Dual Flex-Beam Assembly for Folding Rotor Blade Stiffness
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Solution Overview
Problem
The existing flex-beam joint in folding rotor blades for rotary wing aircraft lacks sufficient stiffness and area to effectively support the desired structural characteristics, particularly when a hinge is positioned inboard from the midspan, limiting the ability to maintain rotor blade stiffness and accommodate folding mechanisms.
Innovation Solution
A dual flex-beam assembly is introduced, comprising a first and second flex-beam with specific attachment points and configurations, including a flex-beam support member with an attachment end and a wrapping end, and a third flex-beam, which provides enhanced structural support and load distribution through strategically placed fasteners and a hinge end, allowing for improved stiffness and folding capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a hinge is positioned inboard from the midspan to enable folding, then folding capability is improved, but the available area and length to support a flex-beam with desired stiffness characteristics deteriorates
Solution Approach 1:
The single flex-beam is segmented into multiple flex-beams (first flex-beam, second flex-beam, and optionally third flex-beam) that are arranged in a distributed pattern around the torque tube. This segmentation allows the stiffness function to be distributed across multiple smaller elements, enabling adequate stiffness support even when the hinge position reduces the available inboard area.
Solution Approach 2:
The flex-beams are arranged in a three-dimensional configuration around the torque tube, utilizing the circumferential dimension. The first and second flex-beams are positioned at different angular locations, and the third flex-beam (if present) wraps around the torque tube, effectively using the third dimension to provide sufficient support area despite the inboard hinge position.
2Device complexity
If a single flex-beam is used with a inboard hinge, then folding mechanism is simplified, but the structural stiffness and load-bearing capacity deteriorates
Solution Approach 1:
Multiple flex-beams are merged into a composite structural system that collectively provides the required load-bearing capacity. The first flex-beam, second flex-beam, and third flex-beam work together to distribute and bear loads, achieving the necessary structural strength while maintaining the inboard hinge configuration for folding capability.
Solution Approach 2:
The assembly of multiple flex-beams creates a composite structural system where the combined effect of the individual flex-beams provides enhanced load-bearing capacity and stiffness. The distributed arrangement of flex-beams around the torque tube creates a composite structure that is stronger and stiffer than a single equivalent flex-beam would be.
3Device complexity
If fasteners are concentrated at a single midspan joint, then the joint design is simplified, but the load distribution and structural efficiency deteriorates
Solution Approach 1:
The concentrated fastener joint at midspan is segmented into multiple distributed fastener connections. The first flex-beam has fasteners at its first end, the second flex-beam has fasteners at its first and second ends, and the third flex-beam has fasteners at its ends. This segmentation of the load path into multiple connection points improves structural efficiency by distributing loads more effectively throughout the rotor blade assembly.
Data Source
AI summary
A rotor blade for a rotary wing aircraft includes a rotor hub including a first flex-beam attachment member and a flex-beam assembly. The flex-beam assembly includes a flex-beam support member having an attachment end and a wrapping end. A first flex-beam includes a first end, a second end and an intermediate portion. The first end of the first flex-beam is connected at the first flex-beam attachment member and the second end of the first flex-beam being connected to the attachment end of the flex-beam support member. A second flex-beam includes first end portion, a second end portion and an intermediate section. The first end portion of the second flex-beam is connected at the first flex-beam attachment member, the second end portion of the second flex-beam being connected at the second flex-beam attachment member and the intermediate section extending about the wrapping end of the flex-beam support member.