# 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)
#### 2.2.4 Lighter-than-Air
Another example is Aeros hybrid cargo airship designed to have zero emission. They are also working on other hybrid solutions based on airships. Another example is Egan airship, which combines a fixed-wing config with the airship to provide transportation and tourism services. Au-30 is another example developed by RosAeroSystems which is designed for long-term flights including low altitude and low speed. Airships may carry up to 1.5 tons of payload and serve for about 25 h [67]. Figure 14 illustrates views of some lighter-than-air aircraft potentially designed for UAM. Neglecting their low speed, they have high capabilities for cargo transportation and tourism applications. Table 8 summarizes the advantages and disadvantages of lighter than air aircraft. The three main problems that this configuration can face during the flight are: aerostat faults, adverse weather conditions, and propulsion and steering system failures. Aerostat faults refer to any sort of problem concerning the aircraft's lighter-than-air segment. In airships, these faults can either present themselves in the form of buoyant gas leaks or problems with the air compression system which allows for altitude adjustments; in the past, this section has been even more sensitive due to the usage of flammable hydrogen gas (which was the main reason behind the well-known Hindenburg accident in 1937). Inballoons, there can be ruptures or the air heater can fail. Faults of this kind can be the most problematic since they affect the aircraft's ability to stay airborne. Dealing with this type of fault has to, for the most part, be done in advance through compartmentalization and redundancies. For example, if an airship utilizes multiple smaller buoyant air containers instead of a single large one (as is the case with most blimp designs), a leak in a container will be far less disruptive. Adverse weather conditions can affect the steering and controllability of the aircraft. In the case of the lighter-than-air configuration, these effects can be more severe due to its sluggish, shiplike nature. This is especially prevalent in balloons which are very susceptible to turbulent weather conditions. This problem can be counteracted, either by limiting flight only to times and locations with acceptable weather (according to forecast) or by flying at higher altitudes which have calmer weather; this, of course, would require additional design considerations. The last type of fault which we shall consider is problems with propulsion and steering. This will mostly only concern airships since balloons usually do not offer that much steering to begin with. Airships often have multiple engines and rudders which allows for the retention of controllability in case of failures. Additionally, the fact the lifting force in this configuration is not provided by high lift devices or engines means that not only is there a better margin available in trimming and control reallocation, but also, in case controllability  
Figure 14: Views of lighter than air aircraft: **(a)** Lockheed Martin LMH-1 [68], **(b)** RosAeroSystems Au30 [67], **(c)** Cameron Balloons Z-type [66], **(d)** Egan Airship [69], **(e)** Aeroscraft Airship [70]. is unrecoverably lost, the aircraft will not be at the risk of immediate crashing and can safely land if the area below is suitable [71; 72; 73].