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

90 Dossier | Aant Farm TPR72 analysis, turbine and compressor aero design and rotor dynamics. The pair also brought in John Dodge, an aerodynamicist whose work extends back over 59 years to the original General Electric TF39 highbypass turbofan. Four complete TPR72 engine sets plus spares have been produced to date (three of which had been assembled at the time of writing). The spare parts include centrifugal impellers, turbine rotors, alternator rotors and ancillaries such as oil pumps. “While this approach is more expensive than building a single prototype, it affords parallel development paths that, in turn, compress the schedule,” Seegers says. “Serial number 001 is on the dyno stand, and we’re using it to develop the starting fuel supply schedule and test the lubrication system. “Engine serial number 002 is instrumented for thermodynamic performance testing. Prototypes 003 and 004 aren’t assigned for testing just yet. We’re keeping them aside principally for any airframe manufacturers who want to flight test a TPR72 at short notice.” Operating stages and principles As with many aircraft gas turbines, the TPR72 is designed mainly around a gas generator core that consists of a compressor, recuperator, burner and turbine, thereby generating hot gas via the Brayton cycle of compression, combustion, and turbine expansion. The resulting hot combustion products that still have useful energy can be sent directly through a nozzle for pure thrust (akin to a turbojet) or to an additional turbine stage for further expansion and additional power extraction. In Aant Farm’s case, the outgoing hot gas drives a single-stage axial turbine, which in turn drives either a gearbox input pinion for the TPR72 or a 60 kW highspeed permanent magnet alternator for the TA65-1. The TPR72 can be regarded as a two-spool turbine, with the highpressure spool in the core, gas generator section, and the low-pressure spool in the rear power extraction section. At full rated power, the core shaft turns at 96,000 rpm, the power extraction turbine at 76,000 rpm. During operation, air first enters the engine through a bellmouth inlet on the front, where it is drawn in by and passes through a first compressor stage (referred to as an axial zero stage) where it is compressed at a ratio of about 1.5:1. Aant Farm notes that adding an axial compressor stage in front of the centrifugal stage has the same effect as a turbocharger on a piston engine, supercharging the engine core to increase the compression ratio and mass of airflow. The air then enters a second centrifugal compressor stage, where it is further compressed as it is directed radially outward and sent through a diffuser to the entrance of the heat recuperation system. In principle, the recuperator is similar in concept to Turbotech’s solution. It consists of metallic microtubes that channel the compressed air towards the burner while crossing paths with the hot exhaust gas in order to transfer the exhaust’s heat into the intake air. “Our recuperator is nearly identical to another one we’d developed 10 years ago for the IARPA Great Horned Owl engine programme [a research effort aimed at producing a quiet fuel-hybrid powertrain for UAVs to minimise their acoustic signatures when flying ISR missions],” Seegers explains. “The compressed air travels first through the outer tube bank, then down around the aft tank head where it is redirected August/September 2023 | Uncrewed Systems Technology Cutaway diagram of the airflow path through the engine. Note the increasing temperature (in red) as air is pre-heated while flowing through the recuperator, then burned before leaving the engine While building four complete engine sets is more expensive than building a single prototype, it affords parallel development paths