Understanding UAVs – Part II
The selection of available UAVs has greatly expanded over the last few years and it has become difficult to keep track of the entire range. The market offers diverse systems, and there is no universal classification. The US military uses a tier system with specific UAV requirements (e.g., they must offer particular levels of range or endurance).
In general, systems tend to be classified by measurements or specifications, which can relate not only to range and endurance but also to size, maximum take-off weight, service ceiling, and price. Other major distinctions are the build type and the engine used. The following table gives a brief overview of the advantages and disadvantages of different build types.
The main types of engine used today in non-military UAVs are the electric engine and the internal-combustion engine. The electric engine is environmentally friendly and operates without much noise; these are important advantages especially in densely populated areas. It is relatively inexpensive to charge the battery, but battery weight is a drawback and UAV range can be limited by battery capacity.
A UAV powered by a comparable internal-combustion engine is likely to have superior range, due to the energy density advantages of fossil fuels and because range can be simply extended by adding fuel tanks. Hybrid systems are currently being developed, trying to combine the best of both worlds – the internal-combustion engine is used for longer distance flights, and the electric engine is used for take-off and landing in areas requiring quiet operation.
This report does not exclude any specific type, but its focus is rather on electrical engines and multicopters, because these appear to be the most promising choice for the logistics industry applications that are discussed in this report.
This reflects both cost and feasibility arguments: While long ranges and high payloads are technically feasible today, UAVs of this type tend to be expensive and may be a bad choice in densely populated environments such as cities, because of horizontal take-offs and noisy engines. This matters less outside urban areas, and in the following chapter we review the varied tasks being Figure 5: Multicopter used for taking low altitude aerial photos; carried out by UAVs today.