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

39 also unafraid to combine concepts from within its own canon to create completely new capabilities. Without doubt the simplest way to launch a small fixed-wing UAV is simply to throw it. Things get more demanding however in terms of support equipment when the vehicle becomes too heavy to launch by hand or needs more airspeed over its wings than human muscles can provide. One proven solution to this problem is the catapult, which has been around in various forms since ancient times. Heavy UAVs that need to achieve high launch speeds over a short distance need robust catapults that can contain and quickly release large amounts of energy, sometimes as much as 400 kJ in less than a second, with instantaneous power figures reaching 600 kW. At the same time, the catapult design must ensure that acceleration forces remain within the limits that the vehicle and its payload can withstand. The interface between the UAV and the catapult is the cradle, which must hold the vehicle securely before releasing it at the right moment without disturbing its attitude. Catapult options For UAVs up to about 10 kg, bungee catapults are widely used. Advantages include great simplicity, low cost and a very low launch signature. Those that are wound up by hand and feature a purely mechanical release mechanism need no electrical power. However, a lack of damping means the initial acceleration can be very jerky, producing large shock loads that might damage the UAV or its payload, and the final velocity can be difficult to predict. Bungee catapults are generally limited to smaller UAVs. Hydraulic catapult launchers have a cylinder containing a piston that separates hydraulic oil from compressible gas. To charge the system, a hydraulic pump forces the piston along the cylinder with the oil to compress the gas. On launch, a valve opens to release the oil into a hydraulic motor through which the pressurised gas – now free to expand – forces it by pushing the piston back along the cylinder. The hydraulic motor powers a winch that launches the UAV. Hydraulic launchers are quiet and highly controllable, and so can produce soft starts to minimise shock loads on the UAV while generating the required launch velocities for a wide range of vehicle sizes and weights. They are also quick to reset and cheap to operate. However, they are complex, expensive, need external power and tend to be heavy and bulky. Pneumatic catapults use compressed air to drive a piston along a cylinder to accelerate the UAV into the air, with a cable and pulley system for example. Like hydraulic catapults, they can provide soft launches and accommodate a wide variety of vehicles of different weights, and can be reset quickly between launches, but they too are cheap to operate, as well as quiet and stealthy. Launch and recovery systems | Focus Unmanned Systems Technology | April/May 2016 Landing gear and arrestor hook down, the Northrop Grumman X-47B UCAV demonstrator is an example of UAV recovery adopting a practice developed for manned vehicles (Courtesy of US Navy) A Falco tactical UAV leaves a Robonic high-pressure pneumatic catapult, which can accelerate UAVs of up to around 100 kg to 70 m/s (Courtesy of Robonic)