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Whisper Aero Unveils 100-Seat Electric Airliner Concept

Graham Warwick March 04, 2024

 

An array of 22 electric ducted fans is integrated into the leading edge of the Whisper Jetliner’s wing.

Credit: Whisper Aero

Ultraquiet propulsion developer Whisper Aero is proposing a concept for a 100-seat battery-electric regional airliner in a bid to help aviation achieve net-zero emissions by 2050.

The U.S. startup has submitted a proposal to further develop the concept under a new NASA program.

The Whisper Jetliner has an array of electric ducted fans integrated into the leading edge of the wing to provide upper surface blowing. This increases lift coefficient and wing loading and improves cruise lift-to-drag ratio.

Similar to the nine-passenger Whisper Jet concept unveiled by the startup in June 2023, the Jetliner has an outboard horizontal tail configuration, with the horizontal and vertical stabilizers mounted on wingtip booms. This keeps the horizontal tail out of the downwash induced by upper surface blowing of the wing, Whisper CEO Mark Moore says.

The startup has submitted a proposal to develop the design under NASA’s Advanced Aircraft Concepts for Environmental Sustainability (AACES) program, which aims to provide a path to net-zero aviation by 2050. A total of $8 million in funding is available under Phase 1 of the program.

AACES is a follow-on to NASA’s N+3 studies in 2010, which developed concepts for ultraefficient airliners that could enter service in 2035. These resulted in NASA’s Boeing X-66A Sustainable Flight Demonstrator, which is planned to flight test the long-span, low-drag transonic truss-braced wing in 2028.

Whisper is a propulsion system developer, and its goal with both the nine-seat and 100-seat concepts is to show how its ultraquiet, ultraefficient electric ducted fans can enable battery-electric regional aircraft.

“We wanted to see if battery-electric aircraft could outcompete economically hydrocarbon-based solutions, so that it becomes a rational business decision to go to a zero-emission aircraft and retire the existing fleet,” Moore says.

“We wanted to project out where our technology would be going over the next 20 years, and how that coincided with other technology invigoration, especially for the battery-electric regional mobility market,” he adds.

Founded in 2020, Whisper has flown a 10-lb.-thrust thruster on a 55-lb. uncrewed aircraft, but has studied scaling up its electric ducted fans to thousands of pounds of thrust under contract from the U.S. Air Force’s AFWERX innovation unit.

“Our foundational technology innovations still apply at this larger scale,” says Ian Villa, chief operating officer. “We’ve already built and tested a production-ready thruster that can generate eight-10 times more thrust than our first proof-of-concept 10 lb. ultraquiet, ultraefficient thruster.”

To bid for the NASA AACES program, Moore says: “We put together a concept so we had confidence that what we were projecting for our technology matched to an aircraft concept that was feasible and could set the stage for what reasonable expectations there could and should be for getting to net zero emissions in the 2050 time frame.”

At the Mach 0.78 cruise speed of a commercial aircraft, Whisper’s propulsion system has a fan pressure ratio close to the ideal of 1.2 compared with 1.4 for geared turbofans, resulting in 5-10% higher propulsive efficiency, Moore says.

The Jetliner has 22 ducted fans, each powered by a 1-megawatt electric motor and producing 1,970 lb. of thrust. Gross weight is 160,000 lb. compared with 139,000 lb. for the Airbus A220-100. Of this, the 14.6 megawatt-hour battery accounts for 51,250 lb. (an energy weight fraction of 32%) compared with 39,000 lb. of fuel (28%) in the A220.

Whisper is projecting battery energy densities by 2050 of more than 800 Wh/kg at the cell level and 640 Wh/kg at the pack level, assuming 3.6% per year improvement. This will give the Jetliner a range of 770 mi.—using a 4-megawatt turbine-based range extender to cover the reserve energy requirements—and compares with 3,500 mi. for the A220.

But the energy cost for a 500-mi. trip is $733 for the Jetliner versus $2,100 for the A220. “We’re trying to get to where existing hydrocarbon-based turbines can’t compete on anything less than 1,000-mi. range because these battery-electric aircraft are so economically compelling,” Moore says.

Battery amortization costs are not included in this calculation, as Whisper expects these to change as battery recycling becomes established. “It’s a lot of battery,” Moore acknowledges. “Even at $400 per kilowatt-hour, it’s a $6 million battery.”

The battery will be discharged 70% on a typical U.S. domestic trip and recharged in 45 min., and Whisper is projecting a useful life of 2,000-2,500 cycles. This is expected to increase to 10,000 cycles when solid-state batteries are commercialized, he says.

“Smaller aircraft are not more feasible for battery electric,” Moore says, echoing the “bigger is better” thinking behind Dutch startup Elysian Aircraft’s 90-passenger electric aircraft concept, unveiled in January and larger than an Airbus A320.

“Actually, the bigger you make them, the higher the structural efficiency. And so the lower the empty weight fraction that you’re able to achieve, the more battery mass fraction you’re able to carve out for more range,” he says.

Noting that carriers such as Southwest Airlines have increased their average stage length from 401 to 678 mi. as less profitable routes have been discontinued, Whisper says “the Jetliner concept can meet the range required at typical U.S. domestic distances to reinvigorate regional airports across midsized cities.”

Whisper’s proposal to NASA looks holistically at the Jetliner within the aviation system, and its ability to operate from thousands of smaller U.S. airports and restore passenger and cargo air service to smaller communities.

“If you can design your propulsion system in a way that delivers less noise and thereby opens up all of these airports, but also allows you to operate at night without affecting the communities, now you’re able to service cargo flights at night,” Villa says.

“We’ve been looking into not only how this aircraft can be used for passenger travel, but also how might we use this for larger pallets,” he says. The outboard horizontal tail leaves the rear fuselage free of structure and allows the tail to swing open to load passenger seats or cargo pallets as “cassettes.”

On the ground, the wingtip booms can also be rotated to raise the outboard horizontal tails to the vertical position, reducing the span of the aircraft and allowing it to use smaller airport gate areas.