Rounded-Hat Composite Stringer for Aircraft Fuel Flow
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Solution Overview
Problem
The manufacturing of composite stringers for aircraft is time-intensive and labor-intensive, prone to wrinkles, and faces challenges with consistency in size and thickness, as well as deficiencies in radius thinning/thickening, Barely Visible Impact Damage (BVID), and internal fuel flow issues, particularly with trapezoidal hat stringers.
Innovation Solution
The introduction of rounded-hat composite stringers, which are manufactured using forming dies to shape pre-cured composite material into a curved profile with internal conduit capabilities, incorporating radius fillers to ensure smooth flow and enhanced structural integrity, allowing for complex contoured designs that minimize impact damage and improve fluid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If composite stringers are manufactured by layering multiple plies by hand using forming mandrels or vacuum hot drape forming, then the stringers can be formed with complex shapes, but the process becomes time-intensive, labor-intensive, and increases the risk of wrinkles and inconsistency in size and thickness
Solution Approach 1:
The patent applies preliminary action by pre-curing the composite material into a solid charge before forming. This allows the material to be prepared in advance with precise thickness and fiber orientation control, then quickly formed into the final shape using heated forming dies, eliminating the time-consuming manual layering process while maintaining complex shape capability
Solution Approach 2:
The patent replaces the manual mechanical layering process with an automated forming system. A solid composite charge is placed in heated forming dies that apply controlled heat and pressure to shape the material, substituting hand-laying operations with a automated thermal-mechanical forming process that improves consistency and productivity
2Ease of manufacture
If trapezoidal hat stringers are used, then manufacturing is simplified, but deficiencies occur related to radius thinning/thickening, Barely Visible Impact Damage (BVID), and internal fuel flow
Solution Approach 1:
The patent applies spheroidality by transitioning from sharp corners to rounded contours throughout the stringer geometry. The rounded hat profile eliminates stress concentration points at sharp corners, improving resistance to impact damage and fatigue, while the rounded internal conduit profile eliminates flow separation and turbulence, improving fuel flow characteristics
Solution Approach 2:
The patent applies local quality by using radius fillers specifically at the curved fillet portions where radius thinning occurs during forming. This localized reinforcement maintains uniform wall thickness in critical areas, preventing structural weaknesses while preserving the overall rounded geometry that improves reliability
3Productivity
If forming dies are used to shape pre-cured composite material, then production time is reduced and consistency is improved, but the process requires construction of specialized forming equipment
Solution Approach 1:
The patent applies parameter changes by using heated forming dies that control the thermal state of the composite material during forming. The heated dies soften the pre-cured composite charge, allowing it to be shaped under pressure, then cooled to set the final shape. This thermal parameter control enables rapid forming with consistent results using relatively simple equipment
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
The rounded-hat composite stringers provide improved structural stiffness, resistance to impact damage, and enhanced fluid flow characteristics, reducing production costs and time while maintaining high structural integrity and aerodynamic efficiency.
Implementation Method 1
pressing the flat composite charge between the lower and upper forming dies to shape the composite charge into a pre-formed stringer
Implementation Method 2
pressing the flat composite charge between the lower and upper forming dies
Implementation Method 3
curing the pre-formed stringer
Data Source
AI summary
Aircraft that incorporates a rounded-hat composite stringer connected to an inner side of the skin of the aircraft to form an elongate conduit that defines a conduit axis, where the conduit axis includes at least one curving portion. The rounded-hat composite stringer can be manufactured by constructing a lower forming die and an upper forming die, each forming die having a length and defining a curve along at least a portion of the length of the die, cutting a pre-cured flat composite charge dimensioned to form the rounded-hat composite stringer, pressing the flat composite charge between the lower and upper forming dies to shape the composite charge into a pre-formed stringer having an inner side between curved fillet portions, contacting a forming member against the inner side of the pre-formed stringer, applying radius fillers to the curved fillet portions of the pre-formed stringer, curing the pre-formed stringer, and removing the forming member from the cured stringer.