Tapered Elastomeric Bearing Layers for Rotor Hub Stability
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Solution Overview
Problem
Conventional elastomeric bearings in rotor hubs face challenges with constant thickness layers, leading to high strain at edges and instability at high cocking angles, and increasing thickness to reduce strain is constrained by clearance issues, while reducing shim layer thickness increases bending and the risk of failure.
Innovation Solution
The use of arc-tapered elastomeric and shim layers, where the center thickness is greater than the edge thickness, reduces tensile strain and improves cocking capability without increasing the overall height of the hub spring assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If constant thickness elastomeric layers are used, then manufacturing is simple, but high strain occurs at edges leading to instability at high cocking angles
Solution Approach 1:
The elastomeric bearing employs layers with non-uniform thickness distribution, where the thickness varies radially to optimize performance. Specifically, the thickness is greater at the center and decreases toward the edges, creating local quality variations that reduce edge strain while maintaining manufacturing feasibility through controlled molding processes.
Solution Approach 2:
The patent changes the geometric parameter of layer thickness from constant to variable. By implementing a thickness profile that decreases from center to edge, the bearing achieves reduced tensile strain at critical edge regions during cocking operations, thereby improving stability without sacrificing manufacturing capability.
2Reliability
If elastomeric layer thickness is increased to reduce strain, then strain distribution improves, but overall height increases causing clearance issues
Solution Approach 1:
Instead of uniformly increasing thickness throughout the elastomeric layers, the patent applies local quality by concentrating greater thickness at the center where it is most effective for strain distribution, while reducing thickness toward the edges. This localized approach optimizes strain distribution without proportionally increasing the overall height of the bearing assembly.
Solution Approach 2:
The patent implements a thickness profile parameter that varies radially across the bearing layers. This parameter change allows the center region to have sufficient thickness for strain management while edge regions maintain reduced thickness, thereby achieving improved strain distribution without the penalty of increased overall height that would result from uniform thickness increase.
3Length of stationary object
If shim layer thickness is reduced, then overall height decreases, but bending increases leading to higher failure risk
Solution Approach 1:
The patent applies local quality to the shim layers by varying their thickness distribution to match the elastomeric layer profile. The shims are thickest at the center and taper toward the edges, creating local reinforcement where it is most needed to prevent bending and failure, while allowing overall height to remain compact.
Solution Approach 2:
The bearing assembly functions as a composite structure combining elastomeric layers with tapered thickness and shim layers with matching tapered thickness. This composite approach allows the shims to work synergistically with the elastomeric material, providing structural support and preventing excessive bending while maintaining reduced overall height through the coordinated thickness profile of both materials.
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 arc-tapered design decreases tensile strain in elastomeric layers under high loads and angles, enhancing the ultimate cocking capability and stability of the hub spring assembly while maintaining a compact package.
Implementation Method 1
The arc-tapered design decreases tensile strain in elastomeric layers under high loads and angles
Data Source
AI summary
A rotor hub for an aircraft that includes a yoke, a rotor mast; and a hub spring assembly. The hub spring assembly includes an upper outer member; an upper inner member; and an upper spring member having a plurality of elastomeric layers and shim layers sandwiched between the upper outer member and the upper inner member, the shim layers being tapered such that a thickness of each shim layer is smaller at a side portion as compared to the thickness of the shim at a center portion.