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The Solar Impulse is really cool technology. It also shows why oil use has been so prolific. the energy-to-weight ratio of jet fuel is a marvel when you conside

The Solar Impulse is really cool technology. It also shows why oil use has been so prolific. the energy-to-weight ratio of jet fuel is a marvel when you consider the size of today's jet aircraft and the distances they fly with hundreds of passengers.

Retric 11y ago
Flight actually scales up really well. Double the volume means less than double the energy required. So, larger craft can get a better cargo to energy efficency and or more speed. Solar impulse is large, but light and can carry two people plus stuff. Keep scaling it up, ditch the pilot, and you can have something between big slow boats and fast, but expencive jet aircraft. A full 50,000 lb 20' shipping container and 1 week China to US is probably viable. (Boats take 2 week to 1 month and unload at ports.)
- dogma1138 11y ago
  Flight actually doesn't scale up that well, especially with solar.
  - Retric 11y ago
    OK, it's better than 1:1 vs cargo even for solar assuming you alter the design to fit your new scale. Beyond that, it's a question of what you want to call "Well" :)
    - dogma1138 11y ago
      No it doesn't scale 1:1 or any way else at least not in any specific manner. The scaling depends on how much lift you generate, the lift is a question of speed and your the available lift surface the nominal lift produced is then divided by surface area to give you your wing loading. Solar is pretty much the most inefficient way of powering virtually any aircraft because you needlessly increase the weight of the lifting surface and batteries weight considerably more than fuel and that weight is dead weight during the entire flight while a fueled aircraft becomes lighter. That said the scaling between the volume and the "surface area" isn't even in question here because you are going to be hitting a wall much quicker and that's takeoff weight as mentioned before lift is a factor of the surface area that can provide lift and the speed of the aircraft (as well as air density and some other things but lets ignore it) the heavier the aircraft the more energy you need to actually get to takeoff speeds, and when you make your lift surface bigger you increase drag as well as weight. The speed you can reach is going to be more or less limited because even a 100% efficiency solar powered engines are going to be limited to the max cell efficiency * cell surface area, the 2nd part of the equation is your wing surface and eventually there is a limit to how big your wings can be and still support themselves and most importantly not flutter. When you take all that and more into account there is absolutely no fucking way that you'll make an aircraft capable of lifting a 50,000lbs of crago, heck you won't build a solar aircraft capable of lifting 50,000 lbs of anything including itself. To put that into perspective 50,000lbs is 1/6th of the maximum structural load that a 747-8F (freighter) can carry, and about 1/4th of the nominal cargo load. To put it into even more perspective Solar Impulse weights 3000 lbs, it's maximum takeoff weight is about 4000 lbs and it has a max speed of 80km/h with a wing span greater than that of a 747. To put it simply there is no freaking way to scale this up, there is a good reason why nature haven't developed heavy flyers the heaviest bird capable of flight weights 35 lbs, the rule of thumb is that when you double the weight you need a 4th time as much wing area and spend 4 times more calories to achieve flight and while mechanical flight isn't exactly the same it's not that different - the amount of energy you can produce more or less limits how well you can fly because at the end if you stick 2 SRB's to a cargo container you don't even need wings. P.S. And that's before we getting into finding a material light enough to be viable for solar flight while still being able to bare the load of 50,000 lbs without collapsing, but even if you'll take perfect carbon nano tubes or any other super material you still won't be getting off the ground. If you want solar cargo air transport blimps are probably the way to go...
      - Retric 11y ago
        Try and make a solar powered fixed wing aircraft fly at 43 mph while being 1 foot wide and reserving 25% of it's weight for cargo and keeping it in the air for 36 hours. You have 45 kW / (200 ^ 2) = 1.1 watts peak solar output to work with. The issue with overly large wings is mechanical stress let's try and get around that. <This is a dumb design> As a thought experiment, take 3 Solar impulse aircraft fly them next to each other with a simple non weight baring cable to share power between them. The outer two can clearly provide more power than they need and supply that extra power to the center one. Now the center one has extra power for 'free'. So, it can have a higher angle of attack and more weight. As to scaling birds, a Quetzalcoatlus had a wing span of 9 to 12 meters. That's huge for a land animal. https://en.wikipedia.org/wiki/Quetzalcoatlus https://en.wikipedia.org/wiki/Quetzalcoatlus Birds are limited by biology not so much aerodynamic issues.
