Issue 39 Unmanned Systems Technology August/September 2021 Maritime Robotics Mariner l Simulation tools focus l MRS MR-10 and MR-20 l UAVs insight l HFE International GenPod l Exotec Skypod l Autopilots focus l Aquaai Mazu

64 architecture to prevent chafing and tearing of its insulations against carbon fibre or metallic surfaces and through- holes. Wiring ties have also been used liberally to prevent connections being shaken loose by routing wires approximately along the engine’s centre of crank rotation. To the side of the electrical plugs is a quick-disconnect fuel connector from Battlefield International. It is designed to work with its high-volume flow, dry coupling systems to prevent any dripping of fuel when unmating during maintenance. “Those fuel couplers really are unparalleled, I think every high-end fuel- powered UAV manufacturer uses them,” West notes. “In pretty much all the lower- cost fuel couplers we’ve looked into, we’ve seen failures in terms of leakages, dripping during disconnection or even causing failures when their UAVs are running, such as clogging of fuel lines. “Battlefield’s don’t suffer any of those issues, which is vital for making our systems safe. They also allow the highest flow rates through the fuel connector.” At the outermost top and bottom of the rear bulkhead are three recesses for the three clips of the latching bracket to snap onto the cover. The bracket itself is 6061 aluminium (for its strength-to-weight ratio and cost advantages) and is designed to be mounted onto the face of a UAV fuselage or nacelle by four fasteners. The ends of the clips bend inwards into the recesses, to hold the rear cover securely in place. During attachment and removal of the GenPod, the unit rests on the bottom clip while the two upper clips are being either engaged or disengaged. While resting in this way it tilts forwards, during which the electrical and fuel connectors are accessible. Underneath the rear cover bulkhead are the fuel pump, ECU and EFI controller. The fuel injection runs below the engine, where the mufflers are also placed. On the sides of the GenPod are decompression valves installed on the cylinders. These work in concert with the generator to relieve compression during engine starting, deactivating afterwards once normal operations have begun. The valves are electrically actuated solenoids that open the cylinders during compression strokes. When combustion occurs, the valves are closed. “The decompression valves really help reduce the resistance of the engine when starting, helping the crank to rotate freely on its bearings,” West adds. “By extension, that allows us to work with much less power from the starter.” Vibration isolation Between the carbon cover and the Desert Aircraft engine (be it the DA-70 on the GenPod 70 or the DA-100 on the GenPod 100) is HFE’s patented vibration isolation system. It is designed to ensure that significant ‘noise’ from the engine cannot be transmitted into the sensitive electronics of the host UAV, wherever the GenPod may be mounted. The key components of this system are four plate-mount vibration isolators from Lord. The engine support framework extends downwards from these, so all vibration must be transmitted (and damped) through them before reaching the cover, hence the rear mounting bracket. The two forwardmost plate isolators are also secured to the carbon cover, and the two rearward isolators are secured to the rear cover, where the GenPod’s fuel and electrical connectors are contained. By connecting the isolators at both the front and back, HFE has sought to limit torque impulse to the centre of the engine, to improve control, prevent torsion and minimise the engine vibration that tends to stem from torque impulse. ECU The ECU features onboard data logging and CAN bus comms, and supports up to two fuel injectors and two spark plugs. An Alpha-N strategy manages the engine, August/September 2021 | Unmanned Systems Technology The ECU communicates using CAN bus and manages the engine using an Alpha-N strategy. The electrical connectors are supplied by Amphenol and Omnetics, with a fuel connector from Battlefield International