Spherical Lead Stop for Rotor Hub Bearing Tension
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Solution Overview
Problem
Fluid-elastomeric lead/lag dampers in rotor systems generate variable loads due to their spring rate, leading to unpredictable rotor blade positioning during braking, which can result in tension on elastomeric bearings, potentially causing rupture, unlike hydraulic dampers that only generate tension when fully extended.
Innovation Solution
A lead stop assembly with spherical contact surfaces on the spindle and rotor hub arm, allowing contact over a range of lead angles to manage tension on elastomeric bearings, preventing tension on the bearings across a wide range of blade lead/lag angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fluid-elastomeric lead/lag damper with spring rate K is used, then the damper generates load at every rotor blade lead/lag position, but this causes unpredictable rotor blade positioning during braking and potential tension on elastomeric bearings
Solution Approach 1:
The lead stop assembly is positioned to engage before the elastomeric bearings can experience tension loads. During rotor braking, the lead stop contacts the lead stop plate at a predetermined lead angle, creating a mechanical constraint that prevents the blade from leading further and potentially placing bearings in tension. This preliminary constraint counteracts the unpredictable positioning caused by the fluid-elastomeric damper's spring rate.
Solution Approach 2:
The lead stop assembly acts as an intermediary mechanical element between the blade and the hub arm. It provides a controlled contact point that mediates the interaction between the fluid-elastomeric damper and the blade retention system, ensuring that bearing loads remain compressive rather than tensile.
2Ease of operation
If hydraulic lead/lag damper with internal hard stops is used, then the damper only reacts torque when fully extended at fixed position, but this allows unrestricted blade lead until bottoming out
Solution Approach 1:
The lead stop assembly segments the blade lead motion into two distinct phases: unrestricted lead motion within the lead angle range, and constrained motion when the lead stop contacts the lead stop plate. This segmentation allows the system to enjoy both free blade lead and controlled bearing loads.
Solution Approach 2:
The lead stop assembly provides a dynamic constraint that activates only when needed. During normal operation, the blade can lead freely within the lead angle range. During braking or abnormal conditions, the lead stop engages to provide the necessary constraint, making the system adaptive to operational conditions.
3Reliability
If lead stop contacts lead stop plate at predetermined lead angle, then tension on elastomeric bearings is limited, but this requires precise positioning of contact surfaces
Solution Approach 1:
The lead stop and lead stop plate feature spherical contact surfaces instead of flat surfaces. This curvature provides self-aligning capability, allowing the contact point to automatically position itself at the correct lead angle during operation. The spherical geometry compensates for manufacturing tolerances and ensures reliable engagement without requiring extremely precise positioning.
Solution Approach 2:
The spherical contact surfaces change the geometric parameters of the lead stop assembly, transforming fixed-position constraints into self-adjusting constraints. This parameter change allows the system to tolerate variations in manufacturing precision while maintaining the intended functional behavior.
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 lead stop assembly effectively reduces tension on elastomeric bearings during rotor braking, ensuring the bearings remain in compression and preventing potential rupture, while allowing for smooth operation across varying lead angles.
Implementation Method 1
Each of said lead stop and said lead stop plate define a respective spherical contact surface
Implementation Method 2
an elastomeric bearing array which supports said spindle relative to said rotor hub arm
Implementation Method 3
a fluid-elastomeric lead/lag damper which has a spring rate K which generates a load at every rotor blade lead/lag position
Implementation Method 4
ensuring the bearings remain in compression and preventing potential rupture
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A rotor system includes a lead stop mounted to a spindle and a lead stop plate mounted to a rotor hub arm, the lead stop operable to contact the lead stop plate over a lead angle range.