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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.
If it takes off vertically, you could possibly provide electrical power from the ground for a certain distance, overcoming the initial lift off energy use at least. But still, better hope battery tech evolves dramatically for any real prospect of fast long distance E flying.
Li-Air have roughly the same specific energy as gasoline. I'm guessing aviation fuel is similar. So if electric engines can be that are more efficient than jet engines...
Who ordered that?
A very expensive Li battery can hit 1 MJ/L. Diesel (jet fuel) is about 36 MJ/L. There needs to be over an order of magnitude improvement before this can work.
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.
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.
On the other hand, as the jet fuel is consumed the weight decreases. Batteries stay the same weight for the entire flight.
An interesting point . . . when a jet needs to make an emergency landing with full tanks, it will ditch the fuel before attempting a landing, because of the fire danger. Will this be necessary with Li-Air? Could there be a danger of a fire if the plane needs to land under "extraordinary circumstances? Like, no landing gear?
So will a Li-Air plane need to have a mechanism to ditch the batteries?
And if the batteries land in my backyard, can I keep them . . . ?
Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
All the inconvenience & cost of air travel with the speed of a train. Why not just argue for an electric zepplin, at least it could probably cross an ocean or a continent.
Electric air planes with lithium-air batteries would weigh the same at landing as they do at takeoff whereas a 747 loses around a quarter of it's weight en-route.
It is even worse then that. Li-Air batteries absorb oxygen as they release electricity. They get heavier the lower the electric charge. The only possible advantage is that they are lightest when they require the most power - take-off.
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.
Musk seems to be assuming an order of magnitude improvement in battery technology for all his investments... maybe he knows something we don't? Lot's of people are claiming improvements right now, none seem to provide energy density exceeding gasoline. Probably hydrogen comes closest in energy per unit weight, but I'd think the storage difficult would negate that.
I've abandoned my search for truth; now I'm just looking for some useful delusions.
An interesting point . . . when a jet needs to make an emergency landing with full tanks, it will ditch the fuel before attempting a landing, because of the fire danger.
No, no they don't. The dump fuel because the maximum landing weight on commercial aircraft is much lower than the maximum takeoff weight. Fuel is too damn expensive to dump just because you don't want to explode. They'll dump fuel until they are under the max landing weight, then land.
You can land at heavier than the max landing weight - but you'd better get it right or you'll never fly again - even if the landing is a good one.
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