What is an 'annular propeller' that can be expected to significantly reduce the noise of drones and boats and improve efficiency?

by MIT Lincoln Laboratory

Airborne drones are already widely used for filming and are expected to help deliver packages without being affected by traffic jams, but the noise emitted by drones can be an obstacle to widespread deployment. A research team at the

Lincoln Research Institute , newly established by the Massachusetts Institute of Technology (MIT) and the US Department of Defense, has developed a `` annular propeller '' that can significantly reduce drone noise.

Toroidal propellers: A noise-killing game changer in air and water

MIT's latest drone propellers are very quiet and efficient

A propeller is a device that converts the power output from a driving force into propulsive force by rotating multiple blades, and has been used in various regions around the world since BC. The basic structure of the propeller has not changed over the years, and propeller-driven airplanes use a design similar to the bamboo dragonfly that children used to play with in China 2,400 years ago. The screw type propeller that is used can also be traced back to the 18th century.

However, drone and boat propellers produce a lot of noise, which is one of the challenges in the widespread deployment of drones, and it has been pointed out that boat noise has a negative impact on marine animals such as dolphins. .

Therefore, the research team at Lincoln Research Institute conducted research to reduce the noise of the drone using a propeller with a shape different from the conventional one. Dr. Thomas Sebastian, senior staff member of the Thermal Fluid Engineering Group at the Lincoln Laboratory, said, ``As we know, the propeller is quite noisy,'' once proposed at the dawn of airplane development. He explains that he worked on the development of a new propeller inspired by the 'annular wing' that was developed.

An annular wing is a cylindrical wing as follows.

A research team led by Dr. Sebastian created a prototype of an annular propeller with a 3D printer.

When I actually rotated the annular propeller, I found that the annular propeller was quieter than the normal propeller.

In a normal propeller, a vortex is generated at the tip of the blade, but in an annular propeller, the vortex is dispersed throughout, making it easier to dissipate in the atmosphere. As a result, the vortex does not spread far and the noise reaching the ears is reduced.

Annular propellers for drones are still in their early stages, but they say they were able to not only achieve silence, but also generate more thrust than conventional propellers at a certain output level. In addition, since the annular propeller has a complicated shape, it is expected that the manufacturing cost will be higher than the conventional propeller, but since the propeller is a relatively cheap part in the drone, even if the cost increases slightly, the overall price may not be affected as much.

Annular propellers are effective not only in the air. A US-based company called

Sharrow Marine is already developing annular propellers for boat propellers.

toroidal propellers turn your drones + boats into noiseless machines

Sharrow MX™ Video-YouTube

Sharrow Marine's annular propellers have blade tips that curve toward the other blade to form a closed loop.

By reducing the vortex and

cavitation generated at the tip of the blade, this reduces overall noise and improves efficiency.

Below is a video comparing the noise difference between a normal propeller (screw) and an annular propeller actually published by Sharrow Marine. By listening and comparing, you can see how the noise of the annular propeller is small.

Standard vs Sharrow MX™ Noise Comparison-YouTube

in Ride,   Science,   Video, Posted by log1h_ik