Minimum fuel cruise by periodic optimization.

Application of periodic optimization to minimum fuel aircraft trajectories is discussed. The most part of a long range trajectory is a cruise segment, which is assumed to be a steady flight in many papers. The steady condition is one of the constraints which lower optimality. In this paper, the optimum cruise segment is considered as an unsteady flight. The cruise segment is devided to subarcs in which same control sequences are used. The solution of minimum fuel problem for the subarc optimizes a total trajectory. The periodic optimization has some advantages in an operation. Zero-order approximate solution is presented as a maximum thrust ascent and a minimum thrust descent. This solution indicates the limitation of the exact one when the final range is specified infinite. Numerical results show the periodic cruise can save fuel 3-4% decrease.