The many moving parts of an aircraft means that there will be a considerable amount of vibration while the aircraft is in operation. As pilots logged 24,142,000 general aviation flight hours in 2015, the same number of hours saw a variety of vibration and treatment for the vibration with portable vibration analyzers. However, not all vibration is the same or even comes from the same elements. To properly analyze an aircraft’s vibrations, know the difference between these types of vibration.
- Vibration: The first type of vibration is, of course, vibration. When a rigid or elastic body is forcibly moved from a position or state of equilibrium, that force creates a motion that we know as vibration. A vibrating motion can be oscillating, reciprocating, or periodic. Vibration can also be either harmonic or random. Harmonic vibration occurs when a vibration’s frequency and magnitude are constant. A vibration is random when the frequency and magnitude vary with time.
- Flutter: This type of vibration is rather dangerous, as it can grow to such a magnitude that it causes the aircraft to fail. Unsteady aerodynamics excite the naturally-occurring frequencies of an aircraft as air flows over it. This creates flutter, which is a highly unstable condition. To prevent flutter, routine maintenance for aircrafts should include using a portable vibration analyzer, ensuring the aircraft is in the best shape possible.
- Buffet: Buffet is the type of vibration with which most people will be familiar, as it is the one that occurs during air turbulence. Aerodynamic excitation is usually the cause of buffet. Buffet is typically random vibration and is commonly associated with separated airflow. As an aircraft’s speed brakes extend and disrupt the airflow around it, the aircraft creates buffet.
- Noise: Any noise you hear is simply a vibration that excites the air and can be heard. With a vibration that is random, the noise tends to be confused or unmusical. With harmonic vibrations, the tone is like that a musical instrument would make or the sound of a whistling drain.
When you monitor vibration, you want to know what it is that you are monitoring for. Knowing the different vibration types is the first step to excellent aircraft maintenance.