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

58 Dossier | Pegasus GE70 reason is that with a UAV installation you won’t have the cooling effect of a propeller ahead of it, and sometimes the engine will even need to be enclosed,” replies McRoberts. “The second reason is that we wanted to have a huge degree of flexibility in our system. Some manufacturers of multi-rotor platforms don’t have experience of engine installation, hence our use of an active cooling system, which always maintains the correct cylinder head temperature.” The water jacketing is simply for the cylinders, not the crankcase, which doesn’t as stock have any finning. “We put a lot of effort into ensuring that our crankcase design can withstand a wide range of operating temperatures,” adds McRoberts. The coolant system consists only of the two water jackets, a radiator, an electrical pump and the necessary hoses – the pump unit serves as a coolant reservoir. The pump is of the centrifugal type, and communicates with the rest of the system to determine the appropriate flow to maintain the desired, consistent cylinder head temperature. Its operating speed is modulated by the GCU to attain the required flow. The flow goes from the pump into one cylinder, then across to the other, then back via the radiator. McRoberts says, “Given the heat capacity of the water and the flow rate we have, the temperature rise across each cylinder will be around 4 C. “From the performance perspective, that is a negligible amount. This approach is beneficially simpler than having a separate circuit for each cylinder – engineering is always a compromise! “It is worth noting that we have past experience of air cooling. The amount of power it takes to have a fan, either mechanically or electrically driven, to blow cooling air over the engine is extraordinarily high compared to the power required to pump fluid through the system. “You can mount the radiator anywhere, and this approach has really paid off because we can maintain the ideal cylinder head temperature regardless of load, ambient conditions and altitude. That also made the engine receptive to the use of fuel injection; it allows us to push the engine to its limits.” How much of a penalty is the aero drag of the radiator? “Normally it will be mounted under one of the UAV’s rotors, so cooling air is blown through it,” McRoberts says. “We have researched that, and it costs a negligible amount of thrust – an amount that on larger platforms is almost indiscernible.” The charge air feed to the Pegasus throttle body is specific to the application – it might be open to the atmosphere or ducted. The bespoke throttle body carries a servo-operated butterfly June/July 2018 | Unmanned Systems Technology The radiator for the GE70 installed in Aerial Alchemy’s Dragonfly multi-rotor UAV