Composite Helicopter Flexbeam Torsion Box Design
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Solution Overview
Problem
Existing composite flexbeams for joining helicopter rotor blades to rotary hub assemblies face challenges in achieving sufficient torsional stiffness while allowing flexibility to accommodate flapping, lead-lag, and pitch movements, often resulting in inappropriate shear loads on unidirectional fibers due to high centrifugal forces and torsion moments.
Innovation Solution
A composite matrix bar with a torsion box structure, featuring upper and lower layers of angled fibers and central unidirectional fibers, which reduces shear loads on unidirectional fibers by absorbing torsion moments within the torsion box, ensuring high torsion stiffness and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the bar uses a flat cross section with high moment of inertia in lead lag direction, then centrifugal force resistance and stiffness are improved, but torsion moments increase due to the flat cross section geometry
Solution Approach 1:
The bar employs a composite material structure with unidirectional fibers arranged in specific orientations (0°, ±45°, 90°) to create anisotropic mechanical properties. This composite construction allows the bar to achieve high stiffness in the lead-lag direction while managing torsional stresses through the coordinated arrangement of fibers with different orientations, resolving the contradiction between centrifugal force resistance and torsion moment resistance.
Solution Approach 2:
The patent applies local quality by varying the fiber orientation angles at different locations and layers of the bar cross-section. The unidirectional fibers are arranged with different orientations in different plies, creating localized mechanical properties that optimize resistance to both centrifugal forces and torsion moments in specific regions of the bar structure.
2Adaptability or versatility
If the bar allows flexibility for flapping, lead-lag, and pitch movements, then adaptability is improved, but structural integrity deteriorates under high centrifugal forces and torsion moments
Solution Approach 1:
The composite material construction with multi-directional unidirectional fibers provides both flexibility and structural integrity. The 0° fibers resist centrifugal forces, the ±45° fibers handle torsion moments, and the 90° fibers provide transverse strength, allowing the bar to maintain structural integrity while accommodating flapping, lead-lag, and pitch movements.
Solution Approach 2:
The patent changes the mechanical parameters of the bar by controlling fiber orientation angles and layer configurations. This allows the bar to exhibit anisotropic mechanical properties with high stiffness in specific directions while maintaining flexibility in others, resolving the contradiction between movement flexibility and structural integrity under load.
Data Source
AI summary
The invention is related to a bar (1) of composite matrix material, said bar (1) having a longitudinal axis (8) perpendicular to a cross section with upper and lower surfaces (2, 3). Said composite matrix material comprises a first group of fibers which extend parallel to the longitudinal axis (8) and a second group of fibers which extend at an angle to the longitudinal axis (8). At least one torsion box (17) is provided inside the cross section along the longitudinal axis (8). Said at least one torsion box (17) comprises an upper and a lower layer (10, 21, 11, 22) respectively offset of the longitudinal axis (8) and of the upper and the lower surfaces (2, 3), said upper and lower layers (10, 21, 11, 22) being laterally joint, while the cross section between the upper and the lower layer (10, 21, 11, 22), between the upper layer (10, 21) and the upper surface (2) and between the lower layer (11, 22) and the lower surface (3) is filled with the first group of fibers extending essentially parallel to the longitudinal axis (8).