69 Paden [chief scientist], Dave Paden [principal mechanical engineer] and their father, Al, who was a Raytheon engineer,” says LaunchPoint chief technology officer Michael Ricci. Critical in that project were Halbach arrays: permanent magnet assemblies configured with enhanced magnetic flux (and hence a strengthened magnetic field) at one side, and almost completely cancelled flux (with no stray field) on the other, as well as not needing back iron in the rotor. Geoff Long (now aircraft chief engineer at Wisk) joined LPT in 2008, and proposed putting the array design from the maglev project into a circle to create a permanent magnet rotor, making for a functioning Halbach array e-motor. This configuration makes a short, flat, pancake e-motor, also known as an axialflux motor. After Long departed, Ricci began researching applications for the e-motor, quickly looking beyond motor-prop drives as axial-flux motors often block propeller airflow with their wide diameters. Instead, through some workshops around 2012, Ricci and his colleagues came upon a NASA project aimed at making a hybrid-electric powertrain for a UAV, intended to achieve greater than 16-hour flight endurances. “The theory of their powertrain concept looked great, but despite being brilliant aeronautical engineers, they had no idea of the electrical, magnetic and mechanical technical details required to actually implement it. We realised there were likely masses of similar aero engineers who hadn’t experienced firsthand that it takes way more than just sticking an alternator onto an engine to create an effective hybrid powertrain,” Ricci says. “We also then realised that axial-flux motors could make great generators. There’s little, if any, airflow for them to block, and their incredibly thin crosssections let them ride right on the crankshaft without separate bearings. Everyone else was doing generators with shaft couplings to the engine, which were heavy, prone to breakage due to the pulsing power-strokes and created numerous other problems.” After agreeing with his colleagues that they should build a generator set (Genset) based on their Halbach motor design, LPT sought and won Small Business Innovation Research (SBIR) funding from NASA to build a prototype. “Simultaneously, the US Navy wanted our technology for an electric helicopter’s tail rotor, replacing the transmission shaft traditionally running turbine to tail, and our proposed design consisted of two 40 kW Halbach generators stacked together to power the associated motor. Designing such a machine was fine, but I knew it would take a lot of high-powered testing,” Ricci recalls. LPT hence bought a Rotax engine as a prime-mover test device to get the US Navy their 40 kW e-generator, and also create a prototype, 40 kW Genset that satisfied the terms of the SBIR. That prototype has been iterated and optimised in the subsequent 10 years as the HPS400 Genset, to date the most powerful of LaunchPoint EPS’s complete solutions for electrified aircraft power. The HPS400 system comes in either a ‘passive’ configuration, weighing 69 kg and outputting electricity over a 215 VDC bus (104 V DC is also available), and an ‘active’ configuration, which weighs 64 kg. In addition to sharing a peak power output of 40 kW, both configurations have a SFC of 566 g/kWh at their maximum continuous power output of 35 kW (achieved at 6000 rpm crankshaft speed). The system is built around a Rotax 582 liquid-cooled two-stroke, being a widely documented and well understood engine, with the components and instructions for maintenance easy to find. We will focus henceforth on LaunchPoint’s unique componentry around this engine and the steps taken by the California-based company to engineer its vision of the ideal hybrid powertrain. Passive vs active Together, the Rotax 582 and the Halbach motor-generator, LaunchPoint’s DHA120 product, form the core of the HPS400. The 48 kW Rotax engine weighs 41.4 kg, making it the heaviest component in the powertrain, while the DHA120 weighs 4.5 kg. The remaining 17 kg or 22 kg (depending on whether the passive Launchpoint EPS HPS400 hybrid powertrain | Dossier Uncrewed Systems Technology | June/July 2024 The HPS400’s passive configuration. The active configuration adds a SiC inverter-controller to give the DHA120 starting and parallel hybrid functionality
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