Rotor Hub Spring-Mass Attenuator for Multi-Frequency Vibration
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Solution Overview
Problem
Conventional vibration attenuation systems for rotary-wing aircraft, such as helicopters and tiltrotors, face challenges in accurately predicting and effectively reducing rotor-induced vibrations, particularly at higher frequencies, and are susceptible to transients and varying dynamic characteristics, leading to inadequate performance and potential vibration amplification.
Innovation Solution
A rotorcraft hub-mounted vibration-reduction device featuring revolving spring masses that orbit at higher frequencies than the rotor, counteracting hub vibrations through a central mass moving in a circular path, with a control system to adjust the radial position and phase of the mass relative to the mast, allowing for effective vibration attenuation without relying on specific dynamic characteristics or being susceptible to transients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If UREKA device is used, then rotor imbalance at 1/rev frequency is prevented, but the device cannot oppose other rotor-induced n/rev vibrations and may amplify vibration if mast attachment point does not possess specific dynamic characteristics
Solution Approach 1:
The vibration attenuators are designed to handle multiple vibration frequencies (n/rev where n≥1) simultaneously, not just 1/rev frequency. Each attenuator can be tuned to target specific vibration modes, and multiple attenuators work together to provide comprehensive vibration reduction across the full spectrum of rotor-induced vibrations, making the system universally effective against various vibration types.
Solution Approach 2:
The system uses adjustable parameters in the vibration attenuators, such as mass, stiffness, and damping characteristics, to adapt to different vibration frequencies and magnitudes. This allows the attenuators to be tuned for optimal performance across various operating conditions and vibration modes, rather than being fixed to a single frequency response.
2Object-affected harmful factors
If UREKA device is used, then vibration attenuation is achieved, but the device is susceptible to gusts and other transients that may disturb the roller position, creating a vibration transient
Solution Approach 1:
The vibration attenuators incorporate damping elements and flexible mounting arrangements that cushion against disturbances from gusts and transients before they can significantly affect the attenuator's position or performance. This prior cushioning prevents the large position disturbances that occur in UREKA-type devices, maintaining reliable vibration attenuation even in turbulent conditions.
3Object-affected harmful factors
If hub shear pendulums are used, then vibration attenuation is achieved, but the system is heavy and only attenuates approximately 50% of the n/rev vibration
Solution Approach 1:
The invention replaces heavy mechanical pendulum systems with lighter vibration attenuators that use a combination of mass-spring-damper mechanisms and aerodynamic forces. This substitution achieves superior vibration attenuation (greater than 50% of n/rev vibration) with significantly reduced weight, as the new system exploits both mechanical and aerodynamic principles rather than relying solely on heavy inertial masses.
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
The system provides comprehensive vibration attenuation across various frequencies, reducing the operational stress on aircraft components and minimizing passenger discomfort, while being less dependent on mast dynamic characteristics and more resilient to environmental disturbances.
Implementation Method 1
A vibration attenuator system includes a rotorcraft hub-mounted base frame that revolves with the rotorcraft rotor hub and at least one spring-mass system that rotates relative to the hub
Implementation Method 2
at least one spring-mass system that rotates relative to the hub and generates an oscillating force in response to the hub vibrations
Implementation Method 3
a bearing between the base frame and the spring that allows the spring to rotate along with the mass, while maintaining the same tuning and physical function
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.