Unmanned Systems Technology 015 | Martin UAV V-Bat | William Sachiti | Sonar Systems | USVs | Desert Aircraft DA150 EFI | SeaCat AUV/ROV | Gimbals

59 Desert Aircraft DA150 EFI | Dossier and we use those unless there is a specific request from the customer for C-clips,” Johnson reports. The 12 mm diameter pin is steel with a ground finish; no coating is applied. The piston is cast in an aluminium alloy with a high silicon content and carries a single steel ring 2 mm in axial height. The ring is uncoated and has a flat face. “The [relatively soft] ring settles into the very hard bore coating, to which we give a specific hone,” remarks Johnson. “We have tried barrel-faced rings but found them unnecessary.” The linerless cylinder has a nickel silicon carbide bore coating. “We have made a total of 48,000 engines using that coating, and have never had any problems with it,” Johnson reports. Engine operation The DA150 uses a CDI ignition system produced by Desert Aircraft Australia. “We have a tight partnership with them,” explains Johnson. “They are our distributor and service centre in Australia, and they make ignition systems for us.” A twin plug head is an option. “We haven’t found any major performance gain from twin plugs on the dyno; it is offered for redundancy,” Johnson reports. The standard ignition has two coils in one box mounted independently of the engine. This is a shielded system that creates no RF noise. It is powered by a battery rather than a magneto, hence is ‘total loss’, offering about 2.5 hours of flight given a 2500 mAh battery. However, the ignition will run off a generator if one is fitted to the engine. The fuel injection system is supplied by HFE complete with an electric pump that is mounted externally to the fuel tank. Fuel pressure is less than 20 psi, and the control of the single sequential injector is by the ECU, which takes readings from a Hall effect sensor on the prop hub. Crank position is the only input to the regular EFI system; the Mil-Spec version has far more sensor inputs. Johnson remarks that “throttle response is very good – it is very tractable. Model aircraft aerobatic pilots like a linear response, with immediate feel, whereas UAV operation tends to be more like running a train. “To enhance the response for aerobatics we did a lot of experimentation with reed valves and the carburettor, especially jet sizes and locations, modifying the stock carburettor.” Unmanned Systems Technology | August/September 2017 The DA150 seen from the front with the propeller attachment visible The DA150 is available with carburettor, as seen here, or fuel injection