# Advancements and Applications of Rim-Driven Fans in Aerial Vehicles: A Comprehensive Review
## 1 Introduction  
In an era where the urgency to mitigate greenhouse gas emissions has reached a critical point, the aviation industry stands as a significant contributor to the global carbon footprint. Presently, aviation is responsible for approximately 2.4% of worldwide CO\({}_{2}\) emissions [1], a statistic that could undergo alarming escalation if air traffic triples by 2050, potentially causing aviation-related emissions to constitute a staggering 20% of global warming pollutants [2]. Addressing this dire scenario necessitates radical advancements in aircraft design and propulsion technology, driven by a commitment to drastically reduce the environmental impact of flight [3; 4; 5; 6; 7]. The introduction of electrical propulsion represents a pivotal turning point in aeronautical engineering, heralding a new chapter of environmentally conscious innovation. Amid this backdrop, organizations like NASA and the Department of Energy have set ambitious benchmarks for motor power density in electric aircraft--a crucial step towards achieving commercially viable electric flight [8; 9]. As the aviation landscape evolves, the spotlight is increasingly trained on the concept of distributed propulsion systems, a designstrategy that promises to usher in enhanced energy efficiency, diminished carbon emissions, reduced operational costs, and even reduced acoustic noise levels [10; 11]. This transformation towards electrification is not merely a theoretical endeavor. Rather, it is propelled by major industry players including NASA, Boeing, Airbus, Joby Aircraft, and Lilium, who are directing substantial investments towards the development of electric airplane technologies [9; 12; 13; 14]. A pivotal aspect of this evolution lies in the utilization of fans powered directly by electric motors, offering a simpler and more versatile alternative to traditional propulsion systems. Notably, the collaborative efforts of these industry giants have yielded promising outcomes in the field of fixed-wing distributed propeller and electric ducted fan aircraft designs. A central tenet of this transition to electric aviation involves the pursuit of high-speed flight capabilities with electric motor technology--a challenge that is being squarely addressed by initiatives like NASA's drive towards electric aircraft motors with exceptional power density and efficiency [14]. Furthermore, the market's growing anticipation of electric aviation's market entry has fortified research and development endeavors, nurturing a fertile ground for the exploration of new possibilities and real-world applications. Electric airplanes, when compared to their traditional counterparts, often employ fans powered directly by electric motors. This system is significantly less intricate than turboprop engines, creating opportunities for more individualized propulsion system configurations that can be fine-tuned to enhance the capabilities of a particular aircraft. NASA, Joby Aircraft, and Lilium's investment in fixed-wing distributed propeller and electric ducted fan aircraft designs has proven to be fruitful [9]. The research and development of these designs have enabled us to explore new possibilities and increase the practical application of electric aviation technology [15]. In order to achieve subsonic speeds for commercial flight, major civil aircraft manufacturers worldwide are adopting comparable methods that rely on hub-driven electric ducted fan technology [13]. Nevertheless, it is widely acknowledged that employing large centralized electric ducted fan (EDF) propulsion and traditional aircraft wing and body configurations introduces inefficiencies in both electrical supply and aerodynamics, which could hinder the overall effectiveness of electric-powered aircraft [16]. The benefits of electric propulsion, including blended wing body and distributed thrust systems, become more evident when contrasted with conventional design approaches [17; 18].