Electric airplanes – is the tipping point upon us?

Just like a Chicago Cubs appearance in the World Series, predictions about the coming electric aircraft boom seem to pop up every year, only to be crushed by reality. A brief stroll around the internet shows that “The Year of the Electric Aircraft” was 2010, then 2011, maybe 2012, definitely 2013 and – seriously this time – 2014. It didn’t happen.

Siemens electric engine
Is Siemens’ new engine a breakthrough?

Given that sorry past, it would be foolish to make any such predictions about 2015, so I won’t. But a reading of the latest trends shows that real progress is being made in the world of electric engines, batteries and aircraft design. If 2015 isn’t “the year,” might 2025 be?

Four recent developments should be intriguing, if not revolutionary, for general aviation pilots:

  • Siemens just introduced a new electric aircraft engine that offers a previously unseen power-to-weight ratio. The 110 lb. motor produces 260kW (roughly 350 hp) at 2500 RPM, and because it turns at a typical piston airplane RPM, heavy and expensive gearboxes are not required. The company’s eventual goal is to build a regional airliner with this engine technology, but Siemens already has a relationship with Diamond Aircraft for an electric motorglider. Might a four place general aviation airplane be in the future?
  • Another European giant, Airbus, is making plans to deliver its E-Fan airplane in 2017. This two seat, low wing airplane is more technology demonstrator than cross-country transporter, but its initial specs alone might make it a compelling trainer. The company is serious enough that it recently announced plans to build a factory in France, and has partnered with Daher (manufacturer of the successful TBM 700/850/900 line of turboprops).
  • Electric car pioneer Tesla Motors is building its monumental, 5 million square foot “gigafactory” in the Nevada desert right now. The company hopes the massive scale will allow it to cut battery costs by 30% as it prepares for its first mass market car. Many businesses, including aviation, are hoping this project offers some trickle down benefits for battery technology, in terms of weight, size, performance and price. After all, a great electric motor is only as good as the batteries that drive it.
  • Finally, the drone revolution is disrupting aviation from below. While the $1000 quadcopters get most of the attention, there is a wide variety of $20,000 to $75,000 Unmanned Aerial Systems (UAS) that are much closer to airplanes than toys. These are making rapid advances, some driven by military requirements, in aircraft construction, propulsion technology and battery design. Some UAS manufacturers are even growing up into full-size electric aircraft, like Yuneec’s partnership on the GreenWing International e430.

As usual, general aviation is too small to really drive a major trend like this. In this case, we’re simply riding the coattails of electric cars, UAS, and European Union environmental standards. All of these industries have plenty of hot money splashing around and thousands of smart people working on the trickiest problems. Some of that might eventually help Cessna pilots.

It’s easy to believe the hype and get carried away – and some have. A more serious thinker must acknowledge that major challenges remain, and “coming soon” probably means 5-10 years, not six months.

One of the first issues to deal with is the FAA’s approach to certifying electric aircraft and batteries. Lithium batteries, in particular, bring up all kinds of certification questions, including how to deal with overcharging and crashworthiness standards. The FAA last year banned electric airplanes from carrying passengers, just the latest sign of its cautious approach. Before an electric Cessna 152 could be certified, the FAA will have to be convinced that safety standards have not been compromised (think 787 battery fires). That takes time.

Electric airplane - E430
Electric-only airplanes are already flying – but will they get certified?

There are also serious hurdles in the arenas of economics and engineering. The ever-present range/payload challenge is here, just like on piston engine airplanes. To carry more passengers, electric airplanes need bigger motors, which demands more batteries, which drives up weight and demands bigger motors. The Airbus E-Fan, for example, has a range of only one hour.

Even assuming these engineering challenges can be solved (probably by major advances in battery technology), pilots may be looking at some expensive airplanes. The latest batteries are not cheap, and neither are potential certification programs. There are a lot of fixed costs to be recovered.

But just as it’s easy to get carried away by the cheerleaders, it’s also possible to give the naysayers too much credit. Even with the (significant) questions in mind, there is real reason for hope. For a start, the latest electric aircraft projects are not hobbies for eccentric entrepreneurs. Airbus, Daher, Siemens and many others are serious about delivering commercial aircraft in the medium term that are powered by electric motors or at least hybrid propulsion systems. There certainly isn’t a similar movement to reinvent piston engines.

Maybe more importantly, electric aircraft would change some fundamental issues of aircraft ownership. For one, the cost of electric power is much less volatile than fossil fuels. If a major war breaks out in the Middle East, electricity prices would certainly be affected, but nothing like we have with 100LL.

