Microturbine technology developer UAV Turbines Inc. (UAVT) has announced the successful demonstration of its Monarch Hybrid Range Extender (HREX), which the company describes as a microturbine powered generator technology that extends the range of electrically powered medium-sized UAS.

With the HREX developmental system, the range of a number of different electrically powered UAS now in development can be extended, while at the same time providing the proven reliability of a gas turbine system.

“It is well-documented that the range of battery-powered electrical air vehicles is sharply restricted by the relatively low power density of currently available batteries. Simply adding more batteries will result in the aircraft becoming too heavy to fly with a practical payload,” explains Kirk Warshaw, CEO of UAV Turbines.

“The solution is a hybrid system that will power the aircraft in flight with battery power providing a boost during critical stages such as take-off, hover, and landing. These capabilities are critical for meaningful real-world missions, like a payload weighing more than 10 pounds that needs to be delivered more than 5 miles away. UAVT’s Monarch microturbine HREX technology provides this important new capability.”

In UAV Turbines’ HREX system, the engine uses the energy it extracts from the fuel to directly power the propulsion motor. Any extra electric power is used to top off the battery charge. With this process, the range is significantly increased before the weight of the added fuel becomes uneconomical.

According to UAVT, there are a number of tradeoffs in optimizing power for any specific system. One tradeoff is that some energy is lost in the extraction process, but as the fuel is consumed, the net weight of the aircraft drops, providing a level of flexibility that allows engine optimizations that otherwise wouldn't be possible with a single power source.

UAVT demonstrated HREX by setting up a system in its laboratory test cell using the same Monarch 5 turboprop engine that was recently used to power a Group 3 Tigershark aircraft. The engine was converted to a turboshaft engine, so it powers an off-the-shelf generator.

According to UAVT, the electrical output of the generator is used via a motor controller to power an electrical motor driving a propeller, as it would in an electrical propulsion airplane.

“The video shows the HREX system in operation, demonstrating its flexibility with major elements connected by cables that can be configured to fit most Group 3 and 4 airframes,” Warshaw explains.

“While this test system was assembled using heavy industrial motors and controllers, a purpose-designed system would be far lighter, hardened for aerospace environments, and optimized for specific military and commercial applications and missions. Increases in flight time will be at least 2 to 3x greater than a vehicle powered solely by batteries if the UAV is a clean-sheet design that contemplates from the outset the use of a UAV Turbines range extender.”