What Is Aircraft Vibration?Virbration is caused by the movement of the aircraft and its engine and typically worsens at certain speeds, velocities, or altitudes. The vibration of an aircraft is measured on a scale expressed in inches per second, or IPS. An IPS of 0-.2 is considered good. Anything up to .4 is considered fair. Over .4 and below .6 is considered slightly rough. Up to .8 is rated as rough, .81 to 1.0 as very rough, and anything over 1.01 is considered a dangerous level of vibration.
What Happens When Vibration Isn’t Corrected?It’s important to monitor vibration with high quality vibration balancing equipment in order to prevent serious issues down the line. Too much vibration can destroy the integrity of rotor blades, shorten the life of all kinds of aircraft components, interfere with navigation equipment and seriously impede the comfort of both the pilot and all passengers. In worst case scenarios, the entire tail rotor of a helicopter can be ripped off the structural assembly because of severe vibration.
Don’t Improved Helicopter Designs Fix This Problem?As helicopter designs have improved, the problems of vibration have gotten better than they were in the past. With these design changes, the average helicopter vibration levels of .05 to .1 IPS are definitely far better than they were in the past; yet they are still much higher than the average on jet engine aircraft and work against the long-term safety and performance of the aircraft. The FAA and the International Helicopter Safety Team have expressed their concern with a need for better high quality vibration analysis and dynamic propeller balance in order to ensure the safety of helicopter travel and minimize accidents and other incidents going forward.
What Causes These Vibrations?The primary cause of vibrations is misalignment, lack of balance, or looseness in the fittings. These three things excite structural resonance within the rotor and shaft and the harmonics build off of one another and escalate at speed. It is also possible for defects and dirt between moving surfaces to cause vibration, as well as insufficient lubrication.
How Can Vibration be Minimized?At the most basic level, keeping everything clean and well-lubricated will help with vibration. It is then necessary to do regular and careful inspections to make sure that all bearings are tight and fitting properly and that there are no overly worn areas. Maintenance for aircraft should also include regular monitor vibration, fan trim balance testing, and regular testing of the blades for balance and fit.
Because the consequences of vibration and helicopters can be so deadly, is of the utmost importance that every helicopter owner do everything possible to minimize this issue. Seeking out the best high quality aircraft maintenance professionals is a step in the right direction.
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