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Transportation Technology

Elon Musk's Next Great Idea? Electric Air Travel (bgr.com) 346

An anonymous reader writes with this excerpt from BGR: Elon Musk is changing the world one idea at a time. First, with Tesla, the man so many people call the real life Tony Stark has done an incredible job of bringing electric vehicles to the mainstream. Second, Musk has been doing an impressive job over at SpaceX in the realm of space travel. And third, Musk's effective rough draft of a high-speed transportation system known as the Hyperloop is being contemplated and conceptualized in a very real way by some extremely smart people. So where does Musk go from here? Why, Mars of course. Recently, Musk said that he plans to unveil SpaceX's Mars roadmap next September. But on another front, Musk has also been thinking about developing an electric airplane capable of taking off and landing vertically. While answering a few questions during a Q&A session at the SpaceX Hyperloop Pod Award Ceremony last week, Musk was asked what his 'next great idea' was. The answer? Electric-powered air travel.
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Elon Musk's Next Great Idea? Electric Air Travel

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  • An electric airplane sounds like an interesting idea, especially for short hop flights...

    It also seems like it would be a nice case for fuel cells because you have a much more limited need for fueling stations (basically just airports) and it would be easier to store enough energy for a moderately long flight.

  • by JoshuaZ ( 1134087 ) on Sunday February 07, 2016 @06:00PM (#51458761) Homepage

    Batteries do not have the energy density of jet fuel. The primary thing that matters here is energy density, which has two forms, energy per mass and energy per volume. https://en.wikipedia.org/wiki/Energy_density [wikipedia.org] Both need to be much better than they are today for electric airplanes to have any chance (lifespan and and number of cycle uses also need to improve but that's in some ways less of a barrier.) Energy density of batteries by both metrics batteries has increased by 5%-10% a year depending on the exact metric and choice of examples https://www.quora.com/Is-it-true-that-battery-energy-density-improves-5-8-per-year [quora.com] which is exponential growth ( but with a much slower doubling time than something like Moore's Law. One has a doubling about once every 8 or 10 years.) Jet fuel has an energy density of around 45 MJ/kg, The most efficient batteries have a little under 1 MJ/kg. So one needs at least about 5 doublings before batteries can reasonably compete which will start to occur if they have an energy density of around 32/ MJ/kg. Similar remarks apply to energy density measured by joules per volume. However, there are technical reasons to think that batteries will stop doubling before that (see theabove quora link for details which argues that we can't make batteries much than four times as efficient before we start running into serious theoretical limits). At around 20 MJ/kg, one maybe could run planes practically but they would be much less convenient and practical than today's jets and that would be at the very upper end of the plausible limits just from a straight energy density estimate.

    However, the situation is even worse than that. When you use jet fuel, you use it up. Depending on the type of airplane, at take off fuel is generally 25% to 50% of the mass of the plane. So one gets serious savings that one doesn't have to move all the used fuel the entire way. That doesn't work with batteries: they are the same mass and volume whether or not they are charged, and dumping them would defeat most of the point. It might be possible to do some sort of staging approach where one uses some set of batteries to nearly empty and then have them break off in a modular plane that returns to the ground site. But that itself would lead to all sorts of additional problems.

    So it is likely that we will still see fossil fuels used for jets for the next 40 or 50 years. Indeed, it is likely that they will be the very last use of fossil fuels.

    • by t0qer ( 230538 ) on Sunday February 07, 2016 @06:13PM (#51458839) Homepage Journal

      To every upvoted point, there has to be a counterpoint.

      Sure jet fuel has a higher energy density, but that isn't the end all to the problem. You also have energy efficiency, which to my knowledge is pretty terrible on jet or turbo prop engines. I've been flying LiPo/Brushless RC aircraft for a while now, and in the right conditions your power efficiency comes right on par there with gas (minus any of the issues with ICE engines) In even better conditions, an electric plane can "recharge" batteries on descent.

