Bjorn’s Corner: Electrical flight, how real?

By Bjorn Fehrm

By Bjorn Fehrm

10 July 2015, ©. Leeham Co: We have just witnessed the first solar electrical aircraft, Solar Impulse 2, cross the ocean from Tokyo to Hawaii. Today, Friday, Airbus Group will cross the English Channel with a battery powered electrical aircraft, the E-Fan.

How real is electrical flying? Real enough to make demonstration flights like the one to Hawaii and to Calais. Both these aircraft are technology demonstrators but it is symptomatic that they do these hops now, 2015.E-Fan cross Channel

Airbus Group’s E-Fan aircraft is preparing to cross the English Channel. Source: Airbus.

We live in the years when electrical cars have gone from exotic one-offs to serial produced products, still expensive but more and more practical. Why should not the aircraft industry follow?

The car industry relied on the computer industry to develop affordable power dense batteries. These were needed for the laptops and it perfected the Lithium-ion chemistry battery and brought the production systems for these hard to produce batteries to mass production. Today Li-ion batteries are produced for smartphones, computers, cars and many other applications.

The Solar power industry that created solar cells to mount on one’s house perfected the solar cell unit and brought this to mass production and affordable prices. Finally the hybrid and full electrical car industry developed the power electronics needed for all the conversions and control of the electrical energy that drives the electrical engines. With all components there, why is the fact that Airbus E-Fan flies across the Channel and that its subsidiary, Voltair, will produce a commercially available electrical trainer for 2017 and a general purpose four seater aircraft for 2019 such a sensation?

The problems involved

To get an airplane to fly is a technological challenge. To get it to fly on electrical power is a mega challenge. The smallest problem is designing the aircraft and finding a suitable electrical motor. Electrical motors have gotten more and more efficient in recent years. An example of the latest development is that Siemens has developed an electrical motor for aircraft which has a power density of 5kw per kg motor instead of the usual 1 kW per kg. Today’s hybrid cars are at 2kW per kg. The engine will deliver 260kW/350hp from 50kg own weight and drive the propeller or fan with the customary 2,500 rpm without reduction gear. The engine should fly in prototype later this year.

While things look good from the engine side, they are less rosy on the source of electricity. We know that the big problem for electrical cars is the batteries and for aircraft it is no different. If one does not want to have an airplane with 60m span wings filled with solar panels on the top, one has to use stored energy somehow or go for a hybrid setup. Battery storage of energy is still troublesome. The car industry drives the technology and the Tesla model S Sport-sedan is perhaps the most successful example rolling on the roads just now, with almost adequate range and good performance.

But it costs; the price one pays for endurance and performance is many standardized Li-ion cells, and these come at a price.  Tesla uses 7,100 Li-Ion cells in a 540kg heavy battery module, which gives you 85kW during one hour or less power during several hours. To feed our 260kW motor we need several of these half tonne battery modules. At 7,100 Li-Ion cells each, the modules cost a pretty penny and weigh half a tonne each.

The battery module for the E-Fan, that has one hour to cross the Channel before the juice is “no more,” has 3000 batteries in the wing-roots weighing 170kg driving its two 30kW motors. Charged batteries as a power source will probably be OK for demo aircraft and perhaps flight trainers, but not for aircraft with longer endurance and therefore range.

Aircraft with range

To get aircraft with range one would have to use a hybrid setup. A hybrid is where an electrical motor would be driven by a smaller battery which is topped up by an electrical generator which in turn is driven by some form of combustion engine. The reason we need thermal engines to help us give the aircraft endurance is that the stored energy in our daily fuels is just amazing. The energy density is hard to beat.  With about 12 kWh per kg fuel, we need less than 8kg normal aviation gasoline or similar fuel to match the Tesla battery energy store of over 500kg.

With this it is easy to understand there is a lot of work with re-chargeable energy store systems before we can use the wall outlet to charge our longer range aircraft. Hybrid concepts like Airbus will use for the larger aircraft will make the E-Fan more universally usable by around 2020. They use the unmatched energy density of conventional fuels and have that drive an electrical generator, which tops up the batteries of the aircraft to give it an acceptable endurance.

The problem from an efficiency standpoint is all the conversions. First, from thermal energy to mechanical, then to electrical and from electrical to mechanical again. As a range extender it can be OK, as the main battery load came from the wall outlet and that energy was produced by our efficient power stations.

