Most drones today are noisy: The whine of motors and the hum of propellers produces an unavoidable din that instantly telegraphs their presence.
By contrast, the small plane that flew across an indoor track on the MIT campus this fall was eerily silent. Though its furthest flights were obviously powered, you could be forgiven for thinking it was some sort of trick. That’s because the plane uses an entirely novel propulsion system, one without even a single moving part.
