Engine bearing support
A turbofan engine comprises an engine case. A gaspath extends through the engine case. A fan has a circumferential array of fan blades. A fan case encircles the fan blades radially outboard of the engine case. A plurality of fan case vanes extend outward from the engine case to the fan case. A front frame assembly includes a plurality of vanes extending radially across the gaspath. A transmission couples a shaft to a fan shaft to drive the fan. A bearing assembly couples the shaft to the front frame assembly. A bearing support extends aftward and radially inward from the front frame assembly to the bearing assembly.
1. A turbofan engine comprising:
an engine case;
a gaspath through the engine case;
a fan having a circumferential array of fan blades;
a fan case encircling the fan blades radially outboard of the engine case;
a plurality of fan case vanes extending outward from the engine case to the fan case;
a front frame assembly comprising a plurality of vanes extending radially across the gas path;
a shaft;
a transmission coupling the shaft to a fan shaft to drive the fan;
a duplex bearing assembly coupling the shaft to the front frame assembly; and
a bearing support extending aftward and radially inward from the front frame assembly to the bearing assembly,
wherein:
the duplex bearing comprises a forward bearing and an aft bearing;
the forward bearing has a center spaced apart from a center of the aft bearing by a bearing distance; and
the forward bearing has an inboard race longitudinally cantilevered by a cantilever distance at least about 20% of said bearing distance.
2. The engine of claim 1 wherein:
the bearing support extends partially within a hub of a compressor; and
the compressor is a low pressure compressor (LPC) having a single hub.
3. The engine of claim 1 wherein:
the shaft is a low pressure/speed spool shaft.
4. The engine of claim 1 wherein:
the shaft is a flex-shaft.
5. The engine of claim 1 wherein:
the bearing support has a main portion tapering at an angle of 10-45° off-axial.
6. The engine of claim 1 wherein:
the bearing support has a main portion tapering at an angle of 10-35° off-axial.
7. The engine of claim 1 wherein:
the bearing assembly has a centerplane within an aft half of a longitudinal span of the LPC.
8. The engine of claim 7 wherein:
the bearing centerplane falls within the hub.
9. The engine of claim 2 wherein:
the duplex bearing comprises a forward bearing and an aft bearing;
the forward bearing has a center spaced apart from a center of the aft bearing by a bearing distance; and
the duplex bearing has a characteristic diameter, a ratio of said bearing distance to said characteristic diameter being between about 0.4:1 and about 3:1.
10. The engine of claim 1 wherein:
the forward bearing has an outboard race longitudinally cantilevered by a second cantilever distance at least about 20% of said bearing distance.
11. A turbofan engine comprising:
an engine case;
a gaspath through the engine case;
a fan having a circumferential array of fan blades;
a fan case encircling the fan blades radially outboard of the engine case;
a plurality of fan case vanes extending outward from the engine case to the fan case;
a front frame assembly comprising a plurality of vanes extending radially across the gas path;
a shaft;
a transmission coupling the shaft to a fan shaft to drive the fan;
a duplex bearing assembly coupling the shaft to the front frame assembly; and
a bearing support extending aftward and radially inward from the front frame assembly to the bearing assembly, wherein:
the duplex bearing comprises a forward bearing and an aft bearing;
the forward bearing has a center spaced apart from a center of the aft bearing by a bearing distance; and
an inboard support at a center of the bearing distance is longitudinally cantilevered by a cantilever distance at least about 10% of said bearing distance.
12. The engine of claim 11 wherein:
the duplex bearing comprises a forward bearing and an aft bearing; and
the forward bearing and aft bearing are both tapered roller bearings.
13. The engine of claim 10 wherein:
a fan bearing assembly couples a forward hub structure to the fan shaft; and
the fan bearing assembly is a duplex tapered roller bearing assembly and a bellows spring engages an outer race of at least one of the bearings of the duplex tapered roller bearing.