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Linedance posted:It always comes down to this though. Why lower your efficiency and add complication by creating a system where the liquid fuel combustion engine turns an electric motor which turns the propulsion mechanism, when you could just directly power the propulsion mechanism from the combustion engine and do away with the middle man? You could still run a secondary independent emergency battery or ram air combination electrical drive as backup in case the combustion engine fails. In fact independent would be the better way of doing it from a safety perspective. High end well designed diesel-electric and diesel-mechanical systems both come in at the 95-97% efficiency range. The issue is torque. An electric motor applies it's full torque output all the time. Even at 0 rpm, if you look at the torque curve for an internal combustion engine you will see that this is not the case. That there is a peak torque output at some rpm value. This is obviously really important when you have a heavy train or huge ship trying to get moving from stopped. I don't think that's as important for aircraft engines though. They can pick their most efficient rpm and just stay there most of the time. If batteries improve dramatically though there will be a case for all electric engines in aircraft just due to fuel efficiency concerns. $ per kW is much, much lower at a big power plant than any portable engine can hope to be.
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Aug 30, 2016 20:20
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Vitamin J posted:Now you're back at the starting point and you have a conventional helicopter. You certainly can do that, and it has been done. If you remember I said one of the benefits of the drone-style multirotor with electric motors is that you replace mechanical complexity with a computer. Since you're flying the copter with a computer it's trivially easy to integrate autopilot features and you could make it fly like a video game so anybody off the street could fly it. Not to mention having far less moving parts means less maintenance and cheaper costs. It will not have the most endurance nor the highest top speed, but it certainly has advantages in a few use cases. 
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Aug 30, 2016 20:23
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Enourmo posted:I'm not a heli expert, but I do know sophomore-level physics. I also think helos maintain autorotation rpm by tilting the blades pitch to a point where the airflow passing through them accelerates the rotor during descent, storing energy in them until they're finally needed to generate lift at a sufficient distance from the ground for a controlled landing. A multirotor lacks that fundamental function.
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Aug 30, 2016 20:24
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Murgos posted:High end well designed diesel-electric and diesel-mechanical systems both come in at the 95-97% efficiency range. Specific energy of kerosene - 46 MJ/kg Specific energy of lithium ion secondary cells - up to 0.875ish MJ/kg Specific energy of lithium ion primary cells - up to 1.8 MJ/kg Lithium ion batteries were a revolutionary improvement over lead acid (0.17 MJ/kg) and nickel metal (0.288 MJ/kg). That means we only need what 20 more revolutions in battery technology to get parity with Jet A?
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Aug 30, 2016 20:24
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um excuse me posted:I also think helos maintain autorotation rpm by tilting the blades pitch to a point where the airflow passing through them accelerates the rotor during descent, storing energy in them until they're finally needed to generate lift at a sufficient distance from the ground for a controlled landing. A multirotor lacks that fundamental function. Oh hey, you're right, didn't even think of that.
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Aug 30, 2016 20:28
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um excuse me posted:I also think helos maintain autorotation rpm by tilting the blades pitch to a point where the airflow passing through them accelerates the rotor during descent, storing energy in them until they're finally needed to generate lift at a sufficient distance from the ground for a controlled landing. A multirotor lacks that fundamental function.
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Aug 30, 2016 20:32
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hobbesmaster posted:Specific energy of kerosene - 46 MJ/kg This is why I can't really see battery electric airliners happening. Even if you do reach parity, you are landing the same weight as you took off with and you are generating thrust in a pre-jet fashion, i.e. purely from a propeller of some sort, not the expanding hot gases as well, like with a turbofan. If the problem is making jet travel green, you just need to burn something green instead of something filthy. Hydrogen or biodiesel are options, each with their own issues which I believe we have discussed many times before. But a Volocopter-ish contraption or other big drone can indeed do many of the jobs a helicopter can, particularly if you don't need to carry any meat servos and their complicated support systems.
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Aug 30, 2016 20:33
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Enourmo posted:Rotational energy scales directly with moment of inertia, which for a rotor (essentially a rod rotating about the midpoint) scales directly with mass, and with the square of length. So even reducing length by half, you'd need four times the mass, so either you've got massive draggy airfoils or you're making your blades out of, like, tungsten to get the same energy storage. And then you've got half the blade length, meaning (probably) less torque from the airflow to spin the rotor up on the way down. And as Vitamin J pointed out earlier, the controllability of a multirotor depends heavily on its ability to rapidly adjust rotor speeds. The flywheel effect is bad in that case.
