Dynamic Modal Analysis and Optimization of a Mechanical Sensor Arm Deployment System for a C-130 Aircraft 2004-01-3129

During structural engineering design two of the most overlooked design facets of a finished product is understanding the behavior characteristics of how the product will react when resonated at its natural frequencies and actually defining and understanding the overall vibration profile responsible for the excitation of the structure. A C-130 mechanical arm/pod system has been developed to accommodate 1,000-pounds of sensor payload deployable in flight from a C-130 Hercules military aircraft (variants B thru J). The mechanical arm/pod system will be subjected to a profile of vibration from numerous sources during deployment and while in the final operating position. A general vibration profile for the mechanical arm/pod will be compiled from the plane’s four T-56-A-15 turboprop engines, the atmospheric turbulence and random gust loads. A pitot-accelerometer sensor probe was used to obtain vibration data of the C-130 ramp during a zero-light turbulence category flight for indicated airspeeds of 130 knots and 150 knots. The mid/low frequency values with worse case scenario magnitudes induced by buffeting, flutter and gust loads were computed.

A formal vibration analysis was conducted utilizing the Finite Element Approach and Modal Analysis using Pro/ENGINEER and Pro/MECHANICA software packages. The natural frequency modes for the mechanical arm/pod system was computed in the x, y and z directions with three different geometrical configurations of the structural cross-member supports.