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I understand the advantages of an electrical motor to an ICE, but I have doubts regarding your third paragraph. The energy density of Li-Ion batteries best-case

I understand the advantages of an electrical motor to an ICE, but I have doubts regarding your third paragraph. The energy density of Li-Ion batteries best-case scenario is around 1 MJ/kg, whilst Kerosene is 42.8-42.6 MJ/kg. That's a 40x !!! difference in energy/weight. Of course the electric engine will have a big efficiency advantage (think 80% vs 40% for ICE), but the gap in energy density is still enormous. The other (huge) advantages in flight safety and reduction in noise and overhead costs still apply, but I don't believe electrical planes will be as disruptive as portrayed without significant advances in battery technology.

anonymous5133 8y ago
Agree. I think the big breakthrough is going to be with figuring out some sort of replacement for the li-ion battery in terms of eletrical powered aircraft. Batteries are just way too heavy for how much energy they hold. There has to be a better way. I think we need some out of the box thinking for this one. I know solar energy is advancing, what about if we put thin-film solar cells on the exterior of the body of the aircraft? That might allow greater distance travel without much additional weight. There is already solar powered aircraft that traveled around the globe called the solar one. It is experimental but still a good concept to look at.
- antocv 8y ago
  Put kerosene in a tank to drive a generator to provide electricity when taking off, and as backup to generate DC for charging batteries when necessary. Now instead of kerosene burning in a jet engine, "we are all fucked if it doesnt work", its burning in a simple compact, "fuck it if it doesnt work", generator.
  - consumer451 8y ago
    Boeing-backed startup Zunum is doing exactly that and is planning on delivering their first 12 seat aircraft to JetSuite in 2022. https://en.wikipedia.org/wiki/Zunum_Aero https://en.wikipedia.org/wiki/Zunum_Aero
  - Scene_Cast2 8y ago
    A turbofan engine is pretty much a turbine "generator" mated to a propeller. Turbine generators are preferred over piston-based generators where weight matters. Airplanes often have a separate turbine generator (called an APU) for on-board electricity.
  - outworlder 8y ago
    That's a good approach, at least on paper. There are a few nice things about this. One is, it decouples your power generation from your thrust generation. If the generator fails, you still have a perfectly usable engine for some time. You can declare an emergency and land at the closest airport (easy to do if you are GA in the US). Same goes for all fuel starvation scenarios, fuel contamination, fuel pump malfunctions (for aircraft that use those). If you are using a turbine as a generator, it can probably burn anything you'd classify as fuel. Electric engines will probably get away with longer periods between overhauls and are more reliable. This will not be cheap though. It also introduces a high voltage, high power electrical bus where there was none before. And it is a more complex approach, with more things to go wrong, even if it may save in maintenance. For instance, take your average Cessna: you can lose your entire plane electrical system and your engine won't care. It has (redundant) magnetos which are coupled to the engine itself and will spark as long as the engine is rotating. Fuel is gravity-fed for the most part. So as long as your have fuel in your tanks (and throttle and mixture controls are in the right positions) the engine will run. Some of your critical instruments (like the artificial horizon) are mechanically powered (vacuum pump) so you can still use them without electric power. If you lose your electrical system in a hybrid (or electric plane), or if you have to turn it off (fire?), this is now a engine-out situation. You are also going to lose your instruments.
- outworlder 8y ago
  < what about if we put thin-film solar cells on the exterior of the body of the aircraft Not much of a gain, unless we are talking about ridiculously large wings (think glider-sized and above).
jillesvangurp 8y ago
Apples and oranges. You also need to factor in the weight of the engines and the reenforced fuselage you need to support jet engines. It's not just the fuel that is heavy. Electrical engines are really light and compact. The resulting planes can be much lighter. Also electical engines can be throttled up and down with much better granularity. An idling jet engine still produces a lot of trust and burns a lot of fuel even before it leaves the ground. So the efficiencies you get from better control over the output are substantial as well. Basically the current state of the art gives you a flight time of typically 1-1.5 hours with most electrical planes. If you double or triple that capacity through better batteries you basically get planes that can do short haul. The expectation is that that is basically happening over the next decade.
