Rotor assembly with structural platforms for gas turbine engines

A platform for a gas turbine engine according to an example of the present disclosure includes, among other things, a platform body that extends in a circumferential direction between first and second sidewalls to define a gas path surface, and opposed rows of flexible retention tabs that extend from the platform body and are dimensioned to wedge the platform between adjacent airfoils.

BACKGROUND

This disclosure relates to a gas turbine engine, and more particularly to a rotor assembly including a hub that carries an array of airfoils.

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.

SUMMARY

A platform for a gas turbine engine according to an example of the present disclosure includes a platform body that extends in a circumferential direction between first and second sidewalls to define a gas path surface, and opposed rows of flexible retention tabs that extend from the platform body and are dimensioned to wedge the platform between adjacent airfoils.

In a further embodiment of any of the foregoing embodiments, the platform body defines a plurality of slots that space apart the retention tabs.

In a further embodiment of any of the foregoing embodiments, each of the retention tabs includes a first portion that extends in the circumferential direction and a second portion that extends in a radial direction from the first portion to mate with a contour of a respective one of the adjacent airfoils.

In a further embodiment of any of the foregoing embodiments, each of the retention tabs is integrally formed with the platform body, and the platform body is made of a metallic material.

In a further embodiment of any of the foregoing embodiments, the platform body includes at least one flange attachable to a rotatable hub.

A rotor assembly for a gas turbine engine according to an example of the present disclosure includes a rotatable hub that has a main body that extends along a longitudinal axis, and that has an array of annular flanges that extend about an outer periphery of the main body to define an array of annular channels along the longitudinal axis. An array of airfoils are circumferentially distributed about the outer periphery. Each one of the airfoils has an airfoil section that extends from a root section received in the annular channels. The airfoil section extends between a leading edge and a trailing edge in a chordwise direction and extends between a tip portion and the root section in a radial direction, and the airfoil section defines a pressure side and a suction side separated in a thickness direction. An array of platforms are releasably secured to the hub. Each of the platforms includes a platform body and opposed rows of resilient support members that abut against adjacent airfoils of the array of airfoils to oppose movement of the respective airfoil section in the circumferential direction.

A further embodiment of any of the foregoing embodiments includes a plurality of retention pins each extending through the root section of a respective one of the airfoils and through each of the annular flanges to mechanically attach the root section to the hub.

In a further embodiment of any of the foregoing embodiments, the airfoil section is pivotable about a respective one of the retention pins in an installed position.

In a further embodiment of any of the foregoing embodiments, the platform body is mechanically attached to the hub. The airfoil section includes a metallic sheath that receives a composite core, and the core includes first and second ligaments received in respective internal channels defined by the sheath such that the first and second ligaments are spaced apart along the root section with respect to the longitudinal axis.

In a further embodiment of any of the foregoing embodiments, each of the support members is a retention tab that abuts against the sheath of a respective one of the adjacent airfoils.

In a further embodiment of any of the foregoing embodiments, the retention tab opposes circumferential movement of the respective one of the adjacent airfoils in response to a load on the respective one of the adjacent airfoils being below a predefined limit, but deflects in response to the load exceeding the predefined limit.

A further embodiment of any of the foregoing embodiments includes a plurality of retention pins each extending through the root section of a respective one of the airfoils and through each of the annular flanges to mechanically attach the root section to the hub, and wherein the airfoil section is pivotable about a respective one of the retention pins in an installed position.

In a further embodiment of any of the foregoing embodiments, the retention tab abuts against the sheath of the respective one of the adjacent airfoils at a position radially outward of the retention pins.

In a further embodiment of any of the foregoing embodiments, the first and second ligaments define a set of bores aligned to receive a common one of the retention pins.

In a further embodiment of any of the foregoing embodiments, the opposed rows of support members extend outwardly from the platform body and are dimensioned to wedge the platform between the adjacent airfoils.

In a further embodiment of any of the foregoing embodiments, each of the support members is a retention tab that abuts against the sheath of a respective one of the adjacent airfoils. The retention tab includes a retention body that has an L-shaped geometry that reacts a load on a respective one of the adjacent airfoils in operation, and the retention body is integrally formed with the platform body.

