Aircraft Drive System Alignment via Directional Reacting Joints
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Solution Overview
Problem
Tiltrotor aircraft face structural load challenges due to the outboard location of nacelles and the need for rotating them, which increases the size and weight of the airframe structure required to support the propulsion system.
Innovation Solution
A drive system with a support assembly that includes a fixed joint and directional reacting joints, providing radial growth freedoms to maintain the output gear of the second gearbox in substantial collinear alignment with the input gear of the first gearbox, reducing structural loads through efficient torque transfer and thermal management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If nacelles are located outboard and rotated to change flight mode, then the aircraft can operate in both helicopter and airplane modes, but the structural size and weight increase significantly
Solution Approach 1:
The drive system is segmented into multiple independent components (first gearbox, second gearbox, common shaft) that can be independently supported and aligned. This segmentation allows each component to be optimized separately, reducing the overall structural weight while maintaining the ability to support both helicopter and airplane flight modes through the rotatable pylon assembly.
Solution Approach 2:
The support assembly incorporates dynamic alignment capabilities through directional reacting joints that allow for radial growth degrees of freedom. This dynamic adjustment mechanism enables the system to maintain proper gear alignment during thermal expansion and structural deformation, reducing the need for overly rigid and heavy structural support while preserving flight mode versatility.
2Manufacturing precision
If rigid structural support is used to maintain gear alignment, then alignment is maintained, but thermal expansion causes misalignment and increased structural loads
Solution Approach 1:
The support assembly changes the physical parameters of the connection joints from rigid fixed connections to directional reacting joints that permit controlled movement. These joints allow for thermal expansion and contraction while maintaining gear alignment through their ability to accommodate radial growth, thereby reducing structural loads without sacrificing alignment precision.
Solution Approach 2:
The system transitions from static rigid support to dynamic support that actively accommodates thermal and operational variations. The directional reacting joints provide dynamic adjustment capabilities that maintain gear alignment precision under varying thermal and load conditions, reducing the structural strength requirements compared to rigid fixed support systems.
3Strength
If fixed joints are used to support the gearbox, then structural support is provided, but thermal expansion causes misalignment
Solution Approach 1:
The support assembly replaces fixed rigid joints with directional reacting joints that incorporate dynamic movement capabilities. These joints maintain structural support capability while allowing controlled radial growth to accommodate thermal expansion, thereby preserving gear alignment precision that would otherwise be lost in fixed joint configurations.
Solution Approach 2:
The connection parameters between the support assembly and gearbox are changed from fixed positional constraints to directional constraints that permit thermal movement. This parameter change allows the system to maintain both structural support and alignment precision by allowing the joints to adapt to thermal expansion through controlled degrees of freedom.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution reduces structural loads and maintains alignment during thermal expansion cycles, optimizing the structural support for tiltrotor aircraft, enabling efficient operation between helicopter and airplane modes.
Implementation Method 1
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 second gearbox in substantial collinear alignment with the input gear of the first gearbox
Data Source
AI summary
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.