Patent Description:
Airfoils in the turbine section are typically formed of a superalloy and may include thermal barrier coatings to extend temperature capability and lifetime. Ceramic matrix composite ("CMC") materials are also being considered for airfoils. Among other attractive properties, CMCs have high temperature resistance. Despite this attribute, however, there are unique challenges to implementing CMCs in airfoils.

<CIT> discloses a prior art vane arc segment according to the preamble of claim <NUM>.

<CIT> discloses a prior art turbine frame having a spindle mounted liner.

According to a first aspect of the present invention, there is provided a vane arc segment as set forth in claim <NUM>.

In a further embodiment of any of the foregoing embodiments, the clevis mount includes first and second prongs that have respective pin holes that are coaxially aligned with each other, and the pin is disposed in the pin hole.

In a further embodiment of any of the foregoing embodiments, the airfoil fairing is ceramic.

In a further embodiment of any of the foregoing embodiments, the spar leg includes forward and aft sides, and the pin is offset toward either the forward side or the aft side.

In a further embodiment of any of the foregoing embodiments, the stop is radially and axially offset from the pin.

In a further embodiment of any of the foregoing embodiments, the stop includes a protruding lip.

In a further embodiment of any of the foregoing embodiments, the protruding lip defines a bearing surface that contacts the ledge. The bearing surface and the ledge having an arced geometry.

According to a further aspect of the present invention, there is provided a gas turbine engine as set forth in claim <NUM>.

"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 T°R = TK x <NUM>/<NUM>).

<FIG> illustrates a line representation of an example of a vane arc segment <NUM> from the turbine section <NUM> of the engine <NUM> (see also <FIG>). It is to be understood that although the examples herein are discussed in context of a vane from the turbine section, the examples can be applied to other vanes that have support spars.

The vane arc segment <NUM> includes an airfoil fairing <NUM> that is formed by an airfoil wall <NUM>. The airfoil fairing <NUM> is comprised of an airfoil section <NUM> and first and second platforms <NUM>/<NUM> between which the airfoil section <NUM> extends. The airfoil section <NUM> generally extends in a radial direction relative to the central engine axis A. The terms such as "inner" and "outer" refer to location with respect to the central engine axis A, i.e., radially inner or radially outer.

The airfoil wall <NUM> is continuous in that the platforms <NUM>/<NUM> and airfoil section <NUM> constitute a one-piece body. As an example, the airfoil wall <NUM> is formed of a ceramic material, an organic matrix composite (OMC), or a metal matrix composite (MMC). For instance, the ceramic material is a monolithic ceramic or a ceramic matrix composite (CMC) that is formed of ceramic fibers that are disposed in a ceramic matrix. The monolithic ceramic may be, but is not limited to, SiC or other silicon-containing ceramic. The ceramic matrix composite may be, but is not limited to, a SiC/SiC ceramic matrix composite in which SiC fibers are disposed within a SiC matrix. Example organic matrix composites include, but are not limited to, glass fiber, carbon fiber, and/or aramid fibers disposed in a polymer matrix, such as epoxy. Example metal matrix composites include, but are not limited to, boron carbide fibers and/or alumina fibers disposed in a metal matrix, such as aluminum. The fibers may be provided in fiber plies, which may be woven or unidirectional and may collectively include plies of different fiber weave configurations.

The airfoil section <NUM> circumscribes an interior through-cavity <NUM>. The airfoil section <NUM> may have a single through-cavity <NUM>, or the cavity <NUM> may be divided by one or more ribs. The vane arc segment <NUM> further includes a spar <NUM> that extends through the through-cavity <NUM> and mechanically supports the airfoil fairing <NUM>. The spar <NUM> includes a spar platform 72a and a spar leg 72b that extends from the spar platform 72a into the through-cavity <NUM>. Although not shown, the spar platform 72a includes attachment features that secure it to a fixed support structure, such as an engine case. The spar leg 72b defines an interior through-passage 72c.

The spar leg 72b has a distal end portion <NUM> that has a clevis mount <NUM>. The end portion <NUM> of the spar leg 72b extends past the platform <NUM> of the airfoil fairing <NUM> so as to protrude from the fairing <NUM>. There is a support platform <NUM> adjacent the platform <NUM> of the airfoil fairing. Although not shown, the support platform <NUM>, the platform <NUM> of the airfoil fairing <NUM>, or both may have flanges or other mounting features through which the support platform <NUM> interfaces with the platform <NUM>.