A gas turbine engine according to an example of the present disclosure includes a fan section that has a fan shaft rotatable about an engine longitudinal axis. The fan section has a rotor assembly. The rotor assembly includes a rotatable hub that has a main body mechanically attached to the fan shaft, and has an array of annular flanges that extend about an outer periphery of the main body to define an array of annular channels along the engine longitudinal axis, An array of airfoils are circumferentially distributed about the outer periphery. Each one of the airfoils includes an airfoil section that extend from a root section received in the annular channels. An array of platforms are releasably secured to the hub. Each of the platforms includes a platform body and opposed rows of flexible support members that extend from the platform body and are dimensioned to wedge the platform between adjacent airfoils and oppose circumferential movement of the adjacent airfoils relative to the engine longitudinal axis.

In a further embodiment of any of the foregoing embodiments, the airfoil section includes a metallic sheath and a composite core. The core includes first and second ligaments at least partially received in respective internal channels defined in the sheath.

A further embodiment of any of the foregoing embodiments includes a plurality of retention pins, each of the retention pins extending through the root section of a respective one of the airfoils, across the annular channels, and through the annular flanges to mechanically attach the root section to the hub.

In a further embodiment of any of the foregoing embodiments, the airfoil section is pivotable about a respective one of the retention pins in an installed position. Each of the support members is an L-shaped retention tab integrally formed with the platform body. The platform body is made of a metallic material, and the retention tab opposes circumferential movement of the respective one of the adjacent airfoils in response to a load on the respective one of the adjacent airfoils being below a predefined limit, but deflects in response to the load exceeding the predefined limit.

DETAILED DESCRIPTION

FIG. 2illustrates a rotor assembly60for a gas turbine engine according to an example. The rotor assembly60can be incorporated into the fan section12or the compressor section24of the engine20ofFIG. 1, for example. However, it should to be understood that other parts of the gas turbine engine20and other systems may benefit from the teachings disclosed herein. In some examples, the rotor assembly60is incorporated into a multi-stage fan section of a direct drive or geared engine architecture.

The rotor assembly60includes a rotatable hub62mechanically attached or otherwise mounted to a fan shaft64. The fan shaft64is rotatable about longitudinal axis X. The fan shaft64can be rotatably coupled to the low pressure turbine46(FIG. 1), for example. The rotatable hub62includes a main body62A that extends along the longitudinal axis X. The longitudinal axis X can be parallel to or collinearly with the engine longitudinal axis A ofFIG. 1, for example. As illustrated byFIG. 3, the hub62includes an array of annular flanges62B that extend about an outer periphery62C of the main body62A. The annular flanges62B define an array of annular channels62D along the longitudinal axis X.

An array of airfoils66are circumferentially distributed about the outer periphery62C of the rotatable hub62. Referring toFIG. 3, with continued reference toFIG. 2, one of the airfoils66mounted to the hub62is shown for illustrative purposes. The airfoil66includes an airfoil section66A extending from a root section66B. The airfoil section66A 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 section66B and a tip portion66C to provide an aerodynamic surface. The tip portion66C defines a terminal end or radially outermost extent of the airfoil66to establish a clearance gap with fan case15(FIG. 1). The airfoil section66A defines a pressure side P (FIG. 2) and a suction side S separated in a thickness direction T. The root section66B is dimensioned to be received in each of the annular channels62D.

The rotor assembly60includes an array of platforms70that are separate and distinct from the airfoils66. The platforms70are situated between and abut against adjacent pairs of airfoils66to define an inner boundary of a gas path along the rotor assembly60, as illustrated inFIG. 2. The platforms70can be mechanically attached and releasably secured to the hub62with one or more fasteners, for example.FIG. 4illustrates one of the platforms70abutting against the airfoil section66A of adjacent airfoils66.

FIG. 5Aillustrates an exploded, cutaway view of portions of the rotor assembly60.FIG. 5Billustrates a side view of one of the airfoils66secured to the hub62. The rotor assembly60includes a plurality of retention pins68for securing the airfoils66to the hub62(seeFIG. 2). Each of the platforms70can abut the adjacent airfoils66at a position radially outward of the retention pins68, as illustrated byFIG. 2.