        dogma1138 11y ago
        Birds are definitely limited by aerodynamics, biology just says well screw this it ain't worth it because life forms are limited by the amount of energy available to them. If we take the heaviest flying bird today it has a wing span of about 3M and a total wing surface of slightly under 1 m/sq the Quetzalcoatlus you've mentioned has a wing span of about 15m and a total wing surface of about 35 m/sq, back of the envelope math means that about a mass increase of about 12 times over the Kori (heaviest bird capable of flight) results in about 30-35 times the increase in lift surface (and we are still unclear if the damn thing was even capable of powered flight or not). And again you are missing the point Solar Impulse can lift about 1000 lbs of w/e if you want to scale it up either increase the thrust by 50 or increase your lift surface by 50 to get to that 50,000 lbs cargo you want. If we ignore load baring and drag than 3 Solar Impulse aircraft combined could lift 3000 lbs that's it. We can argue about this till the sun doesn't shine it won't change the fact that solar flight will never be a viable option for cargo transport. But it can replace other things, things that for example are well in range of the 1000 or lbs of payload that any reasonable designed solar aircraft could carry - surveillance, communications, weather and atmospheric monitoring equipment etc. They could potentially replace satellites, and increase the endurance of both military and civilian drones considerably but no one is looking at them to carry cargo because it's simply silly. Also if you want to move 50,000 lbs today by air it usually won't take less than 6 days, the only thing you can really ship overnight are small things that end up going on commercial flights not cargo flights. And while it's also true that a container ship can take 21-30 days from say China to the US about 14-15 of those days are spent in local transit and loading, the sailing it self a cargo ship can do within 10 days of good weather with the average being probably closer to 12 or so days due to weather and fuel economy.
- barney54 11y ago
  I'm a bit skeptical of scaling up Solar Impulse. The plane only has room for one person. If the plane could care another 250 pounds for another person and gear, I'm sure they would have done it. And Solar Impulse has a 200 foot wingspan--the same as a 747.
  - bikamonki 11y ago
    Progress takes time and money. Imagine they needed to take an 8 month break and raise 20M to fix a battery heating issue. Each component of a complex solution, like a solar plane, makes slow but steady progress: lighter/stronger materials, lighter/more durable batteries, etc. Software will also play a huge role automating and making resource efficiency better. The fact is that step one is cleared: flight around the world on solar power :)
- Gravityloss 11y ago
  Flight scales badly to slow speeds. Let me demonstrate with some very rough calculations: Imagine three aircraft flying the same distance. The first is a large airplane flying at 20 m/s. Solar impulse speed. The second is a large airplane flying at 200 m/s. Basic propeller plane. The third is a small airplane flying at 200 m/s. Slow plane: speed: 1x area: 1x lift: 1x payload: 1x drag: 1x thrust: 1x power: 1x distance: 1x energy: 1x Big fast plane: speed: 10x area: 1x lift: 100x payload: 100x drag: 100x thrust: 100x power: 1000x duration: 0.1x distance: 1x energy: 100x Small fast plane: speed: 10x area: 0.01x lift: 1x payload: 1x drag: 1x thrust: 1x power: 10x duration: 0.1x distance: 1x energy: 1x You can see that you use the same energy per payload no matter how fast you go, but your plane can be a lot smaller if you go fast. (This didn't take into account altitude. That means you can go even faster for the same energy expenditure.)
  - Retric 11y ago
    Things are far more compex than you are suggesting. The tradeoffs for spead work out largely because you can increase altitude which is very useful. I accept that Solar does not work to supplement the onboard generator used for electrical power on jets due to weight and night time flights. At the same time solar is ~1% the fuel cost for that amount of power for 20 years. They say they can scale this up 50x and carry 50 people. IMO, it would be better to build cargo only craft in that size range as this is far to slow outside of sight seeing in VFR. Not to mention wind. That said if you can say double the solar power and add significant altitude and speed that's much more viable. I am assuming this is significantly worse than the best possible solar aircraft we could build in say 30 years.
