As the old saying goes, there's plenty of drones in the sea, and of course the skies are full of them too. We're increasingly seeing drones that cross over between those two worlds, and now engineers from North Carolina State University have developed the EagleRay XAV, an amphibious fixed-wing drone that can fly or dive as needed.

Aerial drones have been taking to the water like ducks in recent years. Some are happy to gently touch down on the surface of a lake to shoot underwater video or soak up some sun to recharge their batteries. Others are more actively aquatic, diving or sinking below the waves to take water samples or perform inspections.

The EagleRay looks most like Imperial College London's AquaMav, but where the latter folds its wings to take a dive, the former keeps its own outstretched. The EagleRay's wingspan is 59 in (150 cm) and it's 55 in (140 cm) long, with a propeller on the nose designed to let it move through both air and water with ease.

This kind of versatility has plenty of advantages. The team says the EagleRay could extend its battery life by setting down on the water, or track and observe wildlife from both above and below the water surface as needed.

"For example, the EagleRay could track a fast-moving pod of dolphins from the air, then spend time loitering in the water if the dolphins stop to take advantage of a good feeding spot," says Warren Weisler, an engineer on the project. "The EagleRay could then resume flight when the dolphins begin moving again."

The amphibious drone could also streamline underwater monitoring better than aerial or submarine drones alone. It could dive to make observations that an airborne drone normally couldn't, before flying to a new location out of reach of a swimming drone.

"The EagleRay could also rapidly move underwater sensors from location to location," says William Stewart, another researcher on the project. "For example, sonar only works underwater. If you're seeking a sonar target, the EagleRay could fly to a site, submerge to take sonar readings, and then resume flight to take readings elsewhere. Historically, an aircraft would have to drop sonobuoys to collect sonar data."

The researchers are currently working on how to scale the EagleRay up and down, as well as designing a custom controller that allows an operator to easily control the craft both in the air and underwater.

A study describing the EagleRay was published in the IEEE Journal of Oceanic Engineering. The team demonstrates the drone in the video below.

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