Keywords: landing gear, crashworthiness, composite tube, energy absorption.

For helicopter landing gear, one of the solutions for crashworthy design is a mechanical device for additional energy absorption. It is installed coaxially to the shock absorber and does not function in normal landing conditions. In the case of a crash landing, it begins to crush and absorb the impact energy. The basic structure of the landing gear assembly is basically composed of four components, which are the cylinder, the piston, the main fitting connecting landing gear with the airframe and the composite tube for additional energy absorption. This composite tube is easily tailored to achieve the desired mechanical characteristics. Under crash conditions, the high impact force causes the failure of the shear pin, which in turn allows the cylinder to slide inside the main fitting. This fragile shear pin is designed to fail at a given load and act as a trigger to activate crash tube. Then the crash tube begins to fail and absorb the energy.

After the shock absorber bottomed (when the piston touches the cylinder head so no more stroke is available for energy absorption), the crash tube begins to absorb the energy by crushing. This contribution is superposed on the original energy curve. From the designated stroke, the energy absorption by the crash tube is added to the original energy curve by the shock absorber. Though two models are separately analyzed which might not represent the realistic situation, it is enough to investigate the overall performance. The peak load transmitted to the airframe can be efficiently controlled by the failure of the crash tube. When only a shock absorber is used, the end peak load becomes very large because of bottoming. By introducing a crash tube, the peak load can be limited and more energy is absorbed by the landing gear. Thus shock absorbing efficiency and the safety of crew can be improved. To absorb the additional energy in case of emergency, the composite crash tube can be a good solution. It reduces the peak load resulting from very high sink speed, which prevents the load transferring to the airframe and human injuries.

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