Most of us have seen images of planes being refueled mid-air via a tethered system. Especially for very long flights, the concept of mid-air refueling has been around for well over 100 years, as shown by the image below from the magazine Punch from 1909.
Lack of power for long flights is a problem that has taken on new significance in the drone industry, as battery life proves a limiting factor for many applications beyond visual line of sight (BVLOS) and over distance, such as linear infrastructure inspections.
Now, the concept of refueling mid-air has been updated for drones with a few novel twists. Researchers Karan P. Jain and Mark W. Mueller explain their idea for in-flight battery switching, an up-to-date concept of aerial refueling, in this recent paper.
Here is brief video that shows the technology in action:
The paper details some key elements of the applied technology.
- “Abstract— We present a novel approach to increase the flight time of a multirotor via mid-air docking and in-flight battery switching. A main quadcopter flying using a primary battery has a docking platform attached to it. A ‘flying battery’ – a small quadcopter carrying a secondary battery – is equipped with docking legs that can mate with the main quadcopter’s platform. Connectors between the legs and the platform establish electrical contact on docking, and enable power transfer from the secondary battery to the main quadcopter. A custom designed circuit allows arbitrary switching between the primary battery and secondary battery.”
- “We present the concept of a ‘flying battery’ – a secondary battery that is mounted on a small quadcopter. While a main quadcopter is performing some task mid-air using a primary battery, a flying battery can fly towards the main quadcopter and dock on it. The main quadcopter can then switch its power source to the secondary battery. Once the secondary battery is depleted, the flying battery can undock, and another
fully charged flying battery can dock in its place. This process can be repeated until the primary battery is depleted. The primary battery is only used from the time when one flying battery undocks until another one docks back. This increases the total flight time and is achieved while the main quadcopter is airborne, so there is no interruption to the mission. “
- “One of the crucial features of our design is seamless switching from the primary battery to the secondary battery and back. Since our system is flying, we cannot afford to cut the power supply during this switch. The two batteries need to be connected in parallel for some time to achieve this.”
This is a different approach to a well documented problem. Other solutions including charging stations that are either stand alone or part of a system, hybrid fuel systems, or added battery capacity to aircraft.