6 ms·

There is a combination of increasing energy density of batteries and decreasing cost of high tech motors that I believe is a bellweather for electric flight exp

There is a combination of increasing energy density of batteries and decreasing cost of high tech motors that I believe is a bellweather for electric flight experimentation, particularly on the LSA/ultralight end of aircraft. While I believe it is unlikely we will see energy densities on the level of gasoline anytime soon, I do think we will see a lot of innovative electric training aircraft soon. If lithium sulfur batteries live up to the hype then we might see even cooler designs.

jeffreyrogers 6y ago
I think there is some potential for hydrogen fuel cell powered planes since the energy density of hydrogen is significantly better than batteries.
- bdamm 6y ago
  But not economic on any known horizon. For some reason fuel cells have repelled good economy (in dollars) for 15 years now.
- tengbretson 6y ago
  The fact that H2 can't be stored as liquid, even under pressure makes me pretty doubtful. I suspect ethanol or plant-derived oil will beat out hydrogen for as long as batteries aren't up to the task.
  - jeffreyrogers 6y ago
    Yeah, I think that's more likely. But for all electric I think hydrogen makes more sense than batteries, since improving batteries enough for real applications requires new chemistries, while I think the obstacles for hydrogen are more about economics.
    - ecpottinger 6y ago
      No, look at the prices and requirements for a hydrogen storage tank, you either need a high pressure tank or one that can handle very low temperatures. Neither is cheap or simple.
      - Hypx 6y ago
        For aviation purposes, it's cheap enough.
  - davedx 6y ago
    H2 can be stored as a liquid, it’s more difficult. Check out AeroDelft who are building a liquid hydrogen plane: https://aerodelft.nl/ https://aerodelft.nl/
  - sa1 6y ago
    There was some news about metal sponges earlier that may be able to hold high volumes of H2 under low pressure. https://www.bbc.com/news/science-environment-52328786 https://www.bbc.com/news/science-environment-52328786
    - mannykannot 6y ago
      You got me thinking, so I looked for some numbers. Hydrogen has a specific energy of 120 MJ/kg, while Kerosine has 46 MJ/kg. According to the abstract of the paper being discussed here, the new material has a deliverable capacity of 14% by weight, corresponding to about 17 MJ/kg - only a bit better than 1/3 that of kerosine, but considerably better than lithium ion batteries, which apparently achieve less than 1 MJ/kg, while the best-performing lithium-sulfur batteries are at about 1.8 MJ/kg. In addition, we must deal with this material only losing 14% of its weight as its hydrogen is used up, while kerosine loses all of its weight - a combustion-powered airplane becomes more efficient as its fuel is consumed. Furthermore, to get that 14% deliverable capacity, you have to start with it at 100 bar, so the tank containing it will have a substantial weight. So we have progress here, but not yet a substitute for liquid hydrocarbons.
  - Hypx 6y ago
    LH2 is a liquid. It's likely airplanes will use liquid hydrogen as a fuel.
- snovv_crash 6y ago
  I think we're more likely to get working Lithium Sulphur batteries first, which would effectively relegate fuel cells to the garbage can. Between the fuel and the cells, batteries are just so much easier to operate once they're out in the field, there's no comparison.
  - Hypx 6y ago
    Lithium sulfur still has a tiny fraction the energy density of hydrogen. It's very unlikely, probably impossible, to ever beat hydrogen on energy density with a battery. Also, Li-S still has too low of energy density for airplanes, and given the long recharge time problem batteries fundamentally are a no-go in aviation.
    - snovv_crash 6y ago
      LiS is only 10x below gasoline. When you account for the difference in efficiency, and the the difference in weight for the motors, and then reliability and redundancy, it is roughly a factor of 2 away. That is fine for shorter routes. Recharging time isn't an issue, just have the batteries swappable.
DoofusOfDeath 6y ago
By training, do you mean for training beginner pilots? I would think there's a lot of benefit from learning on aircraft similar to what you'd pilot post-training.
- jrockway 6y ago
  The fundamentals of flying can be learned in any aircraft. Pilots are already trained on "trainer" type aircraft, because they are more forgiving and more economical to operate than aircraft designed for another task. Yes, changing types will require some training, but it's a big savings if you can get your PPL in a plane with an operating cost of $1/hour. If you look at vendors that are selling production electric aircraft, they claim 70% savings on training operations. That's a big deal. (Link: https://www.pipistrel-aircraft.com/aircraft/electric-flight/alpha-electro/ https://www.pipistrel-aircraft.com/aircraft/electric-flight/...)
- bityard 6y ago
  Almost every pilot starts their training in a Cessna because the basics of flight apply to every aircraft, and operating a small simple aircraft is far less cognitive load than sitting in the glass cockpit of a jumbo jet. An electric plane removes the complexity of operating the engine which is not insubstantial, even in the smallest of general aviation aircraft.
  - dreamcompiler 6y ago
    I kind of hate Cessnas. They feel dramatically underpowered to me. Sailplanes OTOH feel great because they have no engine at all. It--focuses the mind. I've probably learned a lot more about pure flying from sailplanes than from Cessnas. It just feels safer to me to have no engine and a good glide ratio than a small (potentially unreliable) engine and a poor glide ratio. Of course nobody's going to be commuting in a sailplane, but they're awesome for pure fun and learning piloting skills.
- GuB-42 6y ago
  Managing the engine is not the most important part of flying, especially for ultralight aircraft. And in fact, the best pilots tend to be also experienced glider pilots. Also, one specificity of ultralight flying, or at least the way I was taught, is to not trust the engine, no matter how reliable it is supposed to be. One aspect is to make the final approach unpowered. Of course, the engine is still running, but ideally, you should pull the throttle all the way back and leave it here, as if the engine had failed. This is in contrast to the 3° slope commonly taught in general aviation. Of course, a pilot who only flew on an electric plane needs some time with a flight instructor in order to learn the quirks of gas engines, but that should be quick compared to the time it takes to actually learn how to fly.
