Unmanned Systems Technology 011 | C-Astral Bramor ppX | IMUs | Autonomous farming | UAV Turbines UTP50R | London Show report | Advanced materials | Las Vegas Expo report

52 Dossier | UAV Turbines UTP50R 50 hp recuperated gas turbine Frigerio says, “After about a year we had a working combuster. Then we did a lot more work on miniaturising it, and that is one of the technologies that we are very proud of – it is a very small, very compact combuster. “After we got the combuster working, we had to find out how to start the engine without carrying propane [in addition to heavy fuel]. So we had to develop our own system for igniting heavy fuel, while to get the engine up to high speed for starting we needed to develop our own high-speed electrical starter/generator. “We have developed our own patented ignitor using an electrical coil, which acts like a glow plug – albeit hotter than a glow plug – so that we get a ‘pilot flame’. Once you have that flame you can bring in more air and fuel, and the combustion will get up to temperature and sustain itself. You then just have to manage the air-fuel mixture to ensure it doesn’t get too lean or too rich.” The ignitor is located within the combuster: there are two at 180 º apart. “That double-up is for redundancy,” explains Frigerio. “We can operate on one, and you can shut down and restart this engine while the UAV is in the air, which can be an advantage.” The engine has a single-stage centrifugal compressor and a single- stage radial turbine on a single shaft. In a single spool design such as this, (see sidebar: Gas turbine basics) normally that shaft will have one bearing at the front, ahead of the compressor, and one at the rear, usually behind the turbine. The problem then is that the rear bearing is on the hot side. As Frigerio points out, “That is a difficult bearing to keep alive. It is hard to get oil to it and it lives in a very high temperature environment. In our case, both of our hybrid [ceramic ball/ metallic race] angular contact bearings are in front of the compressor. Thus the compressor and the turbine are cantilevered, which gave us issues of rotating assembly dynamics to overcome, but it means both bearings are well- lubricated and located in a single cool compartment. December/January 2017 | Unmanned Systems Technology UAV Turbines’ UTP 50 hp recuperated gas turbine is very compact Compressor impeller with integral cast turbine on the back