Plus, changes in energy policy or environmental regulation would affect the FBO far more than the aircraft owner. Take the unleaded fuel transition for an example. To get from a 100LL industry to a lead-free industry, many pilots will probably have to spend a money on new or modified engines. It’s a seismic shift. In an electric aircraft future, the pilot doesn’t care too much what he plugs into. Infrastructure changes fall on the airport operators, not the pilots. And the infrastructure to deliver electricity to airports is already in place.

Finally, we cannot ignore the environmental and noise impact of our airplanes. I’m hardly a tree-hugger, but pilots in Europe and even California can attest to the battles that often erupt over airport noise or pollution. We can dismiss it or even mock it, but our opponents’ perception is often our reality. Electric aircraft, while hardly a miracle cure, would probably save at least a few airports.

Electric airplanes will not replace Cirrus SR22s or TBM 900s anytime soon – the range and payload numbers simply don’t work for serious transportation. But that may not be all bad. The most beaten down segment of aviation over the last 10 years has been the lower end: student pilots learning to fly in Cessna 172s and recreational flyers in Light Sport Aircraft. If, for now, electric propulsion is only practical for these one hour flights, that would still be a significant boost. It could be less expensive on an hourly basis, but it could also be simpler. Ask a young pilot about the most confusing thing to learn in flight training and you may hear the engine. Hot starting a fuel-injected piston engine is almost ridiculous to an outsider.

Besides, any student of technological history knows that major advances usually come from below, not above. Simple technology is initially dismissed as too limited to make an impact, but over time, it becomes “good enough” to replace the existing model. I’m not investing in any electric aircraft companies just yet, but I may say nicer things about European environmentalists – they might accidentally push general aviation into a brighter future.

Some day, that is.

26 Comments

  • John,

    I wonder why you did not mention anything about the Solar Impulse attempt flight around the globe.
    In lees than a week from today May 9th 2015 is the panned departure day from China. Crossing the Pacific for Hawaii will take five days and five nights.
    http://www.solarimpulse.com/home
    There is a worthy news value for aviation advancement and solar technology, without a doubt.
    I wish them success !!!!!!

  • Electrical propulsion is great (it’s clean, quiet, efficient, and highly reliable), but energy storage via battery cells is hopelessly overweight for aviation … where propulsive system weight and the density of energy storage are key design limitations. Siemens has done a great job reducing the weight of the electrical motor itself, but powered by batteries it’s still a loser unless range doesn’t matter.

    Hydrogen fuel cells would seem to be a much more practical solution than storage batteries. Given the very high fuel efficiency in miles per gallon for hydrogen fuel, and the very high energy density of hydrogen fuel on a weight basis (nearly three times that of gasoline), the potential is to deliver very long range with comparable (to internal combustion engines) total powerplant + fuel weights. Power is delivered with NO harmful emissions (clean water is all that is released), quiet operation, and few moving parts to fail.

    Hydrogen fuel can be produced relatively cheaply today from our abundant natural gas resources. Hydrogen fuel production is also a practical way to utilize solar and wind energy more efficiently than trying to feed either source of power into the existing electrical power grid.

    We’re likely still years away from practical fuel cell powered aircraft being marketed and operated on a mass scale. Though several fuel cell powered automobiles are now being marketed and produced.

    • As mentioned, the current problem is electric battery or electric storage. From a practical standpoint, the energy density of a battery is far worse than that for a typical hydrocarbon fuel, such as avgas. Also, with avgas you only carry part of the energy as fuel, the rest, oxygen in the air, is not part of the weight as it comes from the air intake to the engine and is combusted. Only rockets need to carry both the “fuel” part and oxidizer part. Put another way, the battery must contain all the energy, where hydrocarbon systems only carry a portion of the energy and get the rest from elsewhere. This is a tremendous benefit that most people never consider and is really the reason that powered flight came about. Imagine Orville and Wilbur using auto batteries and an electric motor back in the day.
      On the downside, each time the fuel is burned in a cylinder, an enormous transfer of electrons occurs and we see the result as heat. The heat is used to drive the engine and the electric current that occurred during combustion is lost and wasted.

      This suggests that the ideal solution would be a fuel cell. In this way the hydrocarbon fuel would be carried in the plane, but like with a combustion engine, not the oxidizer (air). The fuel cell would channel the electron exchange and use the electric current produced to drive an electric motor. In this case the heat generated by the fuel cell reaction would be waste and the current would be the energy source.

