Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

58 Immediately ahead of the ScanEagle’s pusher propeller is its ICE, then there is a volume within a fuselage used for engine electronics and payload, and ahead of that again is the fuel tank, extending forward under the wing. Further forward under the wing is normally the battery, which, while larger in the fuel cell version maintains essentially the same position just behind the nose. The ScanEagle’s FC uses a 4-6 Ah battery weighing about 600 g. The FC takes the position of the ICE’s fuel tank, with behind it the hydrogen tank, which extends back almost as far as the propeller. That is possible since the motor is integrated with the propeller, while the motor controls are housed on the stationary tail cone fitted to the back of the propeller hub. We asked: if you were designing from scratch around the FC, would you be able to find more storage volume? “You should be able to,” replies Osenar. “It is all about optimisation. Insitu has made a lot of integration choices associated with retaining the existing platform; disturbing it as little as possible.” Knapp says, “Our intention was to allow users to switch from ICE to FC, essentially by removing the existing propulsion module and plugging a new one into its place.” Performance What are the relative performances of the ScanEagle ICE and FC versions? “The challenge with any engine system is how to integrate it into the vehicle,” replies Knapp. “With the ScanEagle we have a very successful, well-proven vehicle, and we are trying to adapt the fuel cell and hydrogen storage technologies to fit within its envelope and concepts of operation. “The ScanEagle can fly for 22 hours with a two-stroke engine. At present, we won’t get that from the fuel cell; the maximum is expected to be about ten hours. However, in practice, most missions are within a ten-hour window. The ScanEagle’s average flight time – nearly a million hours have been amassed since its introduction – is 8.5 hours. “The take-off weight for the ICE version fuelled for a ten-hour mission with the same payload would be close to that of the fuel cell. In that case though the ICE version does have the scope to carry a heavier payload.” So, we asked, is powertrain weight comparable between FC and ICE? “Right now our goal is to get the empty weight of the ScanEagle with the fuel cell to about 15.5 kg – about 2 kg more than the current version [dry and without payload],” Knapp replies. “However, the fuel mass of the ICE version is 5.5 kg compared with 350 g for the fuel cell. “So the take-off weight could be less June/July 2017 | Unmanned Systems Technology The fuel cell version of the ScanEagle has the motor integrated with the propeller and its control electronics mounted within the stationary cone, seen here