Landing gear suspension systems fulfill the tasks of absorbing the vertical energy of the touch-down as well as providing passenger and crew comfort with a smooth ground ride before take-off and after landing. They are also designed to have optimal performance in the case of a hard landing. In general, the tasks of aircraft landing gears are complex and sometimes lead to a number of contradictory requirements. Although there are existing modifications of aircraft shock absorbers to reduce the problem, the basic design conflict between the requirements for landing and for rolling cannot be fully overcome by a passive suspension layout. Active and semiactive suspension techniques are a solution to this problem and are capable of reducing fuselage vibrations effectively. In order to get satisfactory damping performance with active and semiactive devices, appropriate control laws must be employed. In this paper, we study the use of an adaptive backstepping control with H∞ performance to cope with disturbances, uncertainties and nonlinearities, typical of suspension systems and damping devices. A comparison between active and semiactive strategies is provided through the analysis of simulation results.
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