Aircraft APU Suspension Using Low Stiffness Elastomeric Rod Ends
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Solution Overview
Problem
There is a need for an effective and economical means to isolate aircraft auxiliary power units (APUs) from the aircraft they are mounted on, with improved performance and reliability, as existing systems lack robustness and efficiency in isolating the APU from operational frequencies and vibrations.
Innovation Solution
The implementation of a suspension system using low stiffness elastomeric rod ends with a low spring rate, integrated into a focalized suspension linkage system that terminates with resilient rod ends, providing a natural frequency for the APU below its operational frequency, thereby isolating it from main engine windmilling excitation frequencies and ensuring stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a suspension system with low stiffness elastomeric rod ends is used, then vibration isolation performance is improved, but structural strength and rigidity deteriorate
Solution Approach 1:
The suspension linkage combines rigid structural components with elastomeric rod ends to create a composite system. The rigid portions provide necessary structural strength and load-bearing capability, while the elastomeric rod ends provide vibration isolation through their low stiffness and damping properties. This composite approach resolves the contradiction by integrating materials with complementary characteristics into a unified suspension system.
Solution Approach 2:
The suspension system is divided into distinct functional segments: rigid linkage portions for structural support and elastomeric rod ends for vibration isolation. By segmenting the system into these specialized components, each part can be optimized for its specific function without compromising the other, allowing the rigid sections to maintain strength while the elastomeric sections provide vibration protection.
2Object-affected harmful factors
If the natural frequency is reduced below operational frequency for isolation, then vibration isolation effectiveness is improved, but susceptibility to resonance from main engine windmilling excitation increases
Solution Approach 1:
The system carefully controls the natural frequency parameter of the suspension system, positioning it below the APU operational frequency to achieve vibration isolation while ensuring it remains above the main engine windmilling excitation frequency range. This parameter optimization allows the system to isolate APU vibrations effectively while avoiding resonance with engine frequencies, resolving the contradiction between isolation effectiveness and resonance susceptibility.
Solution Approach 2:
The system converts the potential harm of low natural frequency (resonance risk) into a benefit by strategically positioning the natural frequency in a safe zone between the engine excitation frequency and APU operational frequency. This frequency positioning transforms what could be a harmful resonance condition into a beneficial isolation regime, where the system effectively isolates APU vibrations without risking resonance with engine frequencies.
3Object-affected harmful factors
If low spring rate rod ends are used, then isolation performance is improved, but load-bearing capacity deteriorates
Solution Approach 1:
The suspension linkage is segmented into rigid load-bearing sections and elastomeric isolation sections. The rigid portions of the linkage are designed to handle high loads and provide structural support, while the elastomeric rod ends with low spring rates are designed specifically for vibration isolation. This segmentation allows each component to be optimized for its primary function without compromise.
Solution Approach 2:
The system uses a composite structure combining rigid materials for load-bearing components and elastomeric materials for isolation components. The rigid linkage sections provide the necessary load-bearing capacity and structural integrity, while the elastomeric rod ends provide superior vibration isolation performance through their low spring rate and damping characteristics.
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 solution effectively isolates the APU from operational frequencies, reducing vibrations and ensuring stability, with natural frequency bands positioned above the main engine windmilling excitation frequency, enhancing the reliability and performance of the APU suspension system.
Implementation Method 1
low stiffness elastomeric rod end with a low spring rate wherein the aircraft auxiliary power unit suspension system provides the aircraft auxiliary power unit with a suspended auxiliary power unit natural frequency below the aircraft auxiliary power unit operation frequency
Implementation Method 2
The invention includes an aircraft auxiliary power unit suspension system for isolating an aircraft auxiliary power unit having at least one aircraft auxiliary power unit operation frequency
Data Source
AI summary
The invention provides an aircraft with an auxiliary power unit isolated from the aircraft. An auxiliary power unit suspension system includes at least one suspension linkage. The suspension linkage terminates with a first low stiffness elastomeric rod end. The low stiffness elastomeric rod end has a low spring rate with the aircraft auxiliary power unit suspension system providing the aircraft auxiliary power unit with a suspended auxiliary power unit natural frequency, the suspended auxiliary power unit natural frequency below the aircraft auxiliary power unit operation frequency.