From a nondescript industrial building in the small town of Crossville, Tennessee, the team of engineers at Whisper Aero is planning a revolution in aviation technology.
Previously home to a publisher of magazines, the long-empty property’s cavernous spaces are now filled with multidisciplinary activities that include the creation of a new electric aircraft engine.
The start-up’s propulsion innovation is an advanced electric ducted fan, or EDF, intended to replace the traditional fossil-fuel-burning engines used on most aircraft. Compared to the most efficient jet engines available today, current EDFs can offer at least a five to 10 percent improvement in propulsive efficiency at speeds of 200 to 400 knots.
Whisper Aero claims that its patented design offers key breakthroughs over current state-of-the-art EDFs, namely a very high blade-count fan operating with blade-passage frequencies that are pushed into the ultrasonic range beyond human hearing.
According to the company’s tests, its EDFs are at least 100 times quieter and 20 percent more efficient overall than those of its competitors. Additionally, its engineers say the novel features of their EDFs allow them to achieve 92 percent aerodynamic efficiency, independent of size.
The company is refining its own vision for a nine-passenger electric aeroplane called the Whisper Jet. Simulations performed on the Summit supercomputer at the Department of Energy’s Oak Ridge National Laboratory are enabling the firm dramatically to accelerate the design of a novel, integrated system of its unique EDFs for the Whisper Jet that is substantially quieter and cleaner than traditional aeroplane engines.
Rather than use a few large turbofan or open-propeller engines that emit noise and carbon dioxide, the Whisper Jet integrates 20 to 30 small, quiet EDFs into the leading edge of its wings.
This arrangement forms a ‘jetfoil’ integration of distributed electric propulsion, or DEP, to propel the plane without generating any emissions.
According to the company’s projections, using electric aeroplanes for all US domestic flights under 1,000 miles would reduce aviation-related annual greenhouse gas emissions by 40 percent – or 80 million tons.
Whisper Aero CEO Mark Moore, a NASA Engineer for 32 years who pioneered DEP aircraft design at NASA Langley Research Center, foresees a future of decarbonised regional airlines that offer shorter, less expensive flights by small DEP aeroplanes – or electric vertical take-off and landing aircraft.
Whisper Aero’s EDF also has possibilities for national defence, such as electric drones that could fly 100 times quieter than current models. And even super-quiet leaf blowers that are already on their way into production.
“The fundamental premise of Whisper Aero is that we are changing the objective function of the aircraft design from minimising gross weight to minimising the acoustic impact. Noise is one of the most complex analysis problems that exist,” said Moore, who co-founded the company with Ian Villa, COO and Chief Product Officer.
“And in the DEP framework, we are bringing together the acoustics along with the wing, the propulsion and the control into a much more complex design.”
In addition to its rows of EDF propulsors, the Whisper Jet’s other defining feature is its outboard horizontal tail. Unlike the tails of traditional aeroplanes that provide downforce, the Whisper Jet’s tail works with its jetfoil wings to provide lift.
“While the idea for the outboard horizontal tail has been around since World War II, only now do we have the tools to really understand and optimise these kinds of unique configurations,” Moore said.
“Instead of being isolated disciplines where a wing provides lift and a jet engine provides the thrust, we’re at a stage where they can all merge. It’s all one thing, and that’s just not how we designed aircraft before.”
Devon Jedamski, Whisper Aero’s Chief Engineer, added: “You can design an incredibly quiet fan, but if you integrate it in a bad way, it’s not going to be quiet.
“When you have interactions with multiple fans and the airframe, creating dynamic and unsteady events, it’s a very, very complex analysis problem that requires extensive computational fluid dynamics simulations, which can be done only on large-scale supercomputers.”
If Whisper Aero were going to make progress on the Whisper Jet’s ambitious design, it needed access to far more computing capability than it had available in-house.
Soaring on Summit
Whisper Aero’s engineering team turned to the Oak Ridge Leadership Computing Facility, a DOE Office of Science user facility located at ORNL, for its robust computing power. Through a competitive proposal process, they were awarded time on Summit, the nation’s fourth-fastest supercomputer at 200 petaflops.
Access to Summit and its GPU, or graphics processing unit, architecture gave the company’s researchers a tenfold speedup in compute times., compared to its in-house CPU-only systems and enabled advanced simulations via a unified approach that wasn’t previously possible.
“Using Summit affords us the possibility of expanding the scope of Whisper’s design and analysis activities that benefit aircraft control and aeropropulsive integration,” said Vineet Ahuja, Whisper Aero’s head of flight sciences and an associate fellow at the American Institute of Aeronautics and Astronautics, or AIAA.