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Aug 30, 2016 20:39
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Ola posted:This is why I can't really see battery electric airliners happening. Even if you do reach parity, you are landing the same weight as you took off with and you are generating thrust in a pre-jet fashion, i.e. purely from a propeller of some sort, not the expanding hot gases as well, like with a turbofan. If the problem is making jet travel green, you just need to burn something green instead of something filthy. Hydrogen or biodiesel are options, each with their own issues which I believe we have discussed many times before. With a high bypass turbofan, the amount of thrust that comes directly from the expanding hot gasses is pretty inconsequential. Most of the thrust comes from the fan, which is driven by the turbine which gets its energy from those gasses. If you spun the fan with some other source of power, you'd still get all the jet thrust, without the expanding hot gasses. Without the second (and third if you're a Rolls) stage compressor and turbine core in the way, you could get even more bypass ratio.
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Aug 30, 2016 20:44
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Linedance posted:With a high bypass turbofan, the amount of thrust that comes directly from the expanding hot gasses is pretty inconsequential. Most of the thrust comes from the fan, which is driven by the turbine which gets its energy from those gasses. If you spun the fan with some other source of power, you'd still get all the jet thrust, without the expanding hot gasses. Without the second (and third if you're a Rolls) stage compressor and turbine core in the way, you could get even more bypass ratio. Alright, I thought the hot gassy bit was more important. Would be interesting to see what kind of theoretical performance you could get from a 737-ish shape and 20 tons of LiFePo batteries. e: some napkin math. A 737 has (millions of arguments about this) 18000 hp, let's pull a number from the stratosphere and say takeoff, climb, cruise, descent and landing averages 10000 hp or 7456 kW. With LiFePo energy density 20 tons of batteries is 1800 kWh. So that's 0.24 hours, or just over 14 minutes, from 100% to 0%, not factoring in reduced power output near the lower end. Yeah, no. Another way of putting it: you get 42 seconds of flight per ton of battery. Ola fucked around with this message at 21:11 on Aug 30, 2016 |
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Aug 30, 2016 21:03
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Attatch a small APU to a generator. Or hell, even a small 4 cylinder diesel.
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Aug 30, 2016 21:04
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Hermsgervørden posted:Never stop posting Nebakenezzer. I hope you are well, I need you to live so I can keep reading your awesome posts. Ha, no worries! It was for a medical to confirm I'm not a) an smackhead b) an alcoholic that's capable of working on ships an' such. hobbesmaster posted:Specific energy of kerosene - 46 MJ/kg I keep telling people that petroleum based fuel is so useful if it didn't exist we'd have to invent it, but people don't believe me and don't get the reference. They're* all "IF WE CAN GO FROM ROOM SIZED COMPUTERS TO IPHONES WHY HAVEN'T WE REPLACED OIL?!" *People I know on Facebook
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Aug 30, 2016 21:11
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Vitamin J posted:Now you're back at the starting point and you have a conventional helicopter. You certainly can do that, and it has been done. If you remember I said one of the benefits of the drone-style multirotor with electric motors is that you replace mechanical complexity with a computer. Since you're flying the copter with a computer it's trivially easy to integrate autopilot features and you could make it fly like a video game so anybody off the street could fly it. Not to mention having far less moving parts means less maintenance and cheaper costs. It will not have the most endurance nor the highest top speed, but it certainly has advantages in a few use cases. It feels really simplistic to just say 'replace mechanical complexity with computer, then it's easy to make it flyable for anyone!'. That complexity doesn't actually go away, it just moves into software. And honestly we know a lot less about properly engineering our software than we do engineering our hardware. There are serious maintainability advantages to the software solution of course, but getting there isn't trivial.
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Aug 30, 2016 21:11
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Yes, it's like a lava lamp.
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CommieGIR posted:Attatch a small APU to a generator. Or hell, even a small 4 cylinder diesel. Great. Now there is at least some black smoke at the accident scene so we'll be easier to find.
