Liquid Inertia Pylon Isolation for Compound Helicopter Vibrations
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Solution Overview
Problem
Compound helicopters, particularly those with advancing blade concept rotorcraft, face significant vibration issues due to the combination of harmonics from counter-rotating rotors and stiff high hinge offset rigid rotors, leading to crew fatigue, increased maintenance, and structural instability, with current vibration control systems failing to effectively address the unique dominant harmonics of dual rotor systems.
Innovation Solution
The implementation of a main rotor vibration isolation system using augmented liquid inertia vibration eliminator units with active tuning elements, coupled between the fuselage airframe and pylon assembly, to reduce vibration transmission at specific frequencies, and a wing vibration isolation system with liquid inertia vibration eliminator units to mitigate wing vibrations, both designed to isolate vibrations at critical frequencies such as the blade passage and 2×blade passage frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If counter-rotating rotors are used to overcome retreating blade stall, then forward airspeed is improved, but vibration levels increase due to combined harmonics in the wakes
Solution Approach 1:
The patent introduces pylon vibration isolators as intermediary elements between the rotor pylons and the fuselage. These isolators specifically target and attenuate the combined harmonic vibrations generated by counter-rotating rotors, allowing the high-speed performance to be maintained while reducing the harmful vibration transmission to the fuselage.
Solution Approach 2:
The patent extracts the vibration isolation function from the rigid pylon structure by introducing separate vibration isolator components. This allows the rotor system to maintain its high-speed capability while the isolators selectively remove the harmful harmonic vibrations from the transmission path to the fuselage.
2Object-affected harmful factors
If active force generators are used to reduce fuselage vibration, then vibration levels are reduced, but system weight and complexity increase significantly
Solution Approach 1:
The patent employs passive vibration isolators that are simpler, lighter, and more reliable than active force generators. These isolators require no power source, have no moving parts that can fail, and provide sufficient vibration reduction without the weight and complexity penalties of active systems.
Solution Approach 2:
The passive vibration isolators automatically attenuate vibrations through their inherent mechanical properties without requiring external power or active control systems. The isolators self-regulate the vibration transmission based on the dynamic conditions, eliminating the need for heavy active force generators.
3Strength
If hard mounted main pylons are used for structural support, then structural strength is improved, but vibration transmission to the fuselage increases
Solution Approach 1:
The patent segments the pylon assembly into distinct functional components: the structural pylon elements that provide strength and support, and the vibration isolator elements that reduce vibration transmission. This segmentation allows each component to optimize its specific function without compromising the other.
Solution Approach 2:
The vibration isolators serve as intermediary elements inserted between the hard-mounted pylons and the fuselage. These isolators maintain the structural support function while mediating the vibration transmission, allowing strength and vibration reduction to coexist.
4Speed
If dual rotor systems are used to provide advancing blades on both sides, then retreating blade stall is overcome, but dominant harmonics at blade passage and 2×blade passage frequencies increase
Solution Approach 1:
The patent introduces pylon vibration isolators as intermediary elements that specifically target the dominant harmonic frequencies generated by dual rotor systems. These isolators are tuned to attenuate the blade passage and 2×blade passage frequencies, allowing the dual rotor configuration to maintain its high-speed capability while reducing the harmful harmonic content.
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 proposed vibration isolation systems effectively reduce the transmission of vibrations to the fuselage, improving crew comfort, reducing maintenance costs, and enhancing structural stability by isolating vibrations at key frequencies, thereby addressing the unique vibration challenges of compound helicopters.
Implementation Method 1
a plurality of augmented liquid inertia vibration eliminator units each having an isolation frequency and each coupled between the fuselage airframe and the pylon assembly to reduce transmission of the pylon assembly vibration to the fuselage airframe at the isolation frequency
Implementation Method 2
Each augmented liquid inertia vibration eliminator unit includes at least one active tuning element movable to tune the isolation frequency thereof
Data Source
AI summary
A compound helicopter includes a fuselage including a fuselage airframe, a translational thrust system coupled to the fuselage airframe and a pylon assembly subject to vibration. The pylon assembly includes a transmission and a rotor system having a main rotor assembly. The compound helicopter also includes a main rotor vibration isolation system including a plurality of augmented liquid inertia vibration eliminator units each having an isolation frequency and each coupled between the fuselage airframe and the pylon assembly to reduce transmission of the pylon assembly vibration to the fuselage airframe at the isolation frequency. Each augmented liquid inertia vibration eliminator unit includes at least one active tuning element movable to tune the isolation frequency thereof.