The Air Force awarded LiquidPiston a Small Business Technology Transfer (STTR) contract to adapt its X-Engine technology for use in unmanned aerial systems (UAS) and “orbs”.

Bloomfield, CT – March 4, 2021 – LiquidPiston, Inc., a developer of advanced rotary internal combustion engines, announced today the adaptation of its X-Engine technology for the United States Air Force to use in unmanned aerial systems (UAS) as well as “orbs” – urban air mobility (UAM) vehicles designed to carry people and cargo around. The X-Engine, a next-generation rotary diesel engine, is being evaluated as an enabling technology to power the UAS or orb through a hybrid-electric propulsion system. Because current battery technology limits the range of an orb’s flight, the X-Engine converting the energy contained in jet fuels can enable the Air Force’s UAS/Orb to become a reality.

The Air Force has awarded LiquidPiston a Phase I ($150,000) Small Business Technology Transfer (STTR) contract through its AFWERX operation to enable this development of the X-Engine. The contract is in support of AFWERX’s Agility Prime, a non-traditional program seeking to leverage commercial electric vertical takeoff and landing (eVTOL) and other transformative vertical flight vehicles for government missions in a way that accelerates the emerging commercial market.

Orbs fall into this category and are classified by their eVTOL capabilities but are not to be confused with flying cars or drones. “Our work with the Air Force demonstrates the versatility and utility of our X-Engine across the Department of Defense including our ongoing work with the US Army,” said Alec Shkolnik, CEO and co-founder of LiquidPiston.

“Today’s solutions for power and energy are held back by a lack of technological innovation; gasoline engines are inefficient, diesel engines are big and heavy, and while the world wants to go electric, batteries lack significantly compared to the energy density of fuel. The X-Engine solves these challenges, and with this contract, we look forward to showcasing the value a hybrid-electric configuration can bring to unmanned flight.”

A major issue facing all-electric vehicles – both aerial and ground vehicles – is that modern battery technology simply does not offer sufficient energy density, meaning the range of electric-only vehicles will be limited. For military orb vehicles and commercial urban air mobility to be operationally viable in a range of use cases, a stronger, lightweight power and energy source is needed to significantly extend flight times.

The X-Engine from LiquidPiston takes a hybrid approach to this problem. Because fuel is up to 50 times more energy-dense than today’s batteries, the X-Engine, coupled with a generator, can be configured to charge the battery and keep it charged during flight, significantly extending the range of an electric propulsion system. Alternatively, the X-engine can be configured in parallel with an electric drive, using the engine directly to produce thrust or lift. With the X-Engine’s hybrid approach, the Air Force can leverage the energy density of fuel, while still getting the benefits of an electric drive propulsion system to power an orb or UAS.

LiquidPiston’s X-Engine is a lightweight rotary engine capable of running on JP-8, jet fuel, diesel and other heavy fuels. The modular design of the engine coupled with the lightweight high-speed alternators enables technology to easily scale in size and increase the range of eVTOL UAS and UAM vehicles. The X-Engine is 30% more fuel-efficient than a diesel engine and up to 5-10x smaller and lighter. Compared to a small turbine, the X-engine is up to 2-4x more fuel-efficient while fitting a comparable envelope and weight.

To learn more about these developments and LiquidPiston’s X Engine platform, click here.

About LiquidPiston, Inc. – LiquidPiston, Inc. develops compact, quiet, fuel-efficient, low-vibration, multi-fuel capable combustion engines that are scalable from one horsepower to over 1,000. The company’s patented High Efficiency Hybrid Cycle (HEHC), an improved thermodynamic cycle, and engine architecture enable the company to create engines optimized for fuel efficiency. LiquidPiston’s engines have only two primary moving parts – a shaft and rotor – resulting in compact size and low-vibration operation. Although they are rotary engines, LiquidPiston’s engines are not Wankel engines; they are uniquely configured to adopt the company’s patented thermodynamic cycle and its associated efficiency and low-noise benefits. To learn more, visit

About AFWERX and Agility Prime – The US Air Force established AFWERX to expand technology, talent, and transition partnerships for rapid and affordable commercial and military capability. With respect to UAS and orbs, the Air Force wants to accelerate the development of the American VTOL industry using Air Force and commercial investment funding to develop a “bridge market” for dual-purpose technology with the objective of bolstering the emerging U.S. emerging market and industrial base by building confidence in investors, companies and regulators.