Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

48 Insight | UAVs Research In a new benchmark for alternative UAV power solutions, a collaboration between UK-based fuel cell manufacturer Intelligent Energy and South Korean liquid hydrogen developer MetaVista has led to the setting of a new world record for multi-rotor UAS flight. The flight lasted 12 hours, 7 minutes and 22 seconds (compared with the previous record of 2 hours, 6 minutes and 7 seconds), and was accomplished with a quadcopter using a combination of an Intelligent Energy 800 W fuel cell power module and a MetaVista 6 litre liquid hydrogen storage vessel. With the hydrogen tank and fuel cell installed, the test UAV had a gross weight of 7 kg, and largely hovered about the same spot outside the MetaVista offices for the duration of the flight. “We had never worked with liquid hydrogen before teaming up with MetaVista; liquid hydrogen technology isn’t entirely commercially viable yet, but MetaVista’s research is focused on changing that,” explained Andy Kelly, head of UAV product development at Intelligent Energy. “It stands to provide a much, much higher energy density than the compressed hydrogen gas we’re used to working with – perhaps three or four times higher. Making liquid hydrogen fuel viable is a matter of maintaining a temperature close to absolute zero inside the storage vessel, to keep the hydrogen in liquid form, but once you can do that, the pressure inside is so low that you don’t need a very mechanically robust tank like you do to keep compressed hydrogen gas at 300 bar.” The MetaVista storage solution combines cryogenic insulation with lightweight materials. The boil-off hydrogen gas flows from the liquid storage tank across the anodes of the fuel cell to power it; Intelligent Energy did not have to make any modifications to its fuel cell module before the flight. “We have a fairly loose set of specifications regarding input pressure, flow and temperature of the hydrogen gas, so once you can meet those, our fuel cell will run,” Kelly says. “For example, 0.5 bar is the required input pressure, and as the liquid hydrogen is stored at perhaps 3 bar, only a small regulator was required – much smaller than our standard regulator, which has to regulate 300 bar of compressed gas down to 0.5 bar. MetaVista had to modify the regulator and pressure transducer slightly in order to give accurate readings on the remaining fuel, but that was all.” As Intelligent Energy and MetaVista have signed a memorandum of understanding for long-term partnership and collaboration (which happened after a previous test flight achieved more than 10 hours of flight with a 650 W fuel cell), further tests and development are expected in the months ahead. Further afield, NASA is planning to send its Dragonfly multi-rotor aircraft to Saturn’s moon Titan, where it will look for evidence of prebiotic chemical processes linked to the origins of life on Earth. When it reaches Titan’s surface, in 2034, it will use the density of the atmosphere (which is about 50% higher than that of Earth’s) to ‘leapfrog’ up to 8 km at a time to different locations and environments, collecting samples and making measurements. The mission’s total surface distance will reach 175 km, almost double that travelled by all the Mars rovers to date. Safety Alpha Unmanned Systems has updated its Alpha 800 helicopter UAS with a fully automatic autorotation capability, developed in collaboration with fellow Spanish company UAV Navigation using its Vector autopilot. The autorotation enables emergency ‘gliding’ of the helicopter rotors if the engine, power transmission or tail mechanism fail during flight. As Alvaro Escarpenter, COO of Alpha Unmanned Systems, explains, “In manned aviation, pilots have to train until they reach the point of muscle memorisation for the manoeuvre. In UAVs, autopilots are generally not just programmed to perform autorotation: the rotor rpm is controlled by the engine, and the altitude or height is controlled by the collective pitch angle control or collective lever. “Therefore, during engine failure, the revs are reduced, as is the lift, August/September 2019 | Unmanned Systems Technology A lightweight fuel cell has been combined with liquid hydrogen tank technology to achieve a new world record for multi-rotor endurance (Courtesy of MetaVista)