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 generally to the formation of blades used in compressor rotors, turbine wheels, and bypass fans.

<CIT> relates to seals and in particular to seals interposed between the platforms of blades in a rotor.

<CIT> relates to seals for fan blades of a fan rotor for compressing air.

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

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

"Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (<NUM> °R)]<NUM> (where °R = K × <NUM>/<NUM>).

<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 preimpregnated 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> illustrates a rotor assembly <NUM> according to another example. The rotor assembly <NUM> includes an array of platforms <NUM> that are releasably secured to hub <NUM>. The platforms <NUM> are separate and distinct from the airfoils <NUM>. Each platform <NUM> includes one or more features that support the adjacent airfoils <NUM> to oppose circumferential or other relative movement during engine operation.

Referring to <FIG>, with continued reference to <FIG>, each platform <NUM> includes a platform body <NUM> that extends in a circumferential or thickness direction T between first and second sidewalls <NUM> to define an aerodynamic contour or gas path surface <NUM>. The platform body <NUM> includes at least one bracket or flange <NUM> that is mechanically attachable or otherwise secured to the platform body <NUM>. In other examples, each of the flanges <NUM> is integrally formed with the platform body <NUM>. The flanges <NUM> are mechanically attachable to respective flanges 362B (<FIG>) to mechanically attach or otherwise secure the platform <NUM> to the hub <NUM>. Each airfoil section 366A may be pivotable about a respective retention pin <NUM> in an installed position, which may cause the airfoil <NUM> to pivot or lean in the circumferential direction T, for example.

The platform <NUM> includes a plurality of resilient support members <NUM> that each extend from the platform body <NUM> and are dimensioned to abut against a sheath <NUM> of an adjacent airfoil <NUM> to oppose movement of the airfoil section 366A in the circumferential direction T, for example. Each of the support members <NUM> can be dimensioned to abut against the sheath <NUM> at a position that is radially outward of the retention pins <NUM>.

In the illustrated example of <FIG>, the support members <NUM> are arranged in opposed rows of support members <NUM>-<NUM>, <NUM>-<NUM>. The rows of support members <NUM>-<NUM>, <NUM>-<NUM> are dimensioned to provide a spring bias or force against the airfoils <NUM>, wedge the platform <NUM> between adjacent airfoils <NUM>, and oppose circumferential movement of the adjacent airfoils <NUM> relative to the longitudinal axis X.

Referring to <FIG>, with continued reference to <FIG>, each of the support members <NUM> can be a retention tab including a retention body having first and second portions 394A, 394B. The first portion 394A can extend in the circumferential direction T outwardly from the platform body <NUM>, and the second portion 388B can be flared or otherwise extend in a radial direction R from the first portion 394A and outwardly with respect to the platform body <NUM> to mate with a contour of the airfoil section 366A of the adjacent airfoil <NUM>. The platform body <NUM> can define a plurality of slots or cutouts <NUM> along the sidewalls <NUM> to define and space apart the support members <NUM>. The platform <NUM> can be made of a metallic material such as aluminum or sheet metal, or can be made of a composite material. The support members <NUM> can be integrally formed with the platform body <NUM> such that the support members <NUM> are resilient and ductile or otherwise flexible. In other examples, the support members <NUM> are mechanically attached to the platform body <NUM> utilizing various techniques such as by bonding, welding, or riveting.

The platform <NUM> supports adjacent airfoils <NUM> against gas loads during engine operation. The support members <NUM> are constructed to be relatively strong and ductile to support the adjacent airfoils <NUM> during normal operation and to transfer loads in a manner that reduces a likelihood of permanent deformation, liberation or other degradation of the platforms <NUM> and airfoils <NUM>. For example, the retention pins <NUM> can reduce a bending stiffness of the airfoils <NUM> due the ability of the airfoils <NUM> to pivot about the retention pins <NUM>. The support members <NUM> can be constructed to have different stiffnesses utilizing the techniques disclosed herein, including being relatively stiff and elastic for a flutter mode, but yielding during relatively more severe bending or leaning of the airfoil <NUM>.

Referring to <FIG>, with continued reference to <FIG>, the airfoil section 366A of each airfoil <NUM> may be subject to an internal and/or external load or force F, such as flutter, vibratory or centrifugal loads, or impacts caused by bird strikes or other FOD events. The force F may cause or urge the airfoil to lean or pivot about a respective one of the retention pins <NUM> (<FIG>). The platforms <NUM> including support members <NUM> serve to support and hold the adjacent airfoils <NUM> in a predefined aerodynamic position to increase aerodynamic performance and support the airfoils <NUM> during impact events.