    - Gravityloss 11y ago
      Well, 1/100 the cargo and 1/10 the speed means you need 1000 solar planes for every kerosene plane for the same route revenue. If we assume they cost the same to buy since they are the same size. And that doesn't take into account night flying etc... Much better to have the solar panels on land and do synthetic kerosene for planes. Ships go half the speed of Solar Impulse, but they have a lot more payload per dollar invested.
barrkel 11y ago
Indeed. I expect we'll synthesize jet fuel or a close equivalent (something that burns and reduces airframe weight) from electric or bio sources long after most other engines have moved to electric. Perhaps we'll generate electricity on board, but it will be with a dense, wasting fuel. And we certainly aren't going to use solar to power commercial human air transport any time this millenium; it will always be better, for people, to compress energy before a flight and travel faster, than try to make the flight itself self-sustaining and travel slower. The only exception could be recreational flyers.
- gruturo 11y ago
  I wouldn't be so sure this would not happen this millennium as you say. Maybe not this decade, but I certainly imagine sooner or later we will have I.e. a big satellite beaming power directly to a plane (laser or microwave, you choose). Once launch costs make this plausible and it's deemed safe and secure, why not? Bonus, you now have an orbital death ray if you decide to go Bond villain.
  - Piskvorrr 11y ago
    That would be about as much of a "bonus" as the Chernobyl disaster was a "bonus" to nuclear power. In other words, a threat.
- cmsmith 11y ago
  We've been synthesizing one liquid hydrocarbon fuel for thousands of years; ethanol is pretty similar to jet fuel in energy density and combustion. I think the possibility that in the future we'll have cheap solar/wind grid power and use that to produce ethanol, rather than charge batteries, is more likely than people think. Ethanol production isn't terribly efficient, but if your input power is sustainable it doesn't really matter.
  - elithrar 11y ago
    Ethanol is about 70% of the energy density of Jet A-1: https://en.m.wikipedia.org/wiki/Energy_density https://en.m.wikipedia.org/wiki/Energy_density

Retric 11y ago

Flight actually scales up really well. Double the volume means less than double the energy required. So, larger craft can get a better cargo to energy efficency and or more speed. Solar impulse is large, but light and can carry two people plus stuff. Keep scaling it up, ditch the pilot, and you can have something between big slow boats and fast, but expencive jet aircraft. A full 50,000 lb 20' shipping container and 1 week China to US is probably viable. (Boats take 2 week to 1 month and unload at ports.)

dogma1138 11y ago
Flight actually doesn't scale up that well, especially with solar.
- Retric 11y ago
  OK, it's better than 1:1 vs cargo even for solar assuming you alter the design to fit your new scale. Beyond that, it's a question of what you want to call "Well" :)
  - dogma1138 11y ago
    No it doesn't scale 1:1 or any way else at least not in any specific manner. The scaling depends on how much lift you generate, the lift is a question of speed and your the available lift surface the nominal lift produced is then divided by surface area to give you your wing loading. Solar is pretty much the most inefficient way of powering virtually any aircraft because you needlessly increase the weight of the lifting surface and batteries weight considerably more than fuel and that weight is dead weight during the entire flight while a fueled aircraft becomes lighter. That said the scaling between the volume and the "surface area" isn't even in question here because you are going to be hitting a wall much quicker and that's takeoff weight as mentioned before lift is a factor of the surface area that can provide lift and the speed of the aircraft (as well as air density and some other things but lets ignore it) the heavier the aircraft the more energy you need to actually get to takeoff speeds, and when you make your lift surface bigger you increase drag as well as weight. The speed you can reach is going to be more or less limited because even a 100% efficiency solar powered engines are going to be limited to the max cell efficiency * cell surface area, the 2nd part of the equation is your wing surface and eventually there is a limit to how big your wings can be and still support themselves and most importantly not flutter. When you take all that and more into account there is absolutely no fucking way that you'll make an aircraft capable of lifting a 50,000lbs of crago, heck you won't build a solar aircraft capable