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

60 Did the introduction of fuel injection improve response? “Yes, that made it absolutely linear. It is like a rheostat – impeccable. The pilots were stunned by it. We thought we had achieved good response with our ongoing reed and carburettor work, but when we switched to fuel injection the difference seemed miraculous! “You know, with a carburettor-equipped two-stroke, when you back off the throttle it pops and crackles, but the fuel-injected version doesn’t. It zips up and zips back down.” Johnson says the DA150 will “run on any fuel, typically 88-92 octane [RON + MON/2].” Ignition timing? “About 24° at full advance. It is controlled by the ignition module. The fuel injection is controlled by the ECU, and the ignition module is also under its command.” Is detonation a concern? “It can be, depending on whether you are pushing for a lot of power with a tuned exhaust system, or whether you are running low- octane fuel. “As delivered, the engine isn’t prone to detonation but some customers like to tweak the exhaust, and then you can in effect ramp up the ignition timing and incur detonation. There is no problem using the standard header.” The DA150 runs to a redline of 8500 rpm – “but”, says Johnson, “we race them at 10,000 rpm!” Maximum power at 6500 rpm is 9.9 kW (13.3 bhp). “Power is quite flat across a wide range,” Johnson notes. That for a weight of 8.8 lb including the fuel pump. In terms of development steps over the past 20 years, aside from the introduction of fuel injection, Johnson says, “There has been very little change, and the engine is still in demand. We have improved the metallurgy of the crankshaft – lessons learnt in heat treatment processes – but subtle changes like that have been about all we have done. “There is nothing particularly innovative about it – the DA150 is a straightforward workhorse.” August/September 2017 | Unmanned Systems Technology Dossier | Desert Aircraft DA150 EFI DA150 ignition Another view of the DA150 piston