An electric aircraft engine designed to reduce operational noise to a whisper is now powering piloted aircraft.
Whisper Aero on Wednesday revealed that its “ultra-quiet” eQ250 electric ducted fan propulsion system is being put to the test in Tennessee under an FAA special airworthiness certification. The company said it installed a pair of eQ250s on a modified Aériane Swift 3 glider, with which test pilot Zac Majors conducted three flights spanning 130 minutes, or about 43 minutes on average.
Majors said the aircraft, which the company refers to as the Whisper Powered Swift, produced more thrust and was quieter than the standard propeller version of the glider, “but still great handling.”
“[I] could really do whatever I wanted with it,” Majors said in a statement. “Look forward to flying it again.”
Fortunately for him, the campaign is only just beginning.
Whisper plans to continue testing the Swift in Tennessee before advancing to flight tests and evaluations with “government customers” later this year. The company is under contract with the U.S. Air Force to develop a new family of quiet, efficient, autonomous aircraft for contested logistics, with initial testing planned for 2027.
How It Works
The eQ250 is the flagship product of Whisper’s electric quiet (eQ) engine series.
According to the company, it produces up to 85 pounds of static thrust for fixed-wing aircraft. It can also power Group 3 uncrewed aircraft systems (UAS)—which have maximum weight of 1,320 pounds and speed under 250 knots—or larger drone platforms.
The specialized electric ducted fans are 10 inches in diameter and produce about 20 dB less noise than “comparable quiet propulsion systems,” while also being 20 percent more efficient, according to Whisper’s website. For short takeoff and landing (STOL) aircraft, the eQ250 is designed to enable coefficients of lift as high as 14.
The propulsion system is intended to unlock short-to-medium-range regional air mobility services using small airports. The idea is similar to Electra’s concept for “direct aviation,” which involves the company’s “ultra-short” takeoff and landing EL9. The goal is to replace trips that would take about 90 minutes driving with air service that takes closer to 20 minutes.
Whisper said the Swift’s 26:1 lift-to-drag ratio made it ideal for evaluating handling qualities and the propulsion system’s performance, integration, and acoustics.
The glider’s eQ250s are powered by five Epic 1.0 Energy modules from Whisper partner Electric Power Systems (EPS). According to EPS, they provide 60 minutes of usable flight time with 30 minutes of reserve for trainer, eVTOL (electric vertical takeoff and landing), and “thin-haul” aircraft, which are used for very short trips with a handful of passengers.
Whisper said the aircraft “completed its planned objectives,” which included validating its propulsion integration, battery, control, and other systems. At full throttle at 100 feet agl, Whisper said the engines were quieter than the airframe itself. Ian Villa, co-founder and chief operating officer, told The Air Current that the glider can generate substantial noise without engines.
Flown during the early morning, the aircraft produced about 52 dB(A) of noise compared to 34 dB(A) background noise, Whisper said.
“The ability to fly within the soundscapes of even rural environments…will be critical for flights of FAA MOSAIC aircraft,” the company added.
The Modernization of Special Airworthiness Certification (MOSAIC) took effect in phases over the past few months and permits electric propulsion systems in the light-sport aircraft (LSA) category.
More to Come
Whisper said the test campaign “reduces risk” for the eQ250’s larger civil and defense applications.
The company is developing its JetFoil integration for STOL and VTOL aircraft, designed to enable runway independence. The JetFoil distributes ducted fan engines across the entire leading edge of the wing and would enable near-vertical takeoffs with 50 feet of ground roll. Whisper claims it will do so using half the thrust of tilt-rotor VTOL aircraft while offering more range and double the payload.
Villa earlier this year told FLYING that Whisper is in talks with government customers to build and fly JetFoil-equipped prototypes, the idea being that they could be transitioned to commercial manufacturers who could bring them to market. For example, one could swap the de Havilland Twin Otter’s high wing for a JetFoil and hybrid-electric powertrain.
Whisper said the testing will further support its Collaborative Logistics Aircraft (CLA) program with the U.S. Air Force.
The CLA concept is similar to the service’s Collaborative Combat Aircraft (CCA) framework, which pairs crewed fighter jets with uncrewed “loyal wingmen.” Instead, CLA aircraft would carry between 500 and 3,000 pounds of cargo and operate from austere or degraded runways.
Whisper is studying two CLA concepts that incorporate 12 and 30 eQ250 engines on the leading edge of the wing, using the JetFoil integration. According to the company, at 250 knots, the CLA aircraft would generate reduced noise and heat signatures compared to models they could replace.
Whisper in May 2025 said that initial CLA flight testing would begin in 2027 at White Sands Missile Range in New Mexico.
The company has also shared concepts for a regional Whisper Jet and more robust 100-seat model, both based around its ducted fan and eQ technology.