VTOL Drones & Multirotor UAVs
Multirotor UAVs (Unmanned Aerial Vehicles) and other VTOL (Vertical Take-Off and Landing) unmanned aircraft have the ability to take off, fly and land vertically as well as hover in place. VTOL UAVs may be based around a helicopter design or may feature a multirotor design that incorporates four or more propellers. The propellers create both lift and propulsion for the aircraft.
The majority of multirotor drones are powered by Lithium-Polymer (Li-Po) and Lithium-Ion (Li-ion) batteries. Although liquid fuels provide a higher energy density than batteries they are typically only used by the larger helicopter drones due to the weight of the fuel and the internal combustion engine. Hybrid fuel-electric systems are being developed that will combine the advantages of both methods.
Solar cells are usually not used on multirotor aircraft due to the relatively large surface area required to general sufficient power. Hydrogen fuel cells are available that provide a higher energy density than batteries and thus a greater endurance, while being lighter than combustion-based technologies.
VTOL and multirotor UAVs may be equipped with a wide variety of payloads, including high-resolution cameras, multispectral sensors, and environmental monitoring sensors such as CO2 and radiation detectors.
VTOL and multirotor drones have several advantages over fixed-wing unmanned aircraft. They require much less space to launch and recover, as they do not need to use a runway. They are suited to applications such as inspection and monitoring where the aircraft must maintain a fixed position for a period of time. They are generally more manoeuvrable than fixed-wing aircraft due to the ability to vary the relative speed of each rotor, thus creating changes in thrust and torque.
The main disadvantage compared to fixed-wing UAVS is the lower endurance. This is due to the fact that rotary aircraft use their rotors to generate both lift and thrust, therefore requiring more power, whereas fixed-wing aircraft only require their propulsion system to generate thrust, as the lift is generated by the wings.