Contra-rotating propeller system for an aircraft turbine engine

1. A contra-rotating propeller system for an aircraft turbine engine in which gases circulate from an upstream to a downstream of said turbine engine, comprising:

a free power turbine including a first rotor and second contra-rotating rotor relative to the first rotor;

first and second contra-rotating propellers to be rotated about a longitudinal axis of the propeller system relative to a stator of the system; and

a mechanical transmission device including planetary gear train including:

(i) a sun gear concentric with the longitudinal axis and driven by the first rotor of the free power turbine,

(ii) planet gears meshing with the sun gear,

(iii) a planet carrier driving the first propeller, and

(iv) a ring gear meshing with each planet gear, the ring gear, driven by the second rotor, driving the second propeller,

wherein the mechanical transmission device is arranged between the first propeller and the second propeller.

2. A system according to claim 1 , wherein the first propeller is arranged downstream from the mechanical transmission device and the second propeller is arranged upstream from the mechanical transmission device.

3. A system according to claim 1 , wherein the first rotor of the free power turbine is an internal rotor, and the second rotor of the free power turbine is an external rotor.

4. A system according to claim 1 , wherein the planet carrier is integral with the first propeller, and the ring gear is integral with the second propeller and the second rotor of the free power turbine.

5. A system according to claim 1 , wherein the planet carrier is rotatably mounted with regard to the stator via planet carrier bearings and the ring gear is rotatably mounted with regard to the stator via ring gear bearings.

6. A system according to claim 1 , wherein the planetary gear train is mounted in a ring gear shaft integral with the ring gear and immerged in lube oil, the ring gear shaft including an internal circular groove arranged to get back said lube oil from the planetary gear train under influence of centrifugal forces.

7. A system according to claim 6 , wherein the circular groove is arranged upstream from the planetary gear train.

8. A system according to claim 7 , wherein drain ports are arranged in the ring gear so as to forward the lube oil located downstream from the planetary gear train towards the circular groove.

9. A turbine engine for an aircraft including a contra-rotating propeller system according to claim 1 .

10. A turbine engine according to claim 9 , which is an open rotor.