Each of the retention pins68is dimensioned to extend through the root section66B of a respective one of the airfoils66and to extend through each of the flanges62B to mechanically attach the root section66B of the respective airfoil66to the hub62, as illustrated byFIGS. 3 and 5B. The retention pins68react to centrifugal loads in response to rotation of the airfoils66. The hub62can include at least three annular flanges62B, such five flanges62B as shown, and are axially spaced apart relative to the longitudinal axis X to support a length of each of the retention pins68. However, fewer or more than five flanges62B can be utilized with the teachings herein. Utilizing three or more flanges62B can provide relatively greater surface contact area and support along a length each retention pin68, which can reduce bending and improve durability of the retention pin68.

The airfoil66can be a hybrid airfoil including metallic and composite portions. Referring toFIGS. 6-8, with continuing reference toFIGS. 5A-5B, the airfoil66includes a metallic sheath72that at least partially receives and protects a composite core74. In some examples, substantially all of the aerodynamic surfaces of the airfoil66are defined by the sheath72. The sheath72can be dimensioned to terminate radially inward prior to the root section66B such that the sheath72is spaced apart from the respective retention pin(s)68, as illustrated byFIG. 5B. The sheath72includes a first skin72A and a second skin72B. The first and second skins72A,72B are joined together to define an external surface contour of the airfoil66including the pressure and suction sides P, S of the airfoil section66A.

The core74includes one or more ligaments76that define portions of the airfoil and root sections66A,66B. The ligament76can define radially outermost extent or tip of the tip portion66C, as illustrated byFIG. 6. In other examples, the ligaments76terminate prior to the tip of the airfoil section66A. In the illustrative example ofFIGS. 6-8, the core74includes two separate and distinct ligaments76A,76B spaced apart from each other as illustrated inFIGS. 5B and 6. The core74can include fewer or more than two ligaments76, such as three to ten ligaments76. The ligaments76A,76B extend outwardly from the root section66B towards the tip portion66C of the airfoil section66A, as illustrated byFIGS. 3, 6 and 8.

The sheath72defines one or more internal channels72C,72C to receive the core74. In the illustrated example ofFIGS. 6-8, the sheath72includes at least one rib73defined by the first skin72A that extends in the radial direction R to bound the adjacent channels72C,72D. The ligaments76A,76B are received in respective internal channels72C,72D such that the skins72A,72B at least partially surround the core74and sandwich the ligaments76A,76B therebetween, as illustrated byFIG. 6. The ligaments76A,76B receive the common retention pin68such that the common retention pin68is slideably received through at least three, or each, of annular flanges62B. The common retention pin68is dimensioned to extend through each and every one of the interface portions78of the respective airfoil66to mechanically attach or otherwise secure the airfoil66to the hub62.

Referring toFIGS. 9-10, with continued reference toFIGS. 5A-5B and 6-8, each of one of the ligaments76includes at least one interface portion78in the root section66B.FIG. 9illustrates ligament76with the first and second skin72A,72B removed.FIG. 10illustrates the core74and skins72A,72B in an assembled position, with the interface portion78defining portions of the root section66B. The interface portion78includes a wrapping mandrel79and a bushing81mechanically attached to the mandrel79with an adhesive, for example. The bushing81is dimensioned to slideably receive one of the retention pins68(FIG. 5B). The mandrel79tapers from the bushing81to define a teardrop profile, as illustrated byFIG. 11.

In the illustrative example ofFIGS. 5B and 8, each of the ligaments76defines at least one slot77in the root section66B to define first and second root portions83A,83B received in the annular channels62D on opposed sides of the respective flange62B such that the root portions83A,83B are interdigitated with the flanges62B. The slots77can decrease bending of the retention pins68by decreasing a distance between adjacent flanges62B and increase contact area and support along a length of the retention pin68, which can reduce contact stresses and wear.

Each ligament76can include a plurality of interface portions78(indicated as78A,78B) received in root portions83A,83B, respectively. The interface portions78A,78B of each ligament76A,76B receive a common retention pin68to mechanically attach or otherwise secure the ligaments76A,76B to the hub62. The root section66B defines at least one bore85as dimension receive a retention pin68. In the illustrated example ofFIG. 5B, each bore85is defined by a respective bushing81.

