Strut assemblies

A strut assembly for connecting a gearbox to a helicopter fuselage for transmitting flight loads from the gearbox to the fuselage and for inputting periodic forcing loads into the fuselage as part of an active vibration control system, said strut assembly including an axially elastically extensible tube assembly comprising a plurality of nested concentric tubes arranged in series, and each tube rigidly attached to one end of an adjacent tube for a rigid attachment respectively to said gearbox and said fuselage and an axially extensible actuator rigidly affixed co-axially within and to the tube assembly between the gearbox and the fuselage, the tubes being manufactured from material having mechanical strength and elastic properties selected to provide a predetermined axial stiffness capable of transmitting operational loads and so that reciprocal axial extensions of the actuator cause elastic longitudinal displacements of the strut assembly to input said periodic loads.