Uncrewed Systems Technology 051 l Primoco One 150 l Power management l Ocius Bluebottle USV l Steel E-Motive robotaxi l UAVs insight l Xponential 2023 p Issue 51 Aug/Sept 2023 art 2 l Aant Farm TPR72 l Servos l Tampa Deep Sea Barracuda AUV

92 towards the front again through the inner tube bank. During both passes it is heated by exhaust gas that is travelling radially outward across the tubes. “The heated air then travels radially inward and first enters the plenum that surrounds the annular burner before entering the burner itself. In the burner, the air is mixed with fuel and burned. For ignition, we use a conventional low-tension exciter and semiconductor igniter plug. “After igniting, the gas once again changes direction and travels to the left into the outer transition duct that directs the gases inward, through the vanes of the nozzle for the gas generator turbine,” Seegers says. The hot gas then enters and drives the gas generator turbine, powering the compressors and starter/alternator in the core. The starter/alternator is mounted on the high-pressure core spool. After exiting the gas generator turbine rotor, the hot gas then enters the power turbine nozzle and rotor, where it expands further to power the gearbox, or in the case of the TA65-1, the main alternator. Finally, as stated earlier, gas exiting the power turbine is directed radially outward across the recuperator tubes before being collected and directed out of the engine through the exhaust ducts. Much of the design throughout the engine follows standard practice for gas turbines. For instance, both engine shafts are mounted on ceramic-hybrid bearings that are jet-lubricated with Type II turbine oil, the gears are cut from alloy steel before being carburised and further heat-treated for high strength, while the rotors are cast in an undisclosed high-temperature alloy, having been designed for a cycle life of minimum stress and temperature. The static housings are predominantly machined assemblies, made from 6061 T6 aluminium in the colder sections and a nickel-based alloy in the hotter section. The two front housings are 6061 dip-brazed assemblies, while the rear housings are nickel-based welded and furnace-brazed assemblies. “Our choice of dip brazing and the subsequent heat treatments provided us with the quickest route to a complex monolithic part for our prototype engines,” Seegers says. “However, in series production we’ll switch to investment casting, as that will probably be a less expensive approach.” Like the TPR80-1, the TPR72 features a patented air-blast fuel nozzle design. As a result, the six nozzles require very little fuel pressure beyond that needed to overcome the compressor exit pressure in the burner. As mentioned, maximum continuous power (at sea level in standard day conditions) is 72 kW to the propeller, plus 5 kW electric from the starter/alternator driven by the gas generator. As altitude increases though, the power output falls and the fuel economy increases. “To be exact: at full power [100% shaft speed] the power output to the propeller falls from 72 kW at sea level to 46 kW at 15,000 ft,” Seegers explains. “Specific fuel consumption however improves, from 0.375 to 0.369 kg/kWh. That increase in fuel economy is mainly due to August/September 2023 | Uncrewed Systems Technology The recuperator has a multi-pass configuration, in which the outgoing air from the compressor exit makes two passes through the exhaust flow... ...before entering the burner, which is designed with a re-light capability up to 20,000 ft