The thing that normally limits how long a drone can stay in the air for surveillance or any other type of work is how long the batteries can last. Since most of the unmanned drones are like helicopters they don’t glide when the power stops, they fall to the ground. A new drone from CyPhy called the Parc is in the works and this drone could stay in the air indefinitely.
The way the drone is able to fly for such long periods of time is because it doesn’t get power from an onboard battery. When Parc takes off it pulls a thin microfilament behind it that transmits power for the motors to operate and data from the camera.
The downside to having a drone that uses a tether for power is that it can’t fly very far. The company figures that the drone will be used as a communications relay or for surveillance where it is needed to loiter in the same spot for an extended period.
Parc is a six-rotor flying machine and it carries a high-resolution camera that can produce infrared night vision footage. The line that trails beneath the drone for power is thinner than a headphone cable, but is strong enough to reel the drone in when needed.