Matt Thurber, editor-in-chief at AIN Media Group, has been flying since 1975 and writing about aviation since 1978 and now has the best job in the world, running editorial operations for Aviation International News, Business Jet Traveler, and FutureFlight.aero. In addition to working as an A&amp;P mechanic on everything from Piper Cubs to turboprops, Matt taught flying at his father’s flight school in Plymouth, Mass., in the early 1980s, flew for an aircraft owner/pilot, and for two summer seasons hunted swordfish near the George’s Banks off the East Coast from a Piper Super Cub. An ATP certificated fixed-wing pilot and CFII and commercial helicopter pilot, Matt is type-rated in the Citation 500 and Gulfstream V/550. Based in the Pacific Northwest, Matt and his team cover the entire aviation scene including business aircraft, helicopters, avionics, safety, manufacturing, charter, fractionals, technology, air transport, advanced air mobility, defense, and other subjects of interest to AIN, BJT, and FutureFlight readers.

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While Ampaire’s public-facing activities revolve around its electric EEL engineering test bed aircraft, what the Hawthorne, California&nbsp;company is focusing on now is a supplemental type certificate (STC) for a hybrid-electric conversion of the Cessna Caravan single-engine turboprop utility airplane.
In July, Ampaire owner Surf Air Mobility announced that it had&nbsp;ordered&nbsp;100 Grand Caravan EXs with options for 50 more and that deliveries are set to begin in the second quarter of 2022. Plans call for Ampaire to convert the Caravans to hybrid-electric power&nbsp;once the STC is obtained;&nbsp;then Surf Air Mobility will place them with operating partners that participate in the Surf Air Mobility charter platform. Prior to obtaining the STC, the Caravans will be flown in their normal Pratt &amp; Whitney PT6 turboprop configuration.
Meanwhile, Ampaire continues its work on the electric EEL, a Cessna Skymaster inline twin-piston-engine airplane with the front engine replaced by an electric propulsion system. The electric powerplant runs on batteries, but this configuration isn’t the same as an electric motor powered by batteries charged by a combustion engine.
In any case, Kevin Noertker, Ampaire co-founder and CEO, told FutureFlight&nbsp;in a recent interview that&nbsp;this is still a “hybrid-electric” powertrain. “There are quite a few types of hybrid architectures,” he explained, “so the electric EEL is a hybrid aircraft. At a certain point when you're slicing a hybrid system up, it's a combustion element that provides power, an electric element that provides power, and depending on whether they're mechanically or electrically connected to the same shaft, this is where the architecture is changed.
"But the principles behind it [are similar]," he continued.&nbsp;"The algorithms to control the system safely or to do the battery energy management or the pilot interfaces and displays…all the systems engineering and requirements flow down to ensure the ultimate safe operation of that plane.”
The electric EEL technology helps with the development of the hybrid-electric Caravan, he added. “These are things which do translate from one vehicle to the other and then obviously the experience on the team translates directly, so these are things that help with development of the Caravan STC.”
The Ampaire team is also working on a NASA contract, he said, “where we're studying the 19-passenger twin Otter as a potential commercial product.” This is under NASA’s Electric Powertrain Flight Demonstration project.
The EEL has demonstrated flight operations in California and Hawaii and recently arrived in the UK to participate in the Future Flight Challenge. While the EEL did generate some interest as a commercial product, Noertker said, “we’re focusing our energy [on the Caravan] as a launch product.”
<h3 class="subheading">EEL Flight Ops</h3>
He revealed additional details of the EEL flights, which included tests of single-engine operations, running with one engine or motor producing power while the other was set to idle power. “While I was flying over California last fall, before shipping the airplane to Hawaii, we shut off the combustion engine and flew fully electric for a few minutes," Noertker said,&nbsp;"so it's capable of doing that and still having safe control. The EEL that we've been flying began as an engineering testbed. And it's very much a vehicle for us to continue learning rapidly on, so our flight test program did include single-engine flight in cruise.”
During takeoff and climb, the EEL runs both powerplants at full power; then at cruise and descent, less power is needed. “Depending on the route that we’re flying, we have an optimized power balance between the two systems over the endurance of that flight,” Noertker explained. “You would optimize based on how far you need to fly and what state of charge you target the battery having at the end of the flight. That sets the amount of power you would draw from the electric system over the duration. Then you take the balance of the power needed for cruise and you provide that with the combustion system.” The EEL’s batteries are housed in a cargo pod mounted on the belly of the airplane.
