This project aims to develop an aircraft capable of tethered flight in high-wind environments. Additionally, we aim to extend flight time by extracting power from the wind to reduce the amount of electrical power needed to maintain flight.
Quadrotors have become very popular platforms for autonomous flight in recent years. While mechanically simple and relatively easy to fly, they suffer from several problems including difficulty in flying in high speed winds and short battery life. In low-speed winds, some quadrotors can power through the wind to maintain steady flight, but this just exacerbates the battery life problem.
We introduce using a tether to maintain steady flight in high-wind environments. Tethering the aircraft introduces a measure of passive stability and counteracts much of the drag force created by the wind. This leaves the aircraft to stabilize itself and maintain altitude.
To further extend the flight time, we use a variable-pitch quadrotor with the capability of flying in a low-power "kite mode" where the rotor blades autorotate, extracting power from the wind. Variable-pitch quadrotors provide two modes of actuation, differential motor speed (standard quadrotor actuation) and differential rotor pitch. We use the latter mode of actuation to actuate the aircraft during the "kite mode" as driving motors is relatively power consuming compared to driving servos. Using a combination of body drag and thrust from the autorotating blades, the aircrft can maintain altitude during "kite mode".