Citation: Bravo-Mosquera, P.D.; Cerón-Muñoz, H.D.; Catalano, F.M. Potential Propulsive and Aerodynamic Benefits of a New Aircraft Concept: A Low-Speed Experimental Study. Aerospace 2023, 10, 651. https://doi.org/10.3390/ aerospace10070651 Academic Editors: Karim Abu Salem and Daniel Ossmann Received: 12 June 2023 Revised: 15 July 2023 Accepted: 18 July 2023 Published: 20 July 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). aerospace Article Potential Propulsive and Aerodynamic Benefits of a New Aircraft Concept: A Low-Speed Experimental Study Pedro D. Bravo-Mosquera * , Hernán D. Cerón-Muñoz and Fernando M. Catalano Department of Aeronautical Engineering, São Carlos Engineering School, University of São Paulo, Avenida João Dagnone, nº 1100, São Carlos 13563-120, Brazil; catalano@sc.usp.br (F.M.C.) * Correspondence: pdbravom@usp.br Abstract: The aerodynamic design of a new aircraft concept was investigated through subsonic wind- tunnel testing using 1:28-scale powered models. The aircraft configuration integrates a box-wing layout with engines located at the rear part of the fuselage. Measurements involved a back-to-back comparison between two aircraft models: a podded version whose engines were assembled on pylons and a boundary-layer ingestion (BLI) version that provided several system-level benefits. The flowfield was investigated through the power balance method and a variety of pressure flowfield and inlet flow distortion metrics. The results proved that the BLI configuration enhances the propulsive efficiency by reducing both the electrical power coefficient and the kinetic energy waste due to lower jet velocities. Furthermore, there was a reduction of the total pressure recovery due to pressure gradients inside the duct, thereby causing high distortion. Overall, this research highlights the importance of wind-tunnel testing to bring any aerodynamic technology to a sufficient level of maturity and to enable future new aircraft concepts. Keywords: box-wing; boundary-layer ingestion; wind-tunnel test; power balance; total pressure recovery 1. Introduction Designing new aircraft concepts that aim to reduce climate change is a crucial aspect of the ongoing efforts to mitigate the environmental impact of aviation. The objective behind these designs is to develop aircraft that are more fuel efficient, emit fewer greenhouse gases, and minimize other detrimental effects on the environment. One area of focus is improving aerodynamic efficiency by incorporating features such as blended-wing bodies, non-planar wings, or unconventional wingtip designs that enhance lift-to-drag ratios. These improvements reduce the amount of fuel required to propel the aircraft, thus resulting in lower carbon dioxide (CO 2 ) emissions [1]. Furthermore, advanced propulsion systems, such as hybrid-electric propulsion, boundary-layer Ingestion (BLI) engines, hydrogen fuel cells, and others, can reduce the reliance on conventional jet engines and fossil fuels [2,3]. Another consideration is the use of lightweight and sustainable materials in aircraft construction. Utilizing advanced composite materials or bio-based materials can reduce the weight of the aircraft, thereby leading to decreased fuel consumption and emissions [4]. Several concepts have been proposed over the past few years based on such technolo- gies, thus encouraging the further exploration of unconventional aircraft for long-term sustainable flying. Some configurations include the blended-wing body (BWB), which merges the fuselage and wings into a single, smoothly blended structure. The BWB offers improved aerodynamic efficiency, increased passenger capacity, and potential fuel savings due to a reduced drag and an increased lift-to-drag ratio [5,6]. The box-wing concept is characterized by multiple wing sections that are interconnected to form a box-like structure. Box-wings offer potential advantages, such as an improved lift-to-drag ratio, increased stability, and a reduced weight [7,8]. Truss-braced wings incorporate additional structural supports, wherein they resemble a truss structure between the wings and the fuselage. Aerospace 2023, 10, 651. https://doi.org/10.3390/aerospace10070651 https://www.mdpi.com/journal/aerospace