In addition to the flight demonstrations, Ampaire is participating in a U.S. Energy Department Advanced Research Projects Agency-Energy (ARPA-E) project, Noertker said, “to use a derivative of the electric EEL platform as a flying testbed for advanced technologies, which may one day make it into commercial electric aviation. That’s the next step for us in that electric EEL platform.”
So far, he added, “The EEL has exemplified and proven many of the benefits we had anticipated with hybrid-electric systems. First was the fuel-burn reduction. In that configuration of hybrid, we measured a reduction of over 31 percent compared with the baseline aircraft. [This is] a meaningful demonstration of fuel reduction, which is one of the main value propositions of going hybrid-electric.”
<h3 class="subheading">Gaining an STC</h3>
Ampaire has hired experts in FAA certification processes and is preparing to submit an application for the Caravan STC, according to Noertker. “Across our team—internal and external support—we’ve got over 100 STCs [obtained previously] under our belts," he said.&nbsp;"Bringing Textron Aviation into the fold, they have significant expertise in certification, and specifically on the Cessna Grand Caravan.” Plans call for certifying the hybrid-electric Caravan in 2024.
The reason for choosing a traditional airframe like the Caravan is so that Ampaire can avoid the enormous cost of certification and production of an entire airplane. “It comes down to the fact that the&nbsp;timeline for getting a new-designed aircraft to market is relatively long,” Noertker said. “Historically it’s been 10 to 15 years for a new aircraft of these types to come to market. I don’t think strategically it would be the right decision for us to wait 15 years to bring a plane to market.
"We’ve all seen the story of Eclipse [the many-times bankrupted very light jet manufacturer] and others who have been visionary and successful in certain ways in bringing planes to market," he continued.&nbsp;"It is a big undertaking to do a new aircraft type. We’ve decided to go for a more reliable way to ensure that we get through the process of certification, and that’s by doing a supplemental type certificate.
"If we were using a traditional combustion engine, let’s say we’re putting a different type of [Pratt &amp; Whitney] PT6 into the Caravan, it looks like maybe a 12-month program for that certification. Because the technology is relatively novel—hybrid-electric—that’s why we’re saying 2024. But that one-year re-engineering is an order of magnitude less time than it would have taken for a new airplane. That’s really what the strategic direction and decision were for us to not invest in a new aircraft type for our first product.”
Noertker sees a strong market for hybrid-electric Caravan conversions beyond the 150 airplanes that Surf Air Mobility has ordered, with more than 2,500 Caravans in the field and many other Part 23 airplanes that might benefit from a hybrid-electric propulsion system. “Our strategy is to work with OEMs of those vehicles…to breathe new life into these airframes that have been around in their combustion capacity for quite some time,” he said.
<h3 class="subheading">Caravan Technology</h3>
As to the technology that will be employed to turn the Caravan into a hybrid-electric airplane, Noertker revealed some details, but others are still being held close to the vest. “The analogy I like to use is the system architecture looks and feels kind of like a Prius [hybrid-electric car]," he said.&nbsp;"It doesn’t need to be charged or plugged in at each destination. That’s important because…it mitigated two major issues with early electric cars. Number one was range anxiety. You couldn't go very far just on battery. Number two was a lack of charging infrastructure. Where would you plug in when you got to your destination?”
The hybrid-electric Caravan is intended to operate much like the current jet-A-powered version, with a range similar to that of&nbsp;the original (but for a repositioning flight without passengers in the hybrid-electric version) and no need for any new infrastructure, allowing it to operate efficiently serving customers at many smaller airports.
Eventually, the hybrid-electric Caravan will transition to a plug-in version, where charging the batteries on the ground would extend the range and require less fuel to run the combustion engine. “If you’re more electric, you use less hydrocarbon,” he said, “which is better for the environment and decreases your operating costs further. The way we're architecting it also does enable—if battery technology improves significantly, and there are some really smart people working on that—turning&nbsp;these into all-electric [aircraft], if and when that makes sense.”
