Abstract
An automatic flare control system is formulated as an tracking problem, where the desired values of the altitude and rate of descent are specified as exponential functions of time. The resultant optimal closed-loop scheme has a good performance under the variations of the initial conditions such as altitude and rate of descent.
The mass of an aircraft, on the other hand, varies according to the number of passengers and the amount of fuel. So it is necessary to construct an automatic landing system which leads to the sensitivity reduction under the change of mass in the equilibrium flight condition. The optimal feedback system investigated here is implemented using output feedbacks, and the responses of the optimal closed-loop scheme are used as the nominal solution in this configuration.
The proposed methods satisfying the equilibrium flight condition are as follows;
1) a constant approach velocity with the flaps being used to alter the lift coefficient,
2) a constant lift coefficient with the approach velocity being changed so as to satisfy the equilibrium flight condition.
The output feedbacks of the altitude and rate of descent are used in the synthesis examples, and the optimal feedback gains are determined using the steepest descent method to minimize a given sensitivity performance index. It is shown in the digital simulation that the open- and closed-loop schemes are heavily affected by the mass variation in the equilibrium conditions 1) and 2), respectively. The optimal feedback system, however, shows good performances in both cases.
