When an open pipe is played and a note is heard • the lowest frequency of the note is called second harmonic. • resonance occurs with standing waves set up inside the pipe. • there is a 180 degrees phase change at the open end.
Module 13. Aircraft aerodynamics, structures and systems
Medium vibration of 4 to 6 times per revolution is experienced on a helicopter. The primary control method is • inspect main rotor head and main drive shaft • design of engine and gearbox supports • inspect loose fixtures and fittings
sam1969 asking: • I selected
-Design of engine and gearbox supports
Medium and High frequency Vibrations – Depending on the helicopter the source may be engine and transmission cooling fan and accessories such as air conditioner compressors, or driveline components.