40 ms·

I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to

I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to fly higher - increasing efficiency and speed. Apparently the normal 30,000 feet cruising altitude is not higher because the reduced oxygen levels at higher altitudes impact the gasoline combustion too much. Even at 30,000 feet the air is thick as soup at cruising speed, and that's why planes have not got faster for the last 50 years. Go higher, as electrics could do, and you reduce the air pressure further and could fly faster and more efficiently. Who knows when battery technology will be advanced enough, but it sounds like a goal worth shooting for (as well as the other benefits of noise reduction and environment concerns)

masklinn 11y ago
> I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to fly higher - increasing efficiency and speed. 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).
- simonsquiff 11y ago
  I'm not sure it's ignoring everything - as this article states, electric planes exist today, and are improving at a fast rate. Batteries are also improving (thanks to Musk and others), not that electric planes needs to be battery based - fuel cells could be the answer (though presumably these require oxygen so might have altitude issues). So whilst far away, it's an extrapolation from our current position. Nuclear planes don't exist today in any form, and would have major safety concerns no doubt (any accident would be pretty catastrophic)
  - masklinn 11y ago
    > I'm not sure it's ignoring everything - as this article states, electric planes exist today 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 https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL
    - adventured 11y ago
      "That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing" 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.
      - masklinn 11y ago
        > That's exactly what brings costs down 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.
srb- 11y ago
Like most, I originally assumed that because batteries have poor specific energy compared to fossil fuels, there was no point in considering them for aircraft. 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.)
- sokoloff 11y ago
  Electricity is not especially cheap compared to jet fuel. Jet Fuel has about 128kBTU/gal and is available around $2/gal, so 64kBTU/$. Electricity is about 3400BTU/kWhr and a kWhr is about $0.05, or about 68kBTU/$.
  - coryrc 11y ago
    Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. 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 https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency [2] http://www.ajc.com/news/business/airlines-keep-adapting-to-high-fuel-costs/nQRrf/ http://www.ajc.com/news/business/airlines-keep-adapting-to-h...
    - masklinn 11y ago
      > Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. 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)
cmsmith 11y ago
>Apparently the normal 30,000 feet cruising altitude is not higher because the reduced oxygen levels at higher altitudes impact the gasoline combustion too much. 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.
deleted 11y ago
[deleted]
stcredzero 11y ago
If you could make beamed power work, you wouldn't have to haul your power source up to those altitudes. Of course, this is quite a "big if."
sehugg 11y ago
There are other considerations, like how stall speed and critical Mach intersect as you go higher (https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%29 https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%...). So any plane that can fly above 60,000 feet is likely going to be a supersonic design. More drag, more heat, more complexity. Concorde had plenty of issues that had nothing to do with the power plant.

masklinn 11y ago

> I read a piece by Elon Musk, who was saying that electric planes - whilst very far away - are the future of air travel. Why? Because they will allow planes to fly higher - increasing efficiency and speed. 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).

simonsquiff 11y ago
I'm not sure it's ignoring everything - as this article states, electric planes exist today, and are improving at a fast rate. Batteries are also improving (thanks to Musk and others), not that electric planes needs to be battery based - fuel cells could be the answer (though presumably these require oxygen so might have altitude issues). So whilst far away, it's an extrapolation from our current position. Nuclear planes don't exist today in any form, and would have major safety concerns no doubt (any accident would be pretty catastrophic)
- masklinn 11y ago
  > I'm not sure it's ignoring everything - as this article states, electric planes exist today 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 https://en.wikipedia.org/wiki/Tupolev_Tu-95LAL
  - adventured 11y ago
    "That's a joke right? Tesla's battery innovations are related to manufacturing efficiency and structural sharing" 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.
    - masklinn 11y ago
      > That's exactly what brings costs down 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.

srb- 11y ago

Like most, I originally assumed that because batteries have poor specific energy compared to fossil fuels, there was no point in considering them for aircraft. 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.)

sokoloff 11y ago
Electricity is not especially cheap compared to jet fuel. Jet Fuel has about 128kBTU/gal and is available around $2/gal, so 64kBTU/$. Electricity is about 3400BTU/kWhr and a kWhr is about $0.05, or about 68kBTU/$.
- coryrc 11y ago
  Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. 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 https://en.wikipedia.org/wiki/Jet_engine#Energy_efficiency [2] http://www.ajc.com/news/business/airlines-keep-adapting-to-high-fuel-costs/nQRrf/ http://www.ajc.com/news/business/airlines-keep-adapting-to-h...
  - masklinn 11y ago
    > Except, electricity will be about 85-90% efficient and a turbofan is about 30% efficient [1], roughly tripling the cost advantage. 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)

cmsmith 11y ago

>Apparently the normal 30,000 feet cruising altitude is not higher because the reduced oxygen levels at higher altitudes impact the gasoline combustion too much. 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.

deleted 11y ago

[deleted]

stcredzero 11y ago

If you could make beamed power work, you wouldn't have to haul your power source up to those altitudes. Of course, this is quite a "big if."

sehugg 11y ago

There are other considerations, like how stall speed and critical Mach intersect as you go higher (https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%29 https://en.wikipedia.org/wiki/Coffin_corner_%28aerodynamics%...). So any plane that can fly above 60,000 feet is likely going to be a supersonic design. More drag, more heat, more complexity. Concorde had plenty of issues that had nothing to do with the power plant.