Aircraft Airframe Panel with Stepped Stringer Joints
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Solution Overview
Problem
The shimming operation required to align aircraft wing panels due to manufacturing tolerances results in a high workload, as only one of the three potential contact surfaces between the rib and the lower skin comes into contact, leading to gaps that necessitate the insertion of shims.
Innovation Solution
The airframe panel design features a flat surface connecting adjacent stringers in regions with ribs and a stepped surface in regions without ribs, eliminating the need for shimming by ensuring the rib contacts only a single surface, while maintaining rigidity through thick-walled portions and reducing weight with thin-walled sections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the lower skin includes thick-walled portions and thin-walled portions to conform to ribs, then the rigidity is secured and weight is reduced, but multiple contact surfaces are created requiring shimming operations
Solution Approach 1:
The lower skin is designed with different thicknesses in different regions: thick-walled portions at both sides of the thin-walled portion to provide rigidity and contact surfaces for stringers, and a thin-walled portion in the middle to reduce weight. This local differentiation allows the skin to have exactly one contact surface with the rib edge, eliminating the need for shimming operations while maintaining structural integrity.
2Adaptability or versatility
If multiple contact surfaces are provided between rib and lower skin, then manufacturing flexibility is improved, but gaps occur due to tolerances requiring shims
Solution Approach 1:
The invention extracts the unnecessary contact surfaces from the design. Instead of providing multiple contact surfaces (c1, c2, c3) as in conventional designs, the lower skin is configured to have exactly one contact surface with the rib edge. This single contact surface approach eliminates gaps caused by manufacturing tolerances and removes the need for shimming operations, thereby improving manufacturing precision without sacrificing adaptability.
3Ease of manufacture
If the lower skin has uniform thickness, then manufacturing is simplified, but weight increases and rigidity at stringer locations is compromised
Solution Approach 1:
The lower skin employs local quality differentiation with thick-walled portions at both sides to provide rigidity for stringer attachment and a thin-walled portion in the middle to reduce weight. This localized thickness variation optimizes the weight-strength ratio while maintaining ease of manufacture through a straightforward forming process that creates the desired thickness profile.
Data Source
AI summary
An airframe panel for aircraft having stringers and ribs which enables reduction of the workload of the shimming operation includes a plurality of stringers provided on the inner surface of a lower skin along the spanwise direction of a wing, and a plurality of ribs provided along the chordwise direction of the wing. In a part of the panel in which a rib is provided, a flat support surface connects the two adjacent stringers. In another part of the panel in which no rib is provided, a stepped surface connects the two adjacent stringers where the stepped surface includes a thin-walled groove, and thick-walled bases to be connected to the stringers located at both sides of the groove.