Vibration isolation in helicopter operation is necessary not only for the comfort of the pilot and passengers, but also for the fatigue life of aircraft components. Excessive vibration creates dynamic loads that affect every part of the helicopter; minimizing and controlling these vibrations has been one of the most significant improvements in helicopter design. New developments in elastomeric technology for passive components — bearings, dampers, and isolators — have improved reliability and maintainability while reducing noise and vibration during helicopter operation.
The right design
Maintaining elastomeric components is crucial to the safe operation of the aircraft and for prolonging component life. Understanding the maintainability of these components begins right at the design process. Component manufacturers work very closely with helicopter designers to determine the correct size and life cycle needed for the aircraft.
The goal is to not only design the best performing components but to also assure that the components are maintainable. To achieve this, maintenance personnel are consulted for their opinion on a component’s design and maintainability. This helps to ensure that everyone understands how to operate the helicopter in the most cost-effective manner.
It is important to design the aircraft and its components so that they can be easily taken apart, inspected, and serviced. During maintenance procedures, mechanics will follow the design instructions written by the design team. They closely follow the original guidelines to assess what needs to be corrected during maintenance service.
Elastomeric components are comprised of bonded-rubber elastomeric elements that are specially designed to eliminate certain types of vibration. Compared to coiled metal springs, elastomeric elements allow components to be easily configured in different sizes and shapes, and can be readily integrated into various helicopter designs. Elastomeric parts are multi-directional, simple, lightweight, reliable, and can be designed into a system at a moderate cost compared to more complex methods. They also offer the advantage of an extremely long operating life. The service life of some isolators can be from 5,000 to 10,000 flight hours.
These components are generally maintained through visual inspection, and it is essential for the mechanic to understand how these parts operate, the causes and effects of degradation, and the best maintenance practices. A typical helicopter will have several elastomeric components including a pitch-restraint spring, main rotor lead lag damper, main rotor spindle bearing, main rotor CF bearing, tail rotor bearing, corner Pylon isolator, instrument panel isolator, main rotor hub Frahm damper, rotor head assembly, and tail-light isolator. All of these parts must be periodically inspected and maintained to guarantee a safe, vibration-free ride.
The elastomeric parts found on a helicopter include bearings, isolators, and dampers.
Elastomeric bearings are composed of natural or synthetic rubber bonded to metal devices that accommodate dynamic motions. They are limited to oscillatory motions from 10 to 90 degrees or up to within 1 inch.
Elastomeric dampers attenuate dynamic motions, most often in the rotor, and can be used with or without special fluids. They offer additional force for a given dynamic motion and provide consistent performance with a wide range of temperatures and dynamic motions.
Elastomeric isolators are installed in a load path to minimize the transmission of dynamic loads or motions. They provide optimal isolation of vibration at important vibration frequencies.
Elastomeric components will degrade due to conditions such as fatigue, overload or tension loading, fluid contamination, and environmental attack from heat and ozone. Typically a combination of these degradation conditions will occur, accelerating the component damage. By thoroughly inspecting the parts, a knowledgeable mechanic will be able to assess when an elastomeric part needs to be overhauled or replaced.
Lord was selected by Korea Aerospace Industry (KAI) as one of their top four Elite Suppliers for the Korean Utility Helicopter (KUH) program.
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