Elastic Ball Joint Rod Orientation for Rotor Drag Damping

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Solution Overview

Problem

Existing elastic ball joints used in rotary-wing aircraft rotors are not optimized for reliability when subjected to stresses around directions perpendicular to their preferred direction, leading to reduced lifespan and performance in damping drag movements of rotor blades.

Innovation Solution

An elastic articulated connection is introduced, featuring a rod with its axis of revolution positioned perpendicular to the rotor hub's axis of rotation, connected via a yoke and an elastic ball joint, utilizing frustoconical bearing surfaces and splines to withstand torsional stresses and maintain reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an elastic ball joint is used to connect the drag damper to the blade, then the connection allows rotational movement to damp drag oscillations, but the reliability is reduced when subjected to stresses around directions perpendicular to the preferred direction

Engineering Contradiction:

Improvereliability of elastic ball jointVSAvoidstress in non-preferred direction

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the orientation parameter of the rod connecting the drag damper to the blade, positioning it perpendicular to the rotor hub's axis of rotation. This parameter change aligns the rod with the preferred direction of the elastic ball joint, ensuring that stresses from drag oscillations act along the optimal axis where the joint has maximum reliability and performance.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If the rod's axis is positioned perpendicular to the rotor hub's axis of rotation, then the elastic ball joint operates in its preferred direction improving reliability, but the device complexity increases due to the specific geometric configuration requirements

Engineering Contradiction:

Improvereliability of elastic ball jointVSAvoidgeometric configuration complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent introduces asymmetric positioning of the rod relative to the rotor hub axis, rather than using a symmetric configuration. The rod is specifically oriented perpendicular to the hub axis to align with the elastic ball joint's preferred direction, creating an asymmetric but optimized geometric arrangement that enhances reliability while maintaining manufacturability.

Inventive Principle:

Principle #4Asymmetry

3Strength

If frustoconical bearing surfaces and splines are used to withstand torsional stresses, then the connection's ability to handle torsional forces is enhanced, but the manufacturing precision requirements increase

Engineering Contradiction:

Improvetorsional stress resistanceVSAvoidmanufacturing precision of frustoconical surfaces and splines

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent employs frustoconical (truncated conical) bearing surfaces instead of flat or cylindrical surfaces. The conical geometry provides progressive contact and better load distribution under torsional stresses, enhancing the connection's strength. The curved surfaces also facilitate self-alignment, which can mitigate some manufacturing tolerance issues.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent introduces splines as an intermediary mechanical feature between the rod and the drag damper/blade components. These splines engage to transmit torsional forces while maintaining relative positioning, acting as a mediator that enhances torsional stress resistance through a dedicated load-path mechanism.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 significantly improves the reliability and durability of the elastic ball joints by aligning the rod's axis with the preferred direction of the elastic ball joint, reducing stress in non-preferred directions and enhancing the connection's ability to handle torsional forces, thus improving the rotor's stability and resonance damping performance.

Implementation Method 1

an elastic ball joint intended to be linked to the drag damper

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Implementation Method 2

utilizing frustoconical bearing surfaces and splines to withstand torsional stresses

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP2803571B1Resilient hinged connection between a lag-lead damper and a rotor blade

Publication Date: 2017.03.29 EUROCOPTER FRANCE SA

AI summary

The present invention relates to an elastic articulated joint (1) between a drag damper (10) and a blade (31) of a rotor (30) of a rotary-wing aircraft, said rotor (30) being driven in rotation by a hub about an axis of rotation. Said elastic articulated joint (1) comprises an elastic ball joint (20) connected to said drag damper (10) and having a preferred direction (23) of rotation, a yoke (40) integral with said blade (31), and a rod positioned within said yoke (40) on which said elastic ball joint (20) is positioned. Said rod is positioned along said preferred direction (23) of said elastic ball joint (20) in a plane substantially perpendicular to the axis of rotation of said hub. Furthermore, said rod is fixed in said yoke (40) and in said elastic ball joint (20).