# A Survey of the Effects of Vehicle Configuration on Urban Air Mobility +
## 2 Aerial Urban Vehicle Configurations and Concepts
### Hybrid
#### 2.3.3 Tilt-Wing  
This type of aircraft uses a fixed-wing structure paired with tilting capability for wings. In these vehicles, during the transition phase from VTOL to cruising, the wings and their rotors (or other mounted engines) rotate about 90 degrees, but the rest of the body remains fixed during the transition. The history of this type of aerial vehicle dates back to the 1960s and 1970s when Boeing developed its first tilt-wing, manned aircraft. Compared to tilt-rotors, tilt-wing configurations generally have a more sophisticated and complex design. Furthermore, in low-speeds, like hover, takeoff, and landing phases, \begin{table}
\begin{tabular}{c c} \hline \hline
**Advantages** & **Disadvantages** \\ \hline No need for runway (VTOL) & Complex transition phase \\ High efficiency & Pilot and passenger discomfort during \\  & take-of \\ Higher endurance compared to VTOLs & \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Advantages and disadvantages of tilt-body hybrid configuration. Figure 16: Tilting mechanism of BlackFly: (**a**) vertical take-off, landing, and hover (**b**) horizontal flight [83]. the wings need to be directed upward, which makes them more vulnerable to crosswind. Therefore, developing a tilt-wing AUV requires additional effort in designing control mechanisms to handle attitude stabilization. These AUVs can perform vertical flight similar to helicopters and fly with high speed like fixed-wing aircraft [15]. Of course, the mechanisms required for wing-tilting result in additional weight and increased system complexity [2]. Table 11 summarizes the pros and cons of this configuration. One of the good examples in this category is the Airbus Vahana. This aircraft has two tilting wings with four mounted electric motors. It is capable of flying at speeds up to 220 km/h which provides it with a range of 50 km [82]. Vahana passed its flight tests in 2019 and is being prepared for commercial use. Figure 17 illustrates the schematic of the Airbus Vahana. This type of Urban Air Mobility (UAM) aircraft has five major aerodynamic faults. Firstly, during VTOL flight in windy conditions, the wing rotates vertically, creating a large surface area against the wind, increasing drag, and making the aircraft unstable. Although the controller can stabilize the aircraft, it may be uncomfortable for passengers [85]. Secondly, the wing rotation system and the joint that connects the wing to the body are more susceptible to large moments and stresses, and a large, unaccounted force from drag or torque from the propulsion unit could break this joint, causing the simultaneous loss of a wing and part of the propulsion, leading to a sudden, hard to prevent crash [85]. The third fault arises during the transition between VTOL and cruise mode. In this situation, if an actuator or propulsion unit sustains damage, the aircraft loses its stability and may crash. Designing and controlling the transition mode is the biggest challenge for this type of UAM. If the aircraft experiences any sudden problems during this flight mode, it becomes very difficult for the controller and pilot to handle the situation, which could result in a serious crash [85; 86]. The fourth fault is similar to that of multirotor, tilt-rotor, and fixed-wing aircraft. In VTOL and cruise mode, if the aircraft loses any propulsion unit, it rotates yaw and roll. However, the controllers can control the aircraft by increasing the thrust and RPM in other \begin{table}
\begin{tabular}{c c} \hline \hline
**Advantages** & **Disadvantages** \\ \hline No need for runway (VTOL) & Complex transition phase \\ Efficiency & Complex structure compared to tilt-rotor \\ Higher endurance compared to VTOLs & \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Advantages and disadvantages of tilt-wing hybrid configuration. Figure 17: Airbus Vahana. propulsion units and using the elevator and aileron. If the aircraft loses any wing rotating actuator in VTOL mode, it cannot change its flight mode to cruise and must land quickly.