Simultaneous aircraft sizing and multi-objective optimization considering off-design mission performance during early design

Abstract

Traditional aircraft conceptual design primarily involves determination of top-level sizing parameters, resulting in an initial design which satisfies specified point-performance constraints while flying the so-called design mission. In practical scenarios, commercial aircraft are also expected to operate optimally in the actual missions they fly which may drastically differ from the design mission. To improve performance and reduce operating costs, optimization shall be performed using specific objectives from the on-design mission and from one or more representative off-design reference mission(s). Such multi-mission optimizations may result in different designs for the same performance constraints. Moreover, the size of aircraft and choice of reference mission(s) may also have an effect in the difference resulting from such multi-mission optimizations. This paper solves a series of multi-objective on-design and multi-mission optimization problems in the conceptual design phase on aircraft spanning a range of size-classes, using the Non-dominated Sorting Genetic Algorithm II (NSGA-II). Results shed light on the design differences between formulations that exclusively consider design mission metrics of interest from the ones that consider metrics of interest from disparate, as-flown, i.e., off-design missions. In addition, results also reveal the impact of off-design mission weightings on the designs obtained from the optimization problems.