Hybrid metal-composite drive shaft unit and method of manufacturing same

1. A hybrid metal-composite drive shaft unit for power transmission in a rotary-wing aircraft, the hybrid metal-composite drive shaft unit comprising:

at least one metal drive shaft connector that is at least partly embedded into a composite drive shaft,

wherein the composite drive shaft comprises a thermoplastic polymer being welded to the at least one metal drive shaft connector, wherein a welded connection is provided that defines a first load path for transmission of loads between the at least one metal drive shaft connector and the composite drive shaft,

wherein the at least one metal drive shaft connector and the composite drive shaft comprise, in the region of the welded connection, at least partly a polygonal cross-sectional shape for forming a form-fit connection that defines a second load path for transmission of loads between the composite drive shaft and the at least one metal drive shaft connector.

2. The drive shaft unit according to claim 1 , wherein the thermoplastic polymer comprises a polyetheretherketone thermoplastic polymer.

3. The drive shaft unit according to claim 2 , wherein the composite drive shaft comprises unidirectional layers with continuous fiber reinforcement embedded in the thermoplastic polymer.

4. The drive shaft unit according to claim 1 , wherein the at least one metal drive shaft connector comprises titanium.

5. The drive shaft unit according to claim 1 , wherein the at least one metal drive shaft connector comprises an associated longitudinal extension and an outer circumference that is at least partly conically shaped in the direction of the longitudinal extension.

6. The drive shaft unit according to claim 5 , wherein the at least one metal drive shaft connector comprises a plurality of recesses at a first axial end facing away from the composite drive shaft, each recess being adapted to enable access to an associated coupling adapter.

7. The drive shaft unit according to claim 6 , wherein the plurality of recesses defines a plurality of connecting bridges that are adapted for attachment to the associated coupling adapter.

8. The drive shaft unit according to claim 6 , wherein the at least one metal drive shaft connector comprises a second axial end facing the composite drive shaft, the second axial end comprising a circular cross-sectional shape.

9. The drive shaft unit according to claim 1 , wherein the composite drive shaft comprises at least one further metal drive shaft connector, the at least one metal drive shaft connector and the at least one further metal drive shaft connector being interconnected by the composite drive shaft.

10. The drive shaft unit according to claim 9 , wherein the composite drive shaft comprises an at least substantially cylindrical shape in a region between the at least one metal drive shaft connector and the at least one further metal drive shaft connector.

11. The drive shaft unit according to claim 9 , wherein the composite drive shaft comprises a tubular cross section.

12. A power transmission line comprising:

a hybrid drive shaft unit according to claim 1 ;

another drive shaft unit; and

a coupling adapter coupling the hybrid metal-composite drive shaft unit to the another drive shaft unit, the coupling adapter being adapted for attachment to the corresponding metal drive shaft connector of the hybrid metal-composite drive shaft unit and to the other drive shaft unit.

13. A rotary-wing aircraft comprising:

a first gearbox unit;

a second gearbox unit; and

at least one hybrid metal-composite drive shaft unit according to claim 1 connecting the first and second gearbox units to transmit power therebetween.

14. The drive shaft unit according to claim 1 , wherein the welded connection is formed by a direct interface between the thermoplastic polymer and the metal drive shaft.

15. The drive shaft unit according to claim 1 , wherein the welded connection is formed by a region of coalescence between the thermoplastic polymer of the composite drive shaft and the at least one metal connector.

16. The drive shaft unit according to claim 1 , wherein the welded connection between the thermoplastic polymer and the at least one metal drive shaft connector is without an additional adhesive material.

17. A hybrid metal-composite drive shaft unit for power transmission in a rotary-wing aircraft, the hybrid metal-composite drive shaft unit comprising:

a composite drive shaft formed from a thermoplastic polymer, and

a metal drive shaft connector at least partly embedded into the composite drive shaft, the metal drive shaft with a plurality of recesses at a first axial end facing away from the composite drive shaft, each recess being adapted to enable access to an associated coupling adapter;

wherein the composite drive shaft is welded to the metal drive shaft connector via a welded connection, the welded connection defining a first load path for transmission of loads between the metal drive shaft connector and the composite drive shaft;

wherein the metal drive shaft connector and the composite drive shaft each form, in the region of the welded connection, at least partly a polygonal cross-sectional shape to provide a form-fit connection therebetween, the form-fit connection defining a second load path for transmission of loads between the composite drive shaft and the metal drive shaft connector.