A propulsion system for a tiltrotor aircraft includes an engine supported by the airframe and a fixed gearbox operably coupled to the engine. Inboard and outboard pedestals are supported by the airframe and positioned above the wing. A pylon assembly is rotatably coupled between the inboard and outboard pedestals. The pylon assembly includes a spindle gearbox having an input gear, a mast operably coupled to the input gear and a proprotor assembly operable to rotate with the mast. The spindle gearbox is rotatable about a conversion axis to selectively operate the tiltrotor aircraft between helicopter and airplane modes. A common shaft, rotatable about the conversion axis, is configured to transfer torque from an output gear of the fixed gearbox to an input gear of the spindle gearbox. Each of the inboard and outboard pedestals includes a spherical bearing providing a self-aligning coupling with the pylon assembly.

A support assembly for coupling a first gearbox to an airframe of an aircraft. The first gearbox has an output gear operable to transfer torque to an input gear of a second gearbox via a common shaft rotatable about a longitudinal axis. The support assembly includes a fixed joint proximate the longitudinal axis. A first directional reacting joint remote from the longitudinal axis provides a first radial growth degree of freedom to the first gearbox relative to the longitudinal axis. A second directional reacting joint remote from the longitudinal axis provides a second radial growth degree of freedom to the first gearbox relative to the longitudinal axis. The first radial growth degree of freedom is not parallel with the second radial growth degree of freedom such that the support assembly maintains the output gear of the first gearbox in substantial collinear alignment with the input gear of the second gearbox.

A support assembly for coupling a first gearbox to an airframe of an aircraft. The first gearbox has an output gear operable to transfer torque to an input gear of a second gearbox via a common shaft rotatable about a longitudinal axis. The support assembly includes a fixed joint proximate the longitudinal axis. A first directional reacting joint remote from the longitudinal axis provides a first radial growth degree of freedom to the first gearbox relative to the longitudinal axis. A second directional reacting joint remote from the longitudinal axis provides a second radial growth degree of freedom to the first gearbox relative to the longitudinal axis. The first radial growth degree of freedom is not parallel with the second radial growth degree of freedom such that the support assembly maintains the output gear of the first gearbox in substantial collinear alignment with the input gear of the second gearbox.

A drive system for a tiltrotor aircraft includes a first gearbox rotatably mounted to the airframe and rotatable about a longitudinal axis to operate the tiltrotor aircraft between helicopter and airplane modes. A second gearbox extends generally normal to the longitudinal axis of the first gearbox. A common shaft, rotatable about the longitudinal axis, transfers torque from an output gear of the second gearbox to an input gear of the first gearbox. A support assembly couples the second gearbox to the airframe and includes a fixed joint proximate the longitudinal axis, a first directional reacting joint remote from the longitudinal axis providing a first radial growth degree of freedom to the second gearbox and a second directional reacting joint remote from the longitudinal axis providing a second radial growth degree of freedom to the second gearbox that is not parallel with the first radial growth degree of freedom.

A drive system for a tiltrotor aircraft includes a first gearbox rotatably mounted to the airframe and rotatable about a longitudinal axis to operate the tiltrotor aircraft between helicopter and airplane modes. A second gearbox extends generally normal to the longitudinal axis of the first gearbox. A common shaft, rotatable about the longitudinal axis, transfers torque from an output gear of the second gearbox to an input gear of the first gearbox. A support assembly couples the second gearbox to the airframe and includes a fixed joint proximate the longitudinal axis, a first directional reacting joint remote from the longitudinal axis providing a first radial growth degree of freedom to the second gearbox and a second directional reacting joint remote from the longitudinal axis providing a second radial growth degree of freedom to the second gearbox that is not parallel with the first radial growth degree of freedom.

A reduction gear includes: an orthogonal shaft reduction gear having an orthogonal shaft reduction gear casing; and a parallel shaft reduction gear having a parallel shaft reduction gear casing, which is connected to the orthogonal shaft reduction gear, wherein the orthogonal shaft reduction gear casing and the parallel shaft reduction gear casing are connected through a joint plate, the orthogonal shaft reduction gear casing has a flange portion protruding to the outside of the orthogonal shaft reduction gear casing, and the orthogonal shaft reduction gear casing and the joint plate are connected by a first bolt inserted into the flange portion from the orthogonal shaft reduction gear side, and a second bolt inserted into the joint plate from the parallel shaft reduction gear side.