The support platform <NUM> includes a through-hole <NUM> through which the end portion <NUM> of the spar leg 72b extends such that at least a portion of the clevis mount <NUM> protrudes from the support platform <NUM>. A pin <NUM> extends though the clevis mount <NUM>. The pin <NUM> is wider than the through-hole <NUM>. The ends of the pin <NUM> thus abut the face of the support platform <NUM> and thereby prevent the spar leg 72b from being retracted in the through-hole <NUM>. The pin <NUM> thus locks the support platform <NUM> to the spar leg 72b such that the airfoil fairing <NUM> is mechanically trapped between the spar platform 72a and the support platform <NUM>. It is to be appreciated that the example configuration could be used at the outer end of the airfoil fairing <NUM>, with the spar <NUM> being inverted such that the spar platform 72a is adjacent the platform <NUM> and the support platform <NUM> is adjacent the platform <NUM>. The spar <NUM> may be formed of a relatively high temperature resistance, high strength material, such as a single crystal metal alloy (e.g., a single crystal nickel- or cobalt-alloy).

Cooling air, such as bleed air from the compressor section <NUM>, is conveyed into and through the through-passage 72c of the spar <NUM>. This cooling air is destined for a downstream cooling location, such as a tangential onboard injector (TOBI). Cooling air may also be provided into cavity <NUM> in the gap between the airfoil wall <NUM> and the spar leg 72b. The through-passage 72c is isolated from the gap. Thus, the cooling air in the through-passage 72c does not intermix with cooling air in the gap.

<FIG> illustrates an expanded view of the end portion <NUM> of the spar leg 72b and the support platform <NUM>. In this example, the clevis mount <NUM> includes first and second prongs 76a/76b that have respective pin holes 76c that are coaxially aligned with each other. The pin <NUM> is disposed in the pin holes 76c (after the clevis mount <NUM> is received through the through-hole <NUM> in the support platform <NUM>. The prongs 76a/76b are spaced apart so as to form a forked configuration. The through-passage 72c of the spar leg 72b extends between the prongs 76a/76b. The clevis mount <NUM> thus also serves as an outlet of the through-passage 72c.

<FIG> and <FIG> illustrates a further, modified example. In this example, forward of the prongs 76a/76b the end portion <NUM> of the spar leg 72b includes a stop <NUM>. Relative to forward and aft sides 86a/86b of the spar leg 72b the stop <NUM> in this example is offset toward the forward side 86a, while the pin holes 76c and pin <NUM> are offset toward the aft side 86b. The stop <NUM> is also radially offset from the pin <NUM>. A draft region <NUM> between the stop <NUM> and the prongs 76a/76b is open and thus also serves as a portion of the outlet of the through-passage 72c. The draft region <NUM> increases the overall area of the outlet of the through-passage 72c, in comparison to a straight outlet.

The stop <NUM> in this example is a protruding lip 84a that projects from the sides of the spar leg 72b. The lip 84a defines a bearing surface 84b. The bearing surface 84b generally tracks the shape of the sides of the spar leg 72b, which in this example is an arc geometry. The stop <NUM> can have an alternate geometry, such as a tab or tabs, as long as the stop <NUM> is robust to handle loads transmitted there through. Moreover, as the lip 84a projects from the sides of the spar leg 72b, as opposed to projecting into the through-passage 72c, the stop <NUM> does not interfere with flow through the through-passage 72c.

The side of the through-hole <NUM> of the support platform <NUM> defines a ledge <NUM>. The ledge <NUM> is a band that protrudes from the side of the through-hole <NUM> inboard of the face of the support platform <NUM>. The ledge <NUM> in this example also has an arced geometry, but in general the ledge <NUM> and stop <NUM> will be of complementary geometry that enables the stop <NUM> and ledge <NUM> to seat together with surface-to-surface contact. Thus, when the end portion <NUM> of the spar leg 72b is inserted through the through-hole <NUM> of the support platform <NUM>, the bearing surface 84b seats against the ledge <NUM>. The pin <NUM> is then inserted through the pin holes 76c to lock the support platform <NUM> onto the spar leg 72b.

<FIG> illustrates a local view of the end portion <NUM> of the spar leg 72b and the support platform <NUM>. When the engine <NUM> is running, flow in the core gas path C subjects the airfoil fairing <NUM> to aerodynamic loads. The aerodynamic loads are reacted out of the airfoil fairing <NUM> to the spar <NUM>. In this example, the aerodynamic load tends to urge the airfoil fairing <NUM> in an aft and radially inward direction.

At least a portion of the radial component of the aerodynamic load, represented at AL, is reacted radially inwardly from the airfoil fairing <NUM> to the support platform <NUM>. However, the pin <NUM> abuts the underside of the support platform <NUM> and thereby radially constrains the support platform <NUM>. As a result, since this radial component of the aerodynamic load AL is located toward the aft end of the support platform <NUM>, the support platform <NUM> has the tendency to teeter on the pin <NUM> and thus rotate, as indicated at R1 (clockwise in the illustrated example). If permitted to rotate, the forward end of the platform support <NUM> would tend to rotate radially outwards, as indicated at R2, and exert the load on the forward end of the platform <NUM> of the airfoil fairing <NUM>. However, the ledge <NUM> and stop <NUM> serve as an anti-rotation feature and prevent this. The ledge <NUM> bears against the bearing surface 84b of the stop <NUM> upon rotation of the platform support <NUM>. As the spar <NUM> is fixed, the stop <NUM> limits the platform support <NUM> from further rotation and thereby prevents the forward end of the support platform <NUM> from rotating into the forward end of the platform <NUM>. The load is thus reacted through the stop <NUM> to the spar leg 72b instead of to the platform <NUM>. In this regard, within the available design space, the axial distance between the stop <NUM> and the pin <NUM> may be maximized in order to increase the mechanical advantage and reduce loads. That is, the pin <NUM> is offset to be near the aft side 86b of the spar leg 72b.

