# A Survey of the Effects of Vehicle Configuration on Urban Air Mobility +
## 2 Aerial Urban Vehicle Configurations and Concepts
### Horizontal Take-Off and Landing (HTOL)
#### 2.1.4 Gyroplane  
Gyroplane is one of the oldest concepts in this field. One of the examples in this field comes back to the 1930s when Autogiro Company of America AC-35 was designed to provide a roadable plane solution for short travels. Although it was not a successful attempt, it opened the way for many other similar concepts. Gyroplanes look similar to helicopters but there are major differences between them. The main difference is that in a gyroplane the rotor is not powered and it is only used for lift production while in helicopters the rotor is powered and is responsible for providing both lift and thrust. The main source of thrust in a gyroplane is the propeller situated at the rear or front of the plane. The other difference is that gyroplanes are HTOL planes with short runways while helicopters are VTOL aircraft. In contrast, gyroplanes have more simple structure compared to helicopters and are easier to fly. Considering expenses, gyroplanes are comparatively cheaper than helicopters [15; 36]. Table 4 summarizes the advantages and disadvantages of gyroplane configuration.  
After AC-35, many other examples were introduced in this field. Just to mention some examples, we can mention Butterfly Super Sky Cycle which is a lightweight gyroplane for just one passenger. It can fly with 7.5 gallons of fuel with up to 10 gallons of reserved fuel which provides the passenger with up to 200 km range and a maximum speed of 136 km/h [37]. PAL-V Liberty is one of the latest gyroplanes which is designed for two passengers and is able to fly with the maximum speed of 160 km/h for up to 4 h which provides a range of 400-500 km [38]. Figure 8 illustrates some examples of gyroplanes.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Advantages** & **Disadvantages** \\ \hline Simple structure & Need for runway and infrastructure \\ Low price & Short runway \\ Suitable for short-range flights & \\ Failsafe feature & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Advantages and disadvantages of gyroplanes.  
Figure 8: Examples of gyroplanes: (**a**) PP Sar, (**b**) PAL-V Liberty, (**c**) Butterfly Super Sky Cycle, (**d**) Autogyro Company of America AC-35.  
As alluded to previously, gyroplanes in functionality are more similar to fixed-wing aircraft rather than helicopters. As such, faults in them and the way those faults can potentially be dealt with is also for the most part, similar: partial failure of control surfaces can possibly be addressed through control reallocation and other techniques mentioned in Section 2.1.1 and engine failure would probably necessitate an immediate landing due to the fact that most gyroplane designs utilize a single engine, although in such a case the aircraft wouldn't experience an instantaneous loss of lift due to the auto-rotating rotor. However, when this configuration considerably differs from fixed-wing aircraft (and helicopters for that matter) is in its main source of lift generation: the rotor. A gyroplane's rotor, like that of a helicopter, is a flexible entity that operates in an unsteady flow regime; however, unlike the rotor in a helicopter, it is not powered. This means that the angular speed of a gyroplane's rotor is not able to maintain constant and varies by time. This variation of the rotor's angular velocity and by extension the forces it produces is a result of its aero-elastic interactions with the unsteady, asymmetrical flow around it. This, in turn, means that modeling the aerodynamics of the main rotor accurately and predicting its behavior in all the different flight conditions using today's computational techniques are very difficult if not impossible. Thus, a certain degree of uncertainty is always present with a gyroplane's rotor, in terms of both lift and structural oscillations which could affect other subsystems. Therefore, the best course of action here would be the employment of robust control systems which are capable of withstanding model inaccuracies [39].