# A Survey of the Effects of Vehicle Configuration on Urban Air Mobility +
## 2 Aerial Urban Vehicle Configurations and Concepts
### Vertical Take-Off and Landing (VTOL)
#### 2.2.2 Multirotor  
Multirotors are rotorcraft equipped with multiple horizontally rotating rotors that generate both lift and thrust for flight. Unlike conventional helicopters with articulated blades, multirotors commonly utilize fixed-pitch blades. This configuration allows for precise control, vertical takeoff and landing, and hovering, making multirotors versatile platforms for various applications. Multirotors are typically limited in cruise speed, less efficient during cruise flight, and therefore have a shorter range compared to other configurations. However, they naturally have very good hover and VTOL characteristics [2]. In  
Figure 9: Compound helicopters: (**a**) Piasecki 16H-1 Pathfinder, (**b**) Eurocopter X3 (X-Cubed). addition, they have a simple structure and are easy to build and maintain. Furthermore, they use electrical motors. In fact, a significant portion of the eVTOL industry belongs to the multirotors or hybrid multirotors. Similar to VTOL aircraft they benefit from the possibility of vertical and hover flight which makes them very suitable for urban applications. A significant portion of the eVTOL industry belongs to the multirotors or hybrid multirotors. As well as many VTOL aircraft they benefit from vertical and hover flight which makes them very suitable for urban applications. Due to their numerous advantages, many companies are working on developing urban solutions based on multirotor configurations. They can be found in many forms including tri-rotor, quadrotor, and so on. As examples, we can mention [PERSON] et al. concepts. They have provided some VTOL air taxi concepts for a wide range of applications including single-passenger, and fifteen-passenger [45; 46]. Figure 10 illustrates their concepts. Many big corporations have also started to work on multi-rotor urban air mobility solutions, amongst them we can mention CityAirbus and CityAirbus next gen. Airbus has designed a multirotor UAM aircraft with a capacity for four passengers and 15 min endurance with a cruise speed of 120 km/h. The next generation of the CityAirbus uses a novel design with a combination of a fixed-wing structure, but it does not have any control surfaces [47]. A similar vehicle is also designed by Boeing by the name of Boeing Passenger Air Vehicle [48]. Volocopter VoloCity is another example which by using eighteen electric rotors is able to carry two passengers. VoloCity has an endurance of about 0.5 h which provides a range of 35 km [49]. Another example that uses a quadrotor configuration with coaxial rotors is Moog SureFly. It has a range of about 110 km and can carry up to two passengers using its electrical rotors. Ehang 184 is another commercial example in this category. It can carry up to two passengers for a range of 35 km with its eight electric rotors [50]. Some other companies like Audi have also started to work in this field. Audi Pop Up Next is a conceptual design of an electric flying vehicle that was introduced by Audi at Geneva Motor Show 2018. This concept uses a quadrotor configuration that can be attached to a two-passenger automobile in order to provide flight capability. Figure 11 illustrates some of the well-known multirotor aircraft. Considering the discussed topics in this section, we can summarize the pros and cons of multirotor configuration as is in Table 6.  
However, multirotors flight endurance may can be increased with hybrid gaselectric propulsion system. By integrating a gas-electric power generator alongside traditional battery power, these aircraft can benefit from the increased energy density of fuel while maintaining the electric motors necessary for precise control. This configuration allows for longer flight times as the generator can replenish battery power, effectively overcoming the range limitations typically associated with battery-only systems. Figure 10: Different air taxi concepts by [PERSON] et al. : (**a**) single-passenger quadrotor, (**b**) fifteen passenger hybrid aircraft [46].