Unmanned Systems Technology 020 | Alpha 800 I Additive Manufacturing focus I USVs insight I Pegasus GE70 I GuardBot I AUVSI Xponential 2018 show report I Solar Power focus I CUAV Expo Europe 2018 show report

54 Dossier | Pegasus GE70 (sub-peak) power level over a range of engine speeds it means that a given level of electrical power can be obtained over a range of generator rotor speeds. Moreover, the rectification methodology used by Pegasus is such that the DC output from the GCU does not have to be directly proportional to power input from the generator. In fact, the loading applied by the generator to the crankshaft is not consistent for any given speed; it varies according to its electromagnetic operation as determined by the GCU. McRoberts explains, “Our GCU, through the directly coupled generator, can apply loading to the ICE such that it is controlled extremely tightly to a desired crankshaft speed, effectively locking it to said rpm. The throttle on the engine therefore correlates to the required torque and therefore the electrical output of our system. That means we can select the exact torque and rpm of the engine to get the necessary power.” Consequently, in meeting the real-time electrical demand from the UAV, there is scope via the GCU to tailor the engine/ rotor speed to that within the available range which provides the best brake specific fuel consumption (BSFC). The key to thus maximising the flight time available from a given fuel load is the software operating the GCU, and this is where the key to the Pegasus IP lies. The operation of a UAV is such that there are occasional sudden shifts in power requirement to which the engine/ generator unit (EGU) cannot react quickly enough. There is a small battery in parallel with the EGU to provide supplementary power to cope with such occasional transient demands and also to provide power for the generator to act in reverse, as a starter motor. In normal operation the system battery is used for only a fraction of the time. However, kept fully charged, it does provide redundancy, in that in the event of failure of the EGU electrical supply it could provide power to land the vehicle. GE70 EGU and ancillaries Pegasus’ initial commercial system was the GE35, using a 35 cc single-cylinder engine. That was first bench-tested at the end of 2016, and it first flew early in 2017. The twin-cylinder, 70 cc GE70 described here started bench testing in late 2017 and started flight testing in April 2018. Whereas the GE35 is rated at 2000 W (maximum DC output) the GE70 is rated at 4000 W. Most of the components other than engine size and configuration are identical for both systems. Both plug into the UAV’s standard power distribution system in place of the regular battery supply. The key components of the GE70 are the EGU, a CD ignition box, a fuel pump, a coolant pump and the GCU. Also required, aside from plumbing and a wiring harness, are a radiator and fuel tank. System size and weight are no more onerous than the battery supply it replaces. The EGU is essentially a fuel injected, water-cooled derivative of the well- June/July 2018 | Unmanned Systems Technology In Aerial Alchemy’s Dragonfly the GE70’s GCU is mounted on top, ahead of the motor controllers, which are also used in the battery-only version of this vehicle