Rotor Hub Vibration Attenuator Using Orbiting Spring Masses
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Solution Overview
Problem
Conventional vibration attenuation systems for rotor hubs, such as the UREKA device, are ineffective in addressing n/rev vibrations and can amplify vibrations if the mast attachment point does not possess specific dynamic characteristics, and are susceptible to transients like gusts, particularly in tiltrotor aircraft with varying gross weight and rotor rotational speed.
Innovation Solution
A rotorcraft hub-mounted vibration-reduction device featuring revolving spring masses that move in a circular path proportional to N/REV vibration magnitude, phased 180 degrees from the vibrations, counteracting hub vibrations with a central mass that orbits at N/REV frequency, allowing for steady state spring deformations and increased force output without requiring springs attached to a stationary frame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive mast-mounted rotating balancer (UREKA device) is used to reduce vibrations, then 1/rev frequency vibration is minimized, but n/rev vibrations are not opposed and may be amplified
Solution Approach 1:
The patent employs multiple rotating balancers with different inertias that can independently rotate at different speeds. This dynamic configuration allows the system to respond to multiple vibration frequencies (n/rev where n=1,2,3...) simultaneously, transforming the static single-frequency solution into a multi-frequency adaptive system that covers a broader frequency range.
Solution Approach 2:
The vibration attenuation function is divided into multiple independent rotating balancers, each tuned to specific frequency characteristics. Rather than using a single device for all frequencies, the system segments the vibration counteraction task across multiple specialized components, allowing each balancer to optimize its performance for particular n/rev frequencies.
2Ease of manufacture
If the UREKA device is used without specific mast dynamic characteristics, then installation is simplified, but vibration amplification may occur
Solution Approach 1:
The rotating balancer system is designed to automatically adjust and position itself based on the vibration forces it detects. The balancers self-regulate their rotational positions to counteract vibrations without requiring precise pre-configured mast dynamic characteristics or complex external control systems, making the system more forgiving of varied installation conditions while maintaining reliable vibration attenuation.
Solution Approach 2:
The system allows the rotating balancers to dynamically change their operational parameters (rotational speed, position, inertia distribution) in response to detected vibration patterns. This adaptability enables the system to maintain effective vibration counteraction across varying flight conditions and mast characteristics without requiring precise initial configuration.
3Speed
If the UREKA device position is governed by mast motion, then the device responds to rotor vibrations, but susceptibility to gusts and transients increases
Solution Approach 1:
The rotating balancer system incorporates damping mechanisms and inertia elements that act as cushioning against transient disturbances. These elements provide a buffer that prevents gusts and sudden transients from immediately displacing the balancers from their optimal vibration-counteracting positions, allowing the system to maintain stability while still responding to sustained vibration patterns.
Solution Approach 2:
Rather than having the balancer position directly governed by mast motion (which transmits transients), the system inverts the control relationship by using the balancers' own rotational inertia and detected vibration patterns to determine positioning. This inversion filters out high-frequency transient noise while maintaining response to the underlying vibration frequencies.
4Reliability
If heavy rollers are used in the UREKA device to create oscillatory force, then 1/rev vibration is minimized, but the device becomes heavy and complex
Solution Approach 1:
The patent distributes the vibration counteraction function across multiple rotating balancers with locally optimized inertias rather than using a single heavy roller system. Each balancer uses minimal mass necessary for its specific frequency range, and the collective effect of multiple lightweight, distributed balancers achieves the same vibration attenuation as a single heavy device while reducing overall system weight and complexity.
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 solution effectively attenuates vibrations across the aircraft, reducing the need for specific mast dynamic characteristics and minimizing susceptibility to transients, providing greater force output with the same spring design and maintaining steady state vibration magnitude despite changes in flight path.
Implementation Method 1
revolving spring masses that move in a circular path proportional to N/REV vibration magnitude
Implementation Method 2
a central mass that orbits at N/REV frequency, allowing for steady state spring deformations and increased force output
Implementation Method 3
The mass moves in a circular path that varies in radius proportionally with the N/REV vibration magnitude
Data Source
AI summary
A vibration attenuation system for attenuating vibrations in a mast of an aircraft includes a weight attached to the mast but free to orbit about the mast. The weight can be comprised of one or more weight assemblies. Embodiments can include a single weight, or plural weight assemblies wherein each weight assembly can include a mechanical interconnecting mechanism so that each weight assembly receives feedback regarding the position and movement of one or more other weight assemblies. Each weight can be associated with a spring that urges the weight towards a neutral position. Rotation of the mast can cause the weight to orbit about the mast and self-excite such that the weight acts against the urging of the spring towards an attenuating position.