Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

60 T urning an engine into an integrated power plant means fitting ancillary systems to ensure a supply of clean air, ignite the fuel-air mixture, store fuel and feed it to the engine, and manage the exhaust gases. UAVs make unique sets of demands on all these systems. In small piston engines, grit, sand, dust and even smoke particles can cause problems by clogging passages in carburettors, causing throttles to stick or damaging valves, ports, piston rings and cylinder bores – any of which can lead to premature wear or in-flight failure. With gas turbine engines, the risk is more one of cumulative damage to rapidly rotating components in the intake path, such as compressor blades, leading to loss of power and efficiency. Any engine exposed to such contamination therefore needs protective filtration. The fundamental trade-off here is between the size of the smallest particles the filter can stop and the airflow restriction it causes. The two basic strategies are inertial separation to divert particles away from the intake flow and eject them overboard, or barrier filtration to trap particles. Inertial particle separators were developed in the US in the 1960s, initially to protect helicopter turboshafts and later spreading to armoured vehicles, diesel generators and even hovercraft. They consist of rows of tubes into which the air is drawn. Inside each tube are stationary vanes that cause the air to spin, creating a centrifugal force that propels the dirt and dust to the outer walls, along which their paths end in an opening that is exposed to a scavenging airflow that helps eject them. The clean air in the centre of the flow passes to the engine – or a secondary filter – via a concentric outlet tube. Variants that don’t require scavenging air are also available. A single tube 19 mm in diameter and 66 mm long, for example, has an efficiency of between 92% and 96% in the ISO coarse dust test, and uses 7-10% Peter Donaldson explains the subsystem options available for creating an integrated UAV power plant The complete picture June/July 2017 | Unmanned Systems Technology AAI Textron’s Shadow 200 is one of several tactical UAVs that use an electronic fuel metering unit, which includes the pump that feeds the fuel injection system (Courtesy of the US Department of Defense)