Coupled rotor/fuselage vibration analysis using detailed 3-D airframe models

A comprehensive vibration analysis of a coupled rotor/fuselage system is ca rried out using detailed 3-D finite element models of tile AH-1G airframe f rom the DAMVIBS program. Predicted vibration results are compared with oper ational load survey flight test data of the AH-1G helicopter, Modeling of d ifficult components (secondary structures, doors/panels, etc.) is essential in predicting airframe natural frequencies. Calculated 2/rev vertical vibr ation levels at tile pilot seat show good correlation with the flight test data both in magnitude and phase, but 4/rev vibration levels show fair corr elation only in magnitude. Lateral vibration results show more disagreement than vertical vibration results. Refined aerodynamics such as fi ee wake a nd unsteady aerodynamics have an important role in tile prediction of vibra tion. Main rotor pylon roll mode has a significant contribution (about 26%) on tile 2/rev vibration. Accurate prediction of airframe natural frequenci es up to about 40 Hz appears essential to predict vibration in airframe. (C ) 2001 Elsevier Science Ltd. All rights reserved.