Electric planes

[doug]

It wasn't just an electric plane, it was a supersonic electric plane, which is something else all together. We already discussed it some time ago around here: Electric planes

Hearing it mentioned in Iron Man 2 was a rather insidery joke. No one else with me in the theater got the reference.

 

[jerry33]

LTA?
Please spell out new abbreviations for us mortals, somehow after communing with dark spirits i feel you are talking about airships?

Sorry about that. LTA = Lighter Than Air. There seem to be so many pilots in the forum that I forgot to expand. :redface:

 

[daniel]

I think electricity will be the most economical form of energy, especially once solar goes further than grid parity.

The question for airplanes, where weight is a very significant issue, becomes, Will it work better to store that electricity in heavy batteries, where all it can do is turn a propeller, or will it work better to store that electric energy in the form of liquid synthetic fuels where it can run a reciprocating engine, a turboprop, or a fanjet?

Jets are more efficient, and can fly higher and faster than propeller planes. Thus I think aviation of the future will obtain energy from wind and solar, but will store and carry that energy as a liquid fuel.

Electricity is the ideal way to power cars and trains. I don't think it's the best way to power planes, even though it is definitely possible.

 

[jerry33]

The question for airplanes, where weight is a very significant issue

In any form of transportation where cargo is carried over roads weight is significant:

For highway trucks and freight trains, there is a maximum weight limit so every bit of weight that isn't cargo is lost revenue. There is also a volume limit so there are some cargos, such as furniture, where this doesn't apply. Those could be electrified but the consist of only a small portion of the truck traffic.

In cars and passenger trains weight isn't a problem because cars never approach the weight limit the roads can carry.

In aircraft the limit is how much the runway (the road for an airplane) can hold, so like highway trucks, any weight that isn't cargo is lost revenue. Lighter than air ships never touch the ground, so the limit for them is structural.

 

[Norbert]

The question for airplanes, where weight is a very significant issue, becomes, Will it work better to store that electricity in heavy batteries, where all it can do is turn a propeller, or will it work better to store that electric energy in the form of liquid synthetic fuels where it can run a reciprocating engine, a turboprop, or a fanjet?

Jets are more efficient, and can fly higher and faster than propeller planes. Thus I think aviation of the future will obtain energy from wind and solar, but will store and carry that energy as a liquid fuel.

While I don't know what kind of propulsion exactly Elon has in mind, other than that it is electric, I think that converting to liquid fuels and back will decrease the overall efficiency significantly, and thereby make operating costs higher.

There are already more detailed concepts for supersonic electric airplanes, it seems usually involving superconducting electric motors. The concept below appears to assume that an improvement of battery technology to 1000 Wh/kg, which should be achievable with Lithium-Air, will be sufficient.

EADS VoltAir all-electric aircraft concept unveiled in Paris

EADS anticipates that as the technology is developed, high-density superconducting electric motors will actually exceed the power-to-weight ratio of today's gas turbine engines.

http://www.google.com/url?sa=t&rct=j&q=voltair&source=web&cd=5&ved=0CGgQFjAE&url=http%3A%2F%2Fwww.eads.com%2Fdms%2Feads%2Fint%2Fen%2Fpress%2Fdocuments%2FDossiers%2FDownloads%2FEADS-Brochure_VoltAir_English.pdf&ei=dHXCT8r9FIWciALWje2wCA&usg=AFQjCNFtQtR-ZMlzYS92tpB-ksYNWFsvNQ&sig2=Uxjbi48gqWhvbFW3TFnrew

New materials with promising capabilities are currently being investigated for a new generation of batteries. Some of them are based on lithium-air and lithium-sulfur combinations. Scientists expect these batteries to exceed energy densities of 1,000 Wh/kg (Watt hours per kilogram) within the next two decades, which would result in a more than doubling of today’s performance.

 

[Norbert]

In aircraft the limit is how much the runway (the road for an airplane) can hold, so like highway trucks, any weight that isn't cargo is lost revenue. Lighter than air ships never touch the ground, so the limit for them is structural.

It seems that with vertical take-off, the runway would then not be a problem.

However I like the idea of electric airships as well, they might complement each other for different applications/priorities.

 

[daniel]

Lighter than air ships never touch the ground.

At least, they're never supposed to touch the ground. Sometimes they do, and that's always a bad thing. :crying: However, I am a big fan of blimps and dirigibles. I'd love to go up in one, and if airsickness does not turn out to be a problem (I get sick on porch swings and rocking chairs!) I would totally prefer them over planes and ships.

... I think that converting to liquid fuels and back will decrease the overall efficiency significantly, and thereby make operating costs higher.

My notion was that a jet engine is a batter choice for an airplane. So I envisioned converting electricity to liquid fuel and then burning the fuel in a jet engine. Not converting it back to electricity in the plane for use in an electric motor.

The concept of an airplane with superconducting electric motors and supersonic propellers for supersonic flight, is a new one to me. But note that propellers lose efficiency at higher altitudes. Jets work best at high altitudes, and the wind resistance is less. Also, turbulence is less higher up. I really don't see conversion inefficiency being worse than adding the weight of batteries to an airplane.

 

[jerry33]

The concept of an airplane with superconducting electric motors and supersonic propellers for supersonic flight, is a new one to me. But note that propellers lose efficiency at higher altitudes. Jets work best at high altitudes, and the wind resistance is less. Also, turbulence is less higher up. I really don't see conversion inefficiency being worse than adding the weight of batteries to an airplane.

