This paper deals with the study and comparison of the dynamic response of aircraft with passive and active landing gears due to runway irregularities while the aircraft is taxying. This paper develops a detailed full aircraft mathematical vibration model to describe an active landing gear system. The derived dynamic equations are used to analyze the active landing gear system using proportional integral derivative (PID) controllers. The performance of this system is compared with the passive landing gear system by numerical simulations. The active landing gear system is able to increase the ride comfort and good track holding by reducing the fuselage acceleration, vertical fuselage displacement caused by landing and runway excitations.

In this article, random vibration analysis of full aircraft with passive and active landing gears has been done by numerical simulations on random runway profile. The mathematical model of full aircraft with active landing gears and modelling of runway profiles have been developed for analysing the aircraft bounce, pitch, roll accelerations, displacement and shock strut travel while taxiing on random runways. The results show that vibration levels of the aircraft by the active landing gear system is less than the conventional landing gear system while taxiing on different grades of random runways. Comparison results also show that the active system improves the ride comfort and easiness of pilot handling and thus, increases the fatigue life of the aircraft. NOMENCLATURE MAircraft fuselage mass m 1Nose landing gear tire mass m 2 Rear left landing gear tire mass m 3 Rear right landing gear tire mass ks 1 Nose gear shock strut stiffness ks 2 Rear left gear shock strut stiffness ks 3 Rear right gear shock strut stiffness cs 1 Nose gear shock strut damping coefficient cs 2 Rear left gear shock strut damping coefficient cs 3 Rear right gear shock strut damping coefficient kt 1 Nose gear tire stiffness kt 2 Rear left gear tire stiffness kt 3 Rear right gear tire stiffness ct 1 Nose gear tire damping coefficient ct 2 Rear left gear tire damping coefficient ct 3 Rear right gear tire damping coefficient [M] Mass matrix [C] Damping INTRODUCTIONLanding gear is a critical component of the aircraft which transmits the ground loads to the aircraft structure. It provides ride comfort to the passengers during taxiing on the runways. It also improves the pilot's efficiency to control the aircraft and to read the instruments in the glass cockpits during ground manoeuvres. The landing gear fitted in the aircraft is not able to adjust the damping characteristics in real-time runway conditions. The focus on active landing gear system is essential to overcome the difficulties of passive landing gear. presented a PID controller tuned with Ziegler-Nichols rules for both robustness and vibration suppression performance aspects. The application of proportional controller to active vibration control incorporated with a passive vibration isolator to suppress the resonant oscillation at its natural frequency was studied by Liu [13]. The present study analysed random vibration of full aircraft model with active landing gears under normal landing condition and dynamic response on different grades of random runways. The designed PID controller generates the control force to reduce bounce, pitch, roll displacement and accelerations of fuselage body considerably. This article does not analyse the bank angle response by PID controller during flight. The PID controller requires the bank angle reference command to tackle the unknown banking for turn coordination. However, the bank angle reference is required by the PID controller during crosswind taxiing conditions. Runway roughness affects both the landing gear and the airframe. Nowada...

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Abstract. In this paper, nonlinear vibration analysis of a typical aircraft oleo pneumatic landing gear has been done. Mathematical model of the main landing gear is developed, and dynamic equations have been written incorporating the effect of lift force, friction force to study the landing gear behaviour at touchdown condition. The nonlinear effect of stiffness, damping coefficient properties are considered in the analysis. The displacement, velocity, acceleration values are obtained on different landing velocities by numerical simulations using MATLAB/Simulink. Using the same parameters of the aircraft, landing gear and tire, the dynamic analysis was also done in ABAQUS. The results obtained by the nonlinear vibration analysis using the developed model in MATLAB/Simulink have close agreement with the results obtained from ABAQUS. On the basis of the presented model, dynamic simulations of landing for large transport aircraft were performed for different sink velocities. The developed model is also helpful to fine tune the stiffness and damping properties of landing gear in the design stage itself to reduce the replacement / repair cost and increase the life of landing gear assembly.

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.