It is to be appreciated that the example configuration may be adapted for other aerodynamic load conditions. For instance, if the aerodynamic load on the airfoil fairing <NUM> were instead reacted into the forward end of the platform support <NUM>, the stop <NUM> would instead be offset to the aft side of the spar leg 72b and the clevis mount <NUM> would be offset toward the forward side of the spar leg 72b. That is, since the support platform <NUM> teeters about the pin <NUM>, the stop <NUM> is located on the opposite side of the pin <NUM> from the location in which the load is transmitted into the spar support <NUM>. Moreover, if the aerodynamic load on the airfoil fairing <NUM> were instead transmitted radially outwards, the example configuration could be used at the outer end of the airfoil fairing <NUM>, with the spar <NUM> being inverted such that the spar platform 72a is adjacent the platform <NUM> and the support platform <NUM> is adjacent the platform <NUM>.

The stop <NUM> and ledge <NUM> permit the loads to be borne by the spar <NUM> instead of the platform of the airfoil fairing <NUM>. As a result, there may also be additional design flexibility in the positioning of the spar leg 72b, since the spar leg 72b need not be centrally located in order to balance the loads reacted out at the support platform <NUM>.

<FIG> illustrates another example end portion <NUM> of the spar leg 72b that can be used in any of the aforementioned examples. In this example, the clevis mount <NUM> includes the first and second prongs 76a/76b, but only the first prong 76a has a pin hole 76c for the pin <NUM>. The pin <NUM> is thus cantilevered with respect to the prong 76a. The pin <NUM> may extend across the space between the prongs 76a/76b and contact the second prong 76b or, alternatively stop short of the second prong 76b.

<FIG> illustrates another example end portion <NUM> of the spar leg 72b that can be used in any of the aforementioned examples. In this example, the clevis mount <NUM> includes the first and second prongs 76a/76b, but the prongs 76a/76b converge into a single or compound prong 76d. The pin hole 76c extends through the single prong 76d and the pin <NUM> is received there through. Even though the prongs 76a/76b converge, the draft region <NUM> provides open area for outflow from the through-passage 72c in the spar leg 72b. It is to be appreciated from the examples that a "clevis mount" as used herein refers to a fastening system in which there is at least a single prong (e.g., <FIG>), or more than one prong (e.g., <FIG> and <FIG>), that receives a pin there through in order to fasten the support platform <NUM> and the spar leg 72b together.

Claim 1:
A vane arc segment (<NUM>) comprising:
an airfoil fairing (<NUM>) having first and second fairing platforms (<NUM>, <NUM>) and a hollow airfoil section (<NUM>) extending there between;
a spar (<NUM>) having a spar platform (72a) adjacent the first fairing platform (<NUM>) and a spar leg (72b) that extends from the spar platform (72a) and through the hollow airfoil section (<NUM>), the spar leg (72b) having an end portion (<NUM>) that is distal from the spar platform (72a) and that protrudes from the second fairing platform (<NUM>);
a support platform (<NUM>) adjacent the second fairing platform, the support platform (<NUM>) having a through-hole (<NUM>); and
a pin (<NUM>);
wherein the airfoil is subject to an aerodynamic load and the airfoil fairing (<NUM>) transfers at least a portion of the aerodynamic load to the support platform (<NUM>)
characterized in that:
the end portion (<NUM>) has a clevis mount (<NUM>), the end portion (<NUM>) of the spar leg (72b) extending through the through-hole (<NUM>) such that the clevis mount (<NUM>) protrudes from the support platform (<NUM>), wherein the pin (<NUM>) extends though the clevis mount (<NUM>) and locks the support platform (<NUM>) to the spar leg (72b) such that the airfoil fairing (<NUM>) is trapped between the spar platform (72a) and the support platform (<NUM>), and in that the vane arc segment further comprises a side of the through-hole (<NUM>) defining a ledge (<NUM>), the spar leg (72b) including a stop (<NUM>) that is complementary to the ledge (<NUM>), the support platform (<NUM>) having a tendency to rotate about the pin (<NUM>) under the aerodynamic load received from the airfoil fairing (<NUM>), the stop (<NUM>) bearing against the ledge (<NUM>) and limiting rotation of the support platform (<NUM>).