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

86 engines, but we opted for a low-rpm engine. “By designing and mapping the L 2400 to run at a low rpm, we avoid the need to add a heavy gearbox to what is already quite a big and powerful engine, and we maintain high torque at the output shaft for turning a big propeller.” In addition to the peak values given earlier, the L 2400 DX is capable of a maximum continuous torque of 327 Nm, achieved at its top sustainable power output of 103 kW at 3000 rpm. Enginemanagement The sensors connect to the ECU, which uses an Alpha-N control strategy. The throttle position sensor (TPS) provides one key input for the fuel/air mapping, and an engine speed sensor supplies the other. Fuel flow and ignition advance are given in two basic tables, each with 16 x 16 fields (for TPS and engine rpm) for a total of 256 individual values for each function. Any requirements for operating conditions that don’t correspond precisely to the table entries are interpolated. However, with regard to maintenance, modern UAV manufacturers and operators want more data than that, for analytics on engine health and maintenance information. Accordingly, the sensors on the L 2400 DX provide data on air temperature, air pressure and engine temperature, with others being offered on request for self-installation, such as EGT sensors for individual cylinders, and temperature sensors for coolant airflow between cylinder fins. All of these can be used to adjust the values in the basic mapping to account for non- standard environmental conditions. “Simplicity was a big motivator for this ECU architecture,” Simmerkuss says. “Alpha-N is a simple engine control method and it’s also secure, particularly thanks to the redundant nature of our TPS and the fact that we’ve selected an ECU that can offer CAN bus communication as an option. It also has integrated ignition drivers, and comes with all the functions needed for active control of the turbocharger.” As well as the mapping, the ECU also calibrates the engine’s sensor instruments. This is how the company made the use of 95 octane possible for the L 2400 DX, primarily through minor adaptations of the ignition and combustion timing, as well as some studies of combustion pressure to account for potential signs of knocking. “That was a particular request from our customers in Asia, who don’t have as much access as our European customers to higher octane gasoline, so wanted to run their Limbach engines on 95 or 91 rather than 98 without losing power,” says Martin Schmieder, engine development engineer. “Fuel consumption goes up slightly, but their February/March 2023 | Uncrewed Systems Technology The crankcase of the L 2400 is cast from aluminium and constructed in two halves, with the split running vertically down the length of the block, and eight studs located about the cylinders serving to link the two halves together (along with the cylinders, heads and covers), which are fastened using 8.4 mm washers and M8 nuts. The crankshaft is forged as a single piece from steel for high strength and low porosity. The shaft mounts to the crankcase on four plain bearings, on journals measuring 22.9 mm, 25.9 mm and 26.2 mm in width (in order from front to back). The big-end journal meanwhile is 24.5 mm wide and 58.5 mm in diameter. The maximum diameter of the crankshaft is 142 mm and its length is 374 mm. A spur gear fits on the crankshaft for driving the camshaft, and has a spacer ring and a circlip. A shaft seal ring and a spacer ring sit further forward to hold the front main bearing in place, with two washers and another shaft seal ring holding the rear main bearing. The con rods are two-piece systems, forged as monolithic items before being cracked into separate parts. Two nuts hold each big end together, with a two-piece plain bearing inside each one. Material and coating details on the piston are largely proprietary. Each is 97 mm in diameter and has three rings in the standard compression, oil control and oil scraper arrangement, with a wrist pin and two circlips connecting each piston with the small end of its con rod. The cylinders are machined from aluminium, coated internally with nickel silicon carbide, and mounted to the crankcase with a metal gasket. The heads mount with a metallic, PTFE-coated gasket to the cylinders, on top of which the valve covers are fastened using a metal clamp and a cork gasket. As indicated, the camshaft runs mechanically off the crankshaft, using a gear on its back and the aforementioned spur gear. It is made from steel, sits in a chamber below the crankshaft (held in place by three plain bearings) and has four cam lobes, each responsible for a valve on either opposing cylinder. Each lobe acts on a pushrod via a tappet, which is fastened using a sealing ring to a protective tubing around each pushrod. The pushrod actuates a rocker arm that sits on a rocker shaft and is held by two washers and a spring ring. An M8 nut and screw fix the valve key to the rocker arm, to press and lift the valve via its spring and retainer. The inlet valves are 41 mm in diameter, and the exhaust valves are 35 mm. Anatomy