70 Dossier | Launchpoint EPS HPS400 hybrid powertrain or active HPS400 configuration is chosen) is taken up by power electronics, wiring harnesses, and assorted systems for starting, cooling and control. LaunchPoint’s Power Management Unit (PMU) is the control authority for the powertrain, commanding the Rotax engine’s ECU, the DHA120’s controller, and a BMS via a CAN bus, using LaunchPoint’s communication protocol originally developed for a project with NASA. Depending on the voltage and power electronics configuration, the DHA120 generator can be a three-, six- or 12-phase configuration. Through the PMU and power electronics, the DHA120’s AC output is rectified into one or more DC channels and merged with the output of the end-user’s applicationspecific DC bus batteries. “The passive configuration is a oneway powertrain, with just high-power diodes in the PMU that rectify the DHA120 generator output into DC, and a separate starter motor supplied to start the engine,” Ricci says. “In the active system, we provide a bidirectional inverter-controller, built using silicon-carbide [SiC] MOSFETS to drive the DHA120 as a motor, so that it can start the engine and also provide shaft power in parallel hybrid configurations, where the e-machine can boost engine shaft power instead of generating electricity.” The passive system is electronically simpler and less pricey, but requires a separate starter motor and starter battery. In contrast, the active system power electronics weigh 5 kg more, but a separate starter motor and battery are not required. The active system also achieves greater power efficiency and transient performance than the passive system. LaunchPoint recommends the passive configuration for continuously hovering applications, like multirotors with a constant high-power requirement, whereas the active configuration provides best value to VTOLtransitioning aircraft to provide full power for hover, but then throttle back the engine’s most efficient operating point at 25-50% power in cruise. The active system also works well with a parallel, hybrid-type system that may feature a very large pusher or tractor propeller on the engine shaft, outward of the DHA120 starter-generator. In this case, the motor-generator functions either to provide hover power for the separate electric lift motors or to provide an additional, electric boost to the main shaft for climb and high-performance peaks. Rotax 582 aviation engine LaunchPoint has modified the Rotax 582 with some key components. The first is a high-performance, metal-geared, industrial servo from Futaba to control the throttle, as the engine was originally designed for ultralight aircraft, and hence comes as standard with manual throttle and cable for the pilot to use. “Through that servo, the PMU sets the throttle plate to the starting position, cranks the engine, stabilises rpm and adjusts the throttle as the loads vary, all quite transparently,” Ricci says. The starter motor was similarly modified to accept electronic control from the PMU, rather than manual control from a pilot’s switch. In addition to changes made for control, various other changes were made to the thermal management system to accommodate the reduced ambient airflow found in hovering flight conditions. For example, a heat shield was installed between the exhaust manifold and the oil tank (to prevent the latter from melting after 1.5 hours of continuous running in hover), while a second radiator and two 30 W fans – one per radiator – were integrated into the powertrain’s cooling loop. While the 582 is liquid-cooled, it was designed for fixed-wing aircraft, where normally the airflow from forward flight would dissipate heat from the single, standard radiator. “We’re designing the HPS400 for aircraft that will often hover, without that tremendous cooling airflow from fixedwing flight – and aircraft reciprocating engines are almost never designed to run at full power while stationary,” Ricci notes. “We tried different combinations of thermal management solutions, including automotive aluminium radiators, and eventually doubled up the Rotax radiators and added fans to ensure proper cooling.” Going forwards, LaunchPoint anticipates that its radiators will be customised for end-users, especially as they better June/July 2024 | Uncrewed Systems Technology The HPS400 is built around a Rotax 582 engine, modified with a second radiator (visible at the back) for extra cooling in VTOL and hover
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