Analytical Investigation into the Helicopter Vibration Resulting from Main Rotor Blade (MRB) Ballistic Damage.

Abstract : The effects of main rotor blade ballistic damage on helicopter vibration are investigated using a comprehensive helicopter aeroelastic analysis code. Ballistic damage to the rotor blade is represented in the blade structural model as well as in the aerodynamic analysis. Each blade is treated as being composed of elastic beams undergoing flap bending, lead-lag bending, elastic twist, and axial deflections. The dynamic response of multi-bladed rotor systems is calculated from nonlinear periodic normal mode equations using a finite element in time scheme. Results are calculated for a typical soft in-plane hingeless rotor helicopter with several damage configurations. Blade damage effects are determined in terms of blade mode shapes and frequencies, blade aeroelastic response, blade bending loads, and hub-fixed system vibration. Blade dissimilarity because of ballistic damage can induce a large vibratory component with its frequency the same as the rotor revolution (1/rev) on the helicopter system.