      Because fuel cells are more efficient (produce more electric power) than ordinary combustion (using heat engine principles) this approach coupled with the newer high torque lightweight electric motors would represent a better tradeoff than electric batteries.

      So I would like to see more R&D done with fuel cells. I guess the downside is that a fuel cell will produce CO2 unless the fuel is pure hydrogen. So maybe that is why the interest in battery storage is so high. People’s mindset are on the “latest and greatest” not necessarily the best energy source. However, think about all the coal powered electric plants that are needed to charge those batteries. It’s a false prospect.

      People’s mindset are on the “latest and greatest” not necessarily the best energy source from a energy density standpoint. I don’t see batteries as a good long term prospect for the type of energy storage needed to propel aircraft over reasonable distances. And when you sum up the cost (out of pocket and to the environment) to charge batteries they don’t provide much if any benefit over existing energy sources.

      Jack

      • Jack – thanks … good points there.

        One correction though – a hydrogen fuel cell doesn’t produce any carbon (if one worries about so-called “carbon pollution” – though I don’t worry about that at all). It is possible that carbon can be released in generating hydrogen gas from hydrocarbon fuels such as natural gas, but it is not necessary to do so. Hydrogen fuel can be produced in various other processes that don’t generate any carbon whatsoever (such as nuclear power plants, wind or solar powered electrolysis of water, and catalyzed ammonia based processes).

        The hydrogen fuel cell produces only one byproduct of electricity generation – clean water. The water generated in the cell can either be dumped overboard or retained onboard for other use.

        There’s actually been a ton of R&D work on fuel cells in the automotive industry in the last ten years, and much of that technology would translate directly to aircraft (and quickly, if only we could get the FAA out of the aviation overregulation business!). The most recent Honda fuel cells have significantly reduced the size and weight of the fuel cell stack, to where it’s now smaller than a PC cabinet and weighs a little over 200 pounds. If that sounds heavy, remember that the electrical motors weigh very little, and the hydrogen fuel weight is much lower than the weight of comparable energy content avgas or JP4.

        Other recent research has yielded new cat cracker processes for converting ammonia gas to hydrogen. This allows the use of much lower pressure fuel tanks than needed for pure hydrogen storage. Ammonia tanks can take the form of lightweight conformable plastic tanks that would easily fit into virtually any space in an aircraft structure (wings or fuselage). Ammonia is widely available worldwide, and is produced at very low cost.

        • Duane, you are of course correct that hydrogen fuel cells do not produce carbon pollution. I happen to believe (in concert with about 99% of objective scientific data) that this is a VERY big deal, but that’s a debate for another time and place.

          The use of liquid ammonia as a hydrogen storage means is also interesting. The extraction of the hydrogen by catalytic process would likewise not produce carbon emissions since ammonia is carbon-free. Liquid ammonia would require pressure tanks comparable to those used for propane. Energy density by weight and volume is about a third of gasoline’s, but combined efficiencies of fuel cell and electric motor might be twice that of a typical horizontally opposed aircraft piston engine, so the difference would not be extreme.

          Fuel cell weight is proportional to electrical output, so batteries or “super capacitors,” charged by the fuel cell or externally, might be used for extra power during takeoff and climb, with the fuel cells themselves providing the continuous max output required for cruise.

          It all sounds theoretically feasible, but taking into account the weight and volume of ammonia and its tankage, and the weight of the fuel cells and any auxiliary batteries, we are quite a ways from the level of practicality based on current state of the art. What’s more, in the key issue of energy storage density ammonia, unlike battery/capacitor technology, is not subject to significant improvement through ongoing research.

          • Elliott,

            For normal light aircraft cruising ranges on the order of 500-600 nautical miles, the weight of available hydrogen fuel generated from cat-cracking of anhydrous ammonia (considering both the weight of the ammonia itself plus the lightweight tankage)is comparable to both the very light weight of pure compressed hydrogen along with it’s very heavy high pressure (5,000+ psi) tanks … and is also comparable to the weight of unpressurized avgas in regular aviation fuel tanks. The fuel weight is essentially a wash for equivalent ranges.

            The latest Siemens designs of electric motors are, of course much lighter than the equivalent HP internal combustion engines.

            The advantage of onboard cat-cracking of ammonia gas is that the required storage pressures are relatively low (as you say, similar to the pressures in standard RV or backyard BBQ propane tanks), which provides advantages in cost, weight, and safety. An additional advantage that ammonia is widely available and distributed all over the world, while also being very cheap (it can be produced and distributed much more cheaply than either pure hydrogen gas or avgas).