Each one of the support members <NUM> can be dimensioned to oppose circumferential movement of the adjacent airfoil <NUM> in response to the force or load F on the airfoil <NUM> being below a predefined limit, but can be dimensioned to deflect or yield in response to the load or force F exceeding the predefined limit as illustrated by support member <NUM>' and airfoil <NUM>' (shown in dashed lines for illustrative purposes). Yielding of the support members <NUM> reduces a likelihood that the platform <NUM> will liberate or otherwise degrade due to high energy impacts such as bird strikes. The first and second portions 394A, 394B of each support member <NUM> can be dimensioned to have an L-shaped geometry that reacts the load or force F on a respective one of the airfoils <NUM> in operation. The support members <NUM> serve to cushion the airfoils <NUM> from the force F, which can improve durability and propulsive efficiency of the airfoils <NUM>.

Referring to <FIG>, the rotor assembly <NUM> can be installed as follows. Flanges <NUM> are mounted or otherwise secured to the platform body <NUM>, as illustrated by <FIG>. Thereafter, the platform <NUM> can be moved in direction D1 to wedge the platform <NUM> between adjacent platforms <NUM>, as illustrated by <FIG>. Thereafter, one or more fasteners <NUM>, such as elongated bolts or pins, can be moved in direction D2 to secure the flanges <NUM> to respective annular flanges 362B of the hub <NUM>. The fasteners <NUM> are illustrated in an installed position in <FIG>.

<FIG> illustrate a platform <NUM> for a rotor assembly according to another example. The platform <NUM> includes an elongated flange <NUM> mechanically attached or otherwise secured to platform body <NUM>. A plurality of support members <NUM> extend outwardly from the platform body <NUM> to abut against and support adjacent airfoils. The flange <NUM> extends along a length of platform body <NUM>. The flange <NUM> can have a hollow interior <NUM> that extends between opposed ends of the flange <NUM>. The flange <NUM> defines one or more slots <NUM> (<FIG>) to receive a respective flange of the hub (see, e.g., flanges 362B of <FIG>). A cross-section of the flange <NUM> can have a generally trapezoidal geometry, as illustrated by <FIG>, or another geometry such as a triangular or rectangular profile. The flange <NUM> defines apertures for receiving fasteners <NUM> to mechanically attach the platform <NUM> to a hub, such as hub <NUM> of <FIG>.

Claim 1:
A rotor assembly (<NUM>, <NUM>) for a gas turbine engine (<NUM>) comprising:
a rotatable hub (<NUM>, <NUM>) including a main body (62A) extending along a longitudinal axis (X), and including an array of annular flanges (62B, 362B) extending about an outer periphery (62C) of the main body (62A) to define an array of annular channels (62D) along the longitudinal axis (X);
an array of airfoils (<NUM>, <NUM>, <NUM>, <NUM>) circumferentially distributed about the outer periphery (62C), each one of the airfoils (<NUM>, <NUM>, <NUM>, <NUM>) including an airfoil section (66A, 166A, 266A, 366A) extending from a root section (66B, 266B, 366B) received in the annular channels (62D), the airfoil section (66A, 166A, 266A, 366A) extending between a leading edge (LE) and a trailing edge (TE) in a chordwise direction (C) and extending between a tip portion (66C, 266C) and the root section (66B, 266B, 366B) in a radial direction (R), and the airfoil section (66A, 166A, 266A, 366A) defining a pressure side (P) and a suction side (S) separated in a thickness direction (T); and
an array of platforms (<NUM>, <NUM>) releasably secured to the hub (<NUM>, <NUM>), wherein each of the platforms (<NUM>, <NUM>) includes a platform body (<NUM>, <NUM>), and the platform body (<NUM>, <NUM>) is mechanically attached to the hub (<NUM>, <NUM>),
characterised in that:
each of the platforms (<NUM>; <NUM>) includes opposed rows of resilient support members (<NUM>, <NUM>) that abut against adjacent airfoils (<NUM>, <NUM>, <NUM>, <NUM>) of the array of airfoils (<NUM>, <NUM>, <NUM>, <NUM>) to oppose movement of the respective airfoil section (66A, 166A, 266A, 366A) in the circumferential direction (C); and
the airfoil section (66A, 166A, 266A, 366A) includes a metallic sheath (<NUM>, <NUM>, <NUM>, <NUM>) that receives a composite core (<NUM>, <NUM>, <NUM>), and the core (<NUM>, <NUM>, <NUM>) includes first and second ligaments (76A, 76B) received in respective internal channels (72C, 72D, 172C, 172D) defined by the sheath (<NUM>, <NUM>, <NUM>, <NUM>) such that the first and second ligaments (76A, 76B) are spaced apart along the root section (66B, 266B, 366B) with respect to the longitudinal axis (X).