      There's a brand of starter electric planes called "Parkzone" One model (F-27 Stryker Brushed) was a particular favorite of mine. I went to a Gforce Lan event at Fort Mason, and on a lull between matches I flew it out in the heavy winds of the big green lawn. I kept that thing up there for 3 hours on a NiCd battery (usually only went for 15 minutes) I just sort of hovered it, more like "sailed" it and the motor just kept recharging the battery.

      You can't really put jet fuel back in the tank like that. All sorts of crazy tricks you can do with electric though.

      • by Anonymous Coward on Sunday February 07, 2016 @07:51PM (#51459345)

        The model airplane community is where a lot of delusions about the possibility of electric air travel come from. I'm sure you've seen the "man-carrying" many-copters that even university teams are working on. Do I need to point out why that is a bizarre and stupid waste of time and resources? Quad copters are a great way of building small vehicles, because small propellers accelerate quickly, so steering by modulating the propeller speed is easy and works well. This doesn't scale up. Large multicopters are hilariously inefficient and difficult to control compared to more conventional helicopter designs. Small electric models beat ICE models hands down because internal combustion engines don't scale down well to that size. Just because something works well when you're flying one or two pounds of foam doesn't mean it's a good idea for an actual plane.

      • Good points.
        Another factor which could be looked at is the recharging vs usage capability of a battery.
        Considering that long distance jets fly in the jetstream, we might be able to use the air flow to generate quite a bit of energy. It only has to be above the losses due to the additional drag, and we might be able to go with lesser fuel than required.
        Or, in the future, fly through thunderstorms, somehow able to tap into electrically charged clouds and recharge the batteries straight away (using a thunderbo

    • by brambus ( 3457531 ) on Sunday February 07, 2016 @06:20PM (#51458869)
      So batteries don't necessarily need to directly compete with combustion engines because electric engines could (and I stress "could") have higher efficiencies than either piston or turbine engines (both of which actually lose a fair amount of the energy in the fuel to their engine cycle as exhaust heat). At 20MJ/kg a battery would compare very well to jet fuel. A good high-bypass turbofan can get maybe 40-45% efficiency. An electrically driven fan, might go as high as 80-90%. But AFAIK Musk wanted to make these aircraft supersonic. While a fan-driven engine *theoretically* can go supersonic, in practice it's so horribly inefficient that it's unlikely to be practical. That's where the Brayton cycle comes in and we're back to the 40% efficiency range (regardless if the reaction mass heating is provided by hydrocarbon fuels or an electrically-sourced heating mechanism) and batteries in that case are dead in the water.
      The kicker though, as you correctly identified, is mass loss during flight. Aircraft get a lot of efficiency from this mechanism and also significant mission flexibility (for shorter missions you can take less fuel and more cargo). An electric aircraft would pretty much have to be factory-built for max range from the factor. I highly doubt it's ever going to be practical to reconfigure an electric aircraft on the flight line for shorter haul by taking some batteries out - keep in mind how tricky even comparatively tiny electrical systems are (see Boeing 787 Li-Ion battery fires). Plus the red tape on this is would boggle the mind.
      Lastly, we needn't rely on fossil fuels. The public at large always thinks "smelly fuel = dirty". Not necessarily. We can synthesize a wide range of synthetic jet fuels already. Provided that the carbon source for that fuel is "renewable" (e.g. dissolved carbonic acid in ocean water), we could keep the venerable jet engine in place and simply source the fuel in a renewable manner. Then the fuel simply becomes a liquid chemical battery with fantastic power density and deployment flexibility.
      • Good points which do make my concerns less severe, especially in regards to efficiency. And yes, you are right that we can synthesize fuel directly although it seems like that would be economically very expensive. I like the idea though of capturing carbon from the water.
      • The way I see it you could use electricity for the rotation of the ceramic disk of a Podkletnov device, which would solve your weight problems and also allow you to reach supersonic speeds with just a small jet engine using very little fossil fuel.