            It’s yet to be seen if fuel cell powered light aircraft will either need or have storage batteries. As the weight of fuel cell stacks continues to plummet, while the net power output/pound climbs, there may be no weight advantage to going “hybrid”.

  • Electric airplanes? How shocking! (Sorry)
    It seems likely that electrically powered airplanes will see their only substantial use in the early training environment, in which a 1-2 hour flight time matches the typical student flight profile. However, it is hard to see anyone willing to fly longer distances with long recharging times interrupting the trip. Avgas-powered aircraft would still be necessary for the latter stages of training. Some of our technically informed readers can tell us the likelihood of dramatic advances in battery technology. If the power/duration/weight equation could be solved, great things would happen in light aviation (and ground transportation as well). For one thing, imagine the absence of avgas-fueled fire in light aircraft accidents– many lives might be saved.

    • There are no shortcuts on the battery front, Hunter – at least that’s what the smart people say. It’s an incremental type of improvement each year.

      Now there have been some pretty dramatic improvements in solar technology (and price) over the past few years, so maybe there’s an option to supplement with solar.

      More realistically, I think airplanes might evolve like cars. That is, hybrid powerplants will probably be the first step. Maybe you need gas to take off, then can use electric in cruise and descent.

      • One possible solution to the “charging time” issue that I have seen proposed is basically having a battery truck (similar to a fuel truck) meet the airplane and swap out the depleted batteries for charged ones. This might be a viable solution in the training market for good aircraft utilization within the fleet at the home airport. For cross-country operations, there would need to be a battery standard or the students would need to go to specified airports that use the same technology. Of course, the aircraft manufacturers would need to make a battery swap as easy or easier than fueling any other airplane. Not ideal but a possibility.

        The weight and other issues may be resolved with time and research. I hope…

        • This is already being done by Tesla, though I haven’t tried it yet. The superchargers can add 200 miles of range during the hour it takes to have lunch. Not a perfect solution, but a big step in the right direction.

  • I keep thinking ……..when the Wright Brothers successfully completed the first brief flight ( 59 seconds,852 feet)….what their critics were saying.
    Did they imagine the 747 ? or Apollo 11 ? or the Mission to Mars ?
    ” A journey of 1000 miles, starts with the first step”.
    I am very optimistic and very supportive to the point that……I am already making lesson plans for the first Electric Airplane Lesson !!!!!!!
    The first lesson plan is for my familiarization flight, what are the differences between ICE ( internal combustion engine) and an electric one ?
    How much right rudder( it is right rudder per Siemens photo) will be required and how smoothly will the throttle application should be ?
    Will the throttle be an ” auto-throttle” type ?
    Very possibly !!!!!
    Future students and CFIs will not require much hearing protection….
    A whole new world in aviation and I am ready to explore the future.
    The only constant thing is change !!!!!!
    I love it !!!!!

    • I frequently consider the Wright Bros. point of view also. Then I realize that well, actually they did have the best airplane in the world at the time. A person offering an airplane today that has 1/4 the range and speed of existing airplanes does not have that advantage. So it is much tougher starting out with something different today, even if it is better in some ways.

    • Their critics might have been comparing the Wright Brothers efforts to those of Count Von Zeppelin whose aircraft had begun flights over Lake Constance in 1900. In terms of range, carrying capacity and apparent safety the Zeppelin was well ahead of the Flyer. Of course that changed but in 1903 there was only one photograph as evidence of the Wright’s achievement. The world’s first airline was established in 1908 using Zeppelins while the Wright’s were locked in legal battles over patents.

      On another point the electric light aircraft will be mostly the same as any other light aircraft. Only the propulsion and fuel systems will have changed. Unlike the Wright’s there is no need to invent control systems, useful propellers or even figuring out how to fly. A better analogy would be the change from piston engines to jet turbines. The first experimental jets weren’t that much faster than their piston counterparts.

  • Although most current electric planes have poor performance others are actualy extraordinarly powerful for example the Volta Volare gt4 high performance electric plane

  • A benefit of electric aircraft I hadn’t thought of is reduced noise around airports and– one would hope– reduced citizen noise complaints and better acceptance of airports. And when airplanes did go down sometimes, as they will, there might be a hole, but not the spectacular “smoking hole” that draws new ‘copters and TV talking heads like flies to a spilled Coke.