spitfire 6y ago
Better still with an electric motor you have more options for motor placement. You don't have a big fat engine that has to be placed in the front[1]. The batteries don't have to sit in the wings, they can theoretically sit at the bottom of the plane making weight easier to manage. You also get more options for blade types. Like ducted fans. In short, your plane doesn't have to be designed around a fat gasoline engine and tanks. There's still constraints, but you get much more creative freedom. I expect when we see planes designed around the motor/batteries we'll see aerodynamics get electric planes into GA territory. EDIT: aerodynamic efficiencies. [1] Yes there's that tractor/pusher Cessna, no one liked it.
- sokoloff 6y ago
  In a lot of ways, you prefer the battery weight to be in the wings. The main one is that it reduces the load on the critical wing-fuselage junction (the source of zero-fuel-weight limitations in larger aircraft).
  - spitfire 6y ago
    But now you have that choice. You can package things however you want, even in weird shapes. Not "has to allow liquid to flow downhill, even in rate 2 turn". I'll bet there's still wins to be found even with putting batteries in wings.
jillesvangurp 6y ago
Yes definitely. Most electrical planes currently in the process of certification are hardly using the latest & greatest in terms of battery technology. The reason for this is not that the technology is not there but that resetting the process of certifying the airplane and batteries extends the time to market by years and everybody is scrambling to get certified now so they can start fulfilling orders. Like with EVs, demand is not a problem for any of these manufacturers. This is true for Bye's eflyers, the Eviation Alice, the Pipistrel models, etc. These have modest but usable ranges (currently advertised) and are far enough in the development process that they might hit the market in some modest numbers in the next few years. But that's with battery technology of basically a few years ago. There's obvious room for improvement by simply updating the battery technology. 2-3x over the next decade is not an unreasonable expectation; the biggest hurdle is certification. The real thing to look for with electrical planes is range & operational cost. Yes it's annoying to not be able to fly 5 ours straight. But 2 hours is still pretty good. This would require doubling the power/kg for this plane, which sounds like it should be feasible; if not now than maybe in a few years. Also, turning a 100$ hamburger into a 5$ latte flight is going to be quite literally be the difference between being able afford to fly or not at all for a lot of people. GA flight is a really expensive hobby currently. I think what will happen is the experimental market exploding pretty soon. There's a critical mass of technology coming on the market and it's going to be very tempting for people to start building kit planes they can actually afford to fly. There are some fine examples of some daredevils on youtube flying some DYI contraptions already.
edraferi 6y ago
The article says Lithium Ion batteries deliver 1/15 the power per pound of traditional aviation fuel. That leaves a lot of room for improvement...
- sojournerc 6y ago
  They also don't get lighter as they lose energy, which is key to large passenger jet operations. Large plants often take off heavier than the plane is rated to land normally expecting to burn that weight in flight.
  - llukas 6y ago
    We built fuel burning planes for last 100+ years. They're optimized to take advantage of burning fuel, it doesn't mean it is only option.
    - NikolaeVarius 6y ago
      What kind of HN comment is this? They're optimized for energy efficiency? Yes? What does this gotcha response even mean?
      - llukas 6y ago
        All parts of plane are optimized to work with jet engine. For plane designed from ground up as electric fact that jets land lighter than take off is not relevant. It is only relevant if you want to retrofit electric engine on jet engine optimized chassis - which is not only possible way. Bit more info on how thought process goes: https://spectrum.ieee.org/aerospace/aviation/how-i-designed-a-practical-electric-plane-for-nasa https://spectrum.ieee.org/aerospace/aviation/how-i-designed-...
        mannykannot 6y ago
        Batteries have a much lower specific energy that hydrocarbon fuels to start with, and then that fact that the aircraft weight does not decrease over the duration of the flight is one more disadvantage (currently a second-order issue, given the first difference.) These are constraints that can be designed around, and you have more freedom to do so when designing from scratch, but doing so is not a optimization, it is a straightforward trade-off between weight and duration. There's no optimal hump on that line.
msandford 6y ago
If you weren't so worried about having a reasonably-sized airframe or high speed we're getting pretty close to significantly increased duration/range via solar. http://thundergull.com/specifications.htm http://thundergull.com/specifications.htm It's got 95sqft of wing and a top speed of 63mph. Drag is usually with velocity squared so going 1/2 as fast might only require 1/4 as much power. They state in the article that it takes 10kw to fly level. With 100sqft and an average 10W/sqft you're at 1kw. But cut the speed down to 30mph (2500W) and double the wing area (2000W) and you're very nearly at breakeven. The 11kw battery might then last you 10+ hours after accounting for the power required to climb out. Yes it'll end up being much more of a power glider than a "proper" airplane but that might be a lot of fun.
- sokoloff 6y ago
  Drag force is quadratic with speed. Drag power is cubic with speed. (Power is force times an additional velocity term).
  - msandford 6y ago
    DOH! So if you went ~30MPH and had 25% bigger wings you'd probably have a solar glider then. Or ~40MPH (2/3 the speed) and double the wing size. Turns out that this is a thing: https://www.solar-flight.com/ https://www.solar-flight.com/

