What Are Hybrid Electric Airplanes Good For?

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When I drive around town, I never fail to see some kind of hybrid car, say a Toyota Prius or maybe a Ford Fusion and the occasional Nissan Leaf. This tells me that hybrids and electric vehicles are now dominating the automotive market and airplanes are soon to follow. And here, let me welcome you to Paulie’s Moment of Magical Thinking. The reality is electric vehicles—both hybrids and pure electrics—command less than 2 percent of total market share in the U.S., although it’s greater in other countries. Even in the U.S., electric vehicle sales are on the upswing. Still, tap the brakes here and pitch the nose up for application to airplanes.

Some perspective is needed, especially following the announcement this week that three companies, Tecnam, BRP Rotax and the giant German electrical concern, Siemens, are developing a hybrid drive for aircraft. But read carefully between the lines and you sense what they said—“the project will allow broadening the horizons of knowledge in the field of parallel hybrid propulsion systems”—is describing not a market entry, but a technology demonstrator. I think these companies are smart enough to know that market potential for an aircraft piston hybrid drive is thin at best, non-existent at worst.

Consider the technical points. In a car, a hybrid drive like the Toyota Prius has marginally better economy than the equivalent best-case internal combustion model, but its life cycle costs may actually be more than the equivalent ICE, depending on what you pay for gas and how you drive. If CO2 emissions are a thing for you, hybrids are marginally greener.

What about airplanes? The only hybrid close to fruition is the Euro-sponsored HYPSTAIR, a video of which you can see here. This is a serial hybrid design that has a Rotax 912 or 914 engine powering a generator to charge batteries carried in the wings. The prime power is a 200-kw (270-HP) brushless DC electric motor. The typical operating cycle is to take off on batteries, cruise with ICE while charging the batteries, then complete the trip with theoretically charged batteries. It hasn’t flown yet, so it’s yet to be proven if the claims will pan out There’s also a weight penalty. The hybrid drive system is comparable in weight to a diesel power plant of similar output so useful load will take a hit. Range might or might not be better.

There are some of realistic plusses. One is that the battery-driven motor is unaffected by density altitude, so the full 270 HP is available anywhere, even if max prop efficiency is not. Second, reliability. Although the electric motor is a low probability single-point failure, the ICE is at least there to keep the batteries alive. I would call this a sort of redundancy. Overall efficiency is simply an unknown. While it uses a smaller engine to charge the batteries, there's a conversion penalty over simply throttling back a larger gasoline engine for similar performance sans the hybrid drive. Don’t forget noise. That‘s huge in Europe, a little less so in the U.S.

The Tecnam/Rotax/Siemens project is a parallel hybrid, not HYPSTAIR’s series design. They haven’t revealed details, but this means it uses an electric motor as a kind of helper or torque booster for the gasoline engine. FlightDesign fooled with this idea a few years ago by adding a parallel motor to a Rotax engine. It was sort of a giant starter motor on top of the engine and could be engaged for takeoff—relying on battery power—and in standby mode for emergency power. Of course, to be an effective standby, the electric motor has to have a mechanical path to the prop that won’t be tanked if the crank breaks. Again, there’s a weight penalty here in motor and batteries against the benefit of added takeoff performance.

That’s the market entry challenge. Try this thought test: Does a hybrid drive solve a significant shortcoming of gasoline engines, such as poor takeoff performance, low efficiency and lack of reliability? And if the hybrid does these things, will it attract buyers in sufficient volume to make the juice worth the squeezing? For now, I doubt it. I’m not even seeing a future where it makes much market sense at all except one: where a hybrid is used as a range extender in an electric aircraft that uses distributed power to leverage the advantages of electric motors, say the Volocopter, for example.

Pure electrics are different. Entirely. As Pipistrel is showing, there may be just enough early adopter interest to make airplane BEVs practical. As battery capacity inches upward, the curve will eventually advance to the point that schools can look at the numbers and make a business case for a mix of electrics and gasoline airplanes. Some are almost there now, but we don‘t have enough operational data to verify cost and performance claims for electrics. In the U.S., there are approval details to sort out, but this is just bureaucratic noise. It’ll eventually get done and electrics will carve a share.

At AVweb, we do a lot of coverage in the electric, alternative power and autonomous flight fields. Casual readers may assume that such technologies are gaining increasing momentum and practical market entries are just around the corner. “Much sooner than you think,” as I’ve been told by more than one electric airplane enthusiast. Depends I guess I what they think I’m thinking, which is usually a decade or two.

Still, Tecnam et. al. are pushing this technology hard because they have no choice. If they don’t, someone else will and even in the stodgy backwater of piston general aviation, things don’t stand perfectly still. Only the companies pursuing blue sky initiatives that may go nowhere in the short term will be competitive in that decade or two I’m thinking about. We should all be happy to see such things.

