1 AIRBAG DEPLOYMENT FOR PROTECTION OF DISABLED AIRCRAFT AND HELICOPTERS OPERATING AT SEA

In the present study, the possibility of using airbags as protective devices for disabled aircraft and helicopters operating at sea is considered. A computer simulation of the deployment of an initially folded airbag and its impact with a water surface is performed using the nonlinear finite element program LS-DYNA3D. When the airbag is inflated from different initial positions above the water surface, practically no difference in the unfolding timings of airbag is observed from the timings of the airbag deployed without water surface. When an airbag is attached to the base of a freely falling body such as a disabled helicopter and deployed against the water surface, there exists an optimal distance from which the airbag has to be deployed against the water surface for highest protection. A parametric study is conducted to investigate the influence of airbag parameters on the evolution of pressure, volume and temperature within the airbag when it is inflated against the water surface. Various airbag parameters including venting, fabric density, fabric elasticity and input gas temperature are considered. It is observed that low input gas temperature resulted in improper inflation of the airbag. Higher fabric densities significantly increased the ability of airbag to withstand higher pressures. Also, it is inferred that higher bag elasticities are required to make stiff material bags which can withstand higher pressures involved in helicopter crashes. Though the ability of the bags to withstand higher pressures is an important criteria, the chief purpose of an airbag is to prevent injury to the occupants and damage to the structure during a crash. So a recommendation is made to strike a balance between various airbag parameters such that airbag could withstand higher pressures and at the same time should offer less rebound to the structure and the occupants