Abstract
Random runway roughness effect on the dynamic response of an aircraft with landing gears has been investigated using nine degree of freedom nonlinear mathematical model. The developed mathematical model incorporates nonlinear characteristics of air spring stiffness, landing gear damping, tire stiffness and damping of the oleo pneumatic main landing gears and nose gear. Equation of motion for aircraft and each landing gear have been written considering heave, pitch, roll of aircraft and three vertical motions of landing gears respectively for landing response analysis. The equations for longitudinal motion of each landing gear are also written from the mathematical model will be helpful for longitudinal dynamics. The aircraft touchdown and roll on with variable decent velocities on Grade E random runway represented by nonstationary random process. The excitation of different grades of random runway can be considered as stationary random process when the aircraft landing at constant sink velocity. This work mainly focused on finding the dynamic responses of the aircraft such as heave, pitch, roll acceleration, vertical forces and all the three landing gears vertical vibration levels while landing on random runways. The active landing gear system performance is compared with passive landing gear system by numerical simulation in MATLAB/SIMULINK. The investigation using nonlinear model predicted that the effect of active control landing gear provides significant reduction in vibration levels and vertical reactions during landing at various vertical velocities on random runways. To validate the above mathematical model a multi-body dynamics (MBD) model has been simulated in ABAQUS/CAE and the dynamic responses of landing gear forces are compared with those obtained from the nonlinear mathematical model. The nonlinear model responses are also compared with the results of other authors. This study is more useful to adopt active control landing gear in the aircraft to reduce the landing loads transmit on aircraft structure and landing gears due to landing impact. The reduction of vibration levels and vertical forces by the active system increase the fatigue life of landing gears and structural life of airframe.
Highlights
An Aircraft landing impact and excitations due to uneven runway surfaces are absorbed by the landing gear system
Landing dynamics model of nine degree-of-freedom of aircraft with active landing gears has been developed with the nonlinear spring and damping characteristics
The Landing dynamic response of the aircraft as it negotiates different grades of random runways at various sink velocities have been evaluated by numerical simulations
Summary
An Aircraft landing impact and excitations due to uneven runway surfaces are absorbed by the landing gear system. INVESTIGATION OF RANDOM RUNWAY EFFECT ON LANDING OF AN AIRCRAFT WITH ACTIVE LANDING GEARS USING NONLINEAR MATHEMATICAL MODEL. The transverse drag forces at the axle are balanced by the engine thrust during three-point landing and the relationship of the drag load at the time of maximum vertical load is 0.25 and occurs at the time of maximum vertical load on the gears These assumptions are taken for calculating ground reaction loads on the axle of the landing gears. Tire damping force is considered linear one This investigation helps to determine the vibration levels, vertical reactions of aircraft and landing gears with active control system while landing on damaged runways. The developed nonlinear dynamic model is exactly helps to investigate the dynamic response of the active landing gear during touchdown impact by stationary and non stationary random analysis. Longitudinal dynamics and shimmy vibration analysis would be separately done in the future study
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