jeffreyrogers 6y ago

I think there is some potential for hydrogen fuel cell powered planes since the energy density of hydrogen is significantly better than batteries.

bdamm 6y ago
But not economic on any known horizon. For some reason fuel cells have repelled good economy (in dollars) for 15 years now.
tengbretson 6y ago
The fact that H2 can't be stored as liquid, even under pressure makes me pretty doubtful. I suspect ethanol or plant-derived oil will beat out hydrogen for as long as batteries aren't up to the task.
- jeffreyrogers 6y ago
  Yeah, I think that's more likely. But for all electric I think hydrogen makes more sense than batteries, since improving batteries enough for real applications requires new chemistries, while I think the obstacles for hydrogen are more about economics.
  - ecpottinger 6y ago
    No, look at the prices and requirements for a hydrogen storage tank, you either need a high pressure tank or one that can handle very low temperatures. Neither is cheap or simple.
    - Hypx 6y ago
      For aviation purposes, it's cheap enough.
- davedx 6y ago
  H2 can be stored as a liquid, it’s more difficult. Check out AeroDelft who are building a liquid hydrogen plane: https://aerodelft.nl/ https://aerodelft.nl/
- sa1 6y ago
  There was some news about metal sponges earlier that may be able to hold high volumes of H2 under low pressure. https://www.bbc.com/news/science-environment-52328786 https://www.bbc.com/news/science-environment-52328786
  - mannykannot 6y ago
    You got me thinking, so I looked for some numbers. Hydrogen has a specific energy of 120 MJ/kg, while Kerosine has 46 MJ/kg. According to the abstract of the paper being discussed here, the new material has a deliverable capacity of 14% by weight, corresponding to about 17 MJ/kg - only a bit better than 1/3 that of kerosine, but considerably better than lithium ion batteries, which apparently achieve less than 1 MJ/kg, while the best-performing lithium-sulfur batteries are at about 1.8 MJ/kg. In addition, we must deal with this material only losing 14% of its weight as its hydrogen is used up, while kerosine loses all of its weight - a combustion-powered airplane becomes more efficient as its fuel is consumed. Furthermore, to get that 14% deliverable capacity, you have to start with it at 100 bar, so the tank containing it will have a substantial weight. So we have progress here, but not yet a substitute for liquid hydrocarbons.
- Hypx 6y ago
  LH2 is a liquid. It's likely airplanes will use liquid hydrogen as a fuel.
snovv_crash 6y ago
I think we're more likely to get working Lithium Sulphur batteries first, which would effectively relegate fuel cells to the garbage can. Between the fuel and the cells, batteries are just so much easier to operate once they're out in the field, there's no comparison.
- Hypx 6y ago
  Lithium sulfur still has a tiny fraction the energy density of hydrogen. It's very unlikely, probably impossible, to ever beat hydrogen on energy density with a battery. Also, Li-S still has too low of energy density for airplanes, and given the long recharge time problem batteries fundamentally are a no-go in aviation.
  - snovv_crash 6y ago
    LiS is only 10x below gasoline. When you account for the difference in efficiency, and the the difference in weight for the motors, and then reliability and redundancy, it is roughly a factor of 2 away. That is fine for shorter routes. Recharging time isn't an issue, just have the batteries swappable.

