Definitions for "Resonance Frequency"
The maximum operating frequency that a reed contact can withstand, after which it chatters, or starts sympathetic vibration.
Every rotating or shaking thing has a resonance freqency. When something is at it's resonance frequency, every imbalance adds to itself at every cycle. This leads to a force which mathematically goes to infinity and no helicopter can handle those stresses for long. Using large training gear usually change the resonance frequance to right around that point your helicopter likes to hover. This can result in violent shaking even if your blades are balanced and all your mechanics are good. What you can do is change the resonance frequency, or avoid it by changing your hover rpm. Shorten or lengthen your training gear to easily solve this problem, or increase your rpm a bit.
The frequency at which a component vibrates when being used. For example, a particular loudspeaker may resonate a 50Hz.
a simple example where a system only responds strongly to a particular ordered input