Higher Harmonic and Active Control for Rotorcraft Vibration Suppression
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Solution Overview
Problem
Rotary wing aircraft experience significant vibratory responses due to main rotor system vibrations, which existing active vibration control systems fail to fully suppress, often requiring multiple heavy actuators that reduce payload capacity and efficiency.
Innovation Solution
A dual, counter-rotating, coaxial rotor system with independent control of upper and lower rotor systems, combined with higher harmonic control (HHC) and active vibration control (AVC) systems, uses sensors and force generators to individually suppress twelve vibratory loads, reducing the need for multiple actuators and minimizing airframe vibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If six or more anti-vibration actuators are used to completely suppress aircraft vibration, then vibration suppression is improved, but system weight increases
Solution Approach 1:
The vibration control function is segmented into two distinct systems: HHC actuators on rotor blades for higher harmonic control, and fewer AVC actuators in the airframe for residual vibration suppression. This segmentation allows each system to specialize in specific vibration frequencies and locations, reducing the total number of actuators needed while maintaining effective vibration suppression.
Solution Approach 2:
The HHC system applies partial action by controlling only the higher harmonic vibrations through blade pitch modulation, while the AVC system handles the remaining residual vibrations. This partial action approach divides the vibration control task into manageable portions, reducing the overall actuator requirements compared to attempting complete suppression by a single system.
2Reliability
If rotor-based actuators are oscillated at fuselage vibration frequencies to suppress vibration, then vibration suppression is improved, but the system cannot totally suppress all vibratory loads
Solution Approach 1:
The vibration control is segmented into HHC for higher harmonic frequencies and AVC for residual vibrations across all frequencies. The HHC actuators on rotor blades specifically target higher harmonic vibrations, while the AVC actuators in the airframe suppress remaining vibrations, together providing comprehensive coverage of all vibratory loads.
Solution Approach 2:
The HHC system acts as an intermediary that pre-processes and reduces higher harmonic vibrations before they propagate to the airframe. This intermediate control step reduces the burden on the AVC system, allowing it to focus on suppressing residual vibrations with fewer actuators.
3Productivity
If rotor-based system is tasked with improving rotor efficiency, then rotor efficiency is improved, but vibration reduction capability is reduced
Solution Approach 1:
The control functions are segmented between HHC and AVC systems. The HHC actuators on rotor blades can be tasked with improving rotor efficiency through optimized blade pitch control, while the separate AVC system in the airframe handles vibration suppression. This segmentation allows both objectives to be achieved simultaneously without conflict.
Solution Approach 2:
The HHC actuators serve multiple functions: they can improve rotor efficiency through optimized blade pitch control while simultaneously reducing higher harmonic vibrations. The AVC actuators provide additional multi-functionality by suppressing residual vibrations across all frequencies, ensuring both rotor efficiency and vibration suppression objectives are met.
Data Source
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AI summary
A rotary wing aircraft includes a rotor system rotatable about an axis relative to an airframe. A plurality of blade assemblies is mounted to the rotor system. A higher harmonic control system is operable to generate a harmonic load at the rotor system according to a higher harmonic control signal. An active vibration control system is operable to generate vibration forces about the aircraft according to an active vibration control signal. A controller is operable to issue the higher harmonic control signal and the active vibration control signal to coordinate the higher harmonic control system and the active vibration control system to reduce vibration within the airframe.