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Aug 30, 2016 21:11
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Vitamin J posted:If you remember I said one of the benefits of the drone-style multirotor with electric motors is that you replace mechanical complexity with a computer. Since you're flying the copter with a computer it's trivially easy to integrate autopilot features and you could make it fly like a video game so anybody off the street could fly it. Not to mention having far less moving parts means less maintenance and cheaper costs. It will not have the most endurance nor the highest top speed, but it certainly has advantages in a few use cases. Missing the joke aside, this right here is the biggest "why hoverbikes/volocopters/peepeedrones" argument. • Electric motors are way more responsive (higher torque/faster changes in speed) • It's easy to hook it up to a computer to handle flight calculations • Less stuff to go wrong mechanically It's why it'd be great for a theoretical hoverbike to be electrically powered. It'd suffer from way less endurance, though, which could be mitigated, somehow, if you could somehow cram a small generator in. PittTheElder posted:It feels really simplistic to just say 'replace mechanical complexity with computer, then it's easy to make it flyable for anyone!'. That complexity doesn't actually go away, it just moves into software. And honestly we know a lot less about properly engineering our software than we do engineering our hardware. There's already a lot of proven software for drones and such. It's arguably easier to learn how to code than to learn how to engineer a traditional flying vehicle. And I mean purely in the homemade flying vehicle scenario - if this was something that big companies/government were interested in you can be sure that they'd figure out how to made decent software.
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Aug 30, 2016 21:28
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Inacio posted:There's already a lot of proven software for drones and such. It's arguably easier to learn how to code than to learn how to engineer a traditional flying vehicle. And I mean purely in the homemade flying vehicle scenario - if this was something that big companies/government were interested in you can be sure that they'd figure out how to made decent software. https://www.youtube.com/watch?v=I9gELPxPG8Q
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Aug 30, 2016 21:36
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It's a shame software hasn't advanced in the last 28 years.
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Aug 30, 2016 21:43
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Inacio posted:There's already a lot of proven software for drones and such. It's arguably easier to learn how to code than to learn how to engineer a traditional flying vehicle. And I mean purely in the homemade flying vehicle scenario - if this was something that big companies/government were interested in you can be sure that they'd figure out how to made decent software. Right, but if you're going to let anybody fly it, you need that software properly designed and safety certified. It certainly can be done (Obligatory: They Write the Right Stuff), but it's hard, and expensive, because you're just moving the complexity around. Hell, just look at all the software induced delays in the F-22 program. The hobbyist angle only works because it's the wild west out there for drones.
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Aug 30, 2016 21:43
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The control system for a multirotor, from a software perspective, is not terribly complex. Especially since you're working in a rather narrow envelope of airspeed and altitude.
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Aug 30, 2016 21:48
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One of the most advanced drone software projects around right now is an open-source project called PX4 or Pixhawk developed by the Swiss University ETH Zurich. They're taking it a lot more seriously than you might think, certainly not treating it like the wild west. It was started in 2008 and now it's highly advanced and incredibly reliable. It's not ready for manned aircraft, but it might be sooner than anyone here expects.
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Aug 30, 2016 21:49
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I like how there is no reaction from the photographer/crowd as it is plowing through the trees like that's completely normal.
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Aug 30, 2016 21:51
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Vitamin J posted:Now you're back at the starting point and you have a conventional helicopter. So...you didn't realize that half the suggestions in here were intentionally steering in that direction? Ola posted:Great. Now there is at least some black smoke at the accident scene so we'll be easier to find. 
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Aug 30, 2016 21:56
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Is someone looking into making jet fuel from solar / wind energy and, idk, air CO2 and water or something? Seems like that would solve a bunch of problems with storage / buffering weather-related peaks and troughs in production. I assume it's an efficiency / cost problem?