Various materials can be utilized for the sheath72and composite core74. In some examples, the first and second skins72A,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 core74comprises carbon or carbon fibers, such as a ceramic matrix composite (CMC). In examples, the sheath72defines a first weight, the composite core74defines a second weight, and a ratio of the first weight to the second weight is at least 1:1 such that at least 50% of the weight of the airfoil66is 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 airfoils66can reduce an overall weight of the rotor assembly60.

In the illustrative example ofFIGS. 9 and 10, each of the ligaments76includes at least one composite layer80. Each composite layer80can be fabricated to loop around the interface portion78and retention pin68(when in an installed position) such that opposed end portions80A,80B of the respective layer80are joined together along the airfoil portion66A. The composite layers80can be dimensioned to define a substantially solid core74, such that substantially all of a volume of the internal cavities72C,72D of the sheath72are occupied by a composite material comprising carbon. In the illustrated example ofFIGS. 9 and 10, the composite layers80include a first composite layer80C and a second composite layer80D between the first layer80C and an outer periphery of the interface portion78. The composite layers80C and80D can be fabricated to each loop around the interface portion78and the retention pin68.

The layers80can include various fiber constructions to define the core74. For example, the first layer80C can define a first fiber construction, and the second layer80D 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 layer80-1ofFIG. 14A, 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 layers80, including any of the layers80-2to80-5ofFIGS. 14B-14E.FIG. 14Billustrates a layer80-2defined by a plurality of braided yarns.FIG. 14Cillustrates a layer80-3defined by a two-dimensional woven fabric.FIG. 14Dillustrates a layer80-4defined by a non-crimp fabric.FIG. 14Eillustrates a layer80-5defined by a tri-axial braided fabric. Other example fiber constructions include biaxial braids and plain or satin weaves.

The rotor assembly60can be constructed and assembled as follows. The ligaments76A,76B of core74are situated in the respective internal channels72C,72D defined by the sheath72such that the ligaments76A,76B are spaced apart along the root section66B by one of the annular flanges62B and abut against opposed sides of rib73, as illustrated byFIGS. 5B, 6 and 13.

In some examples, the ligaments76A,76B are directly bonded or otherwise mechanically attached to the surfaces of the internal channels72C,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 ligaments76are moveable relative to surfaces of the internal channels72C,72D to provide damping during engine operation. In the illustrated example ofFIGS. 9-10 and 12-13, the core74includes a plurality of stand-offs or detents82that are distributed along surfaces of the ligaments76. The detents82are dimensioned and arranged to space apart the ligaments76from adjacent surfaces of the internal channels72C,72D. Example geometries of the detents82can include conical, hemispherical, pyramidal and complex geometries. The detents82can be uniformly or non-uniformly distributed. The detents82can 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 ligaments76, for example.

The second skin72B is placed against the first skin72A to define an external surface contour of the airfoil66, as illustrated byFIGS. 6 and 13. The skins72A,72B can be welded, brazed, riveted or otherwise mechanically attached to each other, and form a “closed loop” around the ligaments76.

The detents82can define relatively large bondline gaps between the ligaments76and the surfaces of the internal channels72C,72D, and a relatively flexible, weaker adhesive can be utilized to attach the sheath72to the ligaments76. The relatively large bondline gaps established by the detents82can improve flow of resin or adhesive such as polyurethane and reducing formation of dry areas. In examples, the detents82are dimensioned to establish bondline gap of at least a 0.020 inches, or more narrowly between 0.020 and 0.120 inches. The relatively large bondline gap can accommodate manufacturing tolerances between the sheath72and core74, 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 detents82can also protect the composite from thermal degradation during welding or brazing of the skins72A,72B to each other.

For example, a resin or adhesive such as polyurethane can be injected into gaps or spaces established by the detents82between the ligaments76and the surfaces of the internal channels72C,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 sheath72and composite core74, provide structural damping, isolate the delicate inner fibers of the composite core74from relatively extreme welding temperatures during attachment of the second skin72B to the first skin72A, and enables the ductile sheath72to 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 core74.

The composite layers80can 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 layers80can be pre-formed or pre-impregnated with resin prior to placement in the internal channels72C,72D. The composite core74is cured in an oven, autoclave or by other conventional methods, with the ligaments76bonded to the sheath72, as illustrated byFIGS. 10 and 13.

