String stability of energy-saving aircraft formations

TL;DR

This paper investigates the string stability of energy-efficient aircraft formations, proposing a control method that maintains stability and reduces energy consumption, demonstrated through simulations with turbulence.

Contribution

It introduces a novel control design method that ensures string stability while optimizing for energy efficiency in aircraft formations.

Findings

Controller achieves string stability in simulations.

Energy consumption reduced by 13% on average.

Effective under 2% turbulence conditions.

Abstract

Groups of aircraft have the potential to save significant amounts of energy by flying in formations; all but the leading aircraft can benefit from the upwash of the wakes of preceding aircraft. A potential obstacle as the number of aircraft in such a formation increases is that disturbances at one aircraft, for example caused by turbulence or wake meandering, can propagate and grow as each following aircraft tries to track the optimal energy-saving position relative to the one in front. This phenomenon, known as string instability, has not yet been adequately examined in the context of aircraft formations. We discuss some trade-offs involved in designing string stable controllers whose objective is to minimize energy, and present a control design method to achieve both string stability and energy efficiency of an aircraft formation. In simulations of a 10-aircraft linear formation in the presence of 2% turbulence intensity, our controller achieves string stability while reduced energy consumption by an average of 13% with respect to solo flight.