Military drones may soon fly longer, climb higher, and operate without dedicated liquid cooling systems. A newly tested hybrid engine, built with 3D-printed metal parts and running on standard battlefield fuel, has successfully completed its first demonstration flight.The power unit was installed inside the VICTOR unmanned aircraft, a mid-sized tactical drone developed by the US Army alongside Griffon Aerospace. The flight marks a significant step toward solving one of military aviation’s toughest challenges. It can give mid-sized drones the reach and endurance of far larger platforms without complicating supply lines.Front-line units rely heavily on standard logistics fuels, often referred to as heavy fuels. While diesel and kerosene-based fuels are safer to transport and widely available, burning them cleanly inside a small rotary engine is notoriously difficult. Heavy fuels do not vaporize easily in compact combustion chambers, which often leads to incomplete burning, power loss, and fuel leaks.Using digital fluid-flow simulations“ARL researchers used advanced computational fluid dynamics modeling and a clean-sheet design approach to address the challenges of efficiently burning heavy fuel in a rotary engine,” said the US Army in a press release.Advanced 3D metal printing allowed the engineering team to test, adapt, and reprint intricate engine components within days. This manufacturing method made it possible to cool the engine entirely with ambient air, removing the pumps, radiators, and liquid coolant that normally add bulk and weight to tactical aircraft.The air-cooled rotary engine drives a 400-volt motor-generator in a series-hybrid configuration. The electrical system provides the high bursts of power needed for vertical take-offs and landings, while the fuel engine sustains long-range cruising.According to Dr Chol-Bum “Mike” Kweon, who leads the project at the Army Research Laboratory, moving away from delicate fuels and bulky cooling systems transforms what mid-sized drones can achieve. Extending their operational range beyond the horizon allows commanders to gather intelligence and coordinate missions from safer distances, substantially lowering risks to ground personnel.The propulsion trials are already laying the foundation for how the military plans to operate tactical drones in contested airspace.Adapting the techniques for wider useData from the test flight is feeding into an operational initiative, PULSAR. Under this concept, armed forces aim to coordinate multiple VICTOR drones into autonomous swarms capable of dividing surveillance, reconnaissance, and transport missions in real time.The decade-long project has generated dozens of patents, published hundreds of academic papers, and involved more than 30 universities and 20 defense contractors.Army researchers now plan to hand over the aircraft and hybrid propulsion designs to military evaluation units for tactical field exercises, while commercial partners adapt the manufacturing techniques for wider aerospace use.“For warfighters, the program has transitioned research findings to industry partners for maturation and integration into capabilities that could enable mid-sized drones to operate beyond line of sight, extending the reach of ground commanders and reducing risk to Soldiers,” concluded Kweon.“The use of advanced manufacturing, including 3D metal printing, allowed us to rapidly redesign engine components based on lessons learned through experimentation.”