Whisper Aero Flies Electric Glider on Its Quiet Fans

An experimental glider aircraft equipped with two of Whisper Aero’s eQ250 electric ducted fans has achieved its first flights, the company announced today.

Whisper conducted the flights last week at its flight-test facility in Crossville, Tennessee. Test pilot Zac Majors flew the aircraft, called the Whisper Powered Swift, across three flights totaling more than 130 minutes in the air. The company said the flight-test campaign met all planned test objectives.

Preparation included a phased campaign of progressively ballasted glider flights, aircraft integration testing, formal readiness reviews, and 1,000 hours of ground-based propulsion life testing, Whisper said. Those sorties mark the program’s transition from gliding validation flights to powered test flights.

A modified Aériane Swift 3 glider serves as a flying testbed for propulsion technology that the company has been developing in Crossville since 2020. Whisper previously referred to the glider program as the Whisper Ultralight. Despite the earlier moniker, the modified version of the aircraft no longer qualifies as an ultralight under the FAA’s Part 103 rules, which cap a powered vehicle’s empty weight at 254 pounds and require no airworthiness certificate. Whisper flew the Powered Swift under an FAA special airworthiness certification instead.

Two eQ250 propulsors, each capable of up to 85 pounds of static thrust, powered the aircraft, drawing from five Electric Power Systems Epic 1.0 battery modules. The glider’s 26:1 lift-to-drag ratio means it travels 26 feet forward for every foot it descends. That efficiency keeps it aloft longer on limited battery power, giving engineers more time per flight to evaluate propulsion performance, acoustics, and handling qualities.

Tennessee’s state government awarded the company a $500,000 grant last year to demonstrate quiet flight with the electric glider in partnership with Tennessee Tech University. Faculty and students there supported ground testing and system integration alongside engineers from Whisper and Portland, Oregon-based Flighthouse Engineering, according to the company.

For Whisper, the milestone arrives amid the start-up’s pursuit of an unusually broad range of ambitions, from military drones to regional airliner concepts and even leaf blowers, all built around a single core product. During a recent visit to the company’s headquarters and flight-test facilities in Crossville, executives laid out how those pieces fit together.

“Whisper is building quieter, more efficient propulsion for next-generation aircraft, and we’re doing it because we know that there’s a challenge getting to lower noise and getting to the levels of affordability required, whether that’s for defense or the civil world,” Whisper co-founder, COO, and chief product officer Ian Villa told AIN.

An Electric Engine Company

Whisper does not build aircraft, and says it never will. While other companies spend billions certifying complete electric and hybrid-electric aircraft, Whisper’s roughly 80 employees focus on electric ducted fans, which it aims to supply to airframers across the civil and defense markets.

“There’s already a really great breadth of start-ups who have emerged these last few years—they’re in the thick of it, certifying their eVTOL, certifying their airplanes—and the big unlock we saw to get into this next generation of aircraft is propulsion,” Villa said. “While vertical integration may have been necessary in the early days, as the market matures and expands, there’s going to be greater specialization.”

John Huff, Whisper’s head of ground test, framed the same choice in terms of risk. Supplying propulsion “gives us an opportunity to service a wide range of customers, both commercial and defense, many different programs,” he said. “That’s a much more stable business model than where I have to have risk built up through the whole system, from propellers to motors to an airframe to avionics. We can do what we’re great at, and then we can partner with other people who have the elements where they excel.”

A full-scale mockup of the company’s Whisper Jet, a nine-passenger regional airplane concept with an array of ducted fans embedded in its wing, stands in the Crossville facility not as a product but as a visual aid. “When you have a new technology, it’s hard for people to really visualize or imagine how you would incorporate that into their designs,” Huff said.

Pushing Sound Past Hearing

Whisper says its fans are dramatically quieter than comparable propulsion systems, and the company’s explanation starts with a number called blade passage frequency: how many times per second a blade disturbs the air, calculated from the blade count and rotation speed. That frequency carries most of a fan’s tonal noise, and Whisper’s design pushes it beyond what people can perceive.

“One of the things you’ll see in a Whisper propulsor is a much higher number of blades in the fan, and what that does is change the blade passage frequency—how often something disturbs the flow—it makes it much higher in frequency,” Huff said. “That’s a big part of why the acoustics change, both in terms of how tuned our ear is to it, as well as how quickly it fades into the air.”