Airbus Voltair, which will produce the E-Fan 2.0 trainer by 2017, will stay all battery-powered for the trainer. The endurance of about an hour or so is acceptable for a trainer. After an hour, the pupil learning to fly is exhausted anyway and it is time to land and give him a break and the aircraft a charge. Most likely the aircraft will come with exchangeable battery packs, otherwise there would be long waiting times between training flights.

Artist Impression E-Fan 4.0

Rendering of E-Fan 4.0 four seater general aircraft. Source: Airbus.

For the more general four seater called E-Fan 4.0 available 2019, a range extender is needed. The main energy comes from a battery charged with cheap power-outlet electricity and the aircraft has a small combustion engine-generator to top up the battery to extend the endurance and thereby the range from two hours to three and a half.

The stored energy in batteries takes care of the energy peaks like take-off and as the thermal engine-generator will not be dimensioned for these peaks, it can be made small and light. It remains to see what it costs and how practical the aircraft will be, but one can’t fault Airbus Group Innovation for not trying.

Summary

It is exciting that we are now starting the era of electrical aircraft; they promise extremely good environmental characteristics if one disregard the battery production and disposal process. As usual, everything will not be perfect from start but the potential is there to make inroads on the combustion- driven aircraft’s turf and Airbus is talking about a regional airliner in the pipe for 2050. Its virtue will be all hours operations into town airports as it will be a quiet shadow in the night.

Who would have thought that 2015 would be the year of the electrical aircraft?

27 Comments on “Bjorn’s Corner: Electrical flight, how real?

  1. Pipistrel already has certified an electric trainer similar to what Airbus is trying to achieve (Pipistrel Alpha Electro). You can find videos of it flying around on youtube.

    There’s been some drama this week as they tried to beat Airbus to the punch and fly their Alpha Electro across the channel first. In a move that looks a bit like retaliation, Airbus partner Siemens immediately decided against selling Pipistrel the motors for the Alpha Electro. I’m sure there’s more to the story; I was personally rooting for Pipistrel to complete the crossing first, since they do seem to be a lot closer than Airbus/Voltair to serial production.

    http://www.aopa.org/News-and-Video/All-News/2015/July/07/Siemens-denies-e-motors-to-Pipistrel

    • Be as it may with “being first” (seems an electrical CriCri was first, just pipping Airbus), the nice thing is the ball is rolling and electrical airplanes makes a huge difference when it comes to overhead noise. It can benefit many flying clubs and private pilots.

      I understand there are several gliders also having electrical assist motors. Good that the evolution has started, glider flying is like sailing, much better than with the combustion powered variant. If one can get rid of the tedious tow aircraft the freedom is total.

      • This is motor/electronics reliability fall out.
        ( and single engine versus twin engine )

        • I call BS. people fly the channel and much larger bodies of water in single engine planes all the time.

          this is clearly a deliberate action to prevent Pipistrel from doing the flight before the Airbus aircraft.

          unethical, dirty pool and possibly illegal fraud.

          • Could be unethical, possibly (we really don’t know the details), but how does fraud come into this?

          • Does the Siemens Electric Drive Set sport a regular ESA/ICAO certification?
            I don’t think so.

            I see a lot of blustering on fannish grounds without substance or reaason.

      • Yeah that was pretty bad on Airbus, Siemens and the French aviation authority to play bush league tactics like that.

        It’s not like Airbus doesn’t have metric tons of money to do more and make a better plane. Bad move on their part to jerk around another company just so they can say “we were first”.

        I hope Siemens gets a lot of s*** for it, too. D-bags.

      • Just got round to reading the article you linked. The letter from Siemens to Pipistrel is linked there. It seems Pipistrel was in major breach of contract. The test agreement required Pipistrel to get consent for each flight and they had lent out the plane to someone else without telling Siemens, let alone getting permission. Overflying water was a second issue. Siemens summarily cancelled the contract with Pipistrel . It looks like Pipistrel have been somewhat careless.

  2. What is crossing the channel against crossing the Alps?
    On Wednesday the e-Genius built by IFB (University of Stuttgart) traveled from Hahnweide (near Stuttgart) to Calcinate del Pesce (north of Italy) in 2 hours travelling 320 km and reached a height of over 4,000 m.

    The battery was recharged in Italy and the aircraft flow back on the same day.
    http://www.spiegel.de/wissenschaft/technik/e-genius-elektroflugzeug-ueberquert-erstmals-die-alpen-a-1042687.html (German)

  3. Airbus sponsor there as well. Seems someone in Airbus group has got it and understood the PR value of the technology and trend. Wonder what Beoing’s move will be?