The airfoils66are moved in a direction D1(FIGS. 5A-5B) toward the outer periphery62C of the hub62. A respective retention pin68is slideably received through each bushing81of the interface portions78and each of the flanges62B to mechanically attach the ligaments76to the flanges62B. The platforms70are then moved into abutment against respective pairs of airfoils66at a position radially outward of the flanges62B to limit circumferential movement of the airfoil sections66A, as illustrated byFIG. 2.

Mechanically attaching the airfoils66with retention pins68can allow the airfoil66to flex and twist, which can reduce a likelihood of damage caused by FOD impacts by allowing the airfoil66to bend away from the impacts. The rotor assembly60also enables relatively thinner airfoils which can improve aerodynamic efficiency.

FIGS. 15-16illustrate an airfoil166according 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 skin172A of sheath172defines internal channels172C,172D. The internal channels172C,172D are adjacent to each other and are bounded by a pair of opposing ribs173. The ribs173can extend in a radial direction R, for example, and are spaced apart along an internal gap172F that interconnects the internal cavities172C,172D. The internal gap172F can be spaced apart from the radial innermost and outermost ends of the first skin172A of the sheath172. Composite core174includes a ligament bridge184that interconnects an adjacent pair of ligaments176at a location radially outward of a common pin168(shown in dashed lines inFIG. 15for illustrative purposes). The ligament bridge184can be made of any of the materials disclosed herein, such as a composite material.

The ligament bridge184is dimensioned to be received within the gap172F. The ligament bridge184interconnects the adjacent pair of ligaments176in a position along the airfoil section166A when in the installed position. During operation, the core174may move in a direction D2(FIG. 16) relative to the sheath172, which can correspond to the radial direction R, for example. The ligament bridge184is dimensioned to abut against the opposing ribs173of the sheath172in response to movement in direction D2to react blade pull and bound radial movement of the core174relative to the sheath172. The ligament bridge184serves as a fail-safe by trapping the ligaments176to reduce a likelihood of liberation of the ligaments176which may otherwise occur due to failure of the bond between the sheath172and ligaments176.

FIGS. 17 and 18illustrate an airfoil266according to yet another example. Airfoil266includes at least one shroud286that extends outwardly from pressure and suction sides P, S of airfoil section266A at a position radially outward of platforms270(shown in dashed lines inFIG. 17for illustrative purposes). The shroud286defines an external surface contour and can be utilized to tune mode(s) of the airfoil266by changing boundary constraints. The shroud286can 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 airfoil266can include a second shroud286′ (shown in dashed lines) to provide a dual shroud architecture, with shroud286arranged to divide airfoil between bypass and core flow paths B, C (FIG. 1) and shroud286′ for reducing a flutter condition of the airfoil266, for example.

The shroud286includes first and second shroud portions286A,286B secured to the opposing pressure and suction sides P, S. The shroud portions286A,286B can be joined together with one or more inserts fasteners F that extend through the airfoil section266A. The fasteners F can be baked into the ligaments276, for example, and can be frangible to release in response to a load on either of the shroud portions286A,286B exceeding a predefined threshold. It should be appreciated that other techniques can be utilized to mechanically attach or otherwise secure the shroud portions286A,286B to the airfoil266, such as by an adhesive, welding or integrally forming the skins272A,272B with the respective shroud portions286A,286B. In some examples, the airfoil266includes only one of the shroud portions286A,286B such that the shroud286is on only one side of the airfoil section266A or is otherwise unsymmetrical.

FIG. 19illustrates a rotor assembly360according to another example. The rotor assembly360includes an array of platforms370that are releasably secured to hub362. The platforms370are separate and distinct from the airfoils366. Each platform370includes one or more features that support the adjacent airfoils366to oppose circumferential or other relative movement during engine operation.

Referring toFIG. 20, with continued reference toFIG. 19, each platform370includes a platform body388that extends in a circumferential or thickness direction T between first and second sidewalls390to define an aerodynamic contour or gas path surface391. The platform body388includes at least one bracket or flange392that is mechanically attachable or otherwise secured to the platform body388. In other examples, each of the flanges392is integrally formed with the platform body388. The flanges392are mechanically attachable to respective flanges362B (FIG. 21) to mechanically attach or otherwise secure the platform370to the hub362. Each airfoil section366A may be pivotable about a respective retention pin368in an installed position, which may cause the airfoil366to pivot or lean in the circumferential direction T, for example.

