Aircraft Access Door Misassembly Prevention via Convex-Concave Interference

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Solution Overview

Problem

Aircraft access doors often misassemble due to the concentration of stresses around concave portions in openings, leading to increased weight and complexity in the airframe.

Innovation Solution

The airframe features convex portions in each opening and an incorrect fitting detection portion on the closure member bodies, preventing misassembly by interfering with each other when incorrectly paired, while reducing stress concentrations by avoiding concave portions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a concave portion is formed in the opening to prevent misassembly, then misassembly prevention is improved, but stress concentration increases and weight increases

Engineering Contradiction:

Improvemisassembly preventionVSAvoidstress concentration

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

Instead of forming a concave portion in the opening to prevent misassembly, the patent inverts the approach by forming a convex portion on the closure member body that corresponds to the concave portion in the opening. This inversion transfers the stress concentration from the opening (airframe structure) to the closure member body (removable component), thereby protecting the airframe from stress concentration while still preventing misassembly through the convex-concave engagement mechanism

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If a concave portion is formed in the opening to prevent misassembly, then misassembly prevention is improved, but the weight of the airframe increases

Engineering Contradiction:

Improvemisassembly preventionVSAvoidairframe weight

Core Design Contradiction:

ReliabilityVSWeight of stationary object

Solution Approach 1:

The patent moves the engagement feature from the airframe (opening with concave portion) to the closure member (body with convex portion). This inversion ensures that any additional material required for misassembly prevention is located in the removable closure member rather than the permanent airframe structure, thereby minimizing the weight impact on the stationary airframe

Inventive Principle:

Principle #13The other way round (Inversion)

3Strength

If the thickness of material around the opening is increased to resist stresses, then strength is improved, but the weight of the airframe increases

Engineering Contradiction:

Improvestrength around openingVSAvoidairframe weight

Core Design Contradiction:

StrengthVSWeight of stationary object

Solution Approach 1:

Instead of increasing the thickness of material around the opening in the airframe to resist stresses, the patent inverts the solution by providing stress-resisting features (convex portion and reinforcement) on the closure member body. This allows the airframe opening to maintain its original thin-walled structure and low weight, while the closure member absorbs the stress loads through its reinforced geometry

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9027882B2Airframe of aircraft, panel assembly for aircraft

Publication Date: 2015.05.12 MITSUBISHI HEAVY IND LTD

AI summary

The present invention prevents misassembly of access doors while reducing stress concentrations. A hole-side convex portion 80 is formed in each opening 12 at one or more locations in a circumferential direction, and a door-side rib 70 is formed on each door body 30. The hole-side convex portions 80 formed in the openings 12A to 12C differ in location in the circumferential direction among the plural openings 12A to 12C. The door-side ribs 70 formed on the respective door bodies 30A to 30C are provided in such locations as not to interfere with the hole-side convex portions 80 provided in the openings 12A to 12C in correct combination with the door bodies 30A to 30C.