Aircraft Landing Gear Drag Brace Backup Fitting

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Solution Overview

Problem

Aircraft main landing gear drag brace fittings face challenges in managing high loads during landing and braking, leading to out-of-plane loads on composite rear spars, which can cause delamination and structural integrity issues, and existing backup fitting structures are heavy, complex, and limited in applicability to various wing sizes.

Innovation Solution

The introduction of a backup fitting assembly that includes a side-of-body fitting, an intercostal member, and a rib post, which creates a load path that transfers drag loads in-plane, reducing out-of-plane loads on the rear spar, and is designed to be smaller, lighter, and easier to install, allowing for use in a variety of aircraft wing configurations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a traditional backup fitting structure is used to support the drag brace fitting, then the structural integrity is improved, but the weight and device complexity increase significantly

Engineering Contradiction:

Improvestructural integrityVSAvoidweight of backup fitting

Core Design Contradiction:

StrengthVSWeight of moving object

Solution Approach 1:

The backup fitting is divided into multiple discrete components: a first backup fitting portion that contacts the rear spar, a second backup fitting portion that contacts the drag brace fitting, and a fastener system. This segmentation allows each component to be optimized independently and facilitates easier installation and maintenance while reducing overall weight compared to a monolithic structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The backup fitting uses localized contact surfaces and distributed fasteners rather than a comprehensive heavy structure. The first backup fitting portion provides localized support at the rear spar interface, while the second portion provides localized support at the drag brace fitting interface, reducing material usage and weight while maintaining structural integrity.

Inventive Principle:

Principle #3Local quality

2Strength

If a traditional backup fitting structure is used to support the drag brace fitting, then the structural integrity is improved, but the device complexity and installation difficulty increase

Engineering Contradiction:

Improvestructural integrityVSAvoidcomplexity of backup fitting structure

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The backup fitting assembly serves multiple functions: it provides structural support to the drag brace fitting, transfers loads to the rear spar and wing structure, and maintains the geometric relationship between components. This multi-functionality reduces the need for additional separate components, simplifying the overall device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If the drag brace fitting is supported directly on the rear spar, then the device complexity is reduced, but out-of-plane loads cause delamination and structural integrity issues

Engineering Contradiction:

Improvesimplicity of fitting structureVSAvoidstructural integrity of composite rear spar

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The first backup fitting portion acts as an intermediary between the drag brace fitting and the rear spar. It provides a load path that transfers forces through the fastener system to the rear spar, preventing direct out-of-plane loading that would cause delamination. The intermediary structure distributes loads more favorably across the composite spar.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The harmful out-of-plane load path is extracted from the direct drag brace fitting-to-spar connection. By introducing the backup fitting assembly with its specific fastener configuration, the load path is redirected to follow a more favorable trajectory that avoids delamination-prone regions of the composite rear spar.

Inventive Principle:

Principle #2Taking out (Extraction)

4Strength

If existing backup fitting structures are used, then structural support is provided, but they are limited in applicability to various wing sizes

Engineering Contradiction:

Improvestructural support capabilityVSAvoidapplicability to various wing sizes

Core Design Contradiction:

StrengthVSAdaptability or versatility

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The backup fitting design allows for parameter variations to accommodate different wing sizes and configurations. The fastener spacing, fitting dimensions, and material properties can be adjusted while maintaining the fundamental load path and structural integrity, enabling the same basic design to be adapted across different aircraft types.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentEP3725674B1Aircraft main landing gear drag brace backup fitting assemblies and related methods

Publication Date: 2023.12.20 THE BOEING CO

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AI summary

An example aircraft wing disclosed herein includes a rear spar (200) having a rear side (306) and a front side (308) opposite the rear side, a side-of-body rib (502) coupled to the rear spar, a rib post (510) disposed on the front side of the rear spar, where the rib post is to couple a second rib (508) to the rear spar, a side-of-body fitting (516) coupled to the side-of-body rib, an intercostal member (518) coupled between the side-of-body fitting and the rib post, and a drag brace fitting (216) disposed on the rear side of the rear spar. The drag brace fitting is coupled to the rib post and the side-of-body fitting via a first plurality of fasteners (310(a,b)) extending through the rear spar.