- geezerjay 8y ago
  > Apples and oranges. You also need to factor in the weight of the engines and the reenforced fuselage you need to support jet engines. It's not just the fuel that is heavy. Electrical engines are really light and compact. The resulting planes can be much lighter. Electric engines are lighter than ICEs but batteries are very heavy and unlike jet fuel they don't shed their weight as they are used.
  - favorited 8y ago
    It's also a lot faster to refuel a plane than to recharge those enormous batteries. That's longer turnaround times between flights, huge(r) delays if you need to stop to refuel due to weather, etc.
    - jillesvangurp 8y ago
      Depends, it takes about 20-30 minutes to start a jet; do all the pre-flight checks, etc. Add to that boarding, cleaning, etc. and most planes would be on the ground for at least half an hour and probably closer to an hour in between flights. That's plenty of time to recharge.
    - geezerjay 8y ago
foxes 8y ago
I doubt that you can make batteries with a higher engergy density, otherwise they are quite explosive. How do you make them much lighter? Lithium is a pretty light material. Petrol is so energy dense because you are storing that energy in chemical bonds. Electrical energy is not as "dense". I think we are close to "optimal" batteries.
- netjiro 8y ago
  E.g. you change the other part of the battery. "Air breathing" LiO batteries could reach energy densities in the ballpark of other chemical fuels. I think lab demo cells are around 5MJ/kg nowadays. Traditional chemical fuels have high energy density because we don't include the oxidizer, since it's readily available in the air. Any time you stuff a lot of potential energy into a small space with a low threshold for release you're making something dangerous...
sfifs 8y ago
In other words combining energy density, efficiency difference and lighter construction enabled by electric engines, the effective energy density gap is about 1 order of magnitude. In terms of engineering development over medium term, that is not very much, so I'll bet this will happen.
LoSboccacc 8y ago
hydrogen seems a good fit here. the extraction process can be sustained from renewable or low emission sources, refueling danger risk can be mitigated since these planes are not meant for general populace access. how much safety is of a concern depends on application. for fully autonomous cargo planes you'd already reduce it significantly and can be improved further by routing them around and not above densely populated areas. they'd be highly situational, but for those routes they could be approved for they'd be great.
dogma1138 8y ago
Jet enegines have a combustion efficiency of 100% at low altitude and 98% at cruising altitudes. High bypass jet engines will operate 90%+ propulsive efficiency when you reach cruising speed and altitude. This can include torbo props. https://en.m.wikipedia.org/wiki/Propulsive_efficiency https://en.m.wikipedia.org/wiki/Propulsive_efficiency Fuel has also a very big advantage over batteries and that is that you shed off weight when you use it while an empty battery will weight as much as a full one so you’ll end up carrying much more dead weight for the entire flight. Fuel cells might be a possibility but I don’t think airplanes with hydrogen tanks are a good idea.
- montenegrohugo 8y ago
  You are confusing combustion efficiency with thermal efficiency. Having a combustion efficiency of 100% does not mean that 100% of the energy stored in the propellant is transformed into kinetic energy (the thing the plane is interested in). The ICE engine with highest thermal efficiency reaches just 50%: The Wärtsilä-Sulzer RTA96-C turbocharged 2-stroke Diesel [1] [1]https://en.wikipedia.org/wiki/Thermal_efficiency https://en.wikipedia.org/wiki/Thermal_efficiency
  - tim333 8y ago
    That's quite an engine - I just looked up a picture of it https://pbs.twimg.com/media/DQv24mYUMAAmvQs.jpg https://pbs.twimg.com/media/DQv24mYUMAAmvQs.jpg
  - aunty_helen 8y ago
    The latest F1 tech has started to exceed this using their jet ignition system. https://www.autosport.com/f1/news/131772/mercedes-engine-hits-remarkable-dyno-target https://www.autosport.com/f1/news/131772/mercedes-engine-hit... https://www.enginelabs.com/news/f1-tech-what-is-turbulent-jet-ignition/ https://www.enginelabs.com/news/f1-tech-what-is-turbulent-je...
  - aerodude 8y ago
    Combined cycle gas turbines are actually higher efficiency than this. The current state-of-the-art is somewhere around 63% thermal efficiency.

