Whisper Aero reveals propulsor design and jet mockup for quiet, hybrid-electric flight

Company says ducted fan inaudible from 60 meters due to slow rotation, high blade count

This story has been updated to reflect Whisper Aero’s presentation of its papers.

AIAA AVIATION FORUM, San Diego, Calif. — Whisper Aero’s quiet flight technology consists of a relatively slow spinning ducted fan with a high number of blades, the company revealed in engineering papers presented here on Monday.

The company founded in Tennessee by former NASA engineer and Uber Elevate co-founder Mark Moore described its propulsion method and business plan in three papers presented at the American Institute of Aeronautics and Astronautics 2023 Aviation Forum.

The Whisper ducted fan has been “optimized for lowest noise and highest efficiency,” Moore wrote in his paper, “Unlocking Low-Cost Regional Air Mobility through Whisper Aero-Propulsive Coupling.” Whisper, Moore and his co-founder Ian Villa presented the papers Monday afternoon, but I was permitted to read them prior to the conference.

The high efficiency is “achieved with a very high blade-count fan. The blades are tensioned to an outer shroud, similar to the spokes of a bicycle wheel, for sustained rigidity throughout operation,” Moore told me in an interview Friday before his presentation.

Another Whisper paper describes how the company’s propulsion technology could be installed on aircraft, theoretically, to provide regional air service in trips of 50 to 500 miles. The company envisions integrating its propulsors on the leading edge of an airplane’s wings to maximize aerodynamic efficiency and thrust, although the company has yet to build such a plane. Whisper has run various tests on its ducted fans, including flight testing of a drone powered by a single such ducted fan.

In the Friday interview, Moore said the number of blades is proprietary, but he did share other details.

“Our blades are just like spokes on a bicycle wheel, with a rim so that they are very stiff. They have to be very rigid,” Moore said.

The entire disc of Whisper’s ducted fan, including the thin blades and outer rim, could be made in one piece through pressure injection of thermoplastics, or meltable plastic polymers, Moore said.

“We spin substantially slower — way, way slower — than any propeller or turbofan. We’re not going to say the precise number, but we spin so slowly that the centrifugal forces on this rim aren’t that significant that it would tear apart,” he said.

According to Moore, the slow tip speed and high blade count results in some of the pressure waves, or noise, ending up in an ultrasonic range that is not audible to the human ear but not high enough to be annoying to animals.

“Whisper’s campus in Tennessee is dog friendly. We’ve had five dogs in physical close proximity to our fan tests, and they don’t react at all to them,” Moore said.

Some frequencies of noise from the company’s propulsors would be audible to humans close to the aircraft, but still quiet enough that it wouldn’t be heard from a distance of 60 meters, Moore said.

Whisper plans to reveal a mockup of the Whisper Jet, complete with 16 mockups of its ducted fans, on the exhibition floor at the forum on Tuesday.

The company doesn’t intend to produce this aircraft by itself, Moore said.

“We’re convinced we can be faster by partnering with an established player, like a GKN or a Honda or Cirrus, rather than trying to do it all ourselves,” Moore said. He said he’s not ready yet to say who that partner will be.

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Whisper Aero reveals propulsor design and jet mockup for quiet, hybrid-electric flight