    • Boeing is involved in a project run by NASA looking at electric-hybrid propulsion as well as new fuels called SUGAR

      • Run by Nasa ?.
        So the US taxpayer does all Boeings basic research for it. next thing they will be getting NASA to do all the research for them…oh oh too late

        “Vibratory response of a stiffened, floor equipped, composite cylinder”- Langley research center

        • As I understand it, NASA research is available to the world.

          Yes being the demonstrator company has advantages but the research has been shared.

          Personally I think we should keep it proprietary to the US and or have others pay for it but then I am not in charge.

          As I recall Europe floated 4 billion or so in research funds a while back for the same purpose. I don’t know if that stuff is shared.

          NASA may not share all either, I would like to have someone who knows weight in.

  4. Thanks for the article.
    It points out the major challenge and should educate people that all-electric flight of passengers over distances is still far out, and may be the less attractive option compared to other alternatives.

    Looking at energy density:
    https://upload.wikimedia.org/wikipedia/commons/thumb/c/c6/Energy_density.svg/2000px-Energy_density.svg.png
    Comparing that to energy density of batteries, including those only working in laboratory environments:
    http://www.iccnexergy.com/wp-content/uploads/2014/10/ICCNexergy-Energy-Density-Chart-2Q-2011-hq-enlarge.gif

    Note that ~280Wh are 1MJ, hence the second chart fits into the lower left corner of the first one.

    I would assume that electrical flight might be possible within 10 years (according to some more or less convincing research), but the overall performance will be sobering. One will fly low & slow, and probably prefer a ride on the train.

    Nevertheless, it makes sense to explore this technology.

    • Dear Schorsch,

      you missed an energy source with a rather high density: Methanol!

      Even with a conversion rate to electricity of just 50 % the energy density is still 10 times higher for Methanol.

      There are already direct methanol fuel cells available on the market: http://www.efoy.com/en
      Actual conversion rate is about 70 % and no need for LOx like for Hydrogen fuel cells.

      Like a submarine an aircraft could use the batteries during take off to get high peak power and then switch to fuel cells + solar cells during cruise. For descent the batteries could also be reloaded by the fans working as a generator.

  5. Solar Impulse 2 flew from Nagoya, not Tokyo, to Hawaii. Thanks.

  6. Interesting concept, but doubtful that the technical challenges can be overcome.

    There’s another Airbus project, e-Thrust, which looks at batteries taking over the entire redundancy of aircraft systems. That means an aircraft can manage with a single engine – actually a generator. The battery would need to have enough charge to get the aircraft into the air and back down again in an engine-out situation and to get to the nearest diversion airport if the engine stops working mid-route.

    Again very challenging, but maybe more realistic.

    • An interesting brochure on e-Thrust that explains some of the technologies – that will also be used in the e-Fan.

      The technical issue with the batteries, I believe, is in controlling the chemical reactions. You can come up with a very lightweight, highly reactive battery, but you can’t stop or reverse the reaction for recharging. In other words, it’s relatively easy to come up with a high power-density battery, but not one that will hold its charge or recharge.

        • Hi Jane. My understanding is you release the charge by enabling a chemical reaction, recharge the battery by reversing that reaction, and hold the charge by stopping a reaction. From what I read somewhere we can get a high power to weight ratio now with new powerful chemical reactions. The problem is stopping and reversing that reaction, which is what you need for a useful rechargeable battery.

          I’m not a chemist however.

  7. I believe the Tesla’s battery high weight is mainly due to the fact it serves as part of the car chassis.

  8. Fascinating reading, I am a sever skeptic

    batteries do not burn off weight as you go along,.

    Your aircraft is as heavy at the end as the start so no saving there as aircraft get more economical the lighter they are.

    I think what they are doing has applications for other than aircraft but aircraft themselves are will never work with batteries.

    Even a the trainer at 1 hour, 15 minutes to the training area, same back.
    only 30 minutes of maneuver and some reserves? More than once I had diversions.

    Looking over my log books, typical training flight was average of 1.5 hours, a few as low 1, some approaching 2.

    Maybe part of a curriculum if airfield is out on the country, otherwise just not enough useful time on station as it were.

  9. Pingback: The solar-powered plane trying to fly around the world has been grounded until 2016 - Quartz

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