Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

48 February/March 2016 | Unmanned Systems Technology Northwest UAV NW-44 Multi-fuel, spark-ignited two-stroke Single cylinder 39.0 x 37.0 mm = 44.2 cc Naturally aspirated 92-100 octane gasoline or kerosene-based fuel (Jet A1, JP5, JP8, F34, F35 and so on) Aluminium structure Linerless, nickel silicon carbide-coated bore Two main bearings, roller Steel crankshaft, one pin Steel con rod Rotary valve Light alloy piston; two rings Twin plug electronic ignition Electronic port injection Engine management system 9.5:1 compression ratio Maximum rpm, 8500 The NW-44 has a crankshaft that runs between the propeller it drives and a rotary valve situated just behind it, spinning on the same axis. Made from a non-traditional (undisclosed) material, the floating rotary valve disc runs just inside the rear wall of the crankcase, driven directly by a peg that projects from the end of the crankpin, which is cantilevered. The two main bearings are located on the shaft that projects forward on the other side from the single web carrying the pin and peg. That web is balanced by three tungsten weights inserted into it. Machined from aluminium billet, the crankcase is formed in two parts consisting of the primary housing and the rotary valve housing, which forms the rear wall. The latter slots into the former, with an O-ring seal between them and three attachment screws. The rotary valve housing is sunk such that the wall area against which the disc rotates is far thinner than the circumference of the circular housing. Formed integrally with the housing is the tubular intake passage from the throttle body to the rotary disc port. The injector feeds into that passage, its housing likewise formed by the rotary valve housing. The throttle body attaches directly to the intake passage integral with the rotary valve cover. It carries a butterfly throttle, which is directly operated by an adjacent servomotor. The intake to the throttle body is from a filter housing mounted on it. In turn, that filter housing is submerged in the overall package rather than fed via a scoop. Located at the rear of the engine, it sits just ahead of the plate to which the core engine is mounted and behind which is the electronics package. The I-section con rod, which is uncoated, carries needle roller bearings at big and small ends, these both having a radial slot to permit lubricant to reach the internals. The piston pin is a steel production, 10 mm in outer diameter and straight through-drilled. The uncoated pin runs directly in the forged aluminium alloy piston secured by conventional circlips. Since the piston controls the transfer ports it is full skirt; it carries two interchangeable rings. These steel rings have a symmetrical barrel face and are uncoated. The finned aluminium cylinder has a nickel silicon carbide bore coating. The cylinder finning is offset, so that there is more fin area on the exhaust side than the intake. Four screws attach the cylinder to the crankcase while six attach the head to the cylinder, with a paper gasket at the bottom interface and a copper one at the top. Anatomy of the Northwest UAV NW-44 Components of the NW-44 core engine