The platform370includes a plurality of resilient support members394that each extend from the platform body388and are dimensioned to abut against a sheath372of an adjacent airfoil366to oppose movement of the airfoil section366A in the circumferential direction T, for example. Each of the support members394can be dimensioned to abut against the sheath372at a position that is radially outward of the retention pins368.

In the illustrated example ofFIG. 20, the support members394are arranged in opposed rows of support members394-1,394-2. The rows of support members394-1,394-2are dimensioned to provide a spring bias or force against the airfoils366, wedge the platform370between adjacent airfoils366, and oppose circumferential movement of the adjacent airfoils366relative to the longitudinal axis X.

Referring toFIGS. 21 and 22, with continued reference toFIGS. 19 and 20, each of the support members394can be a retention tab including a retention body having first and second portions394A,394B. The first portion394A can extend in the circumferential direction T outwardly from the platform body388, and the second portion388B can be flared or otherwise extend in a radial direction R from the first portion394A and outwardly with respect to the platform body388to mate with a contour of the airfoil section366A of the adjacent airfoil366. The platform body388can define a plurality of slots or cutouts396along the sidewalls390to define and space apart the support members394. The platform370can be made of a metallic material such as aluminum or sheet metal, or can be made of a composite material. The support members394can be integrally formed with the platform body388such that the support members394are resilient and ductile or otherwise flexible. In other examples, the support members394are mechanically attached to the platform body388utilizing various techniques such as by bonding, welding, or riveting.

The platform370supports adjacent airfoils366against gas loads during engine operation. The support members394are constructed to be relatively strong and ductile to support the adjacent airfoils366during normal operation and to transfer loads in a manner that reduces a likelihood of permanent deformation, liberation or other degradation of the platforms370and airfoils366. For example, the retention pins368can reduce a bending stiffness of the airfoils366due the ability of the airfoils366to pivot about the retention pins368. The support members394can 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 airfoil366.

Referring toFIG. 23, with continued reference toFIGS. 21 and 22, the airfoil section366A of each airfoil366may 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 pins368(FIGS. 20-22). The platforms370including support members394serve to support and hold the adjacent airfoils366in a predefined aerodynamic position to increase aerodynamic performance and support the airfoils366during impact events.

Each one of the support members394can be dimensioned to oppose circumferential movement of the adjacent airfoil366in response to the force or load F on the airfoil366being 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 member394′ and airfoil366′ (shown in dashed lines for illustrative purposes). Yielding of the support members394reduces a likelihood that the platform370will liberate or otherwise degrade due to high energy impacts such as bird strikes. The first and second portions394A,394B of each support member394can be dimensioned to have an L-shaped geometry that reacts the load or force F on a respective one of the airfoils366in operation. The support members394serve to cushion the airfoils366from the force F, which can improve durability and propulsive efficiency of the airfoils366.

Referring toFIGS. 24 and 25, the rotor assembly360can be installed as follows. Flanges392are mounted or otherwise secured to the platform body388, as illustrated byFIG. 24. Thereafter, the platform370can be moved in direction D1to wedge the platform370between adjacent platforms366, as illustrated byFIG. 21. Thereafter, one or more fasteners398, such as elongated bolts or pins, can be moved in direction D2to secure the flanges392to respective annular flanges362B of the hub362. The fasteners398are illustrated in an installed position inFIGS. 21 and 22.

FIGS. 26 and 27illustrate a platform470for a rotor assembly according to another example. The platform470includes an elongated flange492mechanically attached or otherwise secured to platform body488. A plurality of support members494extend outwardly from the platform body488to abut against and support adjacent airfoils. The flange492extends along a length of platform body388. The flange492can have a hollow interior493that extends between opposed ends of the flange492. The flange492defines one or more slots495(FIG. 26to receive a respective flange of the hub (see, e.g., flanges362B ofFIG. 25). A cross-section of the flange492can have a generally trapezoidal geometry, as illustrated byFIG. 27, or another geometry such as a triangular or rectangular profile. The flange492defines apertures for receiving fasteners498to mechanically attach the platform470to a hub, such as hub362ofFIG. 25.