DoofusOfDeath 6y ago

By training, do you mean for training beginner pilots? I would think there's a lot of benefit from learning on aircraft similar to what you'd pilot post-training.

jrockway 6y ago
The fundamentals of flying can be learned in any aircraft. Pilots are already trained on "trainer" type aircraft, because they are more forgiving and more economical to operate than aircraft designed for another task. Yes, changing types will require some training, but it's a big savings if you can get your PPL in a plane with an operating cost of $1/hour. If you look at vendors that are selling production electric aircraft, they claim 70% savings on training operations. That's a big deal. (Link: https://www.pipistrel-aircraft.com/aircraft/electric-flight/alpha-electro/ https://www.pipistrel-aircraft.com/aircraft/electric-flight/...)
bityard 6y ago
Almost every pilot starts their training in a Cessna because the basics of flight apply to every aircraft, and operating a small simple aircraft is far less cognitive load than sitting in the glass cockpit of a jumbo jet. An electric plane removes the complexity of operating the engine which is not insubstantial, even in the smallest of general aviation aircraft.
- dreamcompiler 6y ago
  I kind of hate Cessnas. They feel dramatically underpowered to me. Sailplanes OTOH feel great because they have no engine at all. It--focuses the mind. I've probably learned a lot more about pure flying from sailplanes than from Cessnas. It just feels safer to me to have no engine and a good glide ratio than a small (potentially unreliable) engine and a poor glide ratio. Of course nobody's going to be commuting in a sailplane, but they're awesome for pure fun and learning piloting skills.
GuB-42 6y ago
Managing the engine is not the most important part of flying, especially for ultralight aircraft. And in fact, the best pilots tend to be also experienced glider pilots. Also, one specificity of ultralight flying, or at least the way I was taught, is to not trust the engine, no matter how reliable it is supposed to be. One aspect is to make the final approach unpowered. Of course, the engine is still running, but ideally, you should pull the throttle all the way back and leave it here, as if the engine had failed. This is in contrast to the 3° slope commonly taught in general aviation. Of course, a pilot who only flew on an electric plane needs some time with a flight instructor in order to learn the quirks of gas engines, but that should be quick compared to the time it takes to actually learn how to fly.

spitfire 6y ago

Better still with an electric motor you have more options for motor placement. You don't have a big fat engine that has to be placed in the front[1]. The batteries don't have to sit in the wings, they can theoretically sit at the bottom of the plane making weight easier to manage. You also get more options for blade types. Like ducted fans. In short, your plane doesn't have to be designed around a fat gasoline engine and tanks. There's still constraints, but you get much more creative freedom. I expect when we see planes designed around the motor/batteries we'll see aerodynamics get electric planes into GA territory. EDIT: aerodynamic efficiencies. [1] Yes there's that tractor/pusher Cessna, no one liked it.