For now, however, battery technology is sufficient for the Caravan STC program. “We're using existing technology, so we're not looking for magic,” he said. “This isn't science, it's engineering. A 200-watt-hour-per-kilogram pack is reasonable for a hybrid-electric system. We’ll integrate higher-density batteries over time. We don’t see any major roadblocks regarding the core energy density of the batteries themselves.”
That said, managing weight will be important, as is always the case in aircraft design. “There are some technical challenges and areas where you need innovation in managing the weight of the system,” Noertker said. “It's the thoughtful integration of thermal systems and structural systems to ensure that you have a safe, reliable, and high-performing system while minimizing the weight because anywhere we can minimize weight, you can maximize payload." He added that after the PT6 engine is removed, the existing mounting structure will be used for the hybrid-electric support system and thermal and power management systems.
No details are available yet on the makeup of the combustion engine that will drive a generator to charge the hybrid-electric Caravan’s batteries.
<h3 class="subheading">What the Pilot Sees</h3>
The flight controls and displays are another important aspect of the hybrid-electric Caravan’s design. “We’re trying to maintain the pilot interface to reduce the change that the pilot experiences,” Noertker said, “and make it a flying experience similar to what the pilot is used to. There will be new information the pilot needs to understand, new displays on the state of charge of the batteries, power level, the thermal condition of the batteries, motors, or generator.”
Design of the new pilot information display will be in concert with Textron Aviation, plus, Noertker said, “We have other partners we’ll be working with on these other subsystems.”
One aspect of advanced air mobility technology that Ampaire will not incorporate at this point is autonomous operation—flying without a pilot. Other companies, such as Xwing and Reliable Robotics, are developing autonomous Caravans, but Noertker doesn’t want to duplicate their efforts and spend valuable certification effort on autonomy. “Our core value proposition that we’re beginning with is electrification,” he explained. But at some point, it may make sense to adopt autonomous&nbsp;technology for simplified pilot operation or reduced pilot count. With a background working on robotics for NASA’s Jet Propulsion Laboratory, he added, “When it comes to autonomous systems and navigation, this is a passion of mine. So we've been very thoughtful about whether or not to include it in launch products.”
<h3 class="subheading">Funding the Program</h3>
Flight marketplace Surf Air Mobility, which earlier this year announced plans to acquire Ampaire,&nbsp;is raising funds to see the Caravan STC project to completion. “We have the core team in place and are actively hiring,” Noertker said. “Anybody who reads this, go to our career site;&nbsp;there are plenty of opportunities.”
Looking to the future, Noertker strongly believes that this technology will pay off. “I absolutely love this big vision that we have within Surf Air Mobility for the broader market. This is what we're up to, to prove that all of those key factors are required to come together to fully scale this industry," he said.&nbsp;"This is what we're doing at Surf Air Mobility.&nbsp;It's about the lower cost to operate planes, the efficient airline operations, the passenger aggregation. All of these are needed simultaneously to really scale out the industry.
“That's what we're bringing together. And each of these steps along the way—for example, the Textron announcement—[show that] we have hopefully increased the world's confidence in us that we're going to get this done. And we believe that we can be better together, that bringing together the ecosystem is the way to achieve the big vision.”
But there have been plenty of examples of air taxi operations using small aircraft and helicopters that have grown and failed over the years. Will hybrid-electric aircraft make this business model work?
“The short answer is yes,” Noertker said. “The longer answer is, the market finds its balance of supply and demand based on the price point of operations. And that's either the profitability of the airline or the ticket price for the passenger. We all have our thresholds. Maybe you're not willing to pay more than $250 round trip and you decide to drive instead. But as you bring those costs of operation down, you're able to make the airlines more profitable on routes that weren't previously profitable. You may even be able to enable them to open up routes that they used to fly, but had to cut because of the lack of profitability.”
There are about 5,000 underutilized smaller airports in the U.S. with point-to-point pairs where, Noertker said, “there is demand. We can see people are moving between those locations but it wouldn't make sense to fill a 737 or an ATR, but you can justify a daily route, maybe even five&nbsp;times a day, between these communities because of the beneficial economics of switching over to a hybrid-electric and eventually fully electric [aircraft]. That's what we see as the kickstart to the flywheel that I was describing for the market growth.”

Matt Thurber

Ampaire's electric EEL technology demonstrator is being used to refine a hybrid-electric powertrain that will be used to convert existing aircraft like the Cessna Caravan. (Photo: Ampaire)

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