Unmanned Systems Technology 007 | UMEX 2016 report | Navya ARMA | Launch & recovery systems | AIE 225CS | AUVs | Electric motors | Lethal autonomous weapons

40 Focus | Launch and recovery systems They also share some of the disadvantages of their hydraulic counterparts in terms of initial cost and footprint, while the pneumatic accumulators that act as reservoirs of compressed air require external power and can be slow to pressurise. Purely pneumatic launchers are able to catapult a 500 kg UAV at up to 64 m/s. Size and weight rise significantly with vehicle launch weights, speeds, stroke and system pneumatic pressure. Low launch pressures below about 10 bar (145 psi) can be used to launch medium- weight tactical UAVs of say 150-300 kg at moderate speeds. This eliminates the need for very high-spec components, reducing system lifecycle cost, but the large, long-stroke cylinders required tend to make the systems heavier and bulkier than higher pressure systems of comparable performance. For example, one truck-based low- pressure system that can launch a 300 kg UAV at up to 34 m/s weighs 7000 kg. By comparison, a high-pressure launcher from the same company can accelerate a 500 kg vehicle at up to 65 m/s but is 1000 kg lighter. While pneumatic catapults represent a mature technology, they are still being refined through the use of advanced materials. One portable example can launch UAVs of up 91 kg, pushing the vehicle into the air using a composite rod that emerges from an anodised aluminium tube and falls away from the UAV as it climbs. The launch tube is supported on a lightweight A-frame. The complete system weighs a little over 79 kg and is designed be set up by two people in less than ten minutes, as no single component weighs more than 32 kg. A fourth alternative now under development is the electric launcher, which promises to alleviate many of the logistical issues associated with pneumatic and hydraulic launchers, while providing more positive control of the g -loads during launch and shortening the recycle time between launches. Getting medieval The catapult is not the only ancient weapon that has been reinvented to launch UAVs; the same has happened with the trebuchet. Powered by muscles and gravity, this medieval siege weapon used a counterweight on one end of a long, pivoted throwing arm with a sling to hold the payload on the other end, with the whole mechanism supported in a sturdy frame. Instead of hurling rocks at castles, however, the modern interpretation throws a small fixed-wing UAV into the air, using the vehicle on which it is mounted as the counterweight. To prepare for launch, the supporting frame is unfolded from the vehicle’s roof and set in place so that it can support the weight of the vehicle, the back end of which is then raised with an electric winch. This design is intended to enable launches from small areas, to provide sufficient altitude from launch to clear nearby obstacles. Rocket role To launch heavier UAVs in short distances, Rocket-Assisted Take-Off (RATO) is a proven technique. Near- zero length launches can be achieved with the aircraft supported on a frame and accelerated into the air by a RATO booster bottle, which is jettisoned after burning out so it adds no deadweight. The equipment is light and compact, and initial costs are low. However, the rocket plume is bright, hot, smoky and loud, mitigating against RATO’s use in confined spaces with people or sensitive equipment around. This ‘unstealthy’ method also drops the spent booster along the launch path, enlarging the required safety zone. Storage, transport and handling of pyrotechnics add their own issues, while refilling or replacing spent RATO bottles soon becomes expensive. There is also a brief period of potential instability in which the UAV is airborne but not moving fast enough to generate the airflow that the aerodynamic control surfaces need, restricting its use to calm weather. Leisurely approach The popular watersport of parasailing has also successfully lent equipment to the launch and recovery of UAVs from ships, with the UAV held by a frame suspended from a parafoil towed by the ship. Once high enough, the UAV’s engine is started and the aircraft is released into a steep dive to pick up flying speed. Recovery involves the pilot (or autopilot) flying the UAV into a net suspended from the parafoil. The technique has been proven in trials at sea by the US Coast Guard, which found it best to use a frame that is far heavier April/May 2016 | Unmanned Systems Technology Amores took the principle behind the trebuchet to develop a UAV launcher that uses its transport vehicle as the mass whose potential energy is released to throw the small UAV into the air (Courtesy of Amores)