Comments (20)

"This tells me that hybrids and electric vehicles are now dominating the automotive market'

Actually, the best I could find shows that hybrid sales were down 8.8% from the previous year and hybrid market share was 2.75% of new car sales. That's not "dominating" so much as becoming obsolete. Newer technology is making them the equivalent of the compact fluorescent bulb.

Personally I sold my hybrid Camry this year and bought a much nicer car with more cargo space, less weight, less complexity and the SAME mileage as the older hybrid. I'm not alone in this trend.

As far as pure electric like the Leaf, they are on life support because of subsidies. Take away the tax credits and the sales lots will fill up and production will halt in short order..

Posted by: Mark Fraser | June 5, 2018 8:48 PM    Report this comment

On my office computer, I have a link from a an auto trade group that purports to offer accurate market share for hybrids and electrics, I recall the total being under 2 percent. But I'm in Europe and can't access the same link through the Euro version of Google. It showed a decline in hybrid sales, but I don't have the precise number,

What I could access suggests world market share of electrics is on the rise, mainly because of China and demand from Europe.

Posted by: Paul Bertorelli | June 6, 2018 12:14 AM    Report this comment

Norway and Germany are currently Europe's top dogs in terms of new electric and hybrid vehicles. The market is currently producing triple digit growth trajectories, which isn't all that difficult in a developing market.

However, we're severely lacking in infrastructure and prices when it comes to providing real solutions. No wonder in a country that is occupied by a chancellor who thinks the moon is the limit. 8.000 miles of Autobahn alone in a hopelessly overpopulated country that sports 86 million people and 64 million cars.

The government is currently pushing hard to get electrics on the road, firstly by artificially raising Diesel prices to now near $6.50/Gallon and second by punishing Diesel owners through taxes and looming prohibitions in most larger cities.

Manufacturers are trying to stabilize pricing by offering buy-back guarantees to compensate for peoples fear of when Diesels get outlawed where you live. Further, the purchase of electrics and hybrids is supported by up to 4.000 Euros in credits as well as a 10 year tax free status if purchased and registered before 2020.

Two things stare the effort down. For one, our infrastructure for charging station lacks severely, and second, people are struggling with paying a truckload of money for a vehicle that doesn't do all that much in terms of overall impact on the environment. We are trying to tax and fee the Diesel engine off of our streets at all cost and no common sense, logic, rime or reason may be found in the action.

For example, I own and drive a 2002 BMW 530D (200 HP straight 6 Diesel) that allows me to cruise at 35MPG (Diesel Price 1.39 Euros per Liter this morning, that's $6.75/Gallon) but that old clunker also allows me to cross our construction plagued country from north to south (500 miles) on 3/4's of a tank. The last trip took nearly 12 hours! Paying a premium for the luxury of leaving black smoke puffs is worth it to me, I would not replace this vehicle with a 1.3 liter screamer if you paid me money to do it.

This afternoon I am sitting right seat in a Morane from my local airport to Flensburg in Germany. The round-trip will be just two hours. However, completing the same trip by car would take nearly 10 hours of driving for a 1 hour visit to an attorney. I'd see and stop in no less than 21 construction sites along the way.

We are far from seeing reasonable range and pricing to have electrics revolutionize the way we fly or drive in Europe. I see much more potential in the Diesel/Electric Hybrids, but doubt there will be enough pilots left to pilot them, by the time they come out swinging. Anything with the word Diesel in it is already painfully outdated and on the way out here in Germany.

Posted by: Jason Baker | June 6, 2018 2:28 AM    Report this comment

"What are hybrid electric airplanes good for?"
At this time, the most compelling answer appers to be: "virtue signaling."
For some time, I've thought that diesel-electric hybrids could/would become a great alternative to leaded-gasoline birds (soon to be outlawed) AND to battery-powered pipe-dreams (non-starter payload and endurance). JaBa has put my prescience to rest.
Germany has 25% of the population of the U.S., crammed into 3.6% of America's land area.
Does that comprise a green imperitive? Maybe.
But with apologies to Barry Goldwatter, Americans' LACK of virtue is no vice.

Posted by: YARS (Tom Yarsley) | June 6, 2018 6:52 AM    Report this comment

" ... technology demonstrator." Or maybe "Candy Planes". Ain't gonna make it!

Posted by: Rafael Sierra | June 6, 2018 7:21 AM    Report this comment

"Don't forget noise. That's huge in Europe, a little less so in the U.S."

Regulatory-wise, that may be true, but practicality wise, I don't think noise is any less an issue here in the U.S. Just take your typical "I didn't know there was an airport there" home owner near an airport and they call in noise complaints quite frequently for small propeller-driven aircraft. I think reducing the noise footprint would help a little. Not a lot, but any help would be good.

