Assessment of Crash Survivability of Typical Helicopter Using LS-DYNA Simulation

Contemporary helicopters have a demanding role to play both in military and in civil operations. The helicopter fatality rates are higher than fixed wing aircraft during crashes, mainly due to inherently risky operations close to ground, bad weather conditions and also non-availability of ejection seats. Since crash impact velocities are much lower for helicopters compared with fixed wing, there is a considerable scope for improving helicopter crash survivability as per MIL-STD-1290A (AV). Typically, during crash, the impact energy is judiciously distributed among various energy absorbing structural members namely landing gear, bottom structure and seat. The primary design goal for crashworthiness is to limit the impact forces transmitted to the occupants, and to maintain structural integrity of the fuselage to ensure a minimum safe occupant volume. The rotor, transmission and engine should not disintegrate during crash and cause injury to the occupants. In this chapter, full-scale airframe finite-element model of a typical helicopter was developed and simulated using HyperMesh and LS-DYNA solver. It is considered that seat is certified to withstand 51 g for military applications. Considering the constant landing gear energy, the balance energy absorbed by the bottom structure decides the crash survivability of helicopter. Iterative analysis was carried out to evaluate the conventional bottom structure to ensure uniform load distribution with high-energy absorption. But the requisite crash survivability was not achieved. Hence, the bottom structure was modified by incorporating the additional crashworthy features like kinks, lightening holes and other trigger mechanisms and subsequently iterative analysis was carried out. The results were found encouraging. Graphs were plotted for global energies, velocity and accelerations responses. The energy absorbed by modifying the structure has increased and ‘g’ loads experienced by pilot and co-pilot floor were reduced.