Aant Farm TPR72 | Dossier the increase in the compressor pressure ratio that occurs as the temperature of the inlet air decreases with altitude. An additional effect comes from the need to operate at higher throttle settings at higher altitudes due to the reduced air density, as higher throttle settings mean higher pressure ratios.” Regarding the operational altitude limits, Seegers says, “The burner is designed to have a re-light capability up to 20,000 ft, so there’s no reason why the engine could not operate to 25,000 ft. We don’t want to predict performance at this altitude though until we know more about the engine through testing.” Engine management The ECU remains in development, but is expected to feature start sequencing and speed governing of both spools, as well as alarms and automated shutdowns for turbine overtemperature, overspeed and low oil pressure. “Our plan is to develop an analogue unit for anything crew-rated in order to simplify the certification process,” Seegers says. “In the nearer term, we’re working with Integrated Solutions for Systems, in Alabama, which is developing a digital controller for small gas turbines that we hope to test soon.” Turbine manufacturing network From the onset of the TPR72 programme, Aant Farm has aimed to have sufficient internal manufacturing capabilities to insulate itself from long lead times from suppliers. As a result, it has capabilities across five-axis CNC milling, CNC turning, grinding, sheet metal compound forming, TIG welding, dynamic balancing, tensioned carbon fibre winding and some heat treating at its Arizona facility. However, it does subcontract some highly controlled processing and parts to its supply network. A prime example of this is Mezzo Technologies, a company based in Louisiana that specialises in the design and development of microtube recuperators. Mezzo assisted Aant Farm in the original performance trade studies behind the recuperator in the TPR72 and TA65-1, and then provided the laser welding services for the microtube core assemblies. “We also have High Temp Metals in California as our supplier for a number of critical hot-section materials including Inconel alloys 718, 625 and X-750,” Seegers says. “Also very important is Bescast, in Ohio, which produced the investment castings for both our turbine rotors. We sent them our CNC-machined blue wax patterns for those parts, and they sent us back finished castings. “When it comes to rotor systems, you almost always have to use a highperformance nickel or cobalt-based superalloy, which has to be vacuum cast and which is why you need a company like Bescast.” Much of Aant Farm’s future brazing is set to be provided by fellow Arizona company Joined Alloys, which specialises in highly controlled vacuum furnace brazing and vacuum heat treatment. Lastly, Seegers cites Metalcraft as another key company (also based in Arizona), which provided some critical services. “When we decided to switch our impeller material from an aluminium forging to titanium billet, we knew we would need outside help with machining the parts,” he says. “Metalcraft have a lot of experience with titanium, and they specialise in machining it. “They’ve supplied numerous such parts for Honeywell’s gas turbine engines over the years, so we knew they’d be able to provide the titanium components at the quality we needed.” 93 Uncrewed Systems Technology | August/September 2023 After ignition, the gas travels into the outer transition duct, which directs the gases through the vanes of the nozzle for the gas generator turbine, visible here When it comes to rotor systems you almost always have to use a highperformance nickel or cobalt-based superalloy that has to be vacuum cast
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