    • I sense that noise and pollution, while always issues, are only going to become more important in the next 10 years. In this regard, electric has a major benefit over diesel engines in terms of a 100LL replacement.

  • And look at the safty benefits… Once the battery is down to a certain charge, the computer calculates if the airplane will (or will not) get to its destination, and if needed, offer alternets… No more fuel starvation! We can finally know how much we realy, truly, have “in the tank”.

    WW-II pilots, I am now ready for your dip/time/watch/never trust your “gadgets” comments… Bring it on.

  • Good article that takes a realistic view of the potential of electric power for GA airplanes. However, it fails to mention one important advantage that electric power would provide. Because electric motors don’t breathe air their maximum output power is independent of altitude: a 150 HP electric motor will be able to deliver the same 150 HP at 25,000 ft. (if provided with enough battery capacity to get that high) as it does at sea level. No need for costly and finicky turbocharging! That would mean exceptional cruise speeds for those willing to suck oxygen, but more importantly useful performance for the lowest powered trainers even at hot and high airports.

    • This is a great point, Elliott. Electric changes some fundamental assumptions we make about airplanes and performance – some for the better, some for the worse we should acknowledge. At the very least, it will require some new thinking about how we train new pilots.

    • Elliott – very good point.

      Again, though, battery electric airplanes are still not feasible for anything but hanging around within a few miles of the traffic pattern, due to the low energy storage density on a per pound basis of batteries.

      But in the case of hydrogen fuel cell powered electric aircraft, there is no such limitation. Hydrogen fuel cell vehicles including aircraft can store more than enough energy onboard for long cross country flights, with rapid refueling on the ground (unlike batteries which have to be charged, effectively, overnight).

      So yes, a fuel cell powered electric aircraft will have 100% of its rated power up to any altitude whatsoever, because it does not depend upon atmospheric air pressure to generate power. Indeed, a fuel cell powered aircraft could operate to any altitude that its airframe can attain with the rated power, even at stratospheric altitudes.

    • There are other performance issues associated with operating electric motors in low-ambient-pressure environments. Been there; done that. Not impossible, but not trivial.

  • Let’s not forget that HP output is not the only limitation at altitude, propeller /wing lift performance and limitations exist.

    • The wing designs used for light GA aircraft will work just fine at altitudes to 25,000 feet, which is generally the practical limit for unpressurized aircraft. (Think, for example, of a Turbo Arrow, which has basically the same airfoil as a humble Warrior.) Propellers would have to have some form of variable pitch since the RPM required to deliver full power at high altitudes would otherwise probably be too high.

  • In the opening couple of paragraphs and in the cut line in the photo you refer to the new Siemens product as an electric engine. I recall from a Terry and the Pirates comic book in the ’40s someone referred to the engines on the transport Terry was flying as motors and was severely corrected that they were engines not motors. Motors were electric not piston driven. Sorry just had to nitpick.

  • John, I agree with you that electric has a future in aircraft. As a performance enthusiast, the electric cars gave me no hope for the future; until my friend bought a Tesla and brought it over for me to take a drive. Wow.

    Just to throw out an idea, how about a Cirrus class airplane powered by a hybrid Rotax 914. Batteries large enough to provide electric boost for takeoff and climb. Auto gas for cruise and battery recharge in descent for the next takeoff. With the added incentive of emergency electric power in an emergency.

  • Where are we, 2 and a half years later?
    Airbus has ditched the e-fan on the tune of ‘that was just a marketing pitch you know’, and the only electric plane one can actually buy is the pipistrel alpha trainer, AFAIK (and a few motorgliders too, but the needs are not the same). Batteries have evolved, but have not made the quantum leap necessary for cross country flights.
    OTOH, here in old Europe the constraints of noise and carbon pollution are more stringent than ever, threatening the acceptability of general aviation through many ways, from european regulations to more down to earth problems of parking places in hangars competing with real estate speculation.
    Besides training, there is another GA sextor that could already benefit from electrification : gliders towing, which is often done with old and unmuffled airplanes, contributing to a fair part to neighborhood opposition. We would obviously need a bit more power than the alpha trainer, but the ‘many short flights’ use case may be well served with battery swaps. Alas, it would have to be heavily subsidised to compete with the operation costs of today, without even thinking of certification issues.

    Here as elsewhere, we may have to invest heavily, only for long term benefits (or, better said, less long term adverse consequences).

Leave a Reply

Your email address will not be published. Required fields are marked *