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Aug 30, 2016 22:02
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aphid_licker posted:Is someone looking into making jet fuel from solar / wind energy and, idk, air CO2 and water or something? Yes. https://news.usc.edu/91297/turning-air-into-fuel-usc-scientists-turn-carbon-dioxide-into-methanol/ https://www.chemistryworld.com/research/carbon-dioxide-to-methanol-catalyst-ignites-fuel-from-air-debate/9339.article http://www.scientificamerican.com/article/bionic-leaf-makes-fuel-from-sunlight-water-and-air1/ aphid_licker posted:I assume it's an efficiency / cost problem? Yes. And developing beyond lab conditions. There are tons of ways you can convert electrical energy to some sort of flammable liquid, the trick is finding the best one plus not accidentally polluting terribly anyway plus having the liquid fit our current liquid burning machines plus having sustainably generated electricity in sufficient amounts plus more. But I think something like this is a possible future for airliners. Ola fucked around with this message at 22:16 on Aug 30, 2016 |
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Aug 30, 2016 22:12
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aphid_licker posted:Is someone looking into making jet fuel from solar / wind energy and, idk, air CO2 and water or something? Seems like that would solve a bunch of problems with storage / buffering weather-related peaks and troughs in production. I assume it's an efficiency / cost problem? Depends on what you mean. People have already implemented systems where solar and wind energy use their spare electricity generation for distilling hydrogen via electrolysis, which they then run a fuel cell with when solar/wind are not cutting it. There's also the US military experiments into using a carrier's nuclear reactor to refine jet fuel from the carbon in sea water. Not sure how that is going, but it sounds pretty cool. Then, there's the thought you just had, which I think is to take the US Navy's method of making fuel, and then have it running at a power plant - but only using "excess" electricity that would otherwise be discharged into the earth. Like at three am, the power load is nowhere near what it is at four in the afternoon during a heatwave? I've no idea of the feasibility of that (I think it'd depend on how the US Navy thing works, maybe you need atomic power) but it seems like a good idea to me - especially if it is feasible to run it off of electricity that'd otherwise be lost.
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Aug 30, 2016 22:16
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Man, can't believe only 3 people died in that, and none on impact.
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Aug 30, 2016 22:23
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The big benefit to synthetic hydrocarbons is that unlike stuff out of the ground, they're not contributing any CO2 that wasn't already in the atmosphere. So if you can make it using renewables (wind/solar/nuclear/etc), you effectively have carbon-neutral gasoline. Like, even without getting into the "modern reactor design" discussion, nuclear waste is nasty stuff and we need to figure it out, but it's not going to melt the loving ice caps. Until battery tech surpasses those fuels, it's probably the best way forward. Plus you can use excess output as feedstock for stuff that's not meant to be burned, so you're actually taking carbon out of the atmosphere.
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Aug 30, 2016 22:54
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Enourmo posted:Yeah, the tradeoff for controlability is safety. Airplanes and traditional helicopters can safely land from altitude even with a total powerplant failure; what happens if the battery fails while this thing's flying? Oops, you drop like a stone because you have no wings and can't autorotate like a copter can. Linedance posted:Ah, didn't realize that was the case with how multi rotors worked. Carry on then! I'm thinking that with a multicopter, especially with something like the Volocopter that has so many rotors, it would be quite simple to split the rotors into two completely separate systems. Two sets of rotors and motors with two sets of cabling and two batteries, controlled by two separate control systems that doesn't necessarily even have to be aware of the existance of the other system. They would try to control the copter by themself, there would just be some "turbulence in the air" caused by the other set of rotors. Up to this point I don't we would introduced much inefficiency either, unless you need to have reduced the battery voltage. Behind the batteries could be separate generators, which might cause extra weight. How much do two 10 kW generators weight compared to a single 20 kW? There would probably be only a single turbine powering the generators, but the systems aren't electrically connected so they shouldn't be able to affect each other adversily, as long as a battery doesn't blow up and take the other with it.
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Aug 30, 2016 22:57
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How much water does a 1.5MW nuclear reactor need? Put the reactor on the plane, have it charging enough batteries to give you a few minutes of run time if the turbine fails Nothing could possibly go wrong with this
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Aug 30, 2016 23:54
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Having two systems fighting each other sounds like a way to get Pilot Induced Oscillations in new and exciting ways.
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Aug 30, 2016 23:57
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PittTheElder posted:It feels really simplistic to just say 'replace mechanical complexity with computer, then it's easy to make it flyable for anyone!'. That complexity doesn't actually go away, it just moves into software. And honestly we know a lot less about properly engineering our software than we do engineering our hardware. I'd say the difference is actually significant. Fundamentally, mechanical complexity is something thousands of mechanics have to deal with monthly, where as software complexity is something the manufacturer has to take care of once. Mechanical system has to be checked constantly for tolerances, vibration and who knows what. And you can expect those to be growing and have to determine when they've grown too much. I have minor experience of this maintaining the gliders in my club. Those L'Hotellier balls are my annual bane. The software on the other hand you can expect to behave the same way it was designed, it doesn't just change some time in the future. Sure, faults may crop up in the underlying computer, but you run some system check to find them. Give the software a million different input sets and check that the output for every one of them is as expected. Of course new issues may crop up too. Maybe the mechanical system exhibits unexpected wear, so you end up adding pages to the maintenance manual and all those mechanics will have something new to check regularly. Maybe there is some corner case that the software doesn't handle correctly. The manufacturer creates fixed software, the mechanics install the updates and then they don't have to be concerned with it anymore, just wait for the next fix for some other issue. The multicopter still have some mechanical systems, but they are much simpler and could be easier to check. Maybe just "when you inject X amps of current to a motor the rotor should turn at Y±‰ RPM. If not, replace."
