Uncrewed Systems Technology 048 | Kodiak Driver | 5G focus | Tiburon USV | Skypersonic Skycopter and Skyrover | CES 2023 | Limbach L 2400 DX and L 550 EFG | NXInnovation NX 100 Enviro | Solar power focus | Protegimus Protection

90 The L 550 EFG In addition to supplying the L 2400 DX, Limbach has continued providing the L 275 EF and its larger variant the L 550 EF, the newest version of which is the L 550 EFG. In the company’s words, the L 550 EFG – and its standard-issue version without a gearbox, the L 550 EF – features effectively “two of everything” that the L 275 EF has, aside from a couple of innovations. Starter/generator One is that Limbach has begun integrating starter/generators from ePropelled onto both engines. The L 550 EFG now has an ePropelled SG3000, which generates a peak power of up to 4 kW, although that is available for only 3 minutes as a boost, and a more sustainable 2.5-3.5 kW is available at the engine’s top speed. It measures 127 x 40 mm and weighs 1132 g, including its bearing, winding leads and thermal sensor. The last of these is optional, for users who want to monitor or record their stator winding temperatures. The 18 kW L 275 EF meanwhile will integrate an SG750, which can sustain peaks of 1 kW for 3 minutes and produces 800 W over 50 V AC at 7500 rpm. It measures 101 mm in diameter and 28.6 mm tall, and weighs 440 g with all ancillaries. Both generators are brushless, permanent magnet, three-phase AC types, optimised for power density and for directly mounting on their engines’ crankshafts. They have hand-wound and resin-impregnated stator windings. “These systems appealed to us not just because of their usefulness as range extenders and for powering heavy-duty payloads like Lidars, but also because of that power boost ability,” Simmerkuss comments. “You can put battery energy into the starter/ generator and have it function as a motor, to add potentially up to 4 kW of extra shaft power to the engine. “We’ve planned further testing to see howmuch boost can be added and for how long, aswell as the impact it could have on the TBOof either engine, as it would mean running the crank speed higher than our current specified safe limits. But that capability is important, for instance if you need to suddenly climb quickly, because say of sudden obstacles during flight. “On top of that, having a reasonably high-power generator on the engine shaft means it’s possible to switch temporarily to 100% electric propulsion. If the propeller is driven entirely by the motor/generator, the noise output goes down quite a bit, which is handy for geospatial surveyors or delivery UAVs whose operators don’t want to disturb populated areas.” The generators feature ePropelled’s active air-cooling technology: ducts on the housing enable air to be drawn into the stator by way of the rotor acting as a compressor. This and the stator winding temperature sensors are cited by Simmerkuss and Schmieder as major benefits. Installing the SG3000 first involved some customisation of the generator’s rotor so that it could fit on the engine’s crank journal and so that both systems could handle each other’s rotational movements. That was achieved largely February/March 2023 | Uncrewed Systems Technology The L 550 EF now uses ePropelled’s SG3000 starter/generator (shown here in an exploded view) for up to 3.5 kW of continuous electrical power, as well as short boosts up to 4 kW