From the Floor of Xponential 2025: LiquidPiston’s Hybrid Power System Offers Army Drones Extended Range and Stealth

Company develops hybrid power system for Army drones

by DRONELIFE Features Editor Jim Magill

A small private company, which produces heavy-fuel-capable rotary engines and hybrid electric power systems, has designed a system for the U.S. Army that it hopes can serve as a compact, highly efficient power source for the military’s next generation of UAVs and electric vertical take-off and landing vehicles (eVTOLs).

With the financial support of the Army Innovation Programs, Bloomfield, Connecticut-based LiquidPiston has developed the XTS-210 engine, which the company has demonstrated can be installed in an off-the-shelf drone as part of a hybrid power system, charging the UAV’s batteries in flight for extended range.

“We are basically modifying and integrating those UAVs ourselves in order to learn everything we need to learn and to ensure that we have a proper flight demonstration using our engine,” Per Suneby, LiquidPiston’s senior vice president of corporate development, said on the sidelines of the Xponential 2025 uncrewed systems conference in Houston this week.

Last year, the Army selected LiquidPiston as a participant in its Small Business Innovation Research (SBIR) CATALYST Program. The program provides selected smaller companies with up to $15 million to develop their innovative technologies into practical military applications. The company is currently in Phase 2 of the program, which Suneby said is designed to give small, entrepreneurial companies an opportunity to compete with multi-million-dollar defense contracts for an opportunity to introduce break-through technologies.

“You have to qualify as a small business. So, Lockheed Martin can’t do these, right? We can use Lockheed Martin as a subcontractor,” he said. “They’re focused for innovative young companies to get new technologies and new ideas into the Department (of Defense).”

Suneby said the company is working on completing Phase 2, demonstrating the flight capabilities of a drone equipped with its proprietary 25-horsepower engine, by this summer. He added that LiquidPiston plans to have a second drone modified and ready to fly by December.

The UAV that LiquidPiston has refurbished with its unique engine and hybrid power system has a full takeoff weight of 600 pounds. Suneby estimated that about 60% of the retrofitted aircraft comprises LiquidPiston’s propriety designs. “The battery, power management, flight control, the cooling system, all that stuff we’re doing as part of optimizing the hybrid-electric propulsion system,” he said.

At the heart of the system is the company’s compact X-engine, which can run on standard jet fuel. The rotary engine, used in the HEXE configuration, is up to 90% smaller than an equivalently rated piston diesel engine. According to the company’s website, the X-engines “are uniquely configured to adopt the company’s patented thermodynamic cycle and its associated efficiency and low-noise benefits. LiquidPiston’s X Engine improves virtually all parameters – efficiency, weight, size, vibration and noise.”

The hybrid propulsion system gives the vehicle unique capabilities that are highly desirable for military applications. The drone is powered by two sets of motors. Combustion power provides the extra energy needed for vertical takeoffs and landing. “And then we have an electric motor on the hybrid drive, which is coupled with the combustion engine,” Suneby said.

Once airborne, the drone can be remotely switched to alternate between operating on less noisy battery power for stealthy surveillance missions, and combustion-engine power for longer endurance missions. Or the two power sources can be operated to work in parallel to provide an accelerated boost in performance.

In addition, operators can use the hybrid generators to charge the batteries onboard the aircraft, or the system can even be used as a generator to supply power to troops on the ground.

Suneby said the aircraft can have a flight time of about two hours, depending on how the Army decides to deploy the drone. He said it can be adapted for use in intelligence, surveillance and reconnaissance (ISR) missions, communications or tactical operations, although it’s up to the Army to decide what its ultimate use will be.

“It’s a technology demonstration,” he said. “We’re not going to be in the UAV business. We’re going to be in the UAV propulsion business. So, its use will be whatever the UAV integrator designs for and has a contract for.”

Funding for the private company of about 50 employees is about evenly divided between government contracts and small individual investors. Its military funding comes from contracts with both the Army and the Air Force.

Company officials would like to eventually expand beyond military applications to developing commercial uses for its technology. In the meantime, the military contracts will serve as an ideal launch pad for LiquidPiston’s future ambitions.

Marketing to defense customers serves the company’s needs in a number of ways, primarily by providing a reliable source of funding for bringing its nascent technology to market, Suneby said. “Also, they’re willing to pay for things that make a material difference in terms of size or fuel efficiency to enable them to do things that they can’t do now. So, it’s a low-volume, premium-price market,” he said.

“But, having said that, we intend to take what we do for the military and work with industrial partners to adapt for commercial, non-military uses, and we have had some of those discussions,” he said. “We have a lot of innovation in the pipeline.”

Read more:

• The Pentagon Just Upped its Investment in this MIT Grads Startup to Increase Fight Endurance for Military Drones
• The Drones the US Military is Looking for Now
• Troy Meink’s Confirmation Hearing Highlights the Role of Drones in Modern Military Strategy

Jim Magill is a Houston-based writer with almost a quarter-century of experience covering technical and economic developments in the oil and gas industry. After retiring in December 2019 as a senior editor with S&P Global Platts, Jim began writing about emerging technologies, such as artificial intelligence, robots and drones, and the ways in which they’re contributing to our society. In addition to DroneLife, Jim is a contributor to Forbes.com and his work has appeared in the Houston Chronicle, U.S. News & World Report, and Unmanned Systems, a publication of the Association for Unmanned Vehicle Systems International.