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Aug 31, 2016 00:04
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rscott posted:How much water does a 1.5MW nuclear reactor need? Put the reactor on the plane, have it charging enough batteries to give you a few minutes of run time if the turbine fails 
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Aug 31, 2016 00:26
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Hello I know gently caress all about aircraft and gently caress all about software development and it's my opinion that this wildly impractical thing is in fact a great idea.
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Aug 31, 2016 00:37
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Nebakenezzer posted:Depends on what you mean. I saw a presentation on it. From a cost perspective, it only really makes sense for the US Navy to do it. It's about twice as much as buying JP-5 on the open market, but is cheaper than current delivery contracts and costs. The downside is that despite the reactors on a Nimitz being very large, it's really just going to produce enough fuel for it's use and a trickle for the rest of the ships in the fleet. So either you need to widely expand the use of nuclear power on board ships, or you need some dedicated ships that basically are generating fuel.
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Aug 31, 2016 01:40
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aphid_licker posted:Is someone looking into making jet fuel from solar / wind energy and, idk, air CO2 and water or something? Seems like that would solve a bunch of problems with storage / buffering weather-related peaks and troughs in production. I assume it's an efficiency / cost problem? We've known for years how to synthesize liquid hydrocarbons from carbon-containing compounds; it just takes huge amounts of energy. There's a university pilot plant somewhere in the midwest that sits next to a chicken farm, takes all of the biowaste (bones and organs mostly), puts it in big sealed vats where it's microwaved and cooks under pressure for hours, and gradually decomposes it all into something a lot like crude oil that can be directly refined into gasoline. Duplicates the real geological processes that lead to petroleum formation, but on a way faster scale. It just takes a ton of power to run the microwaves -- not sure if it doesn't break even with the energy content of the output, or if the fuel it makes is just way too expensive for the current market, but either way it's not yet commercially viable. If we had extremely cheap energy (like, fully paid off seawater-fueled deuterium fusion) we could probably synthesize gasoline from atmospheric CO2 and organic residential waste and whatever at a cost similar to what we pay today. Until then...not likely. Sagebrush fucked around with this message at 01:56 on Aug 31, 2016 |
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Aug 31, 2016 01:54
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Are those old carrier reactors?
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Aug 31, 2016 02:02
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They're NERVA engines, I think. Test reactors for a nuclear-powered bomber that would orbit the pole for weeks on end waiting for the president to push the button  e: Aircraft Nuclear Propulsion project, not NERVA. ANP was nuclear-powered planes, NERVA was nuclear-powered space ships. https://en.wikipedia.org/wiki/Aircraft_Nuclear_Propulsion https://en.wikipedia.org/wiki/NERVA Sagebrush fucked around with this message at 02:09 on Aug 31, 2016 |
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Aug 31, 2016 02:07
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aphid_licker posted:Is someone looking into making jet fuel from solar / wind energy and, idk, air CO2 and water or something? Seems like that would solve a bunch of problems with storage / buffering weather-related peaks and troughs in production. I assume it's an efficiency / cost problem? It's a conservation of energy problem. You can't get more energy out than you put in. Synthesizing hydrocarbons from carbon dioxide and water is downright easy it's just way more expensive than pulling it out of the ground.
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Aug 31, 2016 02:33
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Thomamelas posted:I saw a presentation on it. From a cost perspective, it only really makes sense for the US Navy to do it. It's about twice as much as buying JP-5 on the open market, but is cheaper than current delivery contracts and costs. The downside is that despite the reactors on a Nimitz being very large, it's really just going to produce enough fuel for it's use and a trickle for the rest of the ships in the fleet. So either you need to widely expand the use of nuclear power on board ships, or you need some dedicated ships that basically are generating fuel. That's not such a ridiculous idea. We've used dedicated ships that basically are just carrying fuel for over a century.
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Aug 31, 2016 02:59
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