Flutter is a phenomenon of aeroelasticity. It represents a kind of vibrations, namely non-decaying elastic vibrations of parts of an aircraft that appear in flight at a certain critical speed. These vibrations are caused by aerodynamic forces and are classified as self-oscillations. They do not require any external periodic forces and can appear suddenly and in a steady-state flight in non-turbulent air. A random initial momentum, even a small one, can be enough to cause these vibrations. An aircraft can be subjected to different forms of flutter depending on where the most intensive vibrations take place: wing, fin, ailerons, rudders, etc. Flutter can also appear on missiles, propellers, turbine and compressor blades.