of lifting 50,000 lbs of anything including itself. To put that into perspective 50,000lbs is 1/6th of the maximum structural load that a 747-8F (freighter) can carry, and about 1/4th of the nominal cargo load. To put it into even more perspective Solar Impulse weights 3000 lbs, it's maximum takeoff weight is about 4000 lbs and it has a max speed of 80km/h with a wing span greater than that of a 747. To put it simply there is no freaking way to scale this up, there is a good reason why nature haven't developed heavy flyers the heaviest bird capable of flight weights 35 lbs, the rule of thumb is that when you double the weight you need a 4th time as much wing area and spend 4 times more calories to achieve flight and while mechanical flight isn't exactly the same it's not that different - the amount of energy you can produce more or less limits how well you can fly because at the end if you stick 2 SRB's to a cargo container you don't even need wings. P.S. And that's before we getting into finding a material light enough to be viable for solar flight while still being able to bare the load of 50,000 lbs without collapsing, but even if you'll take perfect carbon nano tubes or any other super material you still won't be getting off the ground. If you want solar cargo air transport blimps are probably the way to go...
    - Retric 11y ago
      Try and make a solar powered fixed wing aircraft fly at 43 mph while being 1 foot wide and reserving 25% of it's weight for cargo and keeping it in the air for 36 hours. You have 45 kW / (200 ^ 2) = 1.1 watts peak solar output to work with. The issue with overly large wings is mechanical stress let's try and get around that. <This is a dumb design> As a thought experiment, take 3 Solar impulse aircraft fly them next to each other with a simple non weight baring cable to share power between them. The outer two can clearly provide more power than they need and supply that extra power to the center one. Now the center one has extra power for 'free'. So, it can have a higher angle of attack and more weight. As to scaling birds, a Quetzalcoatlus had a wing span of 9 to 12 meters. That's huge for a land animal. https://en.wikipedia.org/wiki/Quetzalcoatlus https://en.wikipedia.org/wiki/Quetzalcoatlus Birds are limited by biology not so much aerodynamic issues.
      - dogma1138 11y ago
        Birds are definitely limited by aerodynamics, biology just says well screw this it ain't worth it because life forms are limited by the amount of energy available to them. If we take the heaviest flying bird today it has a wing span of about 3M and a total wing surface of slightly under 1 m/sq the Quetzalcoatlus you've mentioned has a wing span of about 15m and a total wing surface of about 35 m/sq, back of the envelope math means that about a mass increase of about 12 times over the Kori (heaviest bird capable of flight) results in about 30-35 times the increase in lift surface (and we are still unclear if the damn thing was even capable of powered flight or not). And again you are missing the point Solar Impulse can lift about 1000 lbs of w/e if you want to scale it up either increase the thrust by 50 or increase your lift surface by 50 to get to that 50,000 lbs cargo you want. If we ignore load baring and drag than 3 Solar Impulse aircraft combined could lift 3000 lbs that's it. We can argue about this till the sun doesn't shine it won't change the fact that solar flight will never be a viable option for cargo transport. But it can replace other things, things that for example are well in range of the 1000 or lbs of payload that any reasonable designed solar aircraft could carry - surveillance, communications, weather and atmospheric monitoring equipment etc. They could potentially replace satellites, and increase the endurance of both military and civilian drones considerably but no one is looking at them to carry cargo because it's simply silly. Also if you want to move 50,000 lbs today by air it usually won't take less than 6 days, the only thing you can really ship overnight are small things that end up going on commercial flights not cargo flights. And while it's also true that a container ship can take 21-30 days from say China to the US about 14-15 of those days are spent in local transit and loading, the sailing it self a cargo ship can do within 10 days of good weather with the average being probably closer to 12 or so days due to weather and fuel economy.
barney54 11y ago
I'm a bit skeptical of scaling up Solar Impulse. The plane only has room for one person. If the plane could care another 250 pounds for another person and gear, I'm sure they would have done it. And Solar Impulse has a 200 foot wingspan--the same as a 747.