Right, the problem isn't when it's in the air. The problem is that a runway is designed to handle only so many psi from a tire and only allows for a certain wingspan. Those two factors limit the size and weight of the plane. That in turn makes the batteries vs. cargo the problem. I'm actually somewhat surprised that they don't take off with a minimum amount of fuel and then add fuel in-flight. That would allow for a much larger cargo/plane ratio--at least for cargo-only planes.

 

[daniel]

I'm actually somewhat surprised that they don't take off with a minimum amount of fuel and then add fuel in-flight.

But then they'd have to have another plane taking off with that extra fuel. Now you have two planes instead of one and you'd still have to use energy to get the fuel up. The military does this, but they have deep pockets, and reasons other than efficiency to want to extend the range or flight time of certain planes.

 

[jerry33]

But then they'd have to have another plane taking off with that extra fuel. Now you have two planes instead of one and you'd still have to use energy to get the fuel up. The military does this, but they have deep pockets, and reasons other than efficiency to want to extend the range or flight time of certain planes.

Right, but it depends upon whether the amount of additional income exceeds the costs of in-flight fueling. The tanker plane could conceivably carry enough fuel for several planes, and wouldn't have to fly very far, so the take-offs shouldn't be one to one. I'm not saying that it will make economic sense to do so, but I can see how you would need to do the calculations to find out.

 

[tdelta1000]

Electric planes are a good idea but weight (battery) could be a factor that may keep the idea grounded.

 

[Norbert]

The concept of an airplane with superconducting electric motors and supersonic propellers for supersonic flight, is a new one to me. But note that propellers lose efficiency at higher altitudes. Jets work best at high altitudes, and the wind resistance is less. Also, turbulence is less higher up.

I haven't read all of this yet, but it seems it might go some way to address your concerns: (it is from 2009)

http://ewh.ieee.org/tc/csc/europe/newsforum/pdf/LuongoC_2AP01.pdf

 

[TEG]

Electric planes are a good idea but weight (battery) could be a factor that may keep the idea grounded.

Battery weight/size/cost could limit them to shorter routes. Also recharge time instead of pack swap. I was thinking the first application might be private/corporate jets that tend to do shorter routes (say a regular LA to SF commute flight) and where the plane can sit unused (recharging) for days at a time.

 

[daniel]

I haven't read all of this yet, but it seems it might go some way to address your concerns: (it is from 2009)

http://ewh.ieee.org/tc/csc/europe/newsforum/pdf/LuongoC_2AP01.pdf

Very interesting! Thanks for posting. I didn't try to read it all, but I scanned through it and read the bits that seemed most interesting and accessible.

While they mentioned the idea of fully electric planes, they were mostly talking about electric propulsion powered by turbine engines driving generators. Both the generator and the electric propulsor have to be superconducting in order to achieve the needed power. They'll need to develop the needed cooling system and design both the generator and propulsor, both of which present new challenges. One possibility is that liquid H2 could be used as the coolant, and then burned as the fuel.

Fully electric planes would require electric storage far more energy-dense than anything available now. (They're talking about transport planes capable of carrying cargo as or more efficiently than present cargo planes, not talking about ultra-light planes such as exist now.)

They think the time line is 20 to 25 years for electric propulsion in a plane that burns fuel to produce the electricity, and an unknown time (if ever) for the development of electric storage sufficient to enable fully-electric planes.

But apparently, and this was a surprise for me, a turbine propulsion engine that burns no fuel, but is driven entirely by a superconducting fan, is possible. Who'd a thunk it?

 

[Lloyd]

Interesting thought...... Ramjet engines have been used for supersonic flight using H2

http://ntrs.nasa.gov/search.jsp?R=19920012288

 

[Norbert]

They think the time line is 20 to 25 years for electric propulsion in a plane that burns fuel to produce the electricity, and an unknown time (if ever) for the development of electric storage sufficient to enable fully-electric planes.

This was written in 2009. Meanwhile, we see many research efforts, including Lithium-Air, developing, and a continuous progress in delivered battery cells. So, at least in my mind, just a matter of time, since eventually fully-electric will be the most cost-effective. 20 to 25 years certainly may be enough for Lithium-Air (and there are already improvements in the laboratory which may bring another 2x in addition to the known 5x- 10x improvement), to be there at the same time.

 

[daniel]

While there may be batteries with adequate energy density by then, I don't think we can assume that there will be. It's also possible that batteries will come up against a theoretical limit. I think it entirely possible that liquid fuels may always have a weight advantage over batteries, and the model that the article concentrates on may remain more cost effective. That is, superconducting electric thrust engines run from electricity produced on board by fuel-burning turbine engines. The trade-off is the weight of the turbine vs the weight of an electric cryogenic cooler, since liquid H2 can serve both as coolant and as fuel.

Which model is eventually the most efficient remains to be seen.

 

[ManuVince]

Not fully electric but hybrid :
Volta Volaré's futuristic GT4 e-hybrid airplane available for order

The spec says 1852 km on a 105 liter tank, that's slightly better than my quite efficient Audi A4 2L TDI...
Not bad for a plane, if it ever flies...

 

[Norbert]

It's also possible that batteries will come up against a theoretical limit.

There is already laboratory proof-of-concept for Lithium-Air. Any theoretical limits are certainly still far away, even for chemical storage of electricity.

 

[Norbert]

Not fully electric but hybrid :
Volta Volaré's futuristic GT4 e-hybrid airplane available for order

The spec says 1852 km on a 105 liter tank, that's slightly better than my quite efficient Audi A4 2L TDI...
Not bad for a plane, if it ever flies...

Nice to see that it is a completely serial hybrid, and that it can take off, and fly some distance, on battery alone.