SUB-FLOOR SKIN PANELS FOR IMPROVED CRASHWORTHINESS OF HELICOPTERS IN CASE OF WATER IMPACT

The tensor-skin concept has been developed at NLR to improve the crashworthiness of helicopters with fuselage structures made of composite materials in case of impacts on water. Traditional composite skin panels may fail early by the transverse pressure loads, but the tensor-skin concept, when applied to the bottom skin sandwich panels of a helicopter, is able to transfer the water pressure load to the substructure, and to make it absorb energy in the crushing mode for which it is designed. The concept is shown to work well in quasi-static tests on square sandwich panels clamped along all four sides. Moreover, in an experiment on an assembly of two sandwich panels and a sine-wave beam, the sandwich panels were shown to survive a transverse pressure load that simulates the water pressure, and to transfer this load to the substructure, i.e., the sine-wave beam. The triggering mechanism of the sine-wave beam was initiated, and a crushing process was started, proving the feasibility of the design concept.