A Discussion of Helicopter Vibration Studies Including Flight Test and Analysis Methods Used to Determine the Coupled Response of a Tandem Type

A discussion of flight test and analysis methods for some selected helicopter vibration studies is presented. One aspect of the flight tests reported is the use of a mechanical shaker in flight to determine the structural response. The analysis methods described are based on determining the power spectral density of the force and the response due to the force. Results based on the above methods are presented which show the coupled response of a tandem helicopter in flight. Some of the limitations of this method of analysis and suggestions for refinement of flight vibration testing are discussed. In addition, some results are presented which illustrate the variation of the relative amplitude of the harmonics of rotor speed with forward speed.