Landing Gear Washer Spring Biasing Against Retraction Creep

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Solution Overview

Problem

Aircraft landing gear systems face issues with unintentional retraction due to the susceptibility of helical springs to vibration, weight, and creep, which affects the stability and reliability of the deployed position.

Innovation Solution

The use of elastically deformable washers, such as conical or hemispherical washers, instead of helical springs, provides a biasing force to maintain the landing gear in a deployed position, with a sliding rod and disk arrangement to prevent buckling and torsional stress, and the use of anisotropic materials like carbon fibre reinforced thermoplastics for improved resilience and reduced creep.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If helical springs are used to provide biasing force, then the landing gear can be deployed, but the system suffers from vibration susceptibility, high weight, and creep

Engineering Contradiction:

Improvestability of deployed positionVSAvoidweight of spring

Core Design Contradiction:

ReliabilityVSWeight of moving object

Solution Approach 1:

The patent changes the fundamental parameters of the spring by transitioning from a helical geometry to a planar washer-based stack. This parameter change enables the system to achieve the required biasing force while significantly reducing weight and eliminating the vibration and creep issues associated with traditional helical springs.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material construction for the washer stack, combining multiple materials with different elastic properties to optimize the biasing force characteristics. This allows the system to achieve reliable deployment stability with reduced weight compared to solid metal helical springs.

Inventive Principle:

Principle #40Composite materials

2Reliability

If helical springs are used to provide biasing force, then the landing gear can be deployed, but the system suffers from aeroelastic vibrations

Engineering Contradiction:

Improvestability of deployed positionVSAvoidaeroelastic vibrations

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the geometric parameters of the spring element from a three-dimensional helical structure to a two-dimensional planar washer stack. This fundamental geometric parameter change alters the aerodynamic characteristics, eliminating the bluff body effect and associated aeroelastic vibrations that plague traditional helical springs in flight environments.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the potential harm of aerodynamic drag on a spring element into a benefit by using flat washers that present minimal aerodynamic profile. The planar geometry that would seem to reduce structural efficiency actually provides superior aerodynamic performance, turning the flight environment from a harmful factor into a neutral or beneficial condition.

Inventive Principle:

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

3Force

If helical springs are constantly in tension, then the landing gear maintains deployment force, but the material suffers from creep over time

Engineering Contradiction:

Improvebiasing forceVSAvoidduration of tensile stress

Core Design Contradiction:

ForceVSDuration of action of stationary object

Solution Approach 1:

The patent inverts the stress state of the spring element from constant tension in helical springs to constant compression in the washer stack. This inversion is achieved by positioning the washers between surfaces that push them together, creating a compressive preload that maintains the biasing force without subjecting the material to prolonged tensile stress, thereby eliminating creep.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the stress state parameter from tensile to compressive by fundamentally altering the spring mechanism geometry. The washer stack configuration naturally generates compressive forces, and this parameter change prevents the creep phenomenon that occurs in materials under sustained tensile loading, significantly extending the service life of the biasing mechanism.

Inventive Principle:

Principle #35Parameter changes

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 enhances the robustness and impact resistance of the landing gear, reduces the likelihood of creep, and minimizes aeroelastic vibrations, resulting in a more reliable and stable deployment mechanism.

Implementation Method 1

a spring coupled to the first and second members, the spring comprising a plurality of elastically deformable washers, the spring being arranged to generate a biasing force between the first and second members

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS12091161B2Aircraft landing gear

Publication Date: 2024.09.17 MESSIER DOWTY

AI summary

An aircraft landing gear comprising: a first member, a second member pivotally coupled to the first member, and a spring coupled to the first and second members, the spring comprising a plurality of elastically deformable washers, the spring being arranged to generate a biasing force between the first and second members to bias the first member toward a predetermined orientation relative to the second member.