Citation: Etewa, M.; Hassan, A.F.; Safwat, E.; Abozied, M.A.H.; El-Khatib, M.M.; Ramirez-Serrano, A. Performance Estimation of Fixed-Wing UAV Propulsion Systems. Drones 2024, 8, 424. https://doi.org/ 10.3390/drones8090424 Academic Editor: Abdessattar Abdelkefi Received: 5 July 2024 Revised: 9 August 2024 Accepted: 23 August 2024 Published: 25 August 2024 Copyright: © 2024 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/). drones Article Performance Estimation of Fixed-Wing UAV Propulsion Systems Mohamed Etewa 1, * , Ahmed F. Hassan 2 , Ehab Safwat 1 , Mohammed A. H. Abozied 1 , Mohamed M. El-Khatib 1 and Alejandro Ramirez-Serrano 3 1 Department of Electrical Engineering, Military Technical College Kobry Elkobbah, Cairo 11766, Egypt; e.khattab@mtc.edu.eg (E.S.); mohammed.abozied@mtc.edu.eg (M.A.H.A.); mohamed.m.elkhatib@ieee.org (M.M.E.-K.) 2 Department of Mechanical Engineering, Military Technical College Kobry Elkobbah, Cairo 11766, Egypt; a.farid@mtc.edu.eg 3 Department of Mechanical Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada; aramirez@ucalgary.ca * Correspondence: mohammed.etewa86@gmail.com Abstract: The evaluation of propulsion systems used in UAVs is of paramount importance to enhance the flight endurance, increase the flight control performance, and minimize the power consumption. This evaluation, however, is typically performed experimentally after the preliminary hardware design of the UAV is completed, which tends to be expensive and time-consuming. In this paper, a comprehensive theoretical UAV propulsion system assessment is proposed to assess both static and dynamic performance characteristics via an integrated simulation model. The approach encompasses the electromechanical dynamics of both the motor and its controller. The proposed analytical model estimates the propeller and motor combination performance with the overarching goal of enhancing the overall efficiency of the aircraft propulsion system before expensive costs are incurred. The model embraces an advanced blade element momentum theory underpinned by the development of a novel mechanism to predict the propeller performance under low Reynolds number conditions. The propeller model utilizes XFOIL and various factors, including post-stall effects, 3D correction, Reynolds number fluctuations, and tip loss corrections to predict the corresponding aerodynamic loads. Computational fluid dynamics are used to corroborate the dynamic formulations followed by extensive experimental tests to validate the proposed estimation methodology. Keywords: UAV; electrical propulsion; blade element; brushless DC motor 1. Introduction In recent years small-scale, battery-powered, and fixed-wing unmanned aerial vehicles (UAVs) have garnered substantial attention [1,2]. Their compact size, reduced weight, and low operational cost render them eminently suitable for a diverse array of applications including surveillance and the delivery of goods. However, the constrained endurance-to- weight ratio of electrically propeller-driven UAVs, particularly vertical takeoff and landing (VTOL) aircraft, presents a formidable challenge in achieving optimal performance across various flight regimes, particularly in long-endurance steady-level flight [3]. Given the limitations imposed by current battery technology, the enhancement of propulsion system efficiency emerges as a practical and needed avenue to extend the flight endurance of electric VTOL and fixed-wing UAVs. A typical electric UAV’s propulsion system comprises a battery pack, electronic speed controllers (ESC), brushless direct-current (BLDC) motors, and a set of propellers [4]. From such elements, the motor and propeller basic building block combination occupies a preeminent position in determining the efficiency of the propulsion system [5]. Importantly, it should be acknowledged that the efficiency of a motor–propeller system varies based on the flight operating conditions, propeller characteristics, and motor parameters, all of which can change over time. Consequently, the overall propulsion Drones 2024, 8, 424. https://doi.org/10.3390/drones8090424 https://www.mdpi.com/journal/drones