Rotor Hub Vibration Attenuator Using Active Shear Forces
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Solution Overview
Problem
Existing vibration attenuation systems for rotor hubs in rotary-wing aircraft, such as the UREKA device, are ineffective in varying dynamic conditions and can amplify vibrations, particularly in tiltrotors with large changes in gross weight and rotor rotational speed, and are susceptible to transients like gusts.
Innovation Solution
A vibration attenuator system with rotating pairs of unbalanced weights driven by electric motors or mast torque, controlled by a microprocessor-based system using feedback from sensors to generate centrifugal shear forces that cancel rotor-induced vibrations, adjustable in amplitude and phase to minimize vibrations transmitted to the airframe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive mast-mounted rotating balancer (UREKA device) is used to reduce vibrations, then rotor imbalance vibrations are minimized, but the device amplifies vibrations when mast attachment point does not possess supercritical shaft characteristics and is susceptible to gusts and transients
Solution Approach 1:
The system uses actively controllable vibration attenuators with variable rotational speeds and adjustable unbalanced weight configurations, allowing the system to adapt to changing flight conditions, gross weights, and rotor speeds rather than relying on fixed passive characteristics
Solution Approach 2:
The control system receives input from vibration sensors and actively adjusts the attenuator operation to minimize vibrations transmitted to the airframe, creating a closed-loop system that responds to actual vibration conditions rather than relying on predetermined dynamic characteristics
2Object-affected harmful factors
If UREKA device with heavy rollers is used to create oscillatory force, then rotor imbalance is prevented, but the device is susceptible to gusts and transients which disturb roller position creating vibration transients
Solution Approach 1:
Vibration sensors detect roller position disturbances and the control system actively adjusts the attenuators to counteract resulting vibrations, creating a closed-loop system that eliminates vibration transients rather than allowing them to propagate
Solution Approach 2:
The system automatically detects and corrects its own disturbances through the feedback control mechanism, adjusting attenuator operation in response to detected vibrations without external intervention
3Object-affected harmful factors
If passive pendulums are used for controlling vibrations in tiltrotors, then some vibration reduction is achieved, but the system is ineffective in varying dynamic conditions with large changes in gross weight and rotor rotational speed
Solution Approach 1:
The system employs actively controllable vibration attenuators with variable rotational speeds and adjustable unbalanced weight configurations, allowing continuous adaptation to changing flight conditions, gross weights, and rotor speeds
Solution Approach 2:
The control system varies operational parameters including rotational speed, unbalanced weight magnitude, and phase angle of the attenuators to optimize vibration cancellation across different flight conditions and vibration frequencies
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 system effectively reduces rotor-induced vibrations throughout the aircraft, improving fatigue life of structural components, reducing avionics and engine vibration, and enhancing passenger comfort, while being lighter and more compact than existing solutions.
Implementation Method 1
Vibratory shear force is generated by rotating pairs of unbalanced weights at high speed to create large centrifugal forces
Data Source
Figure 1
Figure 2
Figure 3A~5B
AI summary
A vibration attenuator for an aircraft has at least one weight mounted in a rotating system of a rotor hub of the aircraft, each weight being rotatable about an axis of rotation of the hub relative to the hub and to each other weight. Drive means are provided for rotating each weight about the axis of rotation at a selected speed for creating oscillatory shear forces that oppose and attenuate rotor-induced vibrations having a selected frequency.