I think a series hybrid-electric would be most likely to gain some traction with the slight bit of redundancy it provides. If the ICE fails (or runs out of fuel), you still have the battery power. And my understanding is that electric motors are generally more reliable than a typical ICE. The weight penalty is still an issue, though.

Posted by: Gary Baluha | June 6, 2018 8:36 AM    Report this comment

Hybrid-electric ( jet-A or avgas plus a hefty lithium-ion battery) practically guarantees a bad outcome in the event of a crunch.

Posted by: Richard Montague | June 7, 2018 8:04 AM    Report this comment

What is it good for? "absolutely nothing..., huh".

Posted by: MICHAEL BROOKER | June 7, 2018 8:32 AM    Report this comment

I don't understand the value proposition for an aircraft that runs at a high percentage of its rated power all the time. The value in cars is the ability to size the engine for cruise power and the electrics for peak power. I just don't see it for aircraft applications.

Posted by: Jonathan Cullifer | June 7, 2018 10:17 AM    Report this comment

The current state of hybrid and full electric aircraft reminds me of where we were with conventional aircraft design in the early 1900s. The Wright Brothers had demonstrated the validity of powered flight, but by 1910, most airplanes were still fragile wood and fabric structures powered by balky and unreliable gasoline engines. Flights rarely lasted more than a few minutes and often ended with bent or broken airplanes and similarly bent pilots. Few people recognized the potential of the new invention and most pooh-poohed the idea of it ever becoming useful. Not even the true believers could foresee what an impact it would have on the future.

Fast forward a hundred years and two world wars and you see what that original idea has become. I'm pretty sure it will not take another century to mature electric flight, but it will take some time and several major technical breakthroughs before it hits its stride. So, for now, we have the odd contraptions that will eventually morph into a truly useful device. Give it time.

Posted by: John McNamee | June 7, 2018 11:25 AM    Report this comment

John, Give it time? After 100+ years there is still no evidence that electric can make it in the FREE market. As said, take away the government subsidies and take away the government laws/mandates, and then all you have left are a few eccentrics and hobbyists.

There is no mass market for electrics UNLESS the government controls the market.

Posted by: Mark Fraser | June 7, 2018 1:37 PM    Report this comment

Michael Brooker, you aren't the only one that heard that Edwin Starr classic when reading the title!
Back to the 70s...HUH!!

Posted by: A Richie | June 7, 2018 3:59 PM    Report this comment

"... to be an effective standby, the electric motor has to have a mechanical path to the prop that won't be tanked if the crank breaks."

For parallel hybrid cars such as the Prius and Fusion, the electric motor and ICE engine feed into sort of a differential-like gearbox that allows the mechanical power to smoothly and seamlessly shift between each power source (it works amazingly well). I doubt you could justify the weight of this in a GA airplane but I have been surpised before.

I can't recall exactly which model, but there has been at least one GA model in the distant past that actually had two engines under the cowling that fed a single propeller with the ability to shut down one engine and proceed to the destination (or crash site :-) Was it a modified Navion or some similar craft, I cannot remember, but it had a power sharing transmission for redundancy of some sort. It met the same fate as the one-bladed propeller; a novelty that never really caught on.

Posted by: A Richie | June 7, 2018 4:25 PM    Report this comment

I'm thinking the biggest benefit of hybrid tech in aircraft will be for applications where you need a whole lot of power for a short time. Ditch the idea that the mechanical and electrical power need to be transmitted to the same prop. Either go to something like the X-57 (distributed electric power) or use some folding electric-powered props to provide additional thrust and a blown-wing effect. Or, stop-and-fold props for VTOL operations like some of the package-delivery drone concepts.

Burt Rutan was planning on using something like this on his Ski-Gull... the Rotax was supplemented by a pair of electric folding props that could give him about 12 minutes or so of power for a takeoff boost or an engine-out.

Posted by: Robert Gatlin-Martin | June 8, 2018 5:57 AM    Report this comment

If the parts that have to be on the aircraft anyway (ex. fuselage, wings, etc.) could be made dual purpose (i.e. energy storage and structural) at an acceptable weight the power plant could be all electrical. Hybrids are a transitory technology until we get a dense energy storage solution. Refueling (recharging) in an acceptable time limit (like the time it takes to pump gas) is a concern.

Posted by: Robert Mahoney | June 8, 2018 10:34 AM    Report this comment

Mr. Fraser,
You say that in 100+ years the electric motor has failed to gain traction without government subsidies. An electric motor is more than capable of propelling an aircraft and has many advantages over either diesel or gasoline engines. The problem is the energy storage systems (A.K.A. the batteries). It's true that battery technology has made little progress in the past, mainly due to a lack of incentive. It has only been the last few years that concern over internal combustion engines has prompted a rise in the need for higher energy storage for transportation. Before that, most battery research was directed at smaller applications like cell phones and laptops. Like you, I am a skeptic of either hybrid or electric airplanes in the short term. But, given the state of several promising research projects on high capacity power storage, I am optimistic that it will come eventually, just not as soon as many hope.

