Unmanned Systems Technology 018 | CES show report | ASV Global C-Cat 3 USV | Test centres | UUVs insight | Limbach L 275 EF | Lidar systems | Heliceo DroneBox | Composites

61 Limbach L 275 EF | Dossier Unmanned Systems Technology | February/March 2018 the charge from the individual intake manifold into the crankcase with no intermediate (reed or rotary) valving. The respective throttle body is mounted on a plastic manifold, while above it is a silicon rubber trumpet carrying a hemispherical wire mesh filter. The throttle body is an aluminium casting that carries a butterfly-type throttle. A linkage between the two throttles running atop the engine allows them to be jointly controlled by a single lever, which in turn is operated by a servo under the command of the craft’s flight control unit. Mounted in the throttle body, a single solenoid-type injector points downwards, its tip located underneath the butterfly such that it sprays across the incoming charge air. Both injectors are served by a common rail across the top of the engine. An inline pump supplies fuel from the tank to one end of the rail while the other end is connected to a fuel pressure regulator. The mechanical regulator maintains a rail pressure of 2.5 bar, sending excess fuel back to the tank. The spark plugs are 14 mm, and the ignition leads are shrouded against electrical interference (the ignition coils and ECU are mounted on the airframe). Engine speed is measured using a toothed wheel attached to a flange on the front of the crankshaft that was originally designed to accommodate a magneto. The engine carries an air temperature sensor that reads the temperature of the ambient air within the engine bay, which is the temperature of the incoming charge air. The ECU houses a pressure sensor that responds to ambient pressure, which in turn is most strongly influenced by altitude. The ECU has altitude compensation in the form of a linear offset according to ambient pressure and a linear offset according to ambient temperature. It also offers cold-start enrichment. There is also a rev-limiter function, which can be programmed to cut ignition and/or injection with soft- and hard-cut possibilities. Normally there is a hard cut at 8000 rpm. An optional electric starter is mounted on a plate attached to the base of the crankcase. Its drive gear contacts a ring gear added to the propeller hub. Alternatively, the engine can be started by manually spinning the propeller. Under development is a starter/generator to supersede the current optional 28 V generator. The length of the L 275 EF from the propeller hub to the back of the generator coupling flange is 221.4 mm, while the width including spark plug caps is 396.8 mm and the height to the top of the intake covers is 294.6 mm. The crankshaft axis is 60 mm above the lowest part of the engine (actually some of the cylinder fins). The engine has four mounting bosses incorporated into the rear of its crankcase. These are tied via 8 mm bolts to a mounting plate that in turn is integrated into the airframe. All engines are dyno tested in house before dispatch, and are supplied with a certificate of performance. Some key component, service and equipment suppliers to the Limbach L 275 EF Crankshaft: Hoeckle Crank pins: Brückner Precision Con rods: Royal Rods Main bearings: SKF Oil seals: Freudenberg Sealing Technologies Engine management system: Trijekt Spark plugs: Bosch Fuel injectors: Magneti Marelli Air pressure sensor: Bosch DLC coatings: Oerlikon Balzers Dyno: Schenck Machine tools: Grob