88 Although turbine engines offer benefits to fuelpowered UAVs in terms of efficiency, reliability, lifespan and noise, their uptake in the UAS industry has been slow relative to reciprocating and rotary engines. The reason for this is their fuel efficiency. When turbine designs are scaled down from those intended for crewed aircraft to something more appropriate for UAVs, their fuel efficiency drops by around twothirds, meaning far shorter ranges, lower payload capacities or higher fuel bills. Much of that drop comes from the clearances and blade tip leakages in a downsized turbine – or ‘microturbine’ – being proportionally bigger compared to those in a ‘normal’ sized turbine. That drop is unavoidable, barring some major advance in manufacturing technology. However, as companies such as UAV Turbines (issue 11, December 2016/ January 2017) and Turbotech (issue 31, April/May 2020) have shown, the loss of fuel efficiency in a microturbine can be compensated for, using a heat recuperation system in which exhaust gases preheat the charge air before it enters the combustion chamber. Doing so means a far lower fuel-to-air ratio becomes sufficient for producing the temperature needed to drive the turbine and hence the propeller. With UAVs getting larger, and demand for heavy fuel compatibility (and efficiency) rising, the time is ripe for more companies to create recuperated microturbines that can provide the efficiencies and TBOs needed to make heavy UAV operations profitable. Aant Farm is the latest contender on the scene in this respect. The Arizonabased company is a derivative and descendant of M-DOT Aerospace, which was founded by Bryan Seegers in 1989, sold to Chase Capital Partners in 2011, and renamed Azmark Aero Systems before being sold again to Imaginetics in 2016. Imaginetics allowed the engineering division to be spun off into Redline Turbine Systems, which now develops some of the world’s smallest turbomachines and where Seegers serves as chief scientist. In 2020, he saw a growing market for a reliable uncrewed aircraft engine running on heavy fuel, and decided to use Redline’s existing hardware and IP to develop a modern version of its TPR60 turboprop. Thus was Aant Farm founded by Seegers and his partner Dave Weier, who now provides technical and operational leadership for the company. The result is the TPR72, a 30 kg turboprop measuring about 905 x 707 x 381 mm, and designed to deliver up to 72 kW (96 bhp) from its gearbox-driven Recuperating heat from exhaust gases gives this microturbine an edge over gasoline engines for heavy UAVs, as Rory Jackson explains The TPR72 is a 30 kg, 72 kW heat-recuperated turboprop capable of running on JP-4, JP-8 and Jet-A, with JP-5 and diesel testing planned (Images courtesy of Aant Farm) Heat treatment
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