Experimental and analytical investigation of the vibration characteristics of a remotely piloted helicopter.
Trainer, William T.
Wood, E. Roberts
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The Department of Aeronautics and Astronautics at the Naval Postgraduate School is involved in an ongoing program of Higher Harmonic Control (HHC) research using Remotely Piloted Helicopters (RPH). To date a host RPH has been acquired and a preliminary HHC design study completed. This thesis reports the results of free vibration shake tests conducted on the host RPH as well as efforts to construct a representative finite element model of the vehicle. Broadband noise was used to excite the structure both laterally and vertically from 10-200 Hz in and attempt to accurately document the airframe and rotor system dynamics. Primary airframe structurl modes were identified in the tail boom and at frequencies well below the characteristic 4/rev (78.3 Hz) main rotor induced vibration frequency. These modes should not be of concern at normal operating rpm. Main rotor blade modes were documented under non-rotating conditions then extended to predict the modes at operating rpm. Finally, a finite element model of the structure was constructed. Difficulties in matching finite element predictions with experimental results, however, will require refinemaents to the computer model before is can become a useful design tool.