Rotor Hub Vibration Attenuator Using Centrifugal 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, especially in tiltrotors with large changes in gross weight and rotor rotational speed, and do not adequately address rotor-induced vibrations.
Innovation Solution
A vibration attenuator system with rotating pairs of unbalanced weights driven by electric motors or torque from the mast, 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 optimize vibration reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the UREKA device is used to reduce vibrations, then vibration attenuation is achieved at the mast attachment point, but vibrations are amplified at other locations on the airframe
Solution Approach 1:
The patent extracts the vibration attenuation function from the airframe and relocates it to the rotor hub by mounting attenuators directly on the hub. This allows vibrations to be reduced at their source rather than attempting to counteract them at distant airframe locations, eliminating the amplification problem that occurs with airframe-mounted systems.
Solution Approach 2:
Instead of mounting vibration attenuators on the airframe and working outward to counteract vibrations, the patent inverts the approach by mounting attenuators on the rotor hub and working inward to cancel vibrations at their source. This reversal of the traditional mounting location eliminates the vibration amplification issue.
2Reliability
If the UREKA device is used for vibration reduction, then it works for specific dynamic characteristics, but it becomes ineffective when dynamic characteristics vary (such as in tiltrotors with large weight and speed changes)
Solution Approach 1:
The patent employs dynamic characteristics of the rotor hub itself (its mass and rotational properties) as the basis for vibration attenuation. Since the rotor hub's dynamic properties are inherent to the rotating system and change predictably with rotational speed, the attenuators can adapt to varying operating conditions without requiring external adjustment mechanisms.
Solution Approach 2:
The vibration attenuation system utilizes the rotor hub's own rotational mass and dynamics to generate the counterbalancing forces needed to cancel vibrations. The system is self-regulating because the rotor hub's varying dynamic characteristics during rotation naturally provide the necessary variation in counterbalancing force to match changing vibration conditions.
3Object-affected harmful factors
If heavy rollers are used in the UREKA device to create oscillatory force, then vibration minimization is achieved, but the device becomes susceptible to gusts and transients that disturb roller position
Solution Approach 1:
The patent removes the vulnerable roller-based oscillatory mechanism from the vibration attenuation system and replaces it with a direct counterbalancing mass system mounted on the rotor hub. This eliminates the mechanical complexity and vulnerability to external disturbances that characterize roller-based systems.
Solution Approach 2:
The patent uses counterbalancing masses mounted on the rotor hub to directly oppose rotor-induced vibrations through centrifugal force. These counterweights are positioned to create forces that cancel vibrations at the hub, providing a more stable and disturbance-resistant approach compared to roller-based oscillatory mechanisms.
4Object-affected harmful factors
If passive pendulums are used for vibration control in tiltrotors, then vibration attenuation is achieved, but the system becomes more complex and less compact
Solution Approach 1:
The patent combines the vibration attenuation function with the existing rotor hub structure by mounting counterbalancing masses directly on the hub. This integration eliminates the need for separate pendulum assemblies and associated support structures, significantly reducing system complexity and improving compactness.
Solution Approach 2:
The rotor hub serves multiple functions: it transmits rotational force from the engine to the rotor blades and simultaneously serves as the mounting platform for vibration attenuation counterweights. This multi-functionality eliminates the need for dedicated vibration control structures, reducing overall system 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 system effectively reduces rotor-induced vibrations throughout the aircraft, improving structural component life, reducing avionics and engine vibration, and enhancing passenger comfort, while being lighter and more compact than previous solutions.
Implementation Method 1
Vibratory shear force is generated by rotating pairs of unbalanced weights at high speed to create large centrifugal forces
Implementation Method 2
The rollers will automatically achieve the correct position to minimize vibration if the mast attachment point possesses specific dynamic characteristics
Data Source
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. A vertically oriented vibration attenuator is configured to oppose and attenuate vertical rotor induced oscillatory forces that would otherwise travel vertical down the rotor mast and into the airframe.