But Musk's assertion has made me reconsider. Has anyone here done the math? What I think he's talking about is NOT a conventional plane with a battery simply replacing the gas tank, but instead essentially a flying battery, where 90% of the plane's mass is battery.
This sounds ridiculous at first, but when you consider how cheap electricity is compared to jet fuel, as well as the other benefits the OP mentioned, there might be something to it (for short-haul flights.)
http://www.aviation.com/general-aviation/elon-musk-toying-de...
Weight is the premium on planes, so the 10% of non-battery you're talking about is a full plane minus fuel tanks. An E-170 is 21t of empty plane, up to 9t of fuel and up to 36t total (MTOW). Given batteries have 1% the energy specificity of aviation fuel (so you need 100 times the weight in batteries for the same stored energy), the math doesn't quite work out.
> This sounds ridiculous at first
And at second, and at third.
> when you consider how cheap electricity is compared to jet fuel
Doesn't compensate the problem of needing a plane 10 times as heavy with 1/10th the payload.
> as well as the other benefits the OP mentioned
Which don't really make sense, lower air density means your turboprops have nothing to work with, there's no such thing as turbofans let alone turbojet so the gains in drag are killed by the inability to actually go forward.
Jet Fuel has about 128kBTU/gal and is available around $2/gal, so 64kBTU/$.
Electricity is about 3400BTU/kWhr and a kWhr is about $0.05, or about 68kBTU/$.
Fuel costs are about 35%[1] of operating costs, so only a ~20% cost reduction is possible for fuel change, so your point is still mostly valid.
[1] https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency
[2] http://www.ajc.com/news/business/airlines-keep-adapting-to-h...
But then batteries store 1% the energy per mass fuel does so even assuming triple the efficiency, the energy storage is 30 times easier (assuming everything else stays constant which it can't because now your craft is an order of magnitude heavier and your short-haul plane is as heavy as a 747)
Musk has said several times that if he wasn't working on space and EVs, he'd be working on hyperloop or electric planes. Wonder what potential he sees in the latter.
If this is true, wouldn't it make more sense to bring liquid oxygen up with you to burn with the fuel? That would only reduce your fuel energy density by a factor of 2 or 3, instead of the factor of 30-100 being claimed for batteries.
Of course that would not make sense, and rockets don't become the most efficient way to travel until you are a few times higher than 30,000 ft. But it's useful to put the idea of batteries in perspective.
That's a meaningless/nonsensical assertion. If we're going to ignore basically everything we can also state that nuclear is the future of air travel (and that's actually a more sensible statement, nuclear fuel has ridiculous specific energy).
Prop toys exist, not "future of aviation" anything. Props being an other issue, electric planes means no turbofans.
> Batteries are also improving
Batteries are not improving at a rate which would increase their specific energy by 2 orders of magnitude (the difference between the specific energy of the best batteries available today and bog-standard jet fuel) in any sort of interesting timescale. And that's before considering environmental issues, most batteries don't appreciates temperatures of -20C and below.
> thanks to Musk
That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing.
> So whilst far away, it's an extrapolation from our current position.
It's not extrapolation it's daydreaming based on what is basically magical thinking. It's less of an extrapolation than dyson spheres are.
> Nuclear planes don't exist today in any form
Nuclear planes were demonstrably feasible (if not necessarily smart) in the 60s: https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL
Now, electric doesn't mean battery. Fuel cells, solar, or even hybrid might all play a part. I believe a large proportion of energy consumption is during takeoff - what if you could draw take off power needs from the airfield rather than from the aircraft? What about hybrid - use gas to get to 30,000 feet, then turn on electric to go higher than that? Yes battery energy density is miles away currently, but if we avoid batteries in part, and improve them too, where might things be in 50 years time? The point is we are on the journey with electric planes, and the goal is a good one for reasons stated. Major problems to overcome - absolutely, but this is not a short or medium term prediction. But 'Magical thinking' required, more so than Dyson spheres? That's harsh.
I think Musk said he'd like this to be a far future project for him. He said he's driven by not wanting to go backwards - how space travel was worse than the 60s, as is air travel (no supersonic public aircraft any more). Electric planes - if possible - would be the solution to faster air travel. With Tesla and SpaceX under his belt, he'd certainly got the necessary chops to tackle it.
But higher altitude means lower air density which means your turboprops windmill into nothingness and have no way to propel the plane forward (even ignoring the issue of staying up in the air at all, existing airliners already fly quite close to the limits of their flight envelopes in normal conditions).
> What about hybrid - use gas to get to 30,000 feet, then turn on electric to go higher than that?
And where would you get the energy to do that in-flight? Certainly not solar, Helios already had a larger wingspan than a 747-8.
> Major problems to overcome - absolutely, but this is not a short or medium term prediction.
Neither are dyson spheres, and at least we've got some idea about how to handle those.
> But 'Magical thinking' required, more so than Dyson spheres? That's harsh.
Is it now?
> no supersonic public aircraft any more
There is no supersonic "public" aircraft because people have decided it wasn't worth the cost and have gravitated towards cheap high-density flying instead, it's not like we're flying any less than in the 60s or less far (a 777LR can go halfway around the globe without stopping) so the comparison to space travel is bonkers.
> Electric planes - if possible - would be the solution to faster air travel.
That doesn't make a lick of sense, electric engines are the slowest thing you can find in the sky. The only way "electric planes" would be faster than turbojets — let alone ramjets or rocket engines — is for the plane itself to be a ballistic component launched by a gigantic railgun, and then — assuming you manage to build the thing in the first place — your passengers are literally paste on takeoff as they eat a few hundred Gs.
That's exactly what brings costs down: economies of scale via efficient mass production. Whether we're talking about dramatically boosting the electric car market, or the giga factory.
Dyson spheres? Now who's exaggerating. Electric airplanes already exist, and will continue to improve for decades to come. Dyson spheres do not exist, and are not on the horizon.
The problem of batteries on airliners is not cost, it's that they don't store enough energy per mass. Even if your batteries are free, when your plane can't take off because its mass has increased >10 fold there's very little point, you're left with an expensive bus too wide to take roads.
> Dyson spheres? Now who's exaggerating.
Same as before.
> Electric airplanes already exist, and will continue to improve for decades to come.
The original assertion is that they're the future of air travel, not the future of small-scale hobbyists.
> Dyson spheres do not exist, and are not on the horizon.
Both of which apply equally to electric airliners. Electric airliners require a literal technological revolution, so do dyson spheres.