Hat Stiffener Composite Fuselage Panels
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Solution Overview
Problem
Current composite aircraft structures require thicker fuselage skins to meet impact resistance and damage tolerance requirements, leading to increased weight and cost due to the need for separate manufacturing processes and fasteners for frames and shear ties, with suboptimal load paths and unnecessary fasteners.
Innovation Solution
A composite panel structure design featuring annular frames and elongated stringers with hat-shaped cross sections, where stringers and frames intersect on opposite sides of the skin, eliminating the need for shear ties and reducing fasteners, with an outer skin providing impact resistance and an inner skin carrying design loads, and using offsets made of rigid foam or polymer for additional stiffness and insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If thicker fuselage skins are used to meet impact resistance and damage tolerance requirements, then structural strength and safety are improved, but weight and manufacturing cost increase
Solution Approach 1:
The patent employs composite materials throughout the fuselage structure, including composite hat-stiffener frames and composite skins. This allows for optimized strength-to-weight ratio by selecting fiber orientations, material compositions, and stacking sequences that provide required impact resistance while minimizing weight compared to traditional homogeneous materials
Solution Approach 2:
The hat-stiffener frames are pre-formed with integrated attachment features and reinforcement elements before being assembled to the fuselage skin. This preliminary structuring allows the skin to be optimized for minimal thickness since the frames provide pre-positioned structural support and load distribution, eliminating the need for excessive skin thickness to compensate for weak attachment points
2Manufacturing precision
If separate manufacturing processes are used for frames and shear ties, then manufacturing precision can be maintained, but device complexity and production cost increase
Solution Approach 1:
The patent eliminates shear ties by integrating frame attachment directly to the skin through bonded and mechanically fastened connections. The frames are designed with integrated attachment features that combine the functions of shear ties, flange attachments, and structural support into single components, reducing the number of distinct parts and manufacturing processes required
Solution Approach 2:
The hat-stiffener frames serve multiple functions simultaneously: they provide structural stiffness, attach the skin to the longitudinal members, transfer loads between skin and stringers, and provide attachment points for other fuselage components. This multi-functionality eliminates the need for separate shear tie components and simplifies the overall manufacturing process
3Stability of the object's composition
If frames and stringers intersect on the same side of the skin, then structural continuity is maintained, but the number of fasteners and assembly complexity increase
Solution Approach 1:
The patent offsets the attachment points of frames and stringers in the thickness direction of the skin, so they attach to opposite sides or at different depths. This dimensional separation allows both stringers and frames to maintain their continuity and load paths without requiring numerous fasteners at intersection points, while still achieving effective load transfer through the skin thickness
4Reliability
If more fasteners are used at stringer-frame intersections, then fail-safety is improved, but manufacturing cost and assembly time increase
Solution Approach 1:
The frames and stringers are pre-assembled with attachment features positioned and configured before final skin attachment. This preliminary arrangement allows for optimized fastener placement and reduced numbers, as the structural relationships are established in advance rather than requiring precise alignment and multiple fasteners during final assembly
Solution Approach 2:
The skin itself acts as an intermediary load transfer element between frames and stringers. Rather than requiring multiple fasteners to directly connect frames and stringers, the skin mediates the load transfer through bonded and mechanically fastened connections, reducing the number of fasteners needed at intersection points while maintaining fail-safety through the distributed attachment scheme
Data Source
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AI summary
A composite panel structure (10) for an aircraft includes a plurality of annular, hat-shaped frames (12) disposed coaxially along a long axis of the aircraft in a spaced, parallel relationship, an inner skin (14) having an inner surface bonded to an outer surface of the hat frames, a plurality of elongated, hat-shaped stringers (16) disposed in a longitudinal direction along an outer surface of the inner skin in a spaced, parallel relationship, a solid or rigid foam offset (18) bonded to an outer surface of each of the stringers, and an outer skin (20) having an inner surface bonded to an upper surface of each of the offsets. The inner skin carries the loads of the structure and the outer skin defines an aerodynamic surface of the aircraft and provides impact and lighting protection. The frames, inner skin and stringers are formed on a single forming tool and cured and bonded with each other simultaneously.