sokoloff 6y ago
In a lot of ways, you prefer the battery weight to be in the wings. The main one is that it reduces the load on the critical wing-fuselage junction (the source of zero-fuel-weight limitations in larger aircraft).
- spitfire 6y ago
  But now you have that choice. You can package things however you want, even in weird shapes. Not "has to allow liquid to flow downhill, even in rate 2 turn". I'll bet there's still wins to be found even with putting batteries in wings.

jillesvangurp 6y ago

Yes definitely. Most electrical planes currently in the process of certification are hardly using the latest & greatest in terms of battery technology. The reason for this is not that the technology is not there but that resetting the process of certifying the airplane and batteries extends the time to market by years and everybody is scrambling to get certified now so they can start fulfilling orders. Like with EVs, demand is not a problem for any of these manufacturers. This is true for Bye's eflyers, the Eviation Alice, the Pipistrel models, etc. These have modest but usable ranges (currently advertised) and are far enough in the development process that they might hit the market in some modest numbers in the next few years. But that's with battery technology of basically a few years ago. There's obvious room for improvement by simply updating the battery technology. 2-3x over the next decade is not an unreasonable expectation; the biggest hurdle is certification. The real thing to look for with electrical planes is range & operational cost. Yes it's annoying to not be able to fly 5 ours straight. But 2 hours is still pretty good. This would require doubling the power/kg for this plane, which sounds like it should be feasible; if not now than maybe in a few years. Also, turning a 100$ hamburger into a 5$ latte flight is going to be quite literally be the difference between being able afford to fly or not at all for a lot of people. GA flight is a really expensive hobby currently. I think what will happen is the experimental market exploding pretty soon. There's a critical mass of technology coming on the market and it's going to be very tempting for people to start building kit planes they can actually afford to fly. There are some fine examples of some daredevils on youtube flying some DYI contraptions already.

edraferi 6y ago

The article says Lithium Ion batteries deliver 1/15 the power per pound of traditional aviation fuel. That leaves a lot of room for improvement...

sojournerc 6y ago
They also don't get lighter as they lose energy, which is key to large passenger jet operations. Large plants often take off heavier than the plane is rated to land normally expecting to burn that weight in flight.
- llukas 6y ago
  We built fuel burning planes for last 100+ years. They're optimized to take advantage of burning fuel, it doesn't mean it is only option.
  - NikolaeVarius 6y ago
    What kind of HN comment is this? They're optimized for energy efficiency? Yes? What does this gotcha response even mean?
    - llukas 6y ago
      All parts of plane are optimized to work with jet engine. For plane designed from ground up as electric fact that jets land lighter than take off is not relevant. It is only relevant if you want to retrofit electric engine on jet engine optimized chassis - which is not only possible way. Bit more info on how thought process goes: https://spectrum.ieee.org/aerospace/aviation/how-i-designed-a-practical-electric-plane-for-nasa https://spectrum.ieee.org/aerospace/aviation/how-i-designed-...
      - mannykannot 6y ago
        Batteries have a much lower specific energy that hydrocarbon fuels to start with, and then that fact that the aircraft weight does not decrease over the duration of the flight is one more disadvantage (currently a second-order issue, given the first difference.) These are constraints that can be designed around, and you have more freedom to do so when designing from scratch, but doing so is not a optimization, it is a straightforward trade-off between weight and duration. There's no optimal hump on that line.

msandford 6y ago

If you weren't so worried about having a reasonably-sized airframe or high speed we're getting pretty close to significantly increased duration/range via solar. http://thundergull.com/specifications.htm http://thundergull.com/specifications.htm It's got 95sqft of wing and a top speed of 63mph. Drag is usually with velocity squared so going 1/2 as fast might only require 1/4 as much power. They state in the article that it takes 10kw to fly level. With 100sqft and an average 10W/sqft you're at 1kw. But cut the speed down to 30mph (2500W) and double the wing area (2000W) and you're very nearly at breakeven. The 11kw battery might then last you 10+ hours after accounting for the power required to climb out. Yes it'll end up being much more of a power glider than a "proper" airplane but that might be a lot of fun.

sokoloff 6y ago
Drag force is quadratic with speed. Drag power is cubic with speed. (Power is force times an additional velocity term).
- msandford 6y ago
  DOH! So if you went ~30MPH and had 25% bigger wings you'd probably have a solar glider then. Or ~40MPH (2/3 the speed) and double the wing size. Turns out that this is a thing: https://www.solar-flight.com/ https://www.solar-flight.com/