U.S. Army tests drone on 3D-printed jet-fuel engine

The U.S. Army has flown a mid-sized drone powered by a 3D-printed rotary engine that runs on jet fuel, the Army Research Laboratory announced, wrapping up a multiyear research program aimed at giving future unmanned aircraft more range, power and endurance.

The engine drives a generator in a series-hybrid system, meaning it produces electricity for the drone’s electric motors rather than turning propellers directly. It powers VICTOR, a vertical takeoff and landing aircraft that the lab developed with Alabama-based Griffon Aerospace and other partners. The Army did not say when the flight took place, how long it lasted or what performance the aircraft reached, though photos released with the announcement show the system being prepared for flight near Huntsville, Alabama.

VICTOR, short for Versatile Intelligence Controlled Tactical Operational Reconnaissance and Attack, is a Group 3 unmanned aircraft. Under the U.S. military’s classification, that covers drones weighing up to about 600 kg (1,320 pounds) that fly below 18,000 feet, larger than the small quadcopters used by infantry squads but well below the size of a Reaper.

The engine burns “heavy fuel,” the kerosene-based jet fuel and diesel that the Army already uses in its vehicles and helicopters. Most engines in small and mid-sized drones are designed for gasoline, which means units in the field have to carry a separate fuel supply just for their unmanned aircraft. Getting a small engine to burn heavy fuel efficiently is difficult because the fuel does not vaporize as easily as gasoline.

Lab researchers used computer modeling of fuel flow and designed the rotary engine from scratch to improve how the fuel sprays and vaporizes, while cutting leaks of compressed air and fuel vapor. A rotary engine uses a spinning triangular rotor instead of pistons, which makes it compact and smooth-running. The engine is air-cooled, and it is paired with a new 400-volt motor-generator.

“The use of advanced manufacturing, including 3D metal printing, allowed us to rapidly redesign engine components based on lessons learned through experimentation. It enabled us to design an air-cooled engine that reduces propulsion-system size and eliminates the need for liquid coolant,” said Dr. Chol-Bum “Mike” Kweon, the program manager at the DEVCOM Army Research Laboratory.

The work came out of the lab’s Versatile Tactical Power and Propulsion program, also known as VICTOR, which over several years involved more than 30 universities, more than 13 federal laboratories and more than 20 companies. The lab said the program produced hundreds of scientific papers and dozens of patents and patent applications, with research spanning combustion chemistry, sensors and controls, materials, batteries and hybrid-electric technology.

“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,” said Kweon.

Griffon Aerospace has worked on similar designs before. Its Valiant, a hybrid-electric VTOL drone with a heavy-fuel engine that generates power for electric rotors, was one of two finalists in the Army’s Future Tactical Uncrewed Aircraft System competition to replace the RQ-7 Shadow before the service cancelled that program.

The Army said the VICTOR drone and a follow-on concept called PULSAR, which would use a swarm of VICTOR aircraft for logistics, strike and reconnaissance missions, will be made available to military partners for further testing and development. Griffon and other industry partners will continue refining the aircraft for other uses.