      • by rtb61 ( 674572 )

        Fast vs cheap, when it comes to major environmental savings for the majority use, fast has to be ignored in favour of cheap. So flying wing, no windows (use VR), more leg room (it comes with the substantial increase in floor area made available by a flying wing, so mass no leg room limits number of passenger), no banking rudder turns only (being further away from the centre line makes banking very, very undesirable, only sufficient banking to counter centrifugally balance out the turn). Big area, means sol

    • It might be possible to do some sort of staging approach where one uses some set of batteries to nearly empty and then have them break off in a modular plane that returns to the ground site. But that itself would lead to all sorts of additional problems.

      You just solved a big part of the problem! LOL Think about gliders. Once towed to altitude, they can soar for a long time. So Musk could have some kind of quadcopter type superstructure, which includes batteries, etc, which boosts the aircraft straight up to say 15,000 feet. The craft then releases and uses standard lifting surfaces and a small electric powered prop to propel it (aka it's a standard type airplane but electric). The quadcopter framework then returns straight back down to the launch point

    • by SuperKendall ( 25149 ) on Sunday February 07, 2016 @06:45PM (#51459001)

      As I posted below, it seems pretty obvious you would use fuel cells instead of batteries for an electric aircraft... from your energy density link compressed hydrogen has an even better energy density (142 MJ/kg) than jet fuel (46 MJ/kg)!

      The cost of hydrogen production is estimated to become close to gasoline production over the next decade or so [energy.gov], but there is a huge pollution benefit to using fuel cells which could drive adoption quicker.

      The currently very low cost of oil is probably the main thing that would keep airplanes from going electric soon.

      • This is a really good point, and it might be that planes are one of the few contexts where hydrogen really is the way to go.
      • and even more efficient would be skipping storage all together for the take-off and landing and simply beaming the energy.
      • Actually hydrogen has great specific energy [wikipedia.org] (energy per unit mass), but lousy energy density [wikipedia.org] (energy per unit volume). Even ignoring the massive weight of a vessel capable of holding hydrogen at >5000 PSI (needed for it to stay liquid at room temperature), liquid hydrogen has only on the order of 1/10 the density as compared to jet fuel (70.85 g/L vs ~800g/L).
      • Re: (Score:3, Insightful)

        by delt0r ( 999393 )
        The problem with hydrogen is storage. Even in liquid form it is only 70kg per m3 compared to about 800kg/m3 for jet fuel. And that is at 20K which is really really really really cold and complicates tank design a lot. other forms of hydrogen storage have massive weight penalties.
    • However, the situation is even worse than that. When you use jet fuel, you use it up. Depending on the type of airplane, at take off fuel is generally 25% to 50% of the mass of the plane. So one gets serious savings that one doesn't have to move all the used fuel the entire way. That doesn't work with batteries: they are the same mass and volume whether or not they are charged, and dumping them would defeat most of the point. It might be possible to do some sort of staging approach where one uses some set of batteries to nearly empty and then have them break off in a modular plane that returns to the ground site. But that itself would lead to all sorts of additional problems.

      A very interesting point! I have never thought of it that way before. I would mod this +1 insightful.

      when people ask me why electric vehicles aren't as good as conventional cars, I explain that gasoline and diesel are basically God's fuel. There's an enormous amount of energy in a gallon, it's a liquid at room temperature and pressure so it's easy to carry around, it doesn't explode and it's cheap and abundant. It's really hard for any alternative fuel to match most of these characteristics. And because of

    • by vux984 ( 928602 )

      Genuinely curious: Can you clarify why your argument doesn't apply to cars?

      Given jet fuel is 45MJ/kg, and the best battery is 1MJ/kg (per your post), then how is it electric cars are already viable, given gasoline is 44MJ/kg?

