some examples, a ratio of the first radius R1 to the second radius R2 is greater than or equal to <NUM>:<NUM>, or more narrowly greater than or equal to <NUM>:<NUM> or <NUM>:<NUM>.

<FIG> illustrate a rotor assembly <NUM> according to another example. Hub <NUM> includes an array of bumpers or retention members <NUM> extending outwardly from each one of the annular flanges 562B. The retention members <NUM> can be arranged in sets or rows such that each set of retention members <NUM> are substantially axially aligned with a respective reference plane RF and support an adjacent airfoil <NUM> (shown in <FIG>). The reference plane RF can correspond to an external surface contour or profile of the adjacent airfoil section 566A.

Referring to <FIG> with continued reference to <FIG>, each retention member <NUM> has a retention body 590A having a generally L-shaped geometry that extends between a first end portion 590B and a second end portion 590C that defines a contact surface 590D. The first end portion 590B is mechanically attached or otherwise secured to an outer diameter of the respective annular flange 562B (shown in dashed lines for illustrative purposes). The contact surface 590D can be contoured to mate with external surfaces of the airfoil section 566A.

Each contact surface 590D of the retention members <NUM> can be dimensioned to abut against a sheath <NUM> of an adjacent airfoil section 566A to support the airfoil <NUM> and transfer loads between the airfoil section 566A and the hub <NUM> during engine operation. For example, the contact surface 590D can be dimensioned to abut against the suction side S, or abut against the pressure side P as illustrated by retention member <NUM>' (shown in dashed lines for illustrative purposes). The airfoil section 566A can be pivotable about a respective one of the retention pins <NUM>. The airfoil section 566A can be moveable between first and second positions (indicated by airfoil section 566A' in dashed lines) such that contact surface 590D' is spaced apart from the airfoil section 566A to define a circumferential gap G in the first position, but abuts against the airfoil section 566A' in the second position.

Each platform <NUM> can be dimensioned to abut against respective pairs of airfoils <NUM> radially inward of the contact surface 590D of each retention member <NUM>. The contact surface 590D of each retention members <NUM> can be radially outward from retention pins <NUM> (shown in dashed lines for illustrated purposes) with respect to the longitudinal axis X. The combination of platforms <NUM> and retention members <NUM> can cooperate to provide relatively greater support to the airfoils <NUM> as compared to the platforms <NUM> alone, and can reduce a weight of the airfoils <NUM>.

Referring to <FIG>, with continued reference to <FIG> and <FIG>, each airfoil <NUM> can experience a load or force F, such as vibratory loads, an impact from a bird strike or another FOD event that may occur during engine operation. Force F may be applied or exerted on the pressure side P of the airfoil <NUM>, for example, causing or otherwise urging the airfoil <NUM> to pivot about or otherwise move relative to retention pin <NUM> and lean in a circumferential or thickness direction T, as illustrated by airfoil section 566A'' of airfoil <NUM>" (shown in dashed lines). Each retention member <NUM> limits or otherwise opposes circumferential movement of the airfoil section 566A of the adjacent airfoil <NUM>.

Each retention member <NUM> can have a construction such that the retention body 590A reacts, but deflects or yields to, load or force F on the respective airfoil <NUM> during engine operation. Each retention member <NUM> can establish a spring force to oppose loads on the airfoil <NUM>. One or more of the retention members <NUM> is moveable from a first position to second position (illustrated by <NUM>" in dashed lines) to react to the force F and oppose circumferential movement of the airfoil <NUM>. The retention member <NUM> can be constructed to yield to force F to at least partially absorb and transfer the force F from the airfoil section 566A to the hub <NUM>.

The retention body 590A of each retention member <NUM> can be made of a metallic material and can be integrally formed with a respective one of the flanges 562B. For example, each retention member <NUM> can be machined from an unfinished portion of the hub <NUM>, which can be a cast component. In other examples, the retention member <NUM> is a separate and distinct component that is mechanically attached or otherwise secured to the respective flange 562B. In some examples, each retention member <NUM> is a frangible structure that is constructed to yield but oppose the force F in response to the force F being below a predefined limit, but is constructed to shear or break in response to the force F exceeding a predefined limit. In the illustrative example of <FIG>, each retention member <NUM> can define one or more cutouts <NUM> in a thickness of the retention body 690A to weaken selective portions of the retention member <NUM>. The cutouts <NUM> can be apertures, grooves or indentations in the retention body 690A, for example. The quantity, size and/or profile of the cutouts <NUM> can be defined with respect to a predefined limit of an expected force or load on the respective airfoil. The cutouts <NUM> can be drilled or machined to cause the retention member <NUM> to bend or buckle in response to a force or load exceeding the predefined limit.

