Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

22 Dossier | UAV Factory Penguin C own mounting frame. The throttle body contains a butterfly-type throttle and feeds into the crankcase through a reed valve. UAV Factory’s injection system uses a solenoid-type injector, which feeds fuel into the throttle body just after the butterfly (ahead of a reed valve). The tiny injector is supplied fuel at 2.5 bar. It works in conjunction with CD ignition firing a 10 mm plug, both controlled by UAV Factory’s own ECU, which is adapted from an automotive unit. The ECU controls injection duration and spark timing on the basis of readings of manifold air pressure and temperature, engine speed and load, cylinder temperature and ambient air pressure. The manifold pressure sensor is the primary input to the map determining injection timing, and the ECU also adjusts the mixture according to altitude. There are two refuelling couplings – for fuel in, or as a vent/overflow. The fuel tank is foam-filled to stop fuel sloshing about and has a sump section at the rear (nearest the engine), from which the fuel line runs. Fuel is drawn out (through a filter) by an electric fuel pump of the diaphragm type (in other words, an electrically driven rotor drives an eccentric arm that pushes against a flexible membrane). The pump supplies fuel to a bellows-type accumulator that dampens fluctuations and is effectively the non-return fuel rail, having travelled via a regulator that sets the delivery pressure at 2.5 bar. Made from carbon fibre, the top-end cooling duct is open to the oncoming airflow and exits very close to the propeller sweep, which means that rotation of the propeller helps draw air through it. This is particularly important pre-launch, when the engine is running but the aircraft is stationary. There is an adjustable carbon fibre flap within the duct, on the exit side; an actuator moves the flap through the range fully open to fully closed as a means of influencing cylinder head temperature. In turn, the actuator is controlled by the ECU in response to readings from a cylinder head temperature sensor. Some customers put a premium on stealth, so the engine silencer is a particularly important item. Although machined from a block of aluminium, it has walls as thin as those of a typical drinks can, and inside are various chambers with many internal perforated walls; glass fibre matting further aids sound absorption. The carefully packaged unit contains a lot of resonators, which absorb different acoustic channels, so it is a hugely complex production. Since a single-cylinder two-stroke is subject to a lot of operational vibration, the engine is rubber-mounted within the power module. It also calls for careful design of electrical and other connections to and from the engine, to avoid the danger of fatigue failure. It can be seen, for example, that the wiring is very carefully arranged with loops to relieve the strain caused by vibration. Such attention to detail is a characteristic of the Penguin C. There is no vibration dampening between the engine and the propeller however. Running at the speed of the crankshaft, the propeller shaft bolts to it with a conical seating arrangement to ensure concentricity. The APC-supplied propeller is sandwiched between a back plate and the front attachment nut/ serrated washer that drives it. The back plate and a spinner cone attached to it rotate with the propeller. Mounted alongside the engine (and parallel with the crankshaft) is a 100 W The Penguin C power module conceals the engine with its clever packaging UAV Factory modifies an automotive ECU to produce the unit that runs the Penguin C engine November 2014 | Unmanned Systems Technology