Composite Stringer End Cap for Aircraft Panel Sealing
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Solution Overview
Problem
Composite stringers in aircrafts are susceptible to impact damage and moisture ingress due to open ends, and manufacturing specific bevel dimensions is costly and impractical.
Innovation Solution
The use of composite stringer end caps with a base, vertically extending wall, and overlap section to protect and seal the open ends, eliminating the need for precise manufacturing of stringer ends, and can be fabricated using methods like 3D printing or co-cured with the panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If composite stringer ends are left open to reduce weight and improve appearance, then manufacturing cost and complexity are reduced, but the stringers become susceptible to impact damage and moisture ingress
Solution Approach 1:
The stringer system is divided into two functional parts: the main stringer body and the end cap. The end cap is a separate component that can be manufactured independently and attached to the stringer end, allowing each part to be optimized separately for manufacturing ease and protective function.
Solution Approach 2:
The end cap serves as a sacrificial protective element that can be easily replaced if damaged, protecting the more valuable and difficult-to-manufacture stringer body. This allows the main stringer to be manufactured with simpler, less precise processes.
2Reliability
If composite stringer ends are pre-cut to final bevel dimensions, then the open ends are protected from damage, but tooling and manufacturing costs increase
Solution Approach 1:
The protective function is separated from the main stringer manufacturing process by using a distinct end cap component. This allows the stringer body to be manufactured using simpler, less expensive processes without requiring precise pre-cutting tooling.
Solution Approach 2:
The end cap is pre-formed with the necessary protective features and bevel dimensions, then attached to the stringer end. This transfers the manufacturing precision requirements to a separate, more easily manufactured component rather than the main stringer body.
3Ease of manufacture
If un-cut composite stringer material is laid up and cured, then manufacturing flexibility is improved, but the stringer ends cannot be machined to final bevel dimensions due to intimate contact with skin plies
Solution Approach 1:
The solution separates the stringer body manufacturing from the end finishing operations by introducing an attachable end cap. This allows the stringer body to be manufactured with full flexibility using un-cut material, while the end cap provides the necessary precise bevel dimensions.
Solution Approach 2:
The end cap acts as an intermediary component between the skin plies and the final beveled surface. It allows the stringer end to achieve precise dimensions without requiring direct machining of the composite material that would damage skin plies.
4Reliability
If end caps are added to protect stringer ends, then protection and sealing are improved, but device complexity increases
Solution Approach 1:
The end cap is designed to perform multiple functions simultaneously: it protects the stringer end from impact damage, seals the open end to prevent moisture ingress, and provides the necessary beveled appearance. This consolidation of functions into a single component minimizes the increase in overall system complexity.
Data Source
AI summary
An aircraft panel assembly including a panel, a number of open-ended composite stringers, and a number of stringer end caps. Each stringer end cap covers an open end of one of the stringers and includes a base, a vertically extending wall, and an overlap section. The base is bonded to the panel near the open end of the stringer. The vertically extending wall is angled upward from the base and includes an upper periphery. The overlap section extends horizontally from the upper periphery and is bonded to the stringer near the open end of the stringer.