Continuous Stiffening Frames for Aircraft Fuselage-Wing Box Joints
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Solution Overview
Problem
The connection between the fuselage and the wing box in aircraft structures is prone to fatigue-related failures due to stress concentrations at the junctions of frames and outer frame lower sections, which complicates the design and increases the risk of mechanical fragility.
Innovation Solution
The solution involves continuous stiffening frames that pass through notches in the wing box panel, eliminating the need for outer frame lower sections, and using fittings such as angles to cover notches and reestablish stiffness by providing heel support to the frames, thereby reducing stress concentrations and enhancing structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional outer frame lower sections are used to connect frames to the rib, then the force path continuity is ensured, but the junction area becomes prone to fatigue-related failures due to stress concentrations
Solution Approach 1:
The invention removes the outer frame lower sections from the structure, eliminating the problematic junction between frames and outer frame lower sections that was prone to fatigue failures. The frames are made continuous through notches in the wing box panel, directly connecting to the rib without the intermediate outer frame lower sections that caused stress concentrations.
Solution Approach 2:
The invention segments the continuous frame into two parts: the main frame body that passes through the panel via notches, and the heel parts that are interrupted before passing through the panel. This segmentation allows the frame to maintain continuity for force transmission while avoiding stress concentration at the panel junction.
2Device complexity
If frames are made continuous through notches in the wing box panel, then the complexity of the connection is reduced and fatigue risks are minimized, but the panel stiffness is weakened
Solution Approach 1:
The invention applies different quality requirements to different parts of the frame: the main frame body is made continuous through the panel to simplify connection and reduce fatigue risks, while the heel parts are interrupted before passing through the panel to preserve panel stiffness. This local differentiation optimizes both connection simplicity and structural strength.
3Strength
If heel parts are positioned at the free ends of frames to increase stiffness, then the frame stiffness is improved, but the panel requires additional notching which increases complexity and potential fatigue issues
Solution Approach 1:
The heel parts are positioned and configured before the frames pass through the panel notches. By interrupting the heel parts before they reach the panel, the design preliminarily establishes the frame stiffness through the heel configuration while avoiding the need for additional complex notching at the heel locations, thus simplifying the overall notching requirements.
Data Source
AI summary
The stiffening frames (14) of an aircraft fuselage (2) remain continuous while passing through an upper panel (5) of the wing box and extend over the ribs (3) situated in that box. The overall mechanical strength of the assembly is improved, despite the notches it is necessary to make in the panel (5).