Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

98 PS | Multi-environment vehicles D ual- and multi-environment drones are now emerging, with several that can operate underwater and in the air, at least one family that can both fly and drive, and a conceptual machine designed to do all three (writes Peter Donaldson). As ever though, nature is millions of years ahead of us in this, and there are many animals that can move about successfully in the air, on or under water and on land. Multi-environment animals have their limitations, however, because features that provide good capabilities in one area tend to bring drawbacks that affect one or more of the others. It is always worth studying how evolution has solved these problems and the compromises that have been made along the way to get an idea of the challenges engineers face in creating multi-environment machines. The most noticeable of these is size, as all multi-environment animals are relatively small and all are either birds or insects. The largest is the pelican, which can weigh up to about 12 kg and is a good flyer, surface swimmer and diver, regularly plunging into water from the air to catch fish. On the other hand, it waddles about rather awkwardly on land, although it does manage to project some swagger while doing so. Gannets are probably the high- performance diving champions. They can hit the water almost vertically at up to 75 mph, folding their wings back on entry and reaching depths of 60 ft, where they chase after fish, propelling and manoeuvring themselves with their wings and feet. Hydrodynamics and aerodynamics are similar enough for wings to double as serviceable paddles, although of course webbed feet are no good for flying. Likewise, unmanned vehicles that can swim and fly tend to use the same propellers in both environments, although they have to be optimised for flight and their underwater limitations accepted, as is evident from their relatively long spans and narrow chords. Moreover, most dual-environment drones are basically waterproofed multi- copters. This applies to the Corrosion Resistant Aerial Covert Unmanned Nautical System developed in 2016 by a team at the Johns Hopkins University Applied Physics Laboratory, the Naviator developed by Rutgers University, and the Spry and Spry+ developed by Swellpro for the sports and leisure market. North Carolina State University has developed a fixed-wing drone called the EagleRay XAV that can ‘fly’ underwater, launch into the air and return to the water. More dramatically, the AquaMAV from Imperial College in the UK enters the water like a gannet, it too folding its wings back as it dives in. Few unmanned vehicles combine flying and driving capabilities, but Robotic Research’s Pegasus family of quadcopters has tracks built into the landing ‘skids’ that also pivot up and out through 90 º to serve as rotor guards in flight. Perhaps uniquely, Cyclopic’s conceptual Cyclopter, which is in the early stages of development, is designed to operate in all three environments. It is a waterproof quadcopter that drives, flies and swims, using rotors built into the wheels that serve as propellers under water and pivot to a horizontal position to create a quadcopter configuration for flight. Aquatic birds have survived for millions of years by finding ecological niches that favour this combination of capabilities; their drone analogues will have to find similar ones in the UAV market. Now, here’s a thing “ ” August/September 2020 | Unmanned Systems Technology Vehicles that can swim and fly tend to use the same propellers in both environments, although they have to be optimised for flight