Ampaire Flies Second Hybrid-Electric Prototype


California-based electric aviation company Ampaire flew its second hybrid-electric technology demonstrator for the first time last week. Ampaire’s “Electric EEL” is a converted Cessna 337 Skymaster powered by tail-mounted 310-horsepower Continental IO-550 and a 200kW—limited to 120 kW—electric motor in the nose. In partnership with Mokulele Airlines and climate change solutions company Elemental Excelerator, Ampaire plans to use the prototype to conduct a series of flight trials in Hawaii later this year.

“Since flying our first Electric EEL last year, we have made substantial improvements to the power train for efficiency, increased performance, reliability and safety,” said Ampaire CEO Kevin Noertker. “This technology is scalable with wide applications for scheduled passenger and cargo services, as well as charter services. Our flights with Mokulele will be an opportunity to test both the aircraft and the infrastructure required to advance electric aviation and transport access in Hawaii.”

According to the company, changes made on the second prototype include moving the battery pack from inside the cabin to the underside of the fuselage, using a lighter, more efficient electric power unit (EPU) and improving cockpit instrumentation and power controls. The demonstrator is designed to cruise at 120 knots with an endurance of 1 hour and 15 minutes plus a 30-minute reserve. As previously reported by AVweb, Ampaire’s first hybrid-electric Skymaster demonstrator completed its initial flight in June 2019.

Video: Ampaire

Kate O'Connor
Kate O’Connor works as AVweb's Editor-in-Chief. She is a private pilot, certificated aircraft dispatcher, and graduate of Embry-Riddle Aeronautical University.

Other AVwebflash Articles


  1. Good point Yars.

    It’s like they are thinking:

    ‘Here we have a perfectly functioning, safe, reliable, fairly high performance, relatively inexpensive, useful and practical centerline thrust twin.’

    ‘How can we ruin all that to solve a problem that does not need to be solved?’

    Fuel remains cheap and plentiful. Even the youngest people reading this will have plenty to use for the rest of their lives, unless governments continue to interfere with the free market economy.

    • 1996: GM EV1 range is 78 miles. A ridiculous development and waste of technology. There is no problem, fuel is plentiful and the air is still good to breathe.

      Still using plastic shopping bags, WK?

    • Here we have a reasonably functioning, low performance, expensive to maintain, found impractical by the market place, centerline thrust twin that has killed people because they did not notice the antique motor in the back was not running…

      Fixed it for you.

      I love the 337 but I realize it’s because I’ve got a disease most of us on this page share. I thank God for people willing to spend their time and money trying to bring us new and better planes, and so should we all.

    • If only William K had been around in 1903 at Kitty Hawk: “120 feet of range? 12 seconds of endurance? 7 MPH top speed? Pathetic! I can run faster! Horse feed remains cheap and plentiful!”

  2. I’ve done the math and yes, it’s substantially cheaper than burning fuel, for short-range flights. As to whether the problem needs to be solved… it does if you want to get the benefit of lower costs.

  3. I’d like to see a comparison of the efficiencies of a propeller vs ducted fan. after all, large aircraft are ALL powered by some form of ducted fan aren’t they?

  4. Why such the negativity about all or partial electric propulsion. First, minus the prop noise, they should be a bit quieter than combustion. Note carefully that I said “a bit” there. Second: they should be a bit cheaper to operate if you don’t have to buy as much or even any avgas at the ridiculous prices currently charged. Third: if used within the designed parameters of weight / range / recharge time, they should be very efficient machines. Fourth: when that machine does a touch and go at Tchepone I will be a believer. Coveys and Ravens will understand that part.

    • People fret when newer technologies emerge. It doesn’t matter much. They end up being there. People fretted when the steam engine displaced horse and then the internal combustion did the same, even though steam had a much superior energy density. We sent people to the moon with a pocket calculator navigating the spaceship. Electric mobility is pretty straightforward even if still in its infancy. Expecting it to come out running before it crawls is funny.

      Burning batteries? Funny when 500,000 gasoline cars go up in smoke every year in the US and about 135,000 gasoline stations do the same without a peep from the media. First battery fire I heard of was a Model S picking up a rod on a highway in its pack. It was strengthened and never happened again. Last battery pack to go up in smoke I heard was due to a faulty charger installation. Batteries are not the weak point, there are others. Boeing using the wrong lithium chemistry on its 787… any EV savvy person would have told them. But that’s Boeing…

      Electric mobility has evolved quickly compared to gasoline technology. A 23L engine put out about 15HP a hundred years ago. Electric motors are highly efficient, about 98%. Battery density is shrinking very fast, currently hitting the 500 Wh per Kilo and 600 is supposed to be out next year making it halfway to kerosene.

      I enjoy diversity. I enjoy engineers stretching the confines of our technology. I enjoy people thinking outside the box. And I enjoy my old Alfa Romeos in my garage next to my electric bikes. I love a good IPA and a lager, red and white wine, French and Dutch cheese. It’s still beer, wine, and cheese. The rest are background reactions to unresolved issues 🙂

      No CEO wakes up in the morning wondering how anyone feels about a technology. They just push through the choral.

      • Very well said Nicolas, it’s good to see that there are a couple of reasonable people reading AvWeb that understand the lifecycle of emerging technology. Electric propulsion is the future and it’s here to stay. In one form or another, all of these R&D projects will lead to more advances that will eventually push the technology beyond an inflection point where it will start to displace conventional technology.

