Issue 45 | Uncrewed Systems Technology Aug/Sept 2022 Tidewie USV Tupan | Performance monitoring | Bayonet 350 | UAVs insight | Xponential 2022 | ULPower UL350i and UL350iHPS | Elroy Air Chaparral | Gimbals | Clogworks Dark Matter

62 membrane (PEM) fuel cells offer an ideal compromise solution, unlocking range- to-weight ratios typical of some fuel engines in tandem with the advantages of zero emissions and low maintenance needs of a battery-electric powertrain. For several years, Doosan Mobility Innovation has kept this growing market in mind as it developed its long-range, heavy-lift multi-rotor UAVs around its proprietary PEM fuel cell ‘powerpack’ systems, offering the latter as a system for other UAV systems integrators as well. Most recently, it has gone further and developed a fixed-wing, VTOL-transition UAV aimed principally at the medium- mile logistics and survey sectors. Doosan’s new UAV, the DJ25, is a VTOL-transitioning craft that was developed in collaboration with JOUAV, using one of the latter’s gasoline engine- powered fixed-wing VTOL-transitioning platforms and replacing the IC engine with the former’s fuel cell system. “Using hydrogen gas as the fuel, it flies for up to 5.5 hours, with about 5-6 lb of payload and no emissions, greenhouse gases or noise from the power unit,” said Soonsuk Roh, manager at Doosan Mobility Innovation. “Our main target during development has always been to match our fuel cell unit to the form factor of lithium batteries, so that UAV makers could use it as a drop-in replacement for battery packs.” This meant that Doosan specifically had a small fuel cell powerpack, the DM15 (see page 68 for more details), in its portfolio as a solution for fixed-wing VTOL-transition UAVs, which only need high power during take-off and landing, as opposed to a multi-rotor which needs to constantly draw high power for hovering. The hydrogen power unit enables a maximum payload capacity of 3.5 kg. The airframe’s wingspan is 4.28 m, it has a length of 2.09 m from nose to inverted vee-tail, while sitting 0.686 m tall. The craft weighs 27.5 kg when empty (assuming a 10.8 litre hydrogen tank), and its MTOW is 31 kg. As standard, the craft will also integrate a hybrid battery system for regulating and stabilising the fuel cell’s voltage output as well as providing power if the fuel cell suffers a fault. It is typically a 2600 mAh pack consisting of two 384 g lithium-ion modules and measuring 117 x 45 x 33 mm. The fuel cell’s energy on the DJ25 normally comes from a 10.8 litre Type 4 tank made from carbon fibre with a polymer liner. It weighs 4.3 kg and is certified to DoT standards in the US, AC418 standards in South Korea, TPED in Europe, WorkSafe standards in Australia and ISO 11119-3 by the CSA Group. The hydrogen gas is pressurised to 350 bar in the cylinder. The check valve for enabling discharge (and preventing backflow) of gas is also CSA-certified for use in the US, Canada, Europe and parts of Asia, and includes a pressure sensor as well as a thermal and pressure-relief device for safe automatic discharge of hydrogen in the event of its temperature exceeding 110 C. Inspection and survey Since 2016, Inspired Flight has been producing UAV systems designed primarily for survey and inspection applications across government and commercial operations from its headquarters in California. To improve the ROI of these applications through longer flight and greater payload capacity, and to continue doing so as a US DoD-approved Blue UAS vendor, the company has developed and recently unveiled its latest aircraft, the IF1200A. “The IF1200A is an iterative update to our pre-existing IF1200, which had been our flagship product for the past 18 months,” says Marc Stollmeyer, director of product at Inspired Flight. “It has major improvements over its predecessor in several key categories, the first being flight time: we can fly for up to 44 minutes, or 85% longer than the IF1200, without significantly changing the UAV’s form factor.” The IF1200A measures 165 x 154 x 77 cm when deployed, and folds down to 48 x 50 x 47 cm. The system also conforms to the Part 107-specified MTOW of 25 kg with a payload capacity of 9 kg, maintaining a 25-minute flight endurance while doing so. “And with a 9 kg payload, we can fly for 40 minutes,” Stollmeyer adds. To enhance the hexacopter’s endurance without piling on excessive weight or increasing the system’s size, the company’s engineers switched to much larger propellers (from 18 in diameter to 24 in) to enhance aerodynamic efficiency, as well as switching to more power- efficient electric motors. “We’ve also overlapped the drives: the IF1200’s motors were all upward-facing, but on the IF1200 A, the clockwise-turning propellers are mounted under their motors, August/September 2022 | Uncrewed Systems Technology Doosan’s DJ25 is hydrogen-powered for VTOL transitioning and endurances up to 5.5 hours while carrying 5-6 lb payloads (Courtesy of Doosan Mobility Innovation)