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

87 Limbach L 2400 DX and L 550 EFG | Dossier costs and uptime are still improved; some of our European customers also request this calibration to save on fuel expenses.” The ECU is a 12 V system, and can be supplied with an emergency switch and relay box to prevent loss of power, as the L 2400 is not designed to function without a power source. If the main voltage bus should drop, the relay box can activate a back-up supply from the generator, the main onboard battery or a back-up battery, depending on the end- user’s electrical configuration. For added safety and redundancy, the L 2400 DX has a dual ignition system. A total of four ignition coils and modules sit inside the ECU housing, with eight NGK DCPR7E spark plugs (two per cylinder) across the engine. Dry-sump oiling The impetus for redesigning the L 2400 DX to use a dry sump came initially through Limbach’s recent airship customer, who needed to incline one of the engines at 45o during take-off. That significantly hindered the oil from lubricating or cooling any of the engine when collected and stored in a wet sump. “We’ve also integrated a new type of oil pump, and we’ve designed the sump with two extraction points, to evacuate the oil more reliably,” Schmieder says. “The oil pump sits at the front of the engine below the prop governor; it runs mechanically off the camshaft and is designed as a three-part system. That configurationmeans we can simultaneously draw from the sump while applying oil pressure to different sections of the engine, such as the camshaft and the crankshaft, via channels drilled through to themain bearing zones. It also allows us to evacuate oil from the turbocharger independently of the rest of the engine.” Oil returning to the sump from the crankcase and turbocharger is piped through a dedicated oil cooler. This is an air-cooled unit, typically mounted directly on the engine cowling, although that can be changed according to where space is available. It consists of a plate that the oil runs through, a NACA inlet and a duct for the air, two elastic seals to prevent any bleeding of air from the duct into the inside of the cowling, and an outlet that must be sized accordingly to enable the warmed air to be evacuated efficiently. Limbach’s engineers make particular note of how important it was to optimise the seals here, as any leakages of air could interfere with the pressure differential that is key to the air cooling elsewhere in the engine. Through this system, the oil temperature is kept below the safe limit of 120 oC and at an optimumof around of 80 oC. Uncrewed Systems Technology | February/March 2023 Developing a dry sump was key to enabling the L 2400 DX to be used in vectored thrust applications, in which the engine had to be inclined and the use of a wet sump became untenable The three-part oil pump is driven mechanically by the camshaft By designing 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