      • You can recharge/refuel more frequently with an electric car. A bit hard to land and recharge in the middle of the Atlantic ocean. So the reduced range of an electric car (around 200 miles for an electric car as opposed to 300-400 miles for a gas car) doesn't matter as much. Also, cars are less dependent on fuel in some sense than planes since planes need to go fast. So you need a lot more fuel proportionally, so its efficiency matters more for planes.
        • by vux984 ( 928602 )

          You can recharge/refuel more frequently with an electric car. A bit hard to land and recharge in the middle of the Atlantic ocean

          Lots of flights are between New York and Chicago, LA and Las Vegas, Miami and New York, Seattle and LA... their is no necessity that that electrics have to do trans-pacific runs before we can start using them.

          o you need a lot more fuel proportionally, so its efficiency matters more for planes.

          I can see that it matters more. I'm not sure its nearly as far away as you suggest. Even if a plane needs some a lot of extra weight in batteries than it would in fuel, if its cheaper to recharge / swap batteries than buy jet fuel then it becomes practical.

          Especially for short hops. For example, LA to Vegas.

      • by Fwipp ( 1473271 )

        Well, cars stay on the ground. Weight isn't nearly as big of a deal for cars as it is for planes.

        • by vux984 ( 928602 )

          Well, cars stay on the ground. Weight isn't nearly as big of a deal for cars as it is for planes.

          Fuel / energy to weight ratio defines the range in a car as much as a plane.

          And yes, a fully loaded trans-pacific jet is half fuel by weight, so a less dense energy storage becomes a big issue, the jet would weight 20x as much if it were battery powered... and that's before counting the energy need to move those batteries so those batteries would themselves need more batteries because of the weight they added... so it just doesn't work.

          But what percentage of the weight is fuel from LA to Vegas or LA to Palm

    • The technical problems with this are immense

      What has Elon Musk done lately where this wasn't the case?

      Batteries do not have the energy density of jet fuel.

      Good place to start. To the science-a-torium!

      C'mon, people. PMA.

    • by AmiMoJo ( 196126 )

      He is only talking about electric take off and landing. The aircraft would need enough battery power to get into the air and switch to a conventional jet engine. It could then re-charge the batteries in flight before landing. He said he was thinking about VTOL, and I get the impression his idea is to make airports much more compact and able to be positioned in areas where pollution would normally prohibit them.

      Somehow I knew the first post would be someone making your exact point, because they didn't bother

      • Is he? I didn't get the impression of that from TFA that it would switch over. TFA talks about both electric and VTOL but not about using conventional power during flight. If that's what he meant, that's much more potentially reasonable but given his long-term goals of dealing with global warming and fossil fuel dependence (which is why he's so in favor of electric cars) that doesn't seem like that's what he means. Do you have a citation or source that he means that?
    • by idji ( 984038 )
      hohum. You've just outed yourself as part of the status quo. stop with your self-congratulatory praise on how well you know it is impossible. put down your pen and put on your thinking cap and come up with a great new step into the future. You will be forgotton for your description of the status quo - you will be immortalized if you find an answer. Elon Musk is not interested in the status quo - he is interesting in solving the big problems and provoking others to solve the big problems You are part of the
  • by 93 Escort Wagon ( 326346 ) on Sunday February 07, 2016 @06:25PM (#51458893)

    Does anyone actually refer to Elon Musk as "the real life Tony Stark", other than some fanboys here on Slashdot? Because this is the only place I ever see it - although you can certainly rely on it happening here, every flipping time he's mentioned.

    • by Tom ( 822 )

      His cameo in the actual Iron Man movies is a pretty good indicator that at least someone at the movie studios also saw the connection, so yes.

      • I didn't see him in the movie, and I watched the whole thing through.

        • by bakes ( 87194 )

          He's in Iron Man 2. Tony Stark is at an event or dinner of some sort, shakes his hand and says 'Hi Elon!'

