AH-1W MSC/NASTRAN FINITE ELEMENT ANALYSIS CORRELATION

As part of a NAVAIR-funded structural investigation of the AH-1W helicopter, a structural dynamics finite-element model (FEM) was refined and correlated to data from both flight and ground vibration tests. The ultimate goal of this investigation was to understand and predict the distribution of oscillatory strains in critical structure throughout the aircraft so that proposed modifications could be accurately assessed. To achieve this goal, a number of corresponding tests and analyses were conducted to improve the FEM correlation for all critical weight configurations and flight conditions. This paper documents the improvement and correlation of the FEM, the development of oscillatory flight loads, and the evaluation of a preliminary proposal for a structural modification to the root of the vertical fin. The importance of increasing the complexity of the FEM or analysis is estimated by assessing the effects of including various airframe components in the FEM (access panels, canopy glass, etc.) or particular dynamic properties (nonlinear thrust stiffening, modal damping, etc.). Furthermore, analytical methods used to improve the test correlation are assessed, and the remaining deficiencies in the model and analyses are identified.