anonymous5133 8y ago

Agree. I think the big breakthrough is going to be with figuring out some sort of replacement for the li-ion battery in terms of eletrical powered aircraft. Batteries are just way too heavy for how much energy they hold. There has to be a better way. I think we need some out of the box thinking for this one. I know solar energy is advancing, what about if we put thin-film solar cells on the exterior of the body of the aircraft? That might allow greater distance travel without much additional weight. There is already solar powered aircraft that traveled around the globe called the solar one. It is experimental but still a good concept to look at.

antocv 8y ago
Put kerosene in a tank to drive a generator to provide electricity when taking off, and as backup to generate DC for charging batteries when necessary. Now instead of kerosene burning in a jet engine, "we are all fucked if it doesnt work", its burning in a simple compact, "fuck it if it doesnt work", generator.
- consumer451 8y ago
  Boeing-backed startup Zunum is doing exactly that and is planning on delivering their first 12 seat aircraft to JetSuite in 2022. https://en.wikipedia.org/wiki/Zunum_Aero https://en.wikipedia.org/wiki/Zunum_Aero
- Scene_Cast2 8y ago
  A turbofan engine is pretty much a turbine "generator" mated to a propeller. Turbine generators are preferred over piston-based generators where weight matters. Airplanes often have a separate turbine generator (called an APU) for on-board electricity.
- outworlder 8y ago
  That's a good approach, at least on paper. There are a few nice things about this. One is, it decouples your power generation from your thrust generation. If the generator fails, you still have a perfectly usable engine for some time. You can declare an emergency and land at the closest airport (easy to do if you are GA in the US). Same goes for all fuel starvation scenarios, fuel contamination, fuel pump malfunctions (for aircraft that use those). If you are using a turbine as a generator, it can probably burn anything you'd classify as fuel. Electric engines will probably get away with longer periods between overhauls and are more reliable. This will not be cheap though. It also introduces a high voltage, high power electrical bus where there was none before. And it is a more complex approach, with more things to go wrong, even if it may save in maintenance. For instance, take your average Cessna: you can lose your entire plane electrical system and your engine won't care. It has (redundant) magnetos which are coupled to the engine itself and will spark as long as the engine is rotating. Fuel is gravity-fed for the most part. So as long as your have fuel in your tanks (and throttle and mixture controls are in the right positions) the engine will run. Some of your critical instruments (like the artificial horizon) are mechanically powered (vacuum pump) so you can still use them without electric power. If you lose your electrical system in a hybrid (or electric plane), or if you have to turn it off (fire?), this is now a engine-out situation. You are also going to lose your instruments.
outworlder 8y ago
< what about if we put thin-film solar cells on the exterior of the body of the aircraft Not much of a gain, unless we are talking about ridiculously large wings (think glider-sized and above).

jillesvangurp 8y ago

Apples and oranges. You also need to factor in the weight of the engines and the reenforced fuselage you need to support jet engines. It's not just the fuel that is heavy. Electrical engines are really light and compact. The resulting planes can be much lighter. Also electical engines can be throttled up and down with much better granularity. An idling jet engine still produces a lot of trust and burns a lot of fuel even before it leaves the ground. So the efficiencies you get from better control over the output are substantial as well. Basically the current state of the art gives you a flight time of typically 1-1.5 hours with most electrical planes. If you double or triple that capacity through better batteries you basically get planes that can do short haul. The expectation is that that is basically happening over the next decade.

