Slashdot Mirror
Elon Musk's Next Great Idea? Electric Air Travel (bgr.com)
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.
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 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 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.
When flying, isn't it weight rather than volume that matters?
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
Yes. Also, you can't ignore comparative efficiencies of engines. Or engine mass to weight ratios. Or the length of time to market, and the expected level of battery change during that time period. Or side benefits (for example, the ability to have small, very light engines was made use of in one NASA experiment that placed numerous small engines along a wing, causing an effect that created drastically more lift at low speeds and allowing for a much shorter takeoff distance).
And beyond that, you can't ignore economics. Having reduced range but getting your fuel at a fraction of a cost may ultimately prove to be more desirable. It's a very complex issue that one can't just make all-encompassing statements based on a single figure like "energy density of batteries vs. energy density of fuel".
Anyway, this is hardly Elon's first time to mention it. Years ago he mentioned that he wants to be the first person to have an electric plane break the sound barrier. If there's anything one can say about Elon, it's that he sure doesn't set the bar low...
It's times like this I wish I had a friend named 'The Professor'.
You might understand math but you don't understand economics. ... This little thing called "scale," and we now have the ability as the average person to purchase said good.
Not everything "scales". Eg gold and land do not "scale". The more people buy gold the dearer it gets.
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, 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.
"There is more worth loving than we have strength to love." - Brian Jay Stanley
I've only heard it from tech press who are constantly cheerleading Tesla and Musk. I've questioned the number of Tesla stories on Slashdot before and been downvoted by fanboys, their marketing, sales methods, spats with journalists etc just aren't technology stories.
No, you are. Telsa price out of range of most people, the batteries are too damn expensive
Are you a typcial progressive-liberal shithead that can't understand hard economonics and engineering?
Exactly, I thought otherwise - and wrongly, when a friend gave me teh lecture while we were tooling down the road in his F-450 Platinum edition Pickup truck. The base model starts at 65 thousand.
A true vehicle for the masses.
And don't say it's a rare bird. I've seen several tooling around in my neck of the woods. Well, actually I've never seen one off the road. It's a really nice truck. But remarkably expensive once you add in the options.
And you don't need to be your "typical liberal progressive shithead" to look up prices on the internet. Parts of that invective might be applicable to some folks who can't be bothered to verify their memes.
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
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.
-1 Stupid.
You're forgetting that 60-75% of the energy in hydrocarbon fuel is wasted in the form of heat when you burn it in a combustion engine. Conversion losses for electricity are a tiny fraction of this.
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.
If information wants to be free, why does my internet connection cost so much?