Unmanned Systems Technology 024 | Wingcopter 178 l 5G focus l UUVs insight l CES report l Stromkind KAT l Intelligent Energy fuel cell l Earthsense TerraSentia l Connectors focus l Advanced Engineering report

90 For example, the inner diameters of hose barbs can be widened through a calculated stretching of the fuel, air or oil tubing, which mitigates the flow restriction point required by the internal barb fittings. That increases the connector’s nominal flow diameter and could eliminate most (or in some cases all) of the flow pinching required of the hose barb, enabling UAV developers or technicians to use smaller and therefore lighter tubing. That is particularly beneficial, as many UAV fuel system designers are stuck with specifying tubing that is excessively thick in its inner as well as outer diameters. With reduced volume and weight taken up by tubing, a UAV’s flight time and range can be increased. The ability to customise barb design could even grow to meet that in electrical connectors. If unmanned vehicle users and manufacturers can list the specifications (or provide samples) of tubing or hoses they aim to use, they can be tested on connectors before manufacturing is complete. That can help ensure that the fit and grip of the connector to the tubing is as required. Relying on generic fluid connectors can also be problematic, as two tubes of identical diameters and thicknesses but different materials could provide different performance levels. It is also critical that any severe side- loading of the tube, when pulled 90 º to the barb plane (for example, when trying to remove it) doesn’t lead to the tubing being cut by the connector inlet or barb. Fluid couplers can also be improved by integrating directional valves, as this enables automatic connections to occur through the coupling and uncoupling process between the ground station’s filling equipment and the aircraft. That can simplify a UAV’s design and maintenance by helping to direct fuel to the holding tank while blocking the ports to the fuel injection, carburettor or other fluid delivery points. Pressure preset relief valves and check valves can also be integrated into AN connectors (a standard for attaching flexible hoses and rigid metal tubing, based on a standard for the US Army and Navy from WW2). Doing this means that when UAV fuel system designers need standard AN connectors as well as check or relief valves, they can use just one component instead of two, combining them while ensuring high nominal flow targets. That reduces the potential number of failure points – particularly in terms of potential new leak paths – which can be dangerously high among UAV fuel systems that rely on industrial or hobby- grade fluid connectors. The drive to reduce component cost and weight can actually be detrimental to the robustness of fuel systems. Using aluminium over heavier stainless steel can mandate the use of larger and thicker fluid connectors to meet pressure requirements, which can actually end up heavier than stainless steel equivalents. Stainless steel can also eliminate the need for surface treatments. Summary The rising demand for information is continuing to push the quality and quantity of what power, signal and fluid connectors can deliver for unmanned vehicles. As custom manufacturing technologies mature, more data will be acquired on the real-world performance levels of newer connector systems. That should be expected to feed back into the overall design quality of connectors, and drive ongoing development of new connector standards and variations to meet the efficiency levels required by newer sensors, avionics and fluid systems. Acknowledgements The author would like to thank Bob Stanton of Omnetics, Greg Jones and Luke Brockman of Ulti-Mate, Eric Eike of Positronic, Stephane Antonetti of Fischer Connectors, Alexis Delassat of Nicomatic, and Steve Fenton at Battlefield International for their help with researching this article. February/March 2019 | Unmanned Systems Technology Designing fluid connectors with reduced inner diameters in their hose barbs can reduce the weight of tubing required, making a UAV lighter (Courtesy of Battlefield International)