Patent attributes
A turbofan engine (300; 600; 700) comprising a fan shaft (120) configured to rotate about an axis (500) of the engine. A fan drive gear system (60) is configured to drive the fan shaft. The fan drive gear system has a centerplane (540). A first spool comprises a high pressure turbine (326) and a high pressure compressor (324). A second spool comprises an intermediate pressure turbine (328), a lower pressure compressor, and a shaft (334) coupling the intermediate pressure turbine to the lower pressure compressor. A third spool comprises a lower pressure turbine (330) coupled to the fan drive gear system to drive the fan. The engine has a plurality of main bearings. The turbofan engine has a single stage fan. Of the main bearings, at least one is a shaft-engaging bearing engaging a driving shaft (336) coupled to the fan drive gear system. A closest (340; 640) of the shaft-engaging bearings engaging the driving shaft behind the fan drive gear system has a centerplane (550) and a characteristic radius (RB). The half angle (θ) of a virtual cone (530) intersecting the core flowpath inboard boundary at the gear system centerplane (540) and said closest of the shaft-engaging bearings at the characteristic radius (RB) is greater than about 32°. A hub-to-tip ratio (HR:FR) of the fan is less than about 0.38.
