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

52 Dossier | Desert Aircraft DA150 EFI it was for. I recall seeing in a science magazine that the DA150 was flying a drone they were featuring. “Early on the DA150 was used by NASA. It was also used by the military for powering target drones, which is a use that continues to this day. They shoot those drones down and we call those DA150s ‘one-flight wonders’. It is a sad day when you line up 50 of them in the ’shop and pack them up. All that nice billet aluminium and all that work, and they are going off for only one flight. “In the past the DA150 has been converted to fuel injection by other companies, and that really expanded its use in UAV applications. It has been used for UAV helicopters, and we have sold engines to Hollywood film companies that use them to power camera platforms. The DA100 – the DA150’s little brother – was used by Insitu for the Integrator/ Blackjack programme. The engine that platform currently uses is derived from the DA100.” When it comes to developing its own EFI version of the DA150, Johnson notes that before he started working with HFE, about four years ago, “We had done some of our own fuel injection development in-house but we were so busy with manufacturing and servicing engines that working with HFE was a good option. First came the Mil- Spec version, then the more affordable regular version. “That was a project to bring fuel injection from the UAV world down to the hobby level,” he explains. “Some customers struggle with carburettor settings. The idea was to make it like the modern car – just get in it and go. To bring the technology to the masses we use, for example, injected-moulded rather than CNC-machined parts, and a lower cost fuel pump. “We are striving to make the regular version even more affordable but it is a big challenge doing everything in micro- size and keeping it as light as possible, and doing the mapping and calibration to cope with changing flying conditions.” Design philosophy The DA150 was a clean-sheet-of-paper design by Johnson and Dave Von Linsowe, a former full-scale pilot who is still Desert Aircraft’s lead designer. Johnson describes the design philosophy as “high power-to-weight ratio – every gramme counts when flying airplanes – good throttle-ability and the happiness to run at sub go-kart rpm. People say their kart makes 20 bhp but it has to run to 18,000 rpm to do so. We don’t have that liberty. “The typical rpm range sees most people topping out at around 6800. That is a function of the prop tip speed – if you go sonic you will shred the prop! “Two-strokes like to get up and rev. Here we are trying to make a two-stroke than runs like a chugging four-stroke. We are trying to have the engine run nice and cleanly at lower rpm, and develop high torque there, which is a different challenge. “For Kart racing you open up the ports and pour fuel through it. We needed a power curve that was lower than that of a typical high-performance two-stroke owing to the prop dynamics. The August/September 2017 | Unmanned Systems Technology A DA150 cylinder barrel The typical rpm range sees most people topping out at about 6800. That is a function of the prop tip speed – if you go sonic you will shred the prop!