Air ducts are integral to modern buildings but are challenging to access for inspection. Small quadrotor drones offer a potential solution, as they can navigate both horizontal and vertical sections and smoothly fly over debris. However, hovering inside air ducts is problematic due to the airflow generated by the rotors, which recirculates inside the duct and destabilizes the drone, whereas hovering is a key feature for many inspection missions. In this article, we map the aerodynamic forces that affect a hovering drone in a duct using a robotic setup and a force/torque sensor. Based on the collected aerodynamic data, we identify a recommended position for stable flight, which corresponds to the bottom third for a circular duct. We then develop a neural network-based positioning system that leverages low-cost time-of-flight sensors. By combining these aerodynamic insights and the data-driven positioning system, we show that a small quadrotor drone (here, 180 mm) can hover and fly inside small air ducts, starting with a diameter of 350 mm. These results open a new and promising application domain for drones.

There are 10 crew members trapped on a spacecraft, carrying out menial tasks to maintain vital systems, but at least one of them is an imposter who wants to sabotage their work and if possible, murder them. What sounds like the premise of a particularly bleak science-fiction movie is in fact the set-up of one of the most popular video games of the year. Developed by a three-person team at InnerSloth and launched to virtual obscurity in 2018, Among Us has suddenly become one of the biggest games on PC and mobile, attracting more than 85m players in the last six months. It's so successful, InnerSloth recently abandoned plans to work on a sequel, instead piling their resources into the original. No one, it seems, is more surprised about the success of this game than its creators.