Sizing Methods for Aircraft of Variable Propulsion System Complexity

This paper compares the computational cost and robustness of a number of different algorithms for the sizing and optimization of aircraft. In particular, three classes of aircraft will be investigated, each with a different level of propulsion system complexity. The first is a conventional turbofan-powered aircraft. A lithium-air battery-powered aircraft, incorporating both energy and power constraints is second. Third is an aluminum-air/lithium-ion battery powered aircraft, which switches to different energy systems depending on the overall propulsion system power requirements. Several different aircraft design problem formulations will be considered for each of these aircraft. Sizing loops as well as determining constraints such as fuel margin by exposing them to the optimizer will both be explored. Results suggest that integrating surrogate models to inform the sizing loop leads to substantially fewer function evaluations than a simple successive substitution, while maintaining a relative insensitivity to a poorly-informed initial guess that optimizer-sizing algorithms lack.