“As a result, aerodynamic design has shown an incredible turnaround time relative to where we were just a few years back in our pre-Summit days. This speedup ultimately benefits vehicle development cycle times, which are reduced by over 20 percent.”
Whisper Aero’s CFD, or computational fluid dynamics, engineers began their Summit research by modelling a drone with an outboard tail architecture that is similar to that of the Whisper Jet and powered by a podded EDF propulsor.
In aircraft design, CFD simulations predict how air will flow around the model of a particular concept – its lift and drag – which provides clues to optimising its aerodynamic performance.
The team primarily used NASA’s open-source FUN3D suite of CFD tools that can model everything from aircraft aerodynamics to propulsion to aeropropulsive integration.
On Summit, the team was able to run complete simulations in an afternoon that typically would have taken a week on commercial high-performance computing, or HPC, systems.
“CFD simulations allow us to understand the pros and cons of various types of integration. But the design space is so large that only with access to a computer like Summit could we tackle the problem,” said Vinod Lakshminarayan, the Whisper Aero CFD Engineer who performed much of the computational work on Summit.
“With so many available GPU nodes, we were able to explore a lot more design parameters compared to what we could have done on another cluster in the same time frame.”
The team’s simulation studies of EDF design, aeropropulsive integration, and airframe design and analysis for their novel drone were accomplished in under three months.
“We have been able to run much larger design-of-experiment studies on Summit than those we were typically constrained to carry out with traditional CPU-based HPC. It’s an increase in not just the number of design variables but also the sample size. For aeropropulsive integration studies, this is critical because we are carrying out propulsor sizing concurrently with wing design,” Ahuja said.
With the data they had collected from Summit by analysing thousands of different design points, Whisper Aero’s mechanical engineers constructed a US Group 2 drone that was a 1/4-scale demonstrator of the Whisper Jet.
Next, they put Summit’s aero predictions to the test by wind-tunnel testing their propulsors at Virginia Tech — with surprising results.
“Summit’s pretest predictions weren’t just close – they were dead on, showing that the simulations are just as good as the real-world data builds a lot of confidence in our design capabilities. If we can’t do that, then it slows down our whole development cycle because we would have to validate every single design choice,” Ahuja said.
Confident that Summit’s simulations were accurately representing what they saw in their physical testing, Whisper Aero’s engineers have advanced their design iterations much more quickly with this predictive tool.
“What I’m really excited about is the speed of execution that Whisper has been able to achieve, thanks to Summit. We’re already taking this technology and designing for commercial aircraft. Being able to move this technology more rapidly to the general public is really an exciting value proposition,” Moore said.
The engineering team scaled up Summit’s CFD results to optimise the size, spacing and orientation of ducted-fan propulsors for a full-size, nine-seat Whisper Jet concept designed to fly 200 knots at 10,000 feet. An early cabin prototype of that plane was unveiled at the 2023 AIAA AVIATION Forum in San Diego, California.
Other applications
Moore has also been in discussions with manufacturers of warehouse drone monitors, makers of bathroom and stovetop exhaust fans and companies that produce computer data centre cooling fans.
He sees applications for Whisper Aero’s EDF propulsor everywhere: airports that need foreign objects or dirt quickly removed from their runways, raceways that need their tracks dried of rainfall, street cleaners that could operate quietly in neighbourhoods and those (currently) propeller-driven airboats that cruise Florida’s waterways.
“It’s going to take five to 10 years for this propulsion technology to get into certified products. But we’re anxious to have it deployed in many industrial and commercial applications outside of aerospace,” Moore said.
Next for Whisper Aero are more CFD studies on a new SummitPLUS project. Ahuja and Lakshminarayan will investigate vertical take-off and landing and short take-off and landing vehicle designs that leverage Whisper’s propulsors.
“This entire field of electric aviation is undefined, uncharted territory. So, innovating at a rapid pace is extremely important.
Summit enables us to model significant changes between propulsor size, efficiency and noise, by harnessing the acceleration of those GPU codes. This capability enables us to iterate designs very, very quickly,” Ahuja said.
By comparison, changing designs via actual fabrication and physical testing could take years.
“It’s also the innovation benefits that help us maintain our technology leadership. I think it’s important to point out that we are doing more with less,” Ahuja added.
With Summit’s ability to solve complex analysis problems quickly, Whisper Aero is now better positioned to bring its ideas to reality sooner.
But what most excites Moore is the technology’s potential to change the way we fly.
“It’s just such an exciting age for aviation,” Moore said. “Access to Summit is allowing us to reinvent how [aero]planes are designed and what they are capable of doing – it’s almost like a Wright brothers age again.”