The existence of a wind-gradient gives a major effect to the flight characteristics of an aeroplane, especially at the final approach at landing. The numerical calculations show that the wind-gradient produces a considerable amount of deviation of path of an aeroplane under particular flight technique. It is very much possible that an aeroplane at landing, being accelerated by the windgradient, touches the ground down earlier than expected.

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The most feasible configuration for automatic gust-alleviation system is investigated. In the system considered, inertial sensors and feedback devices are utilized and both wing-flaps and elevators are operated to reduce the gust-induced airplane motions. Three possible configurations of such a system are proposed: linkage control, noninteracting control and split-control (Figs. 1, 3 and 5, respectively). On the other hand, CHANG's frequency-domain theory is applied to obtain an optimal control system which minimizes the gustresponse according to some criterion. Calculations of the alleviation capability of each system are carried out on an example airplane in order to establish numerical evaluations of relative merits of them. Among the three systems proposed, the split-control system is simplest in the mechanization and quite close to the optimal system in the alleviation capability. Thus, it is concluded that the split-control system is most preferable for practical inclusion in the future airplane.

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Assuming that the vibration deflection of the panel is in its fundamental mode, the nonlinear vibration equation of one degree of freedom is derived from the equations of the large deflection theory of thin plate with the aid of the GALER-KIN method.The excitation is assumed to be uniform with respect to space and a white noise with respect to time. The probability density of the response displacement is obtained as the solution of the FOKKER-PLANCK equation derived under the condition of the stationary MARKOV process. The effect of the buckling deformation and the intensity of random excitalion on the distribution of the probability density of the response displacement and its peak is disclosed by numerical examples. Furthermore, considering the nonlinear relation between stress and displacement, the first-excursion failure and the fatigue failure are studied. The effect of the buckling deformation and the intensity of random excitation on the failure time is numerically presented.

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