# Advancements and Applications of Rim-Driven Fans in Aerial Vehicles: A Comprehensive Review
## 4 Type of Electric Motor  
Induction motors (IM), switching reluctance motors (SRM), permanent-magnet direct-current motors (PMDCM), permanent-magnet alternating-current motors (PMACM), and high-temperature superconducting motors (HTSM) are only some of the electric motor types that may be employed with RDTs. [PERSON] et al. developed an IM-based RDT with a skewed-bar squirrel cage rotor connected to the blade tips [52]. The researchers conducted tests to evaluate the propulsor's performance in terms of speed, thrust, and noise level, and found that it achieved a high level of efficiency with reduced noise compared to traditional gasoline engines. The study highlights the importance of developing eco-friendly technologies as a means to minimize negative environmental impact, and the submersible electric motor propulsor is presented as a promising technology for small boats and watercraft. Additionally, an oil-filled metal container was laser-welded around the entire stator assembly. To streamline the rotor design, a conducting rotor can was implemented in place of the traditional \"deep-bar\" cage and a succession of air-gap cans were used to offer environmental shielding. [PERSON] et al. developed this line-start rim-driven IM for application in RDTs [40; 53; 54]. According to [PERSON] et al., an RDT consists of a three-phase motor with six slots in the stator and twenty slots in the rotor, which together form a switching reluctance motor (SRM). The study focuses on the design and optimization of the motor to meet the requirements of the rim-driven thruster, and testing was carried out to evaluate the performance of the motor. The results showed that the proposed motor design achieved high efficiency with reduced weight and size compared to conventional motors used in marine applications [55]. Because of the significant drag losses brought on by their radially thick ducts and rotors/stators, IM and SRM motors both suffer from low aerodynamic and hydrodynamic efficiency at high advance speeds. This is the case even though both types of motors have similar advance speeds. The poor performance of IM and SRM can be attributed to the wide air gap that is necessary in order to integrate corrosion protective layers on the surfaces of the rotor and stator. PM motors can have a greater number of poles and are more tolerant of larger gaps, as stated by [PERSON] et al. [56; 57]. The studies underscore the significance of PM motors due to their ability to have ultra-thin rotors and stators without compromising performance. They offer experimental and simulation-based evidence in support of the argument that PM motors have an efficiency that is intrinsic to their design, explain why a majority of researchers prefer incorporating this motor type into their RDT designs, and also emphasize the critical factors that affect the total efficiency of a PM motor. These factors include a large number of poles, a small radial thickness, a reasonably huge air gap, short axial length, and relatively thin magnets. The authors present the results of their experiments and simulations to demonstrate these factors' importance and their impact on efficiency. Also they demonstrate the development and optimization of a slot-less PM brushless motor with helical edge-wound laminations and use various simulations and algorithms to obtain efficient and optimal motor designs [58; 59]. [PERSON] also developed and built a slot-less PM brushless DC motor with helically edge-wound laminations for RDTs in order to decrease the expenses associated with producing slotted brushless PM machines and to facilitate their production [39]. The design of the slot-less motor eliminated the tooth ripple component of cogging, reduced the effects of harmonic resonance, and possessed minimal winding inductance. This was feasible because the magnetic gap had to be sufficiently large and there were no slot leakages.