With regard to government subsidies, I don't see any agency promising subsidies for electric aircraft, and big companies like Boeing and Airbus are investing sizable dollars to research anyway. Besides, several hybrid cars have lost their tax advantage status (like the Prius) and seem to be selling quite well without them.

Posted by: John McNamee | June 8, 2018 11:43 AM    Report this comment

Paul, I enjoy your commentaries and think this one is good overall, but your third paragraph is completely false. A Prius gets significantly better mileage than a comparable conventional automobile. My first Prius was a second generation type produced in 2003. I went more than 100,000 miles on the original brakes. This is because the regenerative braking system means the brake pads get much less wear. I track every expenditure on each car I own and that Prius had the lowest cost of ownership of any car I've ever had. My average mileage from LA to Vegas was 52mpg. The Argonne National Labs GREET model assumes an unrealistically short lifespan for the batteries to avoid offending certain interests. In the real world, Prius' frequently exceed 200,000 miles on their original packs. If this seems anecdotal, just look around the country. From coast to coast, taxi fleets are choosing the Prius for it's comfortable size, fuel economy and low cost of ownership. As to whether this translates into a good airplane propulsion system or not, that is another story, but an economy optimized hybrid car (and most are not) is significantly cleaner and has significantly better mileage than an equivalent conventional IC only car.

Posted by: Patrick Wright | June 9, 2018 12:18 AM    Report this comment

You folks aren't keeping up...

The goal has always been to use more of the energy in the fuel for propulsion. The best most engines could recover traditionally was less then half the fuels potential.

Mazda SkyActiv engine is recovering over 50 percent of the fuels potential by increasing the combustion pressures. Other cars have come out in the past couple years with the electric hybrid turbo/superchargers that deliver power more efficiently, faster response, light weight while using less fuel.

These electric superchargers could just be an add-on to your existing engine and give sea level performance at higher altitudes with less weight penalty (35 to 50 lbs). The quicker the aircraft gets to altitude the sooner the benefit from True Airspeed (TAS) gains.

For example a home-built amphibious cub with an O-200 could produce approximately 100 horses up at 17,000 feet with TAS around 120 knots. Using the altitude weather apps on your phone you can find the best altitude for a tail wind and bump your ground speed a little. Figure consistently flight planning over 300 miles 2.5 hours with less then 20 gallons of auto fuel.

Posted by: Klaus Marx | June 9, 2018 2:50 PM    Report this comment

Where can I buy a pressurized Cub on floats, these days? ;-)

Posted by: YARS (Tom Yarsley) | June 9, 2018 4:21 PM    Report this comment

"I'm thinking the biggest benefit of hybrid tech in aircraft will be for applications where you need a whole lot of power for a short time. "

I think you are partially right. I'm not a fan of electric power for sole propulsion, but I have long thought hybrid would be a valuable option for certain classes of airplanes.

An A-36 Bonanza, for example--the combination of the hybrid engine and the battery would produce astounding takeoff and climb numbers--getting the aircraft to tall altitudes where efficiency is best.

The power redundancy would make conventional twins obsolete. There would be no thrust asymmetry to deal with on takeoff or landing. Failure of the piston engine would still allow quite a long period of flight on the electric--enough to land at an airport of your choosing. You would have a lot of reserve electrical power for your instruments.

The weight difference on this size airplane is much reduced, compared to LSA-size airplanes. The difference in weight between a Rotax engine paired with the off-the-shelf battery pack from a Prius is not large, compared to the 2 engines, 2 props, dual alternators, extra mags, extra prop, extra exhaust on a Baron--a similar-size aircraft. Weight difference can be FURTHER ameliorated by the need for less fuel for a given mission compared to a Baron.

One of the big issues for electric airplanes is weight and balance--where to store the batteries. With a very small airplane, space is critical. With a Baron/Bonanza A-36 size airplane, it is less critical as there is more room to place them. It MIGHT even help solve some of the Beech aft-limit CG problems by being able to place the batteries forward (a Piper Lance/Saratoga or Cherokee 6 would also be a good candidate because of the forward baggage compartment, but I picked the Bonanza/Baron as an example instead because of the comparison between those similar airframes.)

Imagine the Hybrid Bonanza flight--a short takeoff (using perhaps 400 horsepower equivalent)--a rapid climb to altitude--cruising on the small engine to provide power to the electric. No worries about thrust asymmetry on takeoff or enroute--virtually no penalty in useful load--low operating costs by not having to maintain the second piston engine and related systems--and the reliability of an electric engine.

I believe we've set our sights too low in concentrating on very light airplanes.

Posted by: jim hanson | June 11, 2018 11:03 AM    Report this comment

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