- bikamonki 11y ago
  Progress takes time and money. Imagine they needed to take an 8 month break and raise 20M to fix a battery heating issue. Each component of a complex solution, like a solar plane, makes slow but steady progress: lighter/stronger materials, lighter/more durable batteries, etc. Software will also play a huge role automating and making resource efficiency better. The fact is that step one is cleared: flight around the world on solar power :)
Gravityloss 11y ago
Flight scales badly to slow speeds. Let me demonstrate with some very rough calculations: Imagine three aircraft flying the same distance. The first is a large airplane flying at 20 m/s. Solar impulse speed. The second is a large airplane flying at 200 m/s. Basic propeller plane. The third is a small airplane flying at 200 m/s. Slow plane: speed: 1x area: 1x lift: 1x payload: 1x drag: 1x thrust: 1x power: 1x distance: 1x energy: 1x Big fast plane: speed: 10x area: 1x lift: 100x payload: 100x drag: 100x thrust: 100x power: 1000x duration: 0.1x distance: 1x energy: 100x Small fast plane: speed: 10x area: 0.01x lift: 1x payload: 1x drag: 1x thrust: 1x power: 10x duration: 0.1x distance: 1x energy: 1x You can see that you use the same energy per payload no matter how fast you go, but your plane can be a lot smaller if you go fast. (This didn't take into account altitude. That means you can go even faster for the same energy expenditure.)
- Retric 11y ago
  Things are far more compex than you are suggesting. The tradeoffs for spead work out largely because you can increase altitude which is very useful. I accept that Solar does not work to supplement the onboard generator used for electrical power on jets due to weight and night time flights. At the same time solar is ~1% the fuel cost for that amount of power for 20 years. They say they can scale this up 50x and carry 50 people. IMO, it would be better to build cargo only craft in that size range as this is far to slow outside of sight seeing in VFR. Not to mention wind. That said if you can say double the solar power and add significant altitude and speed that's much more viable. I am assuming this is significantly worse than the best possible solar aircraft we could build in say 30 years.
  - Gravityloss 11y ago
    Well, 1/100 the cargo and 1/10 the speed means you need 1000 solar planes for every kerosene plane for the same route revenue. If we assume they cost the same to buy since they are the same size. And that doesn't take into account night flying etc... Much better to have the solar panels on land and do synthetic kerosene for planes. Ships go half the speed of Solar Impulse, but they have a lot more payload per dollar invested.

barrkel 11y ago

Indeed. I expect we'll synthesize jet fuel or a close equivalent (something that burns and reduces airframe weight) from electric or bio sources long after most other engines have moved to electric. Perhaps we'll generate electricity on board, but it will be with a dense, wasting fuel. And we certainly aren't going to use solar to power commercial human air transport any time this millenium; it will always be better, for people, to compress energy before a flight and travel faster, than try to make the flight itself self-sustaining and travel slower. The only exception could be recreational flyers.

gruturo 11y ago
I wouldn't be so sure this would not happen this millennium as you say. Maybe not this decade, but I certainly imagine sooner or later we will have I.e. a big satellite beaming power directly to a plane (laser or microwave, you choose). Once launch costs make this plausible and it's deemed safe and secure, why not? Bonus, you now have an orbital death ray if you decide to go Bond villain.
- Piskvorrr 11y ago
  That would be about as much of a "bonus" as the Chernobyl disaster was a "bonus" to nuclear power. In other words, a threat.
cmsmith 11y ago
We've been synthesizing one liquid hydrocarbon fuel for thousands of years; ethanol is pretty similar to jet fuel in energy density and combustion. I think the possibility that in the future we'll have cheap solar/wind grid power and use that to produce ethanol, rather than charge batteries, is more likely than people think. Ethanol production isn't terribly efficient, but if your input power is sustainable it doesn't really matter.
- elithrar 11y ago
  Ethanol is about 70% of the energy density of Jet A-1: https://en.m.wikipedia.org/wiki/Energy_density https://en.m.wikipedia.org/wiki/Energy_density