Human hearing tops out around 18 kilohertz in young adults and declines with age, Huff explained, and the ear is most sensitive in the range of conversation. High-frequency sound also dissipates in the atmosphere far faster than low-frequency sound, which is why thunder rumbles across miles while a hiss dies within feet. Whisper’s fans exploit both effects at once.

Villa said the company made that acoustic target its founding design principle rather than an afterthought. Its fan disc carries many short blades spinning at high rpm but relatively low tip speed, keeping the dominant tone “past human hearing, but still in a way that minimizes the sound pressure levels, and ultimately reduces the perceptibility and really the annoyance to the public,” he explained.

The powered Swift flights gave Whisper its first real-world test of those claims. Flying at full throttle, the aircraft’s propulsion system was quieter than the airframe itself, even at an altitude of 100 feet, the company said. On an early morning flight with an ambient noise level of 34 A-weighted decibels, the aircraft added only 52 A-weighted decibels. Whisper says that level will be necessary for aircraft to operate in rural soundscapes under the FAA’s Modernization of Special Airworthiness Certification rule, known as MOSAIC, without disturbing the surrounding environment.

Majors said the aircraft handled well despite the added thrust. “Whisper Swift was more thrust, quieter than the standard propeller version of the Swift, but still great handling—could really do whatever I wanted with it,” he said. “Look forward to flying it again.”

Precision manufacturing makes the design possible. “The guy that cuts our fan blades also makes heart stents,” Huff said. “That gives you an idea of how delicate these are.”

When embedded in the leading edge of a wing, the fans do more than push an airplane forward. “The motors accelerate the airflow over the top of the airfoil, and that’s what gives you lift in an airplane,” Huff said. “By doing this, we augment the lift and get very high lift coefficients for when we’re trying to take off. So now you can have a short takeoff or a near-vertical takeoff, depending on how you approach it.”

Whisper calls that wing integration JetFoil. In June, the company said that computer simulations show the blown wing achieving lift coefficients far beyond those of any conventional airfoil at very low airspeeds. Whisper has since backed some of that up on the ground, turning the fans’ exhaust to steep angles on a full-scale test rig and demonstrating near-vertical takeoff and landing capabilities on a test stand, according to the company. No JetFoil-equipped aircraft has yet flown in that configuration.

Defense and Civil Markets

Whisper aims its propulsors at a sweeping range of applications: uncrewed aircraft from small drones to larger military cargo airplanes, light sport and MOSAIC-category airplanes, nine-seat Part 23 aircraft, and consumer products. Its Tone subsidiary plans to ship a $599 electric leaf blower this year built on the same fan technology.

On the military side, Whisper has held Department of Defense contracts since 2023, initially for quiet surveillance drones. In June, its work moved from surveillance toward offensive operations. Mach Industries of Huntington Beach, California, named Whisper as its propulsion partner on Atlas, an uncrewed strike aircraft the Defense Innovation Unit selected for its Runway Independent Maritime Expeditionary Strike program. Atlas is designed to launch from ships without large flight decks and operate over a range of up to 1,400 nm while carrying a 1,000-pound payload, according to Mach.

Whisper believes the Swift flights reduce risk for that broader family of defense work. The company plans to apply lessons from the campaign to its collaborative logistics aircraft program, for which it revealed a family of aircraft concepts last year. Villa said Whisper will continue flight-testing the glider in Tennessee before moving it to White Sands Missile Range in New Mexico for evaluation with government customers later this year.

Crossville Roots

Whisper’s presence in Crossville began, Villa said, as “a happy accident.” He and co-founder and CEO Mark Moore, a former NASA distributed electric propulsion researcher, founded the company during the Covid-19 pandemic and scouted locations nationwide, from “old laundromats in San Francisco” to sites in Austin and Dallas, before Moore found a 20-acre resort on the Cumberland Plateau. Initial staff and their families moved in, and the property became a secret laboratory where the company proved out its early propulsors.

Today the start-up operates a 40,000-sq-ft manufacturing and test facility in the former Trade-A-Plane building downtown, an 8,000-sq-ft flight-test hangar at Crossville Memorial Airport that opened with $1.2 million in state funding, and a research office in Nashville. Villa said Whisper expects to add roughly 10,000 square feet to the flight-test facility before the end of this year and added that the company is actively hiring for various roles.