      • by Luthair ( 847766 )
        Larry Ellison also had a cameo in Iron Man.
    • Who TF is this Tony Stark anyway?
    • As far as I can tell, he's mostly a money man. You don't see any pictures of him welding, or running a milling machine, or soldering up a circuit.

    • by k6mfw ( 1182893 )
      Actually every forum and media outlet see Elon as the Second Coming. If anyone in these areas criticizes him, they will be flamed, downvoted, etc.
  • by pesho ( 843750 ) on Sunday February 07, 2016 @06:30PM (#51458915)
    The only practical application of an electric airplane within the near future would be lug around batteries. Which may come handy to Elon with his gigantic battery factory. Stuff the "plane" with fully charged batteries and fly it to the nearest sea port or distribution center.
    • Why not for flight training [pipistrel.si]? Fuel is the biggest cost in running an aircraft, and if you don't need the range, battery powered is fantastic. It's the same trade-off as with electric cars.

  • by alexhs ( 877055 ) on Sunday February 07, 2016 @06:35PM (#51458935) Homepage Journal

    Well, you see the problem: it doesn't fit in the subject line.

    Next time you reference Him, I suggest you use the proper enneagrammaton for The Man Known As The Real Life Tony Stark: TMKATRLTS.

  • He keeps recycling old ideas, and the media keeps claiming he's inventing something new. (They should really do at least 3 minutes of research before jumping to such false conclusions.)
    It seems his real talent is to convince people to go back to old ideas that didn't take off before. That's neither good nor bad, but stop overhyping them.
    • by Pulzar ( 81031 )

      It seems his real talent is to convince people to go back to old ideas that didn't take off before. That's neither good nor bad, but stop overhyping them.

      Why is that not good?

      I don't think anyone's claiming that he invented an electric car, but he's certainly the first to make a viable company out of building them. So, he took an old idea that didn't work and made it work. That's not "neither good nor bad", that's simply good.

  • A plane takes off and lands horizontally because it's safer. They can glide to a landing if something goes wrong. Vertical takeoff and landing seems unnecessarily risky to me, unless Musk wants them to be able to take off from and land just about anywhere. Fine, make that an option, not the primary means of takeoff and landing.
  • Seriously, he needs to keep this to his company while he focuses on the other 3, along with his hyperloop. If SpaceX was to work on this behind the scene for the next 2-3 years, then announce it, he could make a world of changes. ,
  • Yes, I'm kidding.

  • by quax ( 19371 ) on Sunday February 07, 2016 @08:04PM (#51459417)

    No idea how Elon Musk feels about it, but I think it's not quite appropriate.

    The fictional Tony Stark made his money with dubious weapons business.

    Frankly Elon Musk is the better man.

  • The first electric plane to cross the English channel was in 1981.

    On July 7, 1981, the aircraft flew 163 miles from Pontoise – Cormeilles Aerodrome, north of Paris, France to Manston Royal Air Force Base in Manston, United Kingdom, staying aloft 5 hours and 23 minutes, with pilot Stephen Ptacek at the controls. Currently the plane is owned by the Smithsonian Institution's Air and Space Museum.

    And the Solar Impulse series can charge it's batteries enough during the day to fly to the next dawn [wikipedia.org]. It did a non-stop flight from Japan to Hawaii.

    And Airbus has a jump on them as well [wikipedia.org].

  • All this new tech is fantastic, but it is very frustrating when you have the cash to spend on it and the companies that resell his tech (in Australia) will not bother to take on jobs that are more complex than a "plug it in and walk away" type install.

    I really wish Elon Musk would give them a boot up the ass about that attitude because big problems don't get solved by only accepting easy and routine tasks.
  • "...the man so many people call the real life Tony Stark has done an incredible job of bringing electric vehicles to the mainstream."

    Errr, not to quibble, but a base model Tesla costs over $100,000....that's not exactly "mainstream" by any standard I'm aware of.

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