        Every comment I read from the loud voices who like to denounce these projects (because apparently they are way smarter than the engineers who are actually producing these prototypes) makes me sad because it runs counter to the spirit of progress that built this country during the industrial revolution. When I see so many skeptics I begin to fear that our best days are behind us because it indicates lack of a will to push the envelope. Fortunately they are just a loud minority. Electric aviation R&D is still moving forward and the direction is up, even if the slope tends to flatten for short periods of time.

        Any operator see the promise of electric aviation. It’s not just the fuel costs, it’s the total operating and maintenance costs that are attractive. Fewer moving parts and simpler subsystems improve reliability and safety while also lowering maintenance costs. Then there is the benefit of comfort from a more quiet and vibration free operation. And of course, let’s not forget full power at any density altitude! Imagine taking off from a 3000′ strip in Durango, CO with a DA of 8,000′ at max gross (yes, i know DA impacts more than just engine operation like prop efficiency and lift, but still…)

        Battery technology is improving rapidly and in the next 5 years we will see Li-S batteries start to displace Li-Ion batteries. Li-S has a theoretical energy density of 7x that of Li-Ion and they are cheaper and safer. When that happens all of these current R&D projects will see their range increase at least 3 fold! And those companies that are working on electric aviation now will be far ahead of anyone who is waiting for battery technology to hit a critical point before considering jumping into the ring.

        • “Expecting it to come out running before it crawls is funny.”

          That’s not what critics like myself are asserting.

          My simple point is this: assurances about future developments do NOT comprise a justification – or a rationalization – for purchasing an example of TODAY’S technology.

  5. It’s not that I hate electric planes, or that I think my 1930’s era O-360 is such a fantastic instrument of engineering.

    To be honest some of my comments are from me generalizing my distaste for EV owners and advocates, Tesla owners on particular. I detest their holier than though ‘I’m saving the planet’ attitude and their disdain for the things that I enjoy. Like my motorcycle, twin turbo V8 Benz, and of course my lead spewing Maule.

    I am opposed to their desire to crush our values and economy in the pursuit for global warming, which concerns me not at all.

    I agree that the problem of EVs taking over is inevitable. It’s what governments are forcing us into. I also agree that there are advantages which are significant, BUT the problem of very poor energy density, expense, and weight MUST be overcome before battery powered EVs are practical or desirable for people like myself who are motor-sport enthusiasts.

    An electric toaster is a good idea. I prefer my vehicles to be more interesting however.

    Mostly I detest the attitude and politics of the EV intelligentsia.

    • That’s a seriously absurd assessment of “EV owners and advocates”, saying that they want to “crush our values and economy”. I have to shake my head every time I hear nonsense like that. I drive a Prius and I have solar panels on my roof, and when I made those investments, not once was I motivated about “crushing any ones values”. Yes, I love the fact that I am lowering my carbon foot print because anthropogenic climate change is a very real threat (as 97% of climate scientists agree, so unless you somehow know more about climate than than the overwhelming majority of the scientific community, your comments about climate change mean nothing), but I am far more motivated about the money I am saving. I like saving money on electricity and gas so I can spend more money on things that matter, like beer and chicken wings, so I assure you that I am not out to “crush the economy”.

      40 years ago the anti-climate science crowd complained that addressing pollution and climate change meant sacrificing convenience and quality of life while also impacting the economy. Today we see technologies that address climate change are actually boosting the economy and improving quality of life. I know two Tesla owners and while they love how much money they save on fuel and maintenance, they spend a hell of a lot more time talking about how “ludicrous mode” enables them to blow away the Corvette be driven by the guy with mid life crisis on the Southern State Parkway. You say you are a motor sports enthusiast, well, as electric vehicles improve, they not only outperform ICE vehicles in economy, they also blow them away in performance.

      “Politics of the EV Intelligentsia!??” Puh-leeeeese!!!! The only one who makes any of these issues political are the ones who are against them.

      • Daniel,
        Puh-leeese you. You sound like an intelligent guy, but lots of intelligent people have a hard time with checking their priors and bias confirmation. Their is no place more political than the places where they choose who can be a climate scientist. In the span of my lifetime, the Academy has gone from research to inform policy makers to doctoring results to influence policy outcomes.

        In most departments, science just doesn’t mean the same thing anymore. Which is ironic because it’s one of the few words which academics haven’t purposely tried to change the meaning of to tip the scales of political fights.

        At this point, I believe there is more carbon in the atmosphere. I don’t believe that’s a lie or a mistake. After that, it seems to me that nothing more can be trusted from the Academy on the subject until they have shown some serious introspection and shown they are taking action to return to the fundamental ethics of scientists. You may disagree, but if you think my position is outside the norm, or not supportable, I’m afraid it’s you that has issues.

        Lastly, I apologize for any errors, but this site is not working well with my iPad and does not allow edits.

      • “…anthropogenic climate change is a very real threat (as 97% of climate scientists agree, so unless you somehow know more about climate than than the overwhelming majority of the scientific community, your comments about climate change mean nothing)…”

        97% of scientists once asserted that the Earth is flat. 97% of scientists once asserted that the Earth is the center of the Universe. In 1975, scientists warned us about “the coming ice age.”

        Consensus is not evidence.