CH-53A Flexible Frame Vibration Analysis/Test Correlation

The Sikorsky Finite Element Airframe Vibration Analysis FranVibration Analysis has been found to correlate well with data taken in shake tests of the CH-53A. The frequencies of fundamental fuselage bending and transmission modes were predicted by the FRANVibration Analyses to an average accuracy of three percent. In addition, the mode shapes were defined accurately. The modeling techniques and analysis used in the study can be applied during helicopter design and during evaluation of growth versions of current aircraft. These techniques, in combination with an accurate definition of the vehicles structural characteristics, will enable accurate prediction of all transmission and fuselage modes for a vehicle without a cargo ramp.