With the Singapore University of Technology and Design announcing its development of the experimental Transformable Hovering Rotorcraft (THOR) in July 2017, it is worth considering the landscape of drone airframes in the commercial sector. In a marketplace dominated by relatively cheap multirotor systems, the THOR “monocopter” represents an attempt to revive an archaic airframe design to provide the full spectrum of aerial capabilities.
A great deal of attention has been placed on the widening number of commercial sectors that are beginning to leverage drone technology for tasks like data gathering, video monitoring, 3D map creation, inspection, and surveillance. Far less has been paid to the development of the platforms and how the changing demands of small unmanned aerial vehicles (sUAVs) is leading to the increased use of multirotor platforms over alternatives like fixed-wing, single rotor, and hybrids. The recent announcement of a monocopter design from the Singapore University of Technology and Designrepresents an attempt to create alternatives to multirotor systems. This ABI Insight will explain the reason behind the dominance of multirotor systems and why it should be expected to last.
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Multirotor aircraft come with a large number of negatives. They fundamentally lack speed, endurance, and maximum altitude, and require vast amounts of energy just to keep them up in the air. Because they require short bursts of thrust to stabilize themselves, it is ineffective to use gas engines, and so the persistence of the aircraft is determined largely by the electric motors currently used. This gives them anything between 5 and 35 minutes in the air before having to be recharged for hours.
However, these failings are offset by two factors: first, the nature of the task demanded from a drone, and second, the advantages of multirotors. Most commercial tasks for sUAVs (like inspecting or data collection) do not require particularly long flight times or very high altitudes. Those that do, like inspection of power lines or large agricultural spaces, might still warrant multirotor platforms because operators often are happy to use a multirotor a number of times to capture data they could access in one go with a fixed-wing system.
This is because multirotors have major advantages over fixed-wing platforms. They are easily maneuverable and have much simpler takeoff requirements than fixed-wing alternatives. Given that image collection and inspection requires loitering and stability, the fact that fixed-wing craft have to be consistently moving forward negates their positives regarding extended altitude and range. Given that the complexities of the task increasingly relate to software, and the hardware of small, cheap multirotors is currently sufficient, there is precious little reason for operators to choose the more expensive and less maneuverable fixed-wing systems like senseFly’s eBee.
As stipulated, fixed-wing platforms are much better suited to some tasks than multirotor systems. They can reach higher altitudes and survey a wider area for a longer time period. They are more resilient and less likely to break down. They are considerably faster. But these benefits are only relevant for a relatively small selection of tasks that the commercial drone space is offering. For large-scale inspection of a power grid or pipeline, a fixed-wing’s range is useful, but often, inspection requires long wait times of loitering and remaining stable in the air so information can be gathered, in the case of wind turbines or under bridges.
The additional cost of systems like the eBee are keeping them relegated to the fringes of the market, and the vast majority of the millions of acres processed by commercial drones have been from multirotor systems. A small number of prosumers and drone enthusiasts have pushed for single-rotor (helicopter) drones. A recent announcement by Atlas Dynamics promises the building of a sophisticated fixed-wing drone called the Atlas Blue-J. This product is expected to have a flight time of 5 hours and an operational range of 150 km (by comparison, the eBee has a flight time of 50 minutes and range of 12 km). Such new levels of performance will be useful for linear inspection of remote sites like offshore wind farms or large infrastructure like pipelines. It will also be useful for surveying large tracts of agricultural land.
Given the dominance of multirotor systems, there are two technological developments to look out for. On the one hand, hydrogen fuel cell technologies are being retrofitted to be adopted onto multirotor systems, potentially extending maximum flight time from minutes to hours. This has been most recently exemplified by Chinese manufacturer MMC’s HyDrone 1550.
On the other, companies and universities have been researching and developing new hybrid systems that incorporate features of both multirotor and fixed-wing systems. As part of its drone delivery service, Amazon’s Prime Air drone is a fixed-wing aircraft with vertical takeoff and landing (VTOL) capability. Though examples of these hybrids are still at the developmental phase, they can excel at both hovering and forward flight, making them desirable for a number of commercial tasks like delivery. The THOR is another example of trying to get a full spectrum of capabilities including VTOL, forward flight, and greater range.
Depending on the demand for payload increase in the commercial drone space, there could be an additional market for unmanned single-rotor helicopters. They are already well-tested in the manned market, and have far greater efficiency than multirotor systems, while providing the benefits of VTOL. They are best suited to carrying heavier payloads like laser scanners and can be gas powered, thereby increasing range and endurance. However, they suffer from being expensive and having a high degree of technical complexity. There is also an increased safety hazard resulting from the large blade. The desirability of helicopters will thus be determined by how safely it can be made to fly autonomously because remote piloting for such systems requires more training than for alternatives.
But in the long run, greater range is not likely to offset the advantages of multirotor systems. In cases like delivery (where range is key), IBM has already developed a patent forin-flight drone-to-drone package transfers that will increase coverage of service.
The preeminence of software as a service (SaaS) and innovations in commercial drone application services have generally superseded discussion about the trajectory of hardware. This is understandable given that software will account for a great deal more of global revenue and the current multirotor airframes are sufficient for the job requested. Whether demands change or new hybrid airframes become more reliable will be worth considering, but for now, the dominance of multirotor platforms is firmly cemented.