How Do The Zipline Silent Propellers Work?

In a recent video, YouTuber Mark Rober showcased some innovative Zipline drones that are designed to deliver medical supplies in Rwanda. While the drones themselves are impressive, there is one aspect of their design that has caught the attention of many: the Zipline Silent Propellers. Specifically, the propellers are shaped in a way that reduces noise, but how exactly does this work?

Zipline’s Silent Propellers Explained

To understand the noise-reducing design of these propellers, it’s important to first understand how sound is created when a propeller spins rapidly. As the blades move past a stationary point, they create a pressure disturbance that propagates away from the blade. The frequency at which this happens is called the blade passage frequency, and it’s equal to the rotational frequency (i.e. how fast the propeller is spinning) times the number of blades on the propeller.

Traditionally,…