A startup enterprise based in the Seattle area has drawn funding from Boeing and JetBlue Airways to study and develop hybrid-electric regional airplanes that would fly between 10 and 50 passengers as far as 700 miles. Zunum Aero plans to have the airplane ready for service some time early next decade, not a bit too soon for a segment of the airline industry already in the midst of contraction due to escalating costs and regulatory impediments.

Zunum thinks the airplanes can help rejuvenate a network of 5,000 underused regional and general aviation airports in the U.S., while offering what it calls a fast, flexible and affordable alternative to highways and high-speed rail. The Kirkland, Washington-based company characterizes its plan as an effort to “democratize” air travel by lowering operating costs to the point that would allow for 40- to 80-percent lower airfares. Meanwhile, door-to-door travel times would shrink by 40 percent on busy corridors and by as much as 80 percent on less trafficked ones.

“The shift of the industry to large aircraft and long ranges driven by gas turbines has concentrated almost all air traffic to just two percent of our airports, creating a massive transport gap over regional distances where there is no high-speed alternative,” said Zunum Aero CEO and founder Ashish Kumar. “As a result, door-to-door times for most journeys are no better than they were 50 years ago. Hybrid propulsion is an industry-changing solution, enabling midsize aircraft on regional routes to have better cost efficiencies than airliners.”

Although popular perception would suggest that the battery development represents the biggest technological hurdle to overcome, Kumar disagreed. “The [battery] densities that you can get today, which are just about 300 watt hours per kilogram, can actually give you a very viable [proposition]; our early 2020’s aircraft could be in the skies giving you very good economics at that density,” he told AIN. “We talk about a disruptive range being 700 miles for a hybrid and the actual range is longer by the early 2020s, but the economic range might be 500 miles now or just shy of that, which is still a very interesting market for operators.”

Rather than battery capability, said Kumar, the project’s biggest technology challenges reside with the integrated powertrain converters and drives. “From our perspective the long pole is really around how hard are you going to push the power densities on the drives, and similarly on the converters you have on board,” he said. “I think if you had an all-electric aircraft or if you were doing vertical takeoff, I think you’d have challenges on the battery. But if you’re doing a hybrid, no.”

Zunum’s designs focus on what Kumar called "strong hybrids," in which the degree of hybridization totals more than 20 percent, meaning that for a given mission range more than 20 percent of the energy comes from the batteries. In fact, he said one could build a hybrid that could fly much farther than the 700 to 1,000 miles Zunum quotes, but to do so in a way that makes economic sense for operators. “From a commercial transport standpoint, it is economics that are keeping the small airplanes from flying; we need to break that first,” said Kumar.  

From an environmental perspective, the hybrid-electric vehicles would initially cut community noise by 75 percent and emissions by 80 percent. Eventually, as battery densities improve, the company believes it could produce airplanes that generate no greenhouse gas emissions. 

Of course, that doesn’t mean operating an all-electric airplane would not require energy from a powerplant, which produces its own greenhouse gasses. So to arrive at a measurement of the ultimate environmental benefit, one needs to perform a “well-to-wake” analysis. Zunum estimates its first hybrid vehicle will deliver a 40- to 70-percent reduction in well-to-wake greenhouse gas emissions on missions up to 1,000 miles compared with a similarly sized conventional aircraft operating in 2025.

Now three years into development, Zunum Aero has attracted a multidisciplinary team of experts in aircraft engines and electric vehicle disciplines, including leaders of two flying electric vehicle programs and the leader of a NASA-funded program on drives for electric airliners.

Although Zunum’s longer-term plans call for a vehicle that could carry as many as 50 passengers, Kumar explained that initial efforts center on first introducing an FAA Part 23 certified airplane, so one that would seat between 10 and 19 seats. The company does not plan to build its own assembly line, but will rely on partners for production capacity. “We do have a plan of record for that first aircraft...and that’s the basis on which we’ve gone out a raised investment,” he said. “We never intended to build the whole thing ourselves...What we will say is our focus all along has been to be a U.S. manufacturer and that’s one of the reasons we ran for so long under stealth, because we limited intentionally the set of investors that we approached.”  

As for the physical structure of the airframe, Zunum hasn’t yet fully arrived at a firm decision, said Kumar. However, he noted that consultations with several current turboprop operators and potential customers have led the company to plan for a composite fuselage and metallic wings. “The folks that fly this type of aircraft these days are not flying in pristine conditions,” noted Kumar. “One of the first things they told us was, ‘For God’s sake, don’t make them all composite. We need something that can be easily repaired and dealt with.’”

Speeds, meanwhile, will match or exceed those of a typical turboprop. Over time, said Kumar, both range and speeds can increase over the typical 20-year operating life of the airplane because batteries will progressively improve as an operator replaces them regularly.

“Say you buy an aircraft in 2020 and you are running a really frequent service, flipping your batteries maybe twice a year, your range is going to go up and also your speeds could go up because then you can run the higher speed for the longer range.”

Along with backing by Boeing through its Boeing HorizonX “innovation cell” and JetBlue Technology Ventures, Zunum has formed a long-term partnership with the Center of Power Optimization of Electro-Thermal Systems, an NSF Engineering Research Center at the University of Illinois. Separately, the team has engaged with the U.S. Federal Aviation Administration since 2014 on certification standards for electric aircraft. The company said it expects the FAA to develop the first set of standards for electric aircraft next year.