Design principles and digital control of advanced distributed propulsion systems

The integration of advanced distributed propulsion (DP) systems within various aircraft configurations holds the potential to greatly increase aircraft performance, particularly in terms of fuel efficiency, reduction of harmful emissions and reduction of take-off field length requirements. This has been enabled by modern analysis tools, materials technology and control systems which take advantage of the positive interactions between the propulsive configuration and the aerodynamics of the aircraft. In particular, synergies are maximized when the propulsion system uses distributed nozzles, crossflow fans and multiple distributed fans. Recent advances in electric propulsion have encouraged the hybridization of propulsive systems, with airliners having multiple electric fans powered by one or two gas turbine engines. Furthermore, due to recent advances in airframe integration solutions, the propulsive element can become an integral part of the control and stability augmentation capabilities of the aircraft. Thereby, the digital control of advanced DP systems is crucial for the purpose of thrust modulation and intelligent management of engine resources and health. This not only aids in mission optimization but also supports the case for airworthiness certification of novel aircraft configurations integrating advanced DP systems. This paper presents a critical review of the existing literature on the subject of DP, identifying the benefits and drawbacks of this technology as well as its proposed practical applications. The review also discusses contemporary advances in hybrid electric technology, aeroelasticity research and the fundamental design steps to integrate advanced DP systems in fixed-wing aircraft. Additionally, an evolutionary outlook is presented on digital control of DP systems with a focus on advancing the techniques for mission optimization and engine health management for enhanced safety and sustainability. Based on the proposed design principles and digital control methodology, conclusions are drawn about the suitability of advanced DP for various applications and recommendations are made for future research and development. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).