Elastic Flapping Hinge with Divergent Plates for Rotor Hub
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Solution Overview
Problem
Conventional elastic hinge systems in rotary wing aircrafts face challenges in achieving a reduced flapping hinge distance without compromising the structural integrity and maneuverability, leading to high natural flapping frequencies and stress on blade connectors.
Innovation Solution
An elastic flapping hinge system comprising multiple elastically deformable plates with varying bending stiffness for flapping and lead-lag movements, diverging at a predetermined angle to create a V-shaped gap, allowing for a reduced flapping hinge distance while maintaining strength and control responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the flapping hinge distance is reduced to improve control response and maneuverability, then the natural flapping frequency increases, but this leads to high vibrations and large stresses on blade connectors
Solution Approach 1:
The elastic hinge unit is segmented into distinct functional regions: a flapwise-soft region with reduced bending stiffness for flapping movements, lead-lag-soft regions for lead-lag motions, and torsion-soft regions for blade rotation. This segmentation allows each region to be optimized for its specific function, enabling reduced flapping hinge distance while managing vibrations through the specialized soft regions.
Solution Approach 2:
The flexbeam element exhibits spatially varying bending stiffness properties, with the flapwise-soft region having specifically reduced stiffness in the flapping direction while maintaining appropriate stiffness in other directions. This local quality modification allows the structure to be compliant where needed (reducing vibrations) while maintaining overall structural integrity.
2Length of moving object
If the bending stiffness for flapping is reduced to achieve smaller flapping hinge distance, then the flapping hinge distance decreases to 4-8% of rotor-disc radius, but the structural strength to withstand centrifugal forces must be maintained
Solution Approach 1:
The flexbeam element is designed with spatially varying bending stiffness, where the flapwise-soft region has reduced stiffness specifically for flapping movements while other regions maintain higher stiffness. This allows the flapping hinge distance to be reduced to 4-8% of rotor-disc radius while the overall structure remains strong enough to withstand centrifugal forces through the stiffer regions.
Solution Approach 2:
The flexbeam element utilizes composite material construction with fiber reinforcement, allowing precise control of bending stiffness properties in different directions and regions. This enables the creation of the flapwise-soft region with reduced flapping stiffness while maintaining structural strength through the composite architecture and fiber orientation.
3Strength
If conventional elastic hinge systems are used to maintain structural integrity, then the flapping hinge distance remains large at 7-12% of rotor-disc radius, but this results in high natural flapping frequency and increased vibrations
Solution Approach 1:
The elastic hinge unit is divided into specialized soft regions including the flapwise-soft region, lead-lag-soft regions, and torsion-soft regions. This segmentation enables the flapping hinge distance to be reduced while the structured soft regions manage the natural flapping frequency and reduce vibrations, overcoming the limitation of conventional systems that maintain large distances for structural integrity.
Solution Approach 2:
The bending stiffness parameters of the flexbeam element are specifically modified in the flapwise-soft region to reduce flapping stiffness, thereby reducing the natural flapping frequency and associated vibrations. This parameter change is achieved while maintaining structural integrity through the overall flexbeam design and other stiff regions.
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
This configuration reduces peak stresses and allows for a smaller flapping hinge distance, enhancing the scalability and control of rotary wing aircrafts, including larger models, by optimizing the ratio of bending strength to stiffness and reducing the bending stiffness for flapping movements.
Implementation Method 1
an elastic flapping hinge for connecting a rotor blade to a rotor hub of a rotary wing aircraft comprises an elastic flapping hinge member arrangement (11) that includes a hub attachment area (10b) for attachment to the rotor hub (7), a connection area (16) for attachment to the rotor blade (2d), and an elastic flapping hinge area (15) that is arranged between the hub attachment area (10b) and the connection area (16) and adapted to allow flapping movements
Implementation Method 2
During operation, i. e. rotation of the multi-blade rotor, a respective elastic hinge unit must withstand tremendous centrifugal forces that the rotor blades apply thereto
Data Source
AI summary
An elastic flapping hinge for connecting a rotor blade to a rotor hub of a rotary wing aircraft, comprising an elastic flapping hinge member arrangement that includes a hub attachment area for attachment to the rotor hub, a connection area for attachment to the rotor blade, and an elastic flapping hinge area that is arranged between the hub attachment area and the connection area and adapted to allow flapping movements, the elastic flapping hinge member arrangement comprising at least two elastic flapping hinge members having a first bending stiffness for flapping movements and a second bending stiffness for lead-lag movements, the first bending stiffness being smaller than the second bending stiffness, wherein the at least two elastic flapping hinge members diverge from each other in the elastic flapping hinge area by a predetermined divergence angle.