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78 around a hydrogen fuel cell powertrain, without sacrificing the heavier processors, lidar or other sensors the aircraft will carry. “The problem with hydrogen fuel cells is that they need significant space for the fuel tanks and cell stack,” Eio explained. “They’re not shaped to fit easily into a UAV frame, and weight distribution has to be optimised to withstand the change in the centre of gravity as the fuel is consumed.” The company is in talks with unnamed partners about engineering a 150 kg payload UAV, as well as another UAV aimed at ship-to-ship logistics operations. Helix Technologies discussed its dielectric-loaded GNSS antenna design. Although the dimensions of the ceramic core antennas vary according to their operating frequencies, a typical 1.6 GHz unit can measure 13 mm in diameter and 33 mm in height. The antenna could bring a number of benefits to new UAV designs. As John Yates explained, “The general approach for GNSS has been a wideband antenna, which captures the whole band, meaning filters have to be installed to extract the signals you actually want. With our antenna, we can design several specific frequencies onto one antenna, in a bespoke way.” The company designs individual helices onto the ceramic for each desired signal, such as Galileo’s E1, E5a and E5b signals, to pick up only these frequencies (1575.42, 1176.45 and 1207.14 MHz respectively) and no others. That reduces the need for filtering, enabling these antennas to be made smaller and more lightweight than typical designs. SBG Systems displayed its Ellipse 2 Micro INS, the smallest inertial navigation product from the company so far. “On top of the accelerometers and gyroscopes, it integrates processing to compute attitude and heading, as well as position and velocity, if it’s coupled with an external GNSS receiver by serial input over any standard NMEA protocol or any of the supported binary protocols,” said Pierre Inisan. The Ellipse 2 Micro measures about 2 x 1.5 x 1 cm, and outputs pitch and roll to 0.1°. Its 8 g accelerometers are rated to provide 5 m g (milli- g of gravity) one-year bias stability, with 0.2°/s one-year bias stability in its gyroscopes. It also provides heave measurements accurate to 5 cm for marine applications. The University of Central Lancashire’s Aerospace Engineering team exhibited a UAV developed for testing and maturing graphene-based aerospace technologies. “We started working a few years ago with the National Graphene Institute in Manchester, which had carried out experiments examining the physical properties of graphene,” explained Professor Darren Ansell. “They now want to deploy the material in the real world.” “We started in 2015 with a graphene paint on a UAV’s wings, and in 2016 started work with wings built from graphene-enhanced carbon fibre.” The carbon-graphene material was produced by UK-based Haydale Composites. A proprietary process mixes graphene into resin, providing different material properties according to the formulation, such as higher strength-to- weight ratio, electrical conductivity, or thermal conductivity to draw away heat. “The UAV also uses graphene ink tracks for antennas, as it takes mass out of the UAV. We’re also collaborating with a company that makes graphene impact sensors, which can locate impacts on the wing and measure their intensity,” Prof Ansell added. “These, along with graphene batteries, can be tested in the UAV for real-world results, which are far more interesting to aerospace companies than theoretical papers and simulations.” Avid Technology displayed its EVO axial flux (or ‘pancake-type’) BLDC electric motor. “The EVO has two stators, one on either side of the single rotor,” said Paul Middlemiss. “Each stator is bolted to the outer casing, with water/glycol jackets on either side for cooling.” The rotor is carbon fibre, to reduce inertia and hence the energy required to induce or reduce the rotational speed via the stator electromagnets. Twelve magnets are slotted into the rotor, and an additional carbon fibre band is fitted around the outer circumference. The number of windings in the stators varies according to the application- specific speed and voltage requirements. In addition to customised models, however, the company also provides a number of reference EVO models. For example, at 600 V DC, the 82 kg AF240 has a top speed of 5000 rpm, a nominal torque rating of 520 Nm, and produces a nominal 188 kW of power. The 22 kg AF125, meanwhile, runs at 12,000 rpm, with 100 Nm nominal torque and a 59 kW nominal power output. December/January 2019 | Unmanned Systems Technology Show report | Commercial UAV Show 2018 A graphene UAV from the University of Central Lancashire, England