Making aircraft very small, removing the pilot or redefining the mission opens up a lot of new options as to how unmanned air systems take off, fly and land. Early UAS looked like small airplanes (often, like model airplanes). However, the rise of the ubiquitous quadcopter showed that the requirements are often very different and the constraints are different too. The quadcopter is simple, with four identical propulsion units that are also the control effectors, and inherently stable in the hover. If speed is not your bag, and you want a camera platform, the quadcopter does that better than a fixed-wing aircraft flying in circles.
New at AUVSI was a variation on the quadcopter from Latitude Engineering of Tucson – the hybrid quadrotor, or possibly octorotor.
A piston engine drives a generator, turning four electrically powered rotors (on the prototype). The next generation vehicle, weighing 60 lb, will have eight lift rotors installed in pairs, above and below the booms. Latitude says that three of the latter vehicles have been ordered by Naval Air Systems Command for a test program.
A blast from the past comes from Swiss-Swedish newcomer Unmanned Systems Group in the form of the ATRO-X helicopter UAS, shown in the form of a one-third-scale model.
Note the pie-dish-shaped device on the rotor head and the ducts leading to the blades. That is a hot-cycle tip-jet driven helicopter, similar in principle to the monster Hughes XH-17 of the 1950s. The main difference is that the miniaturized jet engine which produces the hot gas is mounted on top of the rotor. The ATRO-X’s designers point out that the helicopter needs no transmission and no tail rotor, and that the jet engine is designed for a higher time between overhauls than the high-revving small reciprocating engines fitted to rivals such as the Scheibel Camcopter and Saab Skeldar. It also burns jet or diesel fuel. The full-size vehicle weighs 770 lb at take-off. The propulsion system is being rig-tested – and one thing is certain, which is that there will be no problems with rotor blade icing. Stealth, on the other hand, might be a challenge – tip-jet helicopters were never famed for being quiet.