Technology company Whisper Aero has unveiled its Whisper Jet concept as part of a larger reveal of the applications of their ultra-quiet ducted fan technology that is currently under development. Whisper Aero’s tech employs a ducted fan with a large number of propellers turning at much slower speeds than conventional designs to achieve its claimed industry-leading quiet noise footprint.
Whisper Aero is drawing attention with this and other information recently shared at the ongoing American Institute of Aeronautics and Astronautics Aviation Forum in San Diego, California. The company’s propulsion technology is claimed to be almost inaudible during overflight at 200′ with a 55 lb drone, according to tweets from COO Ian Villa.
The proposed advancements from Whisper Aero offer much lower noise levels and might solve the challenge of more negative public perceptions toward aerial mobility offerings due to higher noise levels.
According to the developers, it is the world’s quietest and most efficient engine for electric planes. It is “100 times quieter than similar engines” and its efficiency has been “increased by 20 per cent”.
Inside the Whisper propulsion unit, there’s a “propulsion disc” that’s essentially a fan, one with an unusually large number of strong, stiff blades, joined at the outer circumference by a shrouding ring for additional strength. It’s a small diameter fan, in order to keep the blade tip speed low while it’s spinning at flight-relevant RPMs.
The large number of blades, Whisper says, push the “blade passage frequency” over 16,000 Hz, and thus out of the range of human hearing. Mind you, according to an interview with Aerospace America, the frequency doesn’t push high enough to freak dogs out:
“We’ve had five dogs in physical close proximity to our fan tests, and they don’t react at all to them,”
said co-founder and CEO Mark Moore, who also co-founded Uber Elevate and worked as an engineer at NASA.
With lots of blades, you can also spin “way, way, slower than any propeller or turbofan,” Moore continues. “We spin so slowly that the centrifugal forces on this rim aren’t that significant that it would tear apart.”
That shrouding rim joining the fan tips also eliminates the gap between the blade tips and the duct housing, further reducing blade tip vortex noise.
Energy lost to noise is energy that’s not converted to thrust, and Whisper says it’s been able to demonstrate rotor efficiencies up to 92%, “even at 6-inch (15-cm) fan diameters.”
In acoustic testing, Whisper’s 6-inch fan tested as completely inaudible from 200 feet (61 m) away over a 30-decibel background noise floor. They then compared it against two ducted fans and two open propellers, described by Whisper as the quietest commercially available products on the market, all making the same 7.8 lbf (34.7 N) of thrust.
At 100 ft (30.5 m) distance, the whisper fan recorded a remarkable 34.1 dBA noise level. The Schubeler ducted fans measured 44.9 and 52.1 dBA, and the open propellers, from Aeronaut CAMcarbon, measured 49.4 and 58.7 dBA.
The Whisper Jet concept is an odd-looking duck, using a Blohm and Voss Outboard Horizontal Tail (OHT) configuration something like Virgin Galactic’s VSS Unity. It’s got banks of propulsion units along its inner wing surfaces. Theoretically, it could carry a pilot and nine passengers, up to 200 miles (322 km) on a battery charge, at speeds up to 288 mph (463 km/h), using conventional runway takeoff and landing (CTOL). The range could be extended to 500-odd miles (800 km) with a hybrid system.
It’s just a concept; Whisper is more interested in selling the propulsion system than going into the business of making planes. But the company says the propulsion system will work well for short takeoff and landing (STOL) aircraft, drones of all sizes, and potentially, eventually, eVTOL air taxis. It’s working on a range of fan diameters, including 4-in, 10-in, and a 24-in option specifically designed for use in the AFWERX High Speed VTOL program, where it’ll compete with some other fascinating propulsion technologies.
Whisper Aero is a VC-backed company focused on application of their Whisper electric propulsion technology to a wide range of devices – including aerial mobility aircraft but also as part of consumer goods, such as home fans. The company was founded in Tennessee by Mark Moore, who has previously worked at Uber Elevate.
Whisper Aero released images of a concept Whisper Jet, but also stated that their technology is intended to apply to a wider range of applications than one eVTOL configuration.
Sources: New Atlas; TransportUp