Research On Some Key Technologies Of Aircraft Ground Dynamics

The research on aircraft ground maneuver characteristics is very complicated. From modeling aircraft ground maneuver dynamics exactly, combined with the anti-skid braking system modeling, investigation of the dynamic characteristics of aircraft landing, taxing, braking to stop with anti-skid, and steering, is quite significant in guidancing aircraft landing gears and braking systems design, improving aircraft fatigue life, and ensuring aircraft having good ground maneuver characteristics.A mathematic model of aircraft ground movement is established for aircraft with multi-wheels and multi-landing gears, and for aircraft with four wheel bogies, considering the six-degree-of-freedom aircraft body and the flexible landing gear strut and body. The time-domain integral method is adopted to solve the dynamics equations. Then, the aircraft symmetric landing and asymmetric landing are simulated. The results are used to guidance the design of pitch damper and brake balance mechanism of the bogie.A multi-channel anti-skid braking system with slip-ratio-control or with slip-velocity-control is established separately. Based on the aircraft dynamics model, aircraft brakeing to stop with anti-skid on dry runway and on wet runway are simulated. The results indicate that: the slip-ratio-controlled braking syetem can obtain good control effect nowhere on dry runway or on wet runway. The slip-velocity-controlled one can obtain good control effect on dry runway, but bad effect on wet runway. Under asymmetric conditions, using cross protection and self-locked protection system, the braking system with slip-ratio-control can automatically regulate brake torque to avoid deep sliding and correct aircraft course.A new method called multi-disciplinary collaborative simulation is presented for research on aircraft ground maneuver characteristics. The virtual prototyp established in ADAMS/Aircraft, which is taken as core, integrated with the aircraft and landing gear geometry components biult in CATIA, the flex parts exported from PATRAN/NASTRAN, and the control system established in MATLAB, are used to implement the multi-disciplinary collaborative simulation of aircraft ground maneuvers. Then, some important conclusions are obtainted.Using the stochastic central difference formula, together with the time-dependent equivalent linearization, a recursive algorithm for the covariance matrix of the nonstationary random response of nonlinear systems is developed. Then, the equivalent linearization method is modified for the problem of asymmetric nonlinear systems,considering the nonzero mean response induced by the asymmetric term. The derived algorithm is simple,efficient and easy to implement in computers.The examples given in this paper show that the results obtained with the recursive algorithm are in agreement with those from the Monte Carlo simulation, and they are more exact than those obtained in the reference.Active control landing gears are used to alleviate vibration during aircraft taxiing. A simple nonlinear stochastic dynamics model is established, considering the aircraft elastic vibration excited by the random runway. The equivalent linearization method is adopted to make the model linearity near the balance point, and the Gaussian random process of the runway is generated from the Gaussian white noise by a shape filter. Based on the stochastic optimal control theory, the Linear Quadratic Gaussian controller is designed with weighted quadratic performance index related to comfort, shock absorption, and expending lest energy. The aircraft dynamic responses are obtained through the runway random process modeled by Monte Carlo method. The results from simulation show that,compared with the passive ones,active control landing gears can effectively improve comfort and shock absorption of the aircraft.