Whisper Aero flies first piloted tests using ‘ultra-quiet’ electric propulsors

Early morning flights with a 34dB(A) ambient showed only 52dB(A) coming from the aircraft at an altitude of 100ft, reported Whisper.

Last week Whisper Aero flew three crewed flight tests, accumulating more than 130 minutes in the air, at its test facility in Crossville, Tennessee using its novel eQ250 electric ducted fans integrated into a modified Aériane Swift 3 glider, known as the Whisper Powered Swift.

Whisper founder and CEO Mark Moore said the tests are proof that its eQ250s are at a technology readiness level (TRL) of greater than seven. TRL is a nine-point scale developed by NASA to assess the maturity of a technology, ranging from basic principles observed at TRL 1 to a system proven in an operational environment at TRL 9. Clearing TRL 7 means the propulsors are ready to be deployed on partner aircraft, including a Runway Independent Maritime & Expeditionary Strike (RIMES) aircraft it is co-developing with Mach Industries for the US Defense Innovation Unit and a contested logistics strap-on aircraft in development with the US Air Force.

Early morning flights with a 34dB(A) ambient showed only 52dB(A) coming from the aircraft at an altitude of 100ft, reported Whisper. A video released by the company – which dropped the ambient marketing music for the overflight angle – highlighted the noise, or lack of it, produced by the aircraft in flight.

“Any new technology needs strong proof points,” Moore told us. “This is a very strong proof point. These propulsors are absolutely as quiet as we said they are – to be able to add them to a glider that basically makes no noise as it flies over at 100 feet, and have the propulsion at full throttle not adding any noise to it – that’s something no one’s ever done before.

“You’re going to see our propulsors on quite a few more aircraft over the next 18 months, as we’re working with other companies that haven’t yet been announced, to really show what the future of distributed electric propulsion is,” added Moore.

The Whisper Powered Swift aircraft, which features a 46ft (15m) wingspan, was propelled by two of Whisper Aero’s eQ250 electric propulsors, each capable of producing up to 85 pounds of static thrust. These propulsors were powered by five Electric Power Systems Epic 1.0 Energy modules. Whisper said the aircraft’s efficient 26:1 lift-to-drag ratio provided a “flexible platform” for evaluating propulsion performance, aircraft integration, acoustics, and handling qualities.

Certified under FAA special airworthiness, the aircraft was flown by test pilot Zac Majors, who has a multi-engine rating and significant flight hours on the Aériane Swift 3 glider. “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,” said Majors. “Look forward to flying it again.”

The crewed flights followed a phased test campaign that included progressively ballasted glider flights, aircraft integration testing, formal readiness reviews and more than 1,000 hours of “arduous” propulsion life testing, Ian Villa, chief operating officer and chief product officer, Whisper Aero told us. The company first announced plans to build the electric glider, in partnership with Tennessee Tech University, in April 2025.

“We started flying it unmodified, got some baseline acoustic measurements to just see how quiet – or not quiet – this thing was in flight. Then, over the past few months, we’ve retrofitted it with two of our propulsors,” he said. “We put it through our own AS9100 quality management system processes, got a special airworthiness certificate and then flew this last week to prove that our propulsors are flight-worthy all the way up to TRL 7, and that we’re ready to place these on various other customer aircraft.”

MOSAIC-ready

Villa said the successful flight tests set Whisper up to take advantage of the FAA’s Modernization of Special Airworthiness Certification (MOSAIC) regulatory framework. Although there is still more to be understood on the means of compliance, Villa is confident there will be a “sweet spot” in two-to-four-passenger light sport aircraft.

“MOSAIC really opens the door not only to fixed-wing flight, but also to power-lift vehicles or vehicles with distributed electric propulsion. So in this case, on this power glider, we actually went through all of the specifics to look at multi-engine in the context of a vehicle that is more than an ultralight. In total, this is over 600 pounds in weight,” he said.

Through this effort, Whisper aimed to understand what certification requirements are needed in a MOSAIC context. These include electrified system requirements and what it means to have multiple propulsors on an aircraft. Villa said the company has considered multiple certification bases and means of compliance for placing electric propulsors onto aircraft, including Part 23, 2117(B) and Part 33.

“We’re really taking the sum total of these learnings, but then specifically looking at the recent MOSAIC regulation to make sure that we’re positioned well for this nascent portion of the market,” he said.

Proof of ultra-quiet operations

“The quietest way to move air”. That is the quote that greets any visitor to Whisper Aero’s website. It is a bold claim that the development team is acutely aware requires proof. This was the ultimate aim of building the Whisper Powered Swift and subsequent flight tests. The team discovered, as is shown in its marketing video, that if the aircraft flies overhead at 100ft, its propulsors are quieter than the stock airframe.

“When we were flying this, the ambient noise was at about 34dB(A), and when we were flying overhead at that 100 feet altitude, we’re at 52dB(A). Much quieter than really anything else that’s been flown in the electric aviation space. This may be the quietest crewed aircraft with an electrified powertrain,” said Villa.

Anecdotally, Villa was standing further out from the test team during the flights and struggled to hear the aircraft on take off. “I had a bee zooming past my camera lens, and that was louder than the first portion of the take off. So I couldn’t actually get a really accurate feel for the acoustics of the aircraft taking off,” he said.

Noise aside, data is building confidence

Last week’s flight tests have banked more validation data, giving Whisper the confidence to bolt its propulsors on to more, potentially larger, aircraft. “Now that we’ve proven a thousand hours on the ground, that gives really great confidence to actually put it up onto a crewed platform. And similarly, as we think about placing this onto larger, more capable platforms, we can start to look at more of the datasets and build up that confidence – not just with ourselves, but for our customers,” said Villa.

Whisper is also preparing for future tests with the US government. It is working with the US Air Force to take the Whisper Powered Swift platform to White Sands Missile Range in New Mexico for further testing later this year. “Out there, there are some unique facilities where we can really measure the acoustics of this airplane and again further bolster our understanding of its efficiencies in flight, at a much more controlled and performant range,” said Villa.

Tennessee Tech partnership

The initial test flights were part-funded by Tennessee Tech University through a $500,000 Transportation Network Growth Opportunity (TNGO) award from the Tennessee Department of Economic and Community Development. The initiative saw university students and faculty get ‘on the shop floor’ aerospace engineering experience in the build up to the flight test campaign. Work included integration of the aircraft’s propulsors, batteries and controllers, alongside engineers from Whisper Aero and Flighthouse Engineering.

“TNGO is trying to find ways for industry and academia to really collaborate,” said Villa. “Through this collaboration we were able to bring in students from Tennessee Tech to learn about the future of aviation and get real engineering hands-on experience – placing electric engines onto the aircraft and preparing us for our first flight, getting us in a really great spot before the aircraft ever left the ground.”