U-Shaped Flex Beam Rotor Assembly Stiffness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flex-beam rotors for coaxial rotorcraft lack the necessary flat-wise stiffness and vibratory response, leading to potential blade collisions and inadequate performance at higher speeds.
Innovation Solution
The design incorporates U-shaped flexible structural members with arms and end portions having a cross-sectional height greater than thickness, secured rotor blades via inboard and outboard bearings, and features like twist and taper to enhance stiffness and vibratory response, ensuring improved rotor assembly performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional flex-beam rotor is used, then the rotor assembly is lightweight and cost effective, but it lacks the necessary flat-wise stiffness to prevent blade collisions and provide desired vibratory response
Solution Approach 1:
The patent changes the geometric parameters of the flex beam by orienting the principal axis of the cross-section substantially in the flatwise direction, rather than the conventional edgewise orientation. This parameter change increases the moment of inertia in the flatwise direction, thereby increasing stiffness without adding significant weight. The cross-sectional dimensions and material distribution are optimized to provide maximum stiffness-to-weight ratio.
Solution Approach 2:
The patent employs composite material construction for the flex beam, utilizing fiber-reinforced polymers with fibers oriented to maximize stiffness in the flatwise direction. This allows the beam to achieve high stiffness values while maintaining low weight, as composite materials provide superior strength-to-weight and stiffness-to-weight ratios compared to conventional materials.
2Reliability
If rotor blades are secured via traditional single bearing configuration, then the structure is simple, but it provides inadequate vibratory response and stiffness control
Solution Approach 1:
The patent segments the support function by implementing two separate bearings (inboard and outboard) along the flex beam span, rather than using a single bearing. This segmentation allows independent control of different vibratory modes and stiffness characteristics, with the inboard bearing handling root stresses and the outboard bearing controlling blade tip dynamics and flapping motion.
Solution Approach 2:
The flex beam itself acts as an intermediary element between the rotor hub and the blade, with the dual bearing configuration providing intermediate support points. This intermediary arrangement allows the beam to flex and absorb vibrations while maintaining proper blade alignment and reducing transmitted vibrations to the hub.
Data Source
AI summary
A rotor assembly for a rotary wing aircraft includes a rotor hub having a central axis. The rotor hub is rotatable about the central axis. A plurality of flexible structural members extend radially outwardly from the rotor hub. Each flexible structural member is substantially U-shaped having a first arm extending from the hub, a second arm extending from the hub, and an end portion connecting the first arm to the second arm at a radially outboard end of the flexible structural member. The first arm, the second arm and/or the end portion have a cross section with a height along the central axis greater than a thickness of the cross section to increase stiffness of the rotor assembly along the central axis. The rotor assembly further includes a plurality of rotor blades, each rotor blade being secured to each flexible structural member of the plurality of flexible structural members.