FLIGHT MEASUREMENTS OF THE VIBRATIONS ENCOUNTERED BY A TANDEM HELICOPTER AND A METHOD FOR MEASURING THE COUPLED RESPONSE IN FLIGHT

摘要

A discussion of flight-test and analysis methods for some selected helicopter vibration studies is presented. The use of a mechanical shaker in flight to determine the structural response is reported.nThe analysis methods described are based on the determination of the power spectral density of the force and of the response due to the force through use of analog frequency-analysis techniques. Results obtained by these methods are presented to show the coupled response of a helicopter in flight for two different blade configurations. The flight results are compared with results of ground tests to show the presence of coupling in flight. Available theoretical calculations of the coupled structural frequencies are included to show how these approximations compare with flight data. Some of the limitations of these tests and suggestions for refinement of flight vibration testing are discussed.