Aircraft Pipework Fixture Assembly for Wing Flex and Axial Loads
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Solution Overview
Problem
Conventional fixture arrangements for liquid hydrogen pipework in aircraft wings do not adequately address the issues of stress concentrations and axial load reactions, particularly in long spans where the pipework bends and twists with the wing, leading to potential failure and increased stress concentrations.
Innovation Solution
A fixture arrangement using a spherical bearing and tie rod system that allows the pipework to translate and rotate relative to the aircraft structure, with the tie rod handling axial loads and the spherical bearing managing radial loads, minimizing stress concentrations and providing a flexible connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fixture arrangements (saddle clamps, clamp blocks, or p-clamps) are used to locally restrain the pipework, then the pipework is supported at discrete locations, but the pipework cannot react axial loads and stress concentrations increase due to over-constraint
Solution Approach 1:
The fixture arrangement incorporates a spherical bearing that allows the pipework to dynamically adapt its position and orientation relative to the aircraft structure. The spherical bearing enables rotational movement in multiple directions, transforming the static constraint into a dynamic system that can accommodate wing flexure and thermal expansion without creating stress concentrations.
Solution Approach 2:
The invention changes the constraint parameters by introducing a tie rod connected through spherical bearings, which fundamentally alters how loads are distributed. The tie rod transforms the fixture from a purely radial support into a system that can also handle axial loads, changing the mechanical parameters of the connection from single-degree-of-freedom to multi-degree-of-freedom with load-sharing capabilities.
2Strength
If long rigid pipework is routed through a wing box, then the pipework maintains structural integrity, but large stresses are induced into the pipework under wing bending
Solution Approach 1:
The spherical bearing acts as an intermediary element between the rigid pipework and the flexible aircraft structure. It mediates the conflicting requirements by providing a connection point that can accommodate relative movement, allowing the pipework to maintain its structural integrity while the bearing absorbs the stresses induced by wing bending through its rotational degrees of freedom.
Solution Approach 2:
The fixture arrangement segments the load path by introducing the tie rod and spherical bearing as separate functional elements. This segmentation allows the pipework to remain rigid for structural integrity while the spherical bearing and tie rod combination handles the flexible accommodation of wing bending, separating the functions of structural support and flexible accommodation.
3Temperature
If the pipework is made rigid and double-walled with vacuum insulation to maintain low temperatures, then thermal insulation performance is improved, but the pipework becomes more rigid and induces larger stresses under wing bending
Solution Approach 1:
The spherical bearing serves as a mediator that decouples the thermal insulation requirement from the mechanical stress problem. It allows the pipework to maintain its rigid, double-walled vacuum-insulated structure for thermal performance while the bearing accommodates the mechanical stresses through rotational movement, preventing stress concentrations at the fixation points.
4Adaptability or versatility
If the pipework is allowed to bend and twist with the wing flexure, then adaptability to wing movement is improved, but fixture arrangements must minimize stress concentrations from over-constraint
Solution Approach 1:
The spherical bearing creates a dynamic connection that adapts to wing movement in real-time. It provides the necessary degrees of freedom for the pipework to bend and twist with wing flexure while maintaining proper support, transforming a static over-constraint problem into a dynamic system that automatically adjusts to minimize stress concentrations.
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 system effectively reduces stress concentrations and ensures stable pipework support by allowing for relative movement and load distribution, enhancing the durability and reliability of cryogenic fuel lines in aircraft wings.
Implementation Method 1
the spherical bearing comprising a ball mounted to the pipework and a housing coupled to the aircraft structure; the ball comprises a convex spherical bearing surface; the housing comprises a concave spherical bearing surface which mates with the convex spherical bearing surface of the ball
Implementation Method 2
the spherical bearing is configured to transmit radial load between the pipework and the aircraft structure, and the radial load is normal to the spherical bearing surfaces
Implementation Method 3
the axial bearing comprising an inner bearing surface of the ball which mates with an outer surface of the pipework, wherein the axial bearing is configured to enable the pipework to translate relative to the ball in the axial direction
Data Source
AI summary
An aircraft pipework assembly is disclosed including an aircraft structure; pipework; a fixture arrangement between the pipework and the aircraft structure; a tie rod connecting the pipework to the aircraft structure; a first tie rod bearing which connects the tie rod to the pipework; and a second tie rod bearing which connects the tie rod to the aircraft structure. The fixture arrangement includes a spherical bearing, the spherical bearing comprising a ball mounted to the pipework, and a housing coupled to the aircraft structure. The ball includes a convex spherical bearing surface; and the housing comprises a concave spherical bearing surface which mates with the convex spherical bearing surface of the ball. The fixture arrangement is configured to enable the pipework to translate relative to the ball in an axial direction aligned with a longitudinal axis of the pipework.