Unmanned Systems Technology 022 | XOcean XO-450 l Radar systems l Space vehicles insight l Small Robot l BMPower FCPS l Prismatic HALE UAV l InterDrone 2018 show report l UpVision l Navigation systems

73 Prismatic HALE UAV | Digest as individual design points. To maintain the simplicity of the aircraft’s electronics, the team measures the energy used from the battery over the period of flight by recharging it, rather than tracking charge and consumption using battery management sensors and processors. “We also undertake wind tunnel testing, and that has very similar challenges owing to the low speeds and small loads we are measuring in them,” Brooks adds. The first prototype of a PHASE-8 was flown in December 2017, and since then the company has run a further dozen flight tests. There are five PHASE-8s so far. “The first flight was relatively short, at 20 minutes, as the conditions really weren’t suitable, with winds too strong and gusty,” Brooks says. “However, we put great store in testing so we decided to give it a go. “Since then, we have generally aimed for flights lasting two or three hours, as we’ve been undertaking functional and performance testing to support the development of the PHASA-35. “Given that we started work on the PHASA-35 in September 2016, and began the build of the PHASE-8 to support this in July 2017, it has been a very rapid development schedule,” he says. While the main objective – and key result – of the flight tests was to accurately demonstrate aerodynamic and propulsion performance to meet the requirements of the PHASA-35, to enable it to achieve year-round HALE flight, the PHASE-8 was also found to be able to endure much higher winds and gusts than expected. This, the team reports, was the key finding that drove them to consider and offer the PHASE-8 as a valuable UAV in its own right. While the team has made no overall design changes to the vehicle since its first flight, they do pursue improvements in the build and material quality, with the aim of reducing structural mass. The size of the motor pods has also increased to house more battery cells and larger motors with improved energy efficiency. “These changes were not required for the PHASA-35 validation but have instead arisen from our interest in providing extended operations for PHASE-8,” notes Brooks. Going forward, Prismatic plans to undertake an extended-duration flight in early 2019. The current intention is to fly from dawn to dusk, to exercise the full cycle of power transition between solar and battery power. A number of flights will be carried out before that though, to continue testing for the best implementation of the PHASE-8 and PHASA-35. Future work In addition to the ongoing testing and refinement of technologies for the PHASA-35, the company is using its findings from the PHASE-8 flights to develop low-altitude, long-endurance (LALE) vehicle technologies. As Brooks explains, “The key difference between HALE and LALE for solar-powered aircraft is the effect of cloud. HALE aircraft fly above the clouds, and thus are guaranteed solar power during the day.” Augmenting LALE aircraft with solar power requires consideration of the probability and temporal correlation of cloud cover, particularly how often it is cloudy and for how long it might remain so. “Added to that is the need to minimise airspeed to optimise flight duration, which means wind speed becomes a much more significant consideration than for UAVs with internal combustion engines. These environmental factors mean the application of solar LALE needs more consideration than for other UAVs.” Just as the PHASE-8 might be thought of as a LALE vehicle once long- endurance testing has started, Prismatic is developing another solar LALE UAV, the LASA-5. This will fly slightly faster and is designed to host payloads that are more specific to low-altitude operations. At the time of writing, the company had flown the prototype LASA-5 with favourable results and plans to continue with its development, having established its full team in a new facility (in Alton, southern England), which provides the required space for PHASE-8, PHASA-35, LASA-5, and other products. Unmanned Systems Technology | October/November 2018 Since starting flight tests with the PHASE-8, Prismatic’s engineers have incorporated larger motor pods in order to carry bigger, more energy-efficient motors, as well as more battery cells