88 Focus | Launch & recovery Naturally, if catapults can be automated, at least partially, that could remove the risk of injury to humans and make the overall operation more efficient. While we have yet to see any concept for a UGV mounting a catapult on its back – which could travel to remote areas and catapult-launch a long-range, fixed-wing UAV – some solutions integrate battery- or mains-powered electric winches for automatically pulling their elastics or springs to full tension and then releasing them, all by remote trigger. In contrast, mechanical winches must be operated by hand. Recovery nets Given that what goes up must come down, a number of different recovery systems are in use across the industry, and recovery nets continue to be employed for catching UAVs at speed in precisely designated recovery locations. Much like catapults, nets must be engineered for the force with which a UAV is to be recovered; that being a function of their weight and expected operating speed. The greater these are, the larger or more stringently engineered a net must be in order to sufficiently dissipate the kinetic energy from the aircraft’s movement, such that no damage to either the UAV or the net occurs. The design of nets must also take into account the height and width of the aircraft. A flying-wing UAV will typically need a recovery net with a flat, wide shape. Alternately, a UAV with a long, thin fuselage extending ahead of its wings will need a net with thick, vertical straps to enable the fuselage to pass through before the wings are caught; otherwise, all the force of recovery will concentrate at the nose, potentially risking damage to an expensive gimballed payload. However, as UAVs become larger (to carry more energy and payload per mission), nets risk growing inordinately huge to perform recovery safely. As an alternative to building such unwieldy things, one approach is to design a kind of two-stage, mechanical net. That design features a fixed base of struts at the ground, with a net above contained in a structure that can flex, with a mode of energy dissipation somewhat analogous to that occurring when a car body crumples during a crash. The net’s flexing allows it to surround the aircraft during recovery, enabling ‘grabbing’ of its wings and other surfaces to prevent the tension being concentrated in one part to the point of breaking. These collectively comprise the design’s first stage, during which the large, uncrewed aircraft’s speed is greatly diminished, with ballast integrated to prevent the UAV’s impact force from pulling the net away or knocking the net structure over. Next, the upper net structure is permitted to rotate atop its struts, which consumes the UAV’s remaining kinetic energy. That minimises mechanical stress on both the aircraft and the ground equipment by allowing the energy to dissipate over time, rather than attempting to delete it all at once. Naturally, this two-stage design reduces the size of net needed for a given, large UAV, although balances of width, length, ballast, bearings and other engineering qualities can be customised to suit individual companies and aircraft or operating cases. Parachutes As well as recovery systems external to the uncrewed vehicle, those mounted internally to UAVs – including parachutes, air bags and floatation devices for water landings – remain popular for the significantly gentler landings they provide than belly landings, landing gear, and standing recovery infrastructure such as nets and hooks, despite the weight penalty they place on the aircraft carrying them. Unlike ground-recovery infrastructure, parachute-type systems can provide an emergency, backup capability following the failure of onboard propulsion systems, including VTOL lift motors integrated to make recovery equipment unnecessary. Key design targets for parachutes, airbags and the like include ease of integration (and hence testing and evaluation) into existing airframes to ensure UAV manufacturers or operators can use them in different platforms with a minimum of engineering overheads. Depending on the use-case and mission environment, parachutes and airbags may be periodically December/January 2025 | Uncrewed Systems Technology Recovery nets can be designed with weaves, heights, widths and multiple stages of material to safely catch UAVs and dissipate the energy from their impact (Image courtesy of Embention)
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