Method for balancing a propulsive system having non-hull contra-rotating propellers

1. A balancing method for a propulsive system with at least two coaxial non streamlined contra-rotating propellers, each of said propellers comprising a hub concentrically surrounded by a hub envelope and each of said hub envelopes projecting on either part of the plane of the corresponding propeller, said balancing method according to which, to eliminate, or at least to reduce a possible unbalance of said propulsive system, counterweights are arranged on locations being provided on the latter,

wherein said locations are located on said hub envelopes, close to the ends of the latter and being distant from the planes of said propellers,

wherein at least one of said counterweights is at least partially embedded in a cavity arranged on one of said locations, said cavity being configured to receive at least one of said counterweights and extending in a plane that is located orthogonal to an outer surface of said hub envelope,

wherein, for at least one of said hub envelopes, the locations of the counterweights are situated to extend in at least two planes, each of the at least two planes being orthogonal to the propeller axis and orthogonal to said outer surface of said hub envelope, and arranged on either part of the plane of the corresponding propeller, on the ends of said hub envelope.

2. The method according to claim 1 , wherein at least some of said counterweights are at least partially embedded in cavities arranged on some of said locations, said cavities being circumferentially distributed on the corresponding hub envelope.

3. The method according to claim 1 , wherein at least one of said cavities is configured in such a way that the corresponding counterweight, once embedded within said cavity, does not project on the corresponding hub envelope.

4. The method according to claim 1 , wherein at least one of said cavities comprises a threaded housing in which the corresponding counterweight can be inserted, said counterweight presenting then at least partially the shape of a screw.

5. The method according to claim 1 , wherein at least one of said cavities comprises an orifice in which the lower part of the corresponding counterweight can be inserted, the upper end of said counterweight being provided with at least a fastening orifice through which the latter can be fastened to the corresponding hub envelope by means of at least one fastening member.

6. A balancing method for a propulsive system with at least two coaxial non streamlined contra-rotating propellers, each of said propellers comprising a hub concentrically surrounded by a hub envelope and each of said hub envelopes projecting on either part of the plane of the corresponding propeller, said balancing method according to which, to eliminate, or at least to reduce a possible unbalance of said propulsive system, counterweights are arranged on locations being provided on the latter,

wherein said locations are located on said hub envelopes, close to the ends of the latter being distant from the planes of said propellers,

wherein some of said counterweights form a circumferentially non uniform mass ring coaxial to the corresponding hub envelope and inserted within a housing arranged on one of said locations, said housing being bound, on the one side, by the latter, and, on the other side, by a shoulder arranged under said hub envelope, and

wherein said circumferentially non uniform mass ring and the corresponding hub envelope are each provided with at least one lock orifice, said lock orifices being able to be put opposite each other with a view to introduce a lock member.

7. A balancing method for a propulsive system with at least two coaxial non streamlined contra-rotating propellers, each of said propellers comprising a hub concentrically surrounded by a hub envelope and each of said hub envelopes projecting on either part of the plane of the corresponding propeller, said balancing method according to which, to eliminate, or at least to reduce a possible unbalance of said propulsive system, counterweights are arranged on locations being provided on the latter,

wherein said locations are located on said hub envelopes, close to the ends of the latter being distant from the planes of said propellers,

wherein some of said counterweights form a circumferentially non uniform mass ring coaxial to the corresponding hub envelope and inserted within a housing arranged on one of said locations, said housing being bound, on the one side, by the latter, and, on the other side, by a shoulder arranged under said hub envelope, and

wherein the corresponding hub envelope comprises an angular graduation being visible thru said hub envelope.

8. A propulsive system comprising:

at least two coaxial non streamlined contra-rotating propellers, each of said propellers comprising a hub concentrically surrounded by a hub envelope and each of said hub envelopes projecting on either part of the plane of the corresponding propeller; and

counterweights arranged on locations provided on the latter so as to eliminate, or at least to reduce, a possible unbalance of said propulsive system, wherein said locations are located on said hub envelopes, close to the ends of the latter being distant from the planes of said propellers,

wherein some of said counterweights form a circumferentially non uniform mass ring coaxial to the corresponding hub envelope and inserted within a housing arranged on one of said locations, said housing being bound, on the one side, by the latter, and, on the other side, by a shoulder arranged under said hub envelope, and

wherein said circumferentially non uniform mass ring and the corresponding hub envelope are each provided with at least one lock orifice, said lock orifices being able to be put opposite each other with a view to introduce a lock member.

9. The system according to claim 8 , wherein the corresponding hub envelope comprises an angular graduation being visible thru said hub envelope.