GAS TURBINE ENGINE BEARING AND GEARBOX ARRANGEMENT

1 . A gas turbine engine comprising:

propulsor means for providing propulsion;

first compression means for compressing airflow from the propulsor means;

second compression means for compressing airflow from the first compression means;

reduction means for reducing a rotational speed of an output that drives the propulsor means relative to an input, wherein the reduction means defines a speed reduction ratio;

first expansion means for driving the second compression means in response to expanding airflow from the second compression means;

second expansion means for driving the input of the reduction means in response to expanding airflow from the first expansion means;

a drive shaft interconnecting the second expansion means and the propulsor means;

wherein the reduction means is straddle mounted by a first bearing forward of the reduction means and a second bearing aft of the reduction means relative to an engine longitudinal axis;

wherein the reduction means is coupled to an engine case with a compliant flexure at a position between the first bearing and the second bearing relative to the engine longitudinal axis; and

wherein the second bearing supports an aft portion of the drive shaft relative to a rear support of a static structure, and the rear support extends radially inward from a forward frame of the static structure at a position that is aft of the reduction means relative to the engine longitudinal axis.

2 . The engine as recited in claim 1 , wherein the reduction means includes an epicyclic transmission, wherein the epicyclic transmission includes a gear carrier, a ring gear encircling a sun gear, and a plurality of intermediate gears positioned between and enmeshing with the sun gear and the ring gear, and wherein the plurality of intermediate gears are carried by the gear carrier.

3 . The engine as recited in claim 2 , wherein:

the first bearing includes a first race configured to rotate with the gear carrier; and

the second bearing includes a second race configured to rotate with the gear carrier.

4 . The engine as recited in claim 1 , wherein the compliant flexure is axially aligned with an outer diameter of the reduction means relative to the engine longitudinal axis.

5 . The engine as recited in claim 1 , further comprising:

a second shaft including a main portion and a flexible forward portion;

the second expansion means drives the main portion; and

the flexible forward portion interconnects the main portion of the second shaft and the input of the reduction means.

6 . The engine as recited in claim 5 , wherein:

the flexible forward portion extends axially forward of the second bearing relative to the engine longitudinal axis.

7 . The engine as recited in claim 1 , wherein:

the second bearing is forward of the first expansion means relative to the engine longitudinal axis.

8 . The engine as recited in claim 1 , wherein:

the second expansion means includes three or more stages.

9 . The engine as recited in claim 1 , wherein:

the speed reduction ratio is between 2:1 and 13:1.

10 . A gas turbine engine comprising:

propulsor means for providing propulsion;

first compression means for compressing airflow from the propulsor means;

second compression means for compressing airflow from the first compression means;

reduction means for reducing a rotational speed of an output that drives the propulsor means relative to an input;

first expansion means for driving the second compression means in response to expanding airflow from the second compression means;

second expansion means for driving the input of the reduction means in response to expanding airflow from the first expansion means; and

a drive shaft interconnecting the second expansion means and the propulsor means;

wherein the reduction means is straddle mounted by a first bearing forward of the reduction means and a second bearing aft of the reduction means relative to an engine longitudinal axis;

wherein the reduction means is coupled to an engine case with a compliant flexure at a position between the first bearing and the second bearing relative to the engine longitudinal axis; and

wherein a third bearing is situated between an aft portion of the drive shaft and a second shaft that interconnects the input of the reduction means and the second expansion means.

11 . The engine as recited in claim 10 , wherein:

the second bearing is forward and radially outward of the third bearing relative to the engine longitudinal axis.

12 . A gas turbine engine comprising:

propulsor means for providing propulsion;

first compression means for compressing airflow from the propulsor means;

second compression means for compressing airflow from the first compression means;

reduction means for reducing a rotational speed of an output that drives the propulsor means relative to an input;

first expansion means for driving the second compression means in response to expanding airflow from the second compression means;

second expansion means for driving the input of the reduction means in response to expanding airflow from the first expansion means;

a compliant flexure that couples the reduction means to an engine case;

a drive shaft interconnecting the second expansion means and the propulsor means;

a first shaft interconnecting the first expansion means and the second compression means;

a second shaft interconnecting the second expansion means and the input of the reduction means, wherein the second shaft includes a flexible forward portion;

a first bearing and a second bearing configured to rotate with a gear carrier of the reduction means, wherein the first and second bearings are located on opposite axial sides of the reduction means relative to the engine longitudinal axis; and

a third bearing engaging the second shaft and the drive shaft;

wherein the drive shaft is mounted to rotate with the gear carrier as a unit, the unit engages the first bearing axially forward of the gear carrier and engages the second bearing axially aft of the gear carrier with respect to the engine longitudinal axis.

13 . The engine as recited in claim 12 , wherein the reduction means includes an epicyclic transmission, wherein the epicyclic transmission includes the gear carrier, a ring gear encircling a sun gear, and a plurality of intermediate gears positioned between and enmeshing with the sun gear and the ring gear, and wherein the plurality of intermediate gears are carried by the gear carrier.

14 . The engine as recited in claim 12 , wherein:

the third bearing is situated between an aft portion of the drive shaft and the second shaft.

15 . The engine as recited in claim 12 , wherein:

the second shaft includes a main portion and the flexible forward portion; and

the flexible forward portion interconnects the main portion of the second shaft and the input of the reduction means.

16 . The engine as recited in claim 12 , wherein:

the second bearing is situated between the reduction means and the first compression means relative to the engine longitudinal axis.

17 . The engine as recited in claim 12 , wherein:

the second bearing supports an aft portion of the drive shaft relative to a rear support of a static structure; and

the rear support extends radially inward from a forward frame of the static structure at a position that is aft of the reduction means relative to the engine longitudinal axis.

18 . The engine as recited in claim 17 , wherein:

the first bearing supports a forward portion of the drive shaft relative to a forward support; and

the forward support extends inwardly from the forward frame relative to the engine longitudinal axis.

19 . The engine as recited in claim 17 , wherein:

the third bearing is situated between the aft portion of the drive shaft and the second shaft.

20 . The engine as recited in claim 12 , wherein:

the first bearing includes a first race configured to rotate with the gear carrier; and

the second bearing includes a second race configured to rotate with the gear carrier.