CFRP Fuselage Frame and Clevis Securement for Tail Fin Shear Loads

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Solution Overview

Problem

The use of aluminum fuselage frames with CFRP skins in aircraft leads to corrosion and thermal fatigue due to differing thermal expansion coefficients, requiring additional protective measures and extended production times.

Innovation Solution

The implementation of CFRP fuselage frames secured with a securement assembly using clevis members and fasteners to transfer shear loads from the vertical fin assembly, optimizing shear resistance and eliminating the need for corrosion protection and material fatigue inspections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If aluminum fuselage frames are used with CFRP skins, then structural strength is improved, but corrosion occurs due to material incompatibility

Engineering Contradiction:

Improvestructural strengthVSAvoidcorrosion

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The patent applies homogeneity by using CFRP (carbon fiber reinforced polymer) material for both the fuselage frame and skin, eliminating the aluminum-CFRP material incompatibility that causes corrosion. This creates a homogeneous material system where thermal expansion coefficients are matched and galvanic corrosion is prevented.

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The patent utilizes composite materials by replacing traditional aluminum frames with CFRP frames that have similar thermal expansion characteristics to CFRP skins. This composite material solution resolves the corrosion issue while maintaining structural strength requirements.

Inventive Principle:

Principle #40Composite materials

2Strength

If aluminum fuselage frames are used with CFRP skins, then structural strength is improved, but thermal fatigue occurs due to different thermal expansion coefficients

Engineering Contradiction:

Improvestructural strengthVSAvoidthermal fatigue resistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The patent applies homogeneity by using CFRP material for both frames and skins, ensuring matched thermal expansion coefficients. This eliminates the thermal expansion mismatch that causes thermal fatigue in aluminum-CFRP composite structures.

Inventive Principle:

Principle #33Homogeneity

Solution Approach 2:

The patent changes the material parameter (thermal expansion coefficient) by selecting CFRP frames with thermal expansion characteristics similar to CFRP skins, thereby eliminating thermal fatigue issues while maintaining structural strength.

Inventive Principle:

Principle #35Parameter changes

3Ease of manufacture

If metallic frames are used, then ease of manufacture is improved, but production time increases due to de-burring and sealing requirements

Engineering Contradiction:

Improveease of manufactureVSAvoidproduction time

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The patent extracts and eliminates the time-consuming post-processing steps (de-burring and fay surface sealing) by using CFRP frames that do not require these operations, thereby reducing production time while maintaining ease of manufacture.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent adopts CFRP frames that eliminate the need for costly and time-consuming corrosion protection measures and fatigue inspections required for aluminum frames, reducing overall production time and costs.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 solution reduces production costs and time by eliminating the need for corrosion protection and thermal fatigue inspections, while providing optimal shear load resistance using CFRP materials with similar thermal expansion characteristics.

Implementation Method 1

A second end portion of the first clevis member is secured to a first fuselage frame constructed of a composite material, with a first fastener which extends through the second end portion and the first fuselage frame in a first direction transverse to the first fuselage frame.

Methodology Applied

Scientific EffectShear load transfer: Shear Stress

Implementation Method 2

Aluminum, for example, has a thermal expansion co-efficient greater than that of the CFRP. Aluminum experiences contraction in cold conditions and expands in hot conditions relative to the CFRP material which in comparison is thermally neutral.

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS12404003B2CFRP fuselage frame with securement to vertical tail fin

Publication Date: 2025.09.02 THE BOEING CO

AI summary

A securement assembly for securing a vertical tail fin assembly to an aircraft includes a first lug member secured to the vertical tail fin assembly. The securement assembly further includes a first clevis member. The first clevis member includes a first end portion of the first clevis member is engaged to the first lug member. A second end portion of the first clevis member is secured to a first fuselage frame constructed of a composite material with a first fastener which extends through the second end portion and the first fuselage frame in a first direction transverse to the first fuselage frame.