Aircraft engine reduction gearbox

1. An aircraft engine reduction gearbox, comprising:

a power input and a power output; and

an epicyclic gear train engaged with the power input and the power output, the epicyclic gear train including:

a sun gear engaged with the power input and centrally disposed defining a center axis of the epicyclic gear train;

compound planet gears mounted to a carrier and rotatable about respective planet gear axes, each compound planet gear having an input gear in meshed engagement with the sun gear, and output gears axially spaced from the input gear; and

ring gears axially spaced apart from each other, the ring gears rotatable about the center axis and engaged with the power output, each ring gear includes an outer meshing member engaged with the power output, and an inner meshing member disposed radially inwardly of the outer meshing member and in meshed engagement with one of the output gears.

2. The aircraft engine reduction gearbox of claim 1 , wherein the carrier is fixed, the sun gear being engaged with the power input to be driven thereby in a first rotational direction, and cause the ring gears to rotate about the center axis and drive the power output in a second rotational direction opposite to the first rotational direction.

3. The aircraft engine reduction gearbox of claim 1 , wherein the epicyclic gear train is the only epicyclic gear train of the aircraft engine reduction gearbox.

4. The aircraft engine reduction gearbox of claim 1 , wherein the input gear is disposed axially between the output gears.

5. The aircraft engine reduction gearbox of claim 1 , wherein each of the compound planet gears is mounted about an oil-film bearing.

6. The aircraft engine reduction gearbox of claim 5 , wherein each compound planet gear includes an annular body defining an inner journal surface delimiting a cavity of the annular body, the oil-film bearing disposed in the cavity in engagement with the inner journal surface.

7. The aircraft engine reduction gearbox of claim 1 , comprising a spline in meshed engagement with the ring gears, and engaged with the power output.

8. The aircraft engine reduction gearbox of claim 7 , wherein the spline is in meshed engagement with the ring gears at a first axial position being axially spaced from axial positions of the meshed engagement of the ring gears with the output gears.

9. The aircraft engine reduction gearbox of claim 8 , wherein the first axial position is axially between the axial positions of the meshed engagement of the ring gears with the output gears.

10. The aircraft engine reduction gearbox of claim 1 , wherein a diameter of the input gear is greater than a diameter of the output gears.

11. The aircraft engine reduction gearbox of claim 1 , wherein the power output includes an output shaft, a passage extending radially through the output shaft to an opening at a radially-outer surface of the output shaft.

12. The aircraft engine reduction gearbox of claim 1 , wherein each of the compound planet gears is mounted about an oil-film bearing, the oil-film bearing including a bearing shaft extending along one of the planet gear axes between opposed axial ends, one or more annular grooves defined in each of the axial ends of the bearing shaft.

13. A method of operating a reduction gearbox of an aircraft engine, the reduction gearbox having an epicyclic gear train with a sun gear, compound planet gears, and axially spaced-apart ring gears, the method comprising: driving the sun gear to rotate an input gear of the compound planet gears, and to rotate output gears of the compound planet gears axially spaced from the input gear, rotation of the output gears rotating a radially-inner portion of the ring gears meshed with the output gears about a center axis of the epicyclic gear train, and rotating a radially-outer portion of the ring gears about the center axis.

14. The method of claim 13 , wherein driving the sun gear includes stopping rotation of the compound planet gear about the center axis of the epicyclic gear train.

15. The method of claim 13 , wherein driving the sun gear includes rotating the sun gear in a first rotational direction to rotate the ring gears in a second rotational direction opposite to the first rotational direction.

16. The method of claim 13 , comprising driving only one of the epicyclic gear train of the reduction gearbox.

17. The method of claim 13 , wherein driving the sun gear includes rotating the ring gears to drive a power output at a first axial position, and driving the sun gear includes rotating the output gears to rotate the ring gears at axial positions being axially spaced from the first axial position.

18. The method of claim 17 , wherein the first axial position is axially between the axial positions.