<FIG> illustrates an annular hub <NUM> for a rotor assembly according to an example. Flanges 762B of hub <NUM> includes a plurality of scallops 762F arranged in rows 762F-<NUM> to 762F-<NUM> about an outer periphery 762C of main body 762A. A perimeter of each scallop 762F can have a generally arcuate geometry that slopes toward valleys <NUM> defined between adjacent scallops 762F such that an outer perimeter <NUM> of each of the rows 762F-<NUM> to 762F-<NUM> has a generally sinusoidal profile about longitudinal axis X. Each scallop 762F defines at least one bore 762E for receiving a retention pin <NUM> (one shown in dashed lines for illustrative purposes) to secure an airfoil to the hub <NUM>. The arrangement of scallops 762F can lower stresses, which can reduce wear of the retention pins, and can also reduce installation complexity.

<FIG> and <FIG> illustrate an annular hub <NUM> for a rotor assembly <NUM> according to another example. The hub <NUM> can include hub portions <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> that are mechanically attached or otherwise secured to each other to define an assembly. Each of the hub portions <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> includes one or more flanges 862B to receive retention pins <NUM> (one shown in dashed lines in <FIG> for illustrative purposes). Each of the hub portions <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> includes one or more mounting flanges <NUM> that extend inwardly from a respective main body 862A. Composite reinforcement members <NUM> can be received in annular channels 862D defined by the hub portions <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM>. The hub portions <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> can be mechanically attached or otherwise secured to each other with one or more fasteners F received through bores defined in the mounting flanges <NUM>, for example.

<FIG> and <FIG> illustrates a rotor assembly <NUM> according to another example. <FIG> illustrates an isolated view of a segmented retention pin <NUM> of the rotor assembly <NUM>. Each retention pin <NUM> includes a plurality of segments 968A linked together by an elongated carrier 968B. Each of the segments 968A is separate and distinct and includes a main body 968AA and a pair of end portions 968AB that can taper from the main body 968AA to define a substantially cone-cylinder-cone geometry. An outer periphery of the main body 988AA defines an outer diameter DP (<FIG>). In some examples, the segments 968A are dimensioned such that the outer diameter DP of the segments 968A is progressively smaller along the retention pin <NUM>. Each segment 968A can be made of a metallic material, such as steel, for example. The carrier 968B can be a flexible wire, for example. The segments 968A can be slideably received onto and supported by the carrier 968A. Although five segments 968A are shown, fewer or more than five segments 968A can be utilized.

The carrier 968B defines a pin axis P. The pin axis P can be substantially straight or can be curved including one or more curved portions such that the pin axis P is not parallel to the longitudinal axis X when in an installed position, as illustrated by <FIG>. The profile of the pin axis P can be defined with respect to a contour of a respective airfoil <NUM>.

During assembly, each segment 968A is received in a respective bore 862E defined by a respective flange 962B of the hub <NUM> and a respective ligament <NUM> of an airfoil <NUM>, as illustrated by <FIG>. The bores 862E can be defined in the flanges 962B to establish a contour of the pin axis P.

The arrangement of the retention pin <NUM> including a curved profile of the pin axis P can be utilized to reduce stresses in the respective ligaments <NUM> and can reduce a distance between adjacent retention pins <NUM> that may otherwise overlap with the use of substantially straight profiles, which can reduce weight and can improve tuning and aerodynamic efficiency of the airfoils.

Claim 1:
A rotor assembly (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) for a gas turbine engine (<NUM>) comprising:
a rotatable hub (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) including a metallic main body (62A, 362A, 562A, 762A, 862A) extending along a longitudinal axis (X), and including an array of annular flanges (62B, 362B, 462B, 562B, 762B, 862B, 962B) extending about an outer periphery (62C, 362C 462C, 562C, 762C) of the main body (62A... 862A) to define an array of annular channels (62D, 362D, 462D, 562D, 762D, 862D) along the longitudinal axis (X); and
wherein each of the annular channels (62D... 862D) receives a composite reinforcement member (<NUM>, <NUM>, <NUM>, <NUM>) that extends about the outer periphery (62C...762C) of the hub (<NUM>...<NUM>).