The first aircraft were limited by the endurance of the human pilot, the capabilities of the machine, and fuel. By 1923, human pilots had demonstrated air-to-air refueling, eliminating one leg of the triad, provided a pilot could maneuver into position to be refueled.

Drones, flying machines defined by a lack of human on board, could reduce the endurance problem to one of mechanical endurance, if only they could find a way to be consistently recharged.

Among its many tasks, the experimental X-47B demonstrated mid-air refueling in 2015, which bodes well for the future of plane-sized vehicles that run on traditional fuels. But what of electric engine drones?

Quadcopters, as ubiquitous as they are constrained by short flight times, are an ideal candidate for in-air recharging. Researchers at the High Performance Robotics Laboratory (HiPeRLab) at the University of California - Berkeley demonstrated an aerial recharging ability, one that almost doubled the flight time of the recharged drone.

Batteries are both essential for electric drone flight and also the heaviest component of the vehicle, reaching a point where increasing battery size will diminish flight time. With recharging, a hovering drone can instead sustain longer flight, so long as it can continuously be resupplied by the fresh batteries of smaller feeder craft.

As with most experimental research, the use cases are all early extrapolations from proofs of concept. Fortunately for military planners and designers, a large component of what quadcopters do is hover, so anything that extends hover time could add value to a drone.

With an average quadcopter flight time of around 20 minutes, troops have to be mindful of how to best use that limited window. If a patrol wants to place a scout over the corner of a building to catch potential movement, it has to hope that the drone sees what it needs to in that short flight time. With recharging, a drone could stay focused on a point for closer to 40 minutes, allowing more people to move into position.

A flight time of 40 minutes is long for a drone and short for a sensor mast, but the option for a temporary sensor tower, flown into place and then sustained through a small fleet of resupply batteries, is likely just the beginning.

The researchers, after all, just have to prove the concept. It’s up to the designers to find a use and the engineers to iterate it into being.

Watch a video of the drones recharging below:

Kelsey Atherton blogs about military technology for C4ISRNET, Fifth Domain, Defense News, and Military Times. He previously wrote for Popular Science, and also created, solicited, and edited content for a group blog on political science fiction and international security.

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