Numerical simulation of a crashworthy rotorcraft substructure including hard and soft surface impacts

A design study was performed using Finite Element Analysis. The objective of the study was to demonstrate the feasibility of developing a crashworthy substructure to protect rotorcraft drew in the event of vertical impacts involving landings on both hard surfaces, for example concrete, and water or soft surfaces. Differences in the impacted surfaces behavior can change the mechanisms of loading and render hard surface energy absorption mechanisms ineffective in a water impact. The objective of this thesis was to investigate the possibility of employing a skin to transfer loads from the water to a conventional hard surface energy absorbing structure. Finite element models were developed using the LS-INGRID preprocessor and analyzed with the LS-Dyna commercial FEA code. Use of the LS-Dyna code for simulating water impacts was validated by development of a model and comparison with experimental data in the literature. Models were developed which simulated rotorcraft substructures composed of both composites and aluminum alloys. Rotorcraft model parameters were selected based upon the Bell Helicopter model 412EP, but the model was only intended to be similar to the model 412EP, not an exact copy. Crashworthiness was successfully demonstrated for a 26 feet per second vertical impact onto both hard surfaces and water with both the aluminum alloy and composite structures.