Four-Bar Flapping Rotor Hub for Lead-Lag Vibration Reduction

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Solution Overview

Problem

Existing rotor designs, such as rigid and fully articulated rotors, face challenges with weight, fuel consumption, payload capacity, and lead-lag vibrations, while semi-rigid and fully articulated rotors compromise on response times and require additional dampers.

Innovation Solution

The use of a four-bar linkage in rotor blades allows for a flapping motion that limits lead-lag vibrations by shifting the center of gravity's instantaneous rotation, reducing the radius of movement and requiring smaller dampers, while maintaining rapid response to control inputs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If rigid rotors are used to couple rotor blades to the hub, then structural strength is improved, but weight increases and fuel consumption increases

Engineering Contradiction:

Improvestructural strengthVSAvoidweight

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

The rotor system is segmented into multiple functional components: rigid hub structure for strength, semi-rigid blade roots for stress relief, and articulated flapping hinges for vibration control. This segmentation allows each component to be optimized for its specific function rather than requiring the entire system to be overly rigid.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The rotor design incorporates dynamic elements including flapping hinges that allow blades to move in response to aerodynamic forces, and lead-lag dampers that actively manage vibrations. This dynamic capability reduces the need for excessive structural rigidity throughout the entire system, thereby reducing weight while maintaining strength where needed.

Inventive Principle:

Principle #15Dynamics

2Stress or pressure

If semi-rigid rotors are used to reduce stresses on the hub, then stress on hub is reduced, but response time deteriorates

Engineering Contradiction:

Improvestress on hubVSAvoidresponse time

Core Design Contradiction:

Stress or pressureVSLoss of time

Solution Approach 1:

The semi-rigid rotor design incorporates flapping hinges that provide controlled movement capability. This allows the blades to dynamically respond to aerodynamic forces and control inputs, maintaining rapid response characteristics while the hub structure experiences reduced peak stresses due to the compliance provided by the hinge mechanisms.

Inventive Principle:

Principle #15Dynamics

3Stress or pressure

If fully articulated rotors are used to eliminate moments transferred to the hub, then moments on hub are reduced, but device complexity increases

Engineering Contradiction:

Improvemoments on hubVSAvoiddevice complexity

Core Design Contradiction:

Stress or pressureVSDevice complexity

Solution Approach 1:

The fully articulated rotor system is divided into distinct functional segments: flapping hinges for vertical plane movement, lead-lag hinges for horizontal plane movement, and pitch control mechanisms. This segmentation allows each component to handle specific moments and forces, reducing the overall moment load on the hub while keeping each individual component relatively simple and manageable.

Inventive Principle:

Principle #1Segmentation

4Stress or pressure

If articulated rotors are used to reduce moments on hub, then moments transferred to hub are reduced, but lead-lag vibrations increase

Engineering Contradiction:

Improvemoments on hubVSAvoidlead-lag vibrations

Core Design Contradiction:

Stress or pressureVSObject-generated harmful factors

Solution Approach 1:

The lead-lag dampers are designed to convert the harmful vibrational energy into useful damping effects. The dampers absorb and dissipate the lead-lag vibrations through controlled friction or viscous damping mechanisms, transforming the harmful oscillatory motion into heat energy, thereby reducing vibrations while maintaining the moment-reducing benefits of the articulated design.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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

This design reduces lead-lag vibrations, minimizes the size and weight of the rotor hub, and enhances the agility and response of the rotorcraft by distributing forces and moments effectively.

Implementation Method 1

The use of a four-bar linkage in rotor blades allows for a flapping motion that limits lead-lag vibrations by shifting the center of gravity's instantaneous rotation

Methodology Applied

Scientific EffectFour-bar linkage: Four-Bar Linkage

Implementation Method 2

This design reduces lead-lag vibrations, minimizes the size and weight of the rotor hub, and enhances the agility and response of the rotorcraft by distributing forces and moments effectively

Methodology Applied

Scientific EffectForce distribution: Force

Data Source

PatentUS12528578B2Four-bar flapping rotors for aircraft and associated methods

Publication Date: 2026.01.20 THE BOEING CO

AI summary

Four-bar flapping rotors for aircraft and associated methods are disclosed. An example a flapping rotor hub described herein includes a rotor hub having a first end and a second end, the first end opposite the second end along an axis of rotation of the rotor hub, a first link rotatably coupled to the rotor hub at the first end, the first link to rotate in a plane parallel to the axis of rotation, a second link rotatably coupled to the rotor hub at the second end, the second link to rotate in the plane, and a pitch housing rotatably coupled to the first link at a third end of the pitch housing, the pitch housing rotatably coupled to the second link at a fourth end of the pitch housing, the pitch housing to rotate and translate in the plane, the pitch housing to receive a rotor blade.