Tilted Rotors Make Drones More Stable

Researchers in Japan have demonstrated that the stability of unmanned aerial vehicles in heavy winds can be improved by angling the rotors of drones outwards by 20 degrees.

AsianScientist (Feb. 20, 2018) – In a study published in the International Journal of Micro Air Vehicles, scientists in Japan have discovered that drones fly more stably when their rotor blades are angled outwards by 20 degrees.

Multi-rotor drones have gotten much smaller since the turn of the century, and they have many uses, including inspection, surveillance and transportation. A multi-rotor setup allows for both vertical takeoff and hovering in calm conditions, but they are unstable in wind.

Under windy conditions, the rotors flap and the drone pitches upwards in a headwind. Pitching can occur because of three factors: the drag of the body, the asymmetry-induced flow distribution on the rotors in wind and the thrust difference between the front and rear rotors.

In the present study, Dr. Hikaru Otsuka and colleagues at Tohoku University set out to evaluate whether angling the rotor blades differently would improve control of quad-rotor drones in winds. The team first estimated how the front rotors affected airflow over the rear rotors. They demonstrated that by angling the drone at 75 degrees in flight, the airflow over each rotor blade remained isolated. However, increasing the angle to 90 degrees or above meant that the airflow over the front rotors affected that of the rear rotors.

They then tested various angles of rotor attachment and the effect on drone pitching. The scientists used a drone placed inside a wind tunnel, measuring the effects of outward and inward tilting of the rotor blades for five different angles. They found that by tilting all four rotors by 20 degrees to the outer side, the pitching of the drone was reduced by 26 percent.

The authors thus concluded that tilting of the rotors to the outer side reduces the pitching moment of quad-rotor drones in winds. Their work could have implications for both hobbyists and for professionals who want to use multi-rotor unmanned vehicles for inspecting wind turbines and disaster sites, or for rescue activities.

The article can be found at: Otsuka et al. (2017) Reduction of the Head-up Pitching Moment of Small Quad-rotor Unmanned Aerial Vehicles in Uniform Flow.


Source: Tohoku University; Photo: Pixabay.
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