Unmanned Systems Technology Dec/Jan 2020 | Phoenix UAS | Sonar focus | Construction insight | InterGeo 2019 | Supacat ATMP | Adelan fuel cell | Oregon tour | DSEI 2019 | Copperstone Helix | Power management focus

32 the prototype for an exploitable platform and complying with official airworthiness and certification requirements. The intention at the start of the project was to conclude with outdoor flight trials. To do that, the aircraft and its operation had to achieve certification through the UK’s Civil Aviation Authority (CAA). This certification has a series of weight thresholds, with 150 kg being the limit for national approval (through the CAA) under a ‘permit to fly’. Heavier than that and an approval by the European Aviation Safety Agency (EASA) would have been needed, which was unrealistic owing to the project’s budget and timescale. Given a 150 kg all-up mass (including the mass of the lift gas), a payload of 10 kg was chosen as a reasonable ambition. However, the aircraft does not comply with any conventional certification categories, and traditional aircraft design methods are not appropriate, so novel approaches had to be developed to achieve a successful and compliant design. The successful demonstration of the prototype, and of a variable-buoyancy propulsion system for an aircraft, opens up a completely different approach to several mission requirements. Removing the need for electric motors, and the associated power requirement, provides three major advantages. December/January 2020 | Unmanned Systems Technology Dossier | Phoenix UAS • Materials and fuselage design, systems integration and flight trials: Banks Sails • Development and application of the solar cells: IQE • Flight control system software development and integration, systems integration and flight trials: Stirling Dynamics • Design and manufacture of the pumps and valves, and flight control actuation system design and integration: TCS Micropumps • Project management, and the development and application of the solar cells: Centre for Process Innovation • Flight control system hardware development and integration: Manufacturing Technology Centre • Design and manufacture of carbon-fibre structural components (wings and empennage): National Composites Centre • Design and manufacture of carbon fibre structural components (wings and empennage, including the WrapToR truss structures), and stress calculations: University of Bristol • Chief engineer, aircraft architect, aerodynamic design and wind tunnel testing, and flight trials: University of the Highlands and Islands • Development and evaluation of a reversible hydrogen fuel cell: University of Newcastle • Wind tunnel testing: University of Sheffield • Design and integration of rechargeable battery, and overall power management system: University of Southampton Project partners Fig. 9 – Behaviour of the differential pressure protection Fig.10 – The battery, flight control system and pumps and valve were mounted on a gondola plate on the bottom of the fuselage to provide the required centre-of-gravity position