geezerjay 8y ago
> Apples and oranges. You also need to factor in the weight of the engines and the reenforced fuselage you need to support jet engines. It's not just the fuel that is heavy. Electrical engines are really light and compact. The resulting planes can be much lighter. Electric engines are lighter than ICEs but batteries are very heavy and unlike jet fuel they don't shed their weight as they are used.
- favorited 8y ago
  It's also a lot faster to refuel a plane than to recharge those enormous batteries. That's longer turnaround times between flights, huge(r) delays if you need to stop to refuel due to weather, etc.
  - jillesvangurp 8y ago
    Depends, it takes about 20-30 minutes to start a jet; do all the pre-flight checks, etc. Add to that boarding, cleaning, etc. and most planes would be on the ground for at least half an hour and probably closer to an hour in between flights. That's plenty of time to recharge.
  - geezerjay 8y ago

foxes 8y ago

I doubt that you can make batteries with a higher engergy density, otherwise they are quite explosive. How do you make them much lighter? Lithium is a pretty light material. Petrol is so energy dense because you are storing that energy in chemical bonds. Electrical energy is not as "dense". I think we are close to "optimal" batteries.

netjiro 8y ago
E.g. you change the other part of the battery. "Air breathing" LiO batteries could reach energy densities in the ballpark of other chemical fuels. I think lab demo cells are around 5MJ/kg nowadays. Traditional chemical fuels have high energy density because we don't include the oxidizer, since it's readily available in the air. Any time you stuff a lot of potential energy into a small space with a low threshold for release you're making something dangerous...

sfifs 8y ago

In other words combining energy density, efficiency difference and lighter construction enabled by electric engines, the effective energy density gap is about 1 order of magnitude. In terms of engineering development over medium term, that is not very much, so I'll bet this will happen.

LoSboccacc 8y ago

hydrogen seems a good fit here. the extraction process can be sustained from renewable or low emission sources, refueling danger risk can be mitigated since these planes are not meant for general populace access. how much safety is of a concern depends on application. for fully autonomous cargo planes you'd already reduce it significantly and can be improved further by routing them around and not above densely populated areas. they'd be highly situational, but for those routes they could be approved for they'd be great.

dogma1138 8y ago

Jet enegines have a combustion efficiency of 100% at low altitude and 98% at cruising altitudes. High bypass jet engines will operate 90%+ propulsive efficiency when you reach cruising speed and altitude. This can include torbo props. https://en.m.wikipedia.org/wiki/Propulsive_efficiency https://en.m.wikipedia.org/wiki/Propulsive_efficiency Fuel has also a very big advantage over batteries and that is that you shed off weight when you use it while an empty battery will weight as much as a full one so you’ll end up carrying much more dead weight for the entire flight. Fuel cells might be a possibility but I don’t think airplanes with hydrogen tanks are a good idea.

montenegrohugo 8y ago
You are confusing combustion efficiency with thermal efficiency. Having a combustion efficiency of 100% does not mean that 100% of the energy stored in the propellant is transformed into kinetic energy (the thing the plane is interested in). The ICE engine with highest thermal efficiency reaches just 50%: The Wärtsilä-Sulzer RTA96-C turbocharged 2-stroke Diesel [1] [1]https://en.wikipedia.org/wiki/Thermal_efficiency https://en.wikipedia.org/wiki/Thermal_efficiency
- tim333 8y ago
  That's quite an engine - I just looked up a picture of it https://pbs.twimg.com/media/DQv24mYUMAAmvQs.jpg https://pbs.twimg.com/media/DQv24mYUMAAmvQs.jpg
- aunty_helen 8y ago
  The latest F1 tech has started to exceed this using their jet ignition system. https://www.autosport.com/f1/news/131772/mercedes-engine-hits-remarkable-dyno-target https://www.autosport.com/f1/news/131772/mercedes-engine-hit... https://www.enginelabs.com/news/f1-tech-what-is-turbulent-jet-ignition/ https://www.enginelabs.com/news/f1-tech-what-is-turbulent-je...
- aerodude 8y ago
  Combined cycle gas turbines are actually higher efficiency than this. The current state-of-the-art is somewhere around 63% thermal efficiency.