Whisper Aero prepares to speak up

By Paul Brinkmann|May 10, 2023

Company plans to present first details of its quiet propulsion concept in three papers at next month’s AIAA Aviation Forum

Whisper Aero has long promised that the propulsion technology it is developing for the U.S. Defense Department and its own Whisper Jet will be “ultra low noise.” The company has so far described the drive mechanism only as an amazingly quiet ducted fan technology.

That looks about to change.

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

Whisper announced in April that it has raised $32 million to bring its technology to market. At the time, the company said it had designed and manufactured a ducted fan propulsor with very slow tip speeds, resulting in quiet performance because some of the noise occurs in ultrasonic ranges inaudible to the human ear.

Ducted fans have attracted aircraft designers over the years, in part because installing rotor blades inside a shroud affords more protection for passengers and ground crews, but also for other reasons.

“Theoretically, the duct is supposed to shield noise a little better and provide more efficient thrust per unit of power, because it reduces wingtip vortices,” says Cengiz Camci, a professor emeritus of aerospace engineering at Pennsylvania State University who has published several papers about ducted fan research.

Camci says he looks forward to seeing Whisper’s research when it is published. But he adds that noise in ultrasonic ranges can come with downsides.

“Environmentalists may get crazy about this. Because maybe we don’t hear that sound, but all other creatures can hear it perfectly,” he says.

Whisper has held back on exactly how it has accomplished what it describes as the next generation in aircraft propulsion. It plans to reveal a scale model of its Whisper Jet, a conventional takeoff and landing fixed-wing airplane, at the AIAA forum.

“One of the really cool things that will come out in the papers we present is that this ducted fan looks very different from any other ducted fan,” Moore told me in an interview.

He said the jet will be covered by a sheet on the first day of the forum and revealed on the afternoon of June13.

“We’re going to explain in much more detail why the propulsors are so enabling and can create this new way to integrate propulsion,” Moore says.

Ian Villa, the company’s co-founder and chief operating officer, says part of the innovation lies in the blade strategy.

“These electric ducted fans have a novel design so they can spin slowly, but still push sounds it makes into the ultrasonic range, which humans can’t hear,” Villa says.

Whisper’s new openness comes as another company in the advanced air mobility space, Textron, has abandoned the use of ducted fans on its proposed air taxi, the Nexus. A Textron engineer told me in March that the company had ditched ducted fans partly because they are noisy in vertical liftoff mode.

Only one other major air taxi developer in addition to Whisper, Lilium of Germany, continues to tout ducted fans.

Asked about Textron’s move away from ducted fans, Moore said only that Whisper’s propulsion is much different than either the Nexus design or Lilium’s current technology.

According to Whisper, its ducted fans are 20% more efficient at producing thrust than the best ducted fans in use today.

The Whisper propulsor is now in its ninth generation of design and testing, which was validated by flying a 55-pound (25-kilogram) drone. Flying at 200 feet overhead, the drone was not audible to the human ear, Whisper says.

The company has been working with the Department of Defense under six contracts valued at $2.2 million.

By the end of the year, Whisper anticipates selling the propulsors to DoD for use on drones. After that, plans call for partnering with an aircraft manufacturer to develop the Whisper Jet. The company also expects its quiet ducted fans will be useful in consumer equipment like leaf blowers or vacuums.