Multicopter drones are neat and everything, but they do make a high-pitched whine – just image how annoying the sound of a large passenger-carrying version might be. It was with this in mind that electrical engineer Derek Schwartz recently went to Kickstarter with his Whisper Drone.
Currently in prototype form, the Whisper Drone mostly looks like a regular consumer quadcopter. Instead of the traditional propellers, however, it utilizes ring-shaped vaned rotors that Schwartz invented. These still provide static thrust – although currently with not as much efficiency as a regular propeller – yet produce a sort of whooshing sound as opposed to a whine.
Derek tells us it's also likely that his polyurethane foam rotors are more collision-resistant than more fragile traditional props, and that because their internal stresses are lower, they can be constructed from a smaller amount of material while offering the same amount of strength.
Additionally, they should be more resistant to vortex ring states. "The thick layer of accelerated air caused by the tall vanes seems to provide some insulation from downward flows of turbulent air," he tells us. "To my understanding, recirculated turbulent air sucked down into the conventional rotors can cause catastrophic loss of lift when VTOL [Vertical Take-Off and Landing] rotorcraft descend."
Schwartz adds that with each prototype he makes, the thrust efficiency improves. Even if it never quite matches the efficiency of a regular prop, however, his invention could conceivably still be applied to drones utilizing a hybrid system.
"The downward flow of air generated by operation of the rotor is located at the periphery, which opens up space on the interior," he explains. "An independently driven traditional propeller, or other means of thrust could be placed in that area as a source of alternative/supplemental thrust. As an example, a future craft might go into 'low noise mode' around populated areas by increasing power to the Whisper Drone's ring-like rotor, and decreasing power from the traditional propeller which could be placed in that central cylindrical area."
The current Kickstarter campaign is aimed at raising money to further develop the technology. A pledge of US$395 will get backers a Whisper Drone quadcopter with a remote-control unit, when and if the funding goal is met.
You can see and hear the prototype in flight, via the link below.
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