Could you create a battery powered plane?

[cjl]

Quite a few companies are working on drone like air taxis. However conventional wisdom is that planes are more efficient than helicopters.

I'm not sure I'd call that conventional wisdom so much as a nearly inevitable consequence of the different ways aircraft and helicopters make lift.

 

[etudiant]

There is a real world effort to introduce electric power to the commuter air market around Vancouver, Canada.

https://www.forbes.com/sites/jeremy...-50-year-old-canadian-seaplanes/#2152464b2c3b
The project seems realistic for the short haul market that it addresses.
Imho, this kind of real world kludge is much more indicative of the way forward than a series of finely honed prototype demonstrators.

 

[member 656954]

Metal air batteries while technically interesting are in no way a solution to any power source where CO2 reduction is the goal. The battery it self may not produce CO2, but "recharging" it absolutely does, and a lot of it.

It is an aspect of metal-air that is usually ignored, for sure, @essenmein. The focus on energy density is the single goal, the CO2 generation is rarely discussed. I'm not bullish on them in any event, controlling the oxidation so the materials do not quickly degrade appears to be an intractable problem.

 

[etudiant]

The offset to the CO2 generated during the battery recharge is that the overall internal combustion energy efficiency is abysmal, well under 10% for cars. That gives battery powered vehicles a huge leg up, even if the charging process is inefficient.

 

[cjl]

The offset to the CO2 generated during the battery recharge is that the overall internal combustion energy efficiency is abysmal, well under 10% for cars. That gives battery powered vehicles a huge leg up, even if the charging process is inefficient.

No, most cars are on the order of 20-25% efficient, with peak thermal efficiencies on some modern engines getting up into the 40s.

 

[etudiant]

Thought I'd read that the 20-25% efficiency was the basic engine, but that the actual performance once the engine is harnessed to drag around a lump of metal under normal conditions with occupants is far less, on the order of 5%.

 

[member 656954]

Appreciate we're getting off topic from electric planes, but this recent report from the International Energy Agency puts CO2 generation into a lifecycle perspective, which is probably more useful than engine energy efficiency.

Figure 6 from the report is for comparative life-cycle GHG emissions of a mid-size global average car by powertrain, based on various assumptions. It will be interesting to see how electric planes - if they ever take off (yes, pun intended) - compare to their av-gas equivalents.

 

[essenmein]

The offset to the CO2 generated during the battery recharge is that the overall internal combustion energy efficiency is abysmal, well under 10% for cars. That gives battery powered vehicles a huge leg up, even if the charging process is inefficient.

Unfortunately you couldn't be more wrong.

1kg of gasoline (or ahem, petrol) releases 2.3kg of CO2 and 45MJ of energy.
1kg of Aluminium in Al-air battery (excluding mass of oxygen) produces 29MJ (theoretical maximum) and the primary production of Aluminium from bauxite (ie Al2O3) produces 10.4kg of CO2 per kg of Al, no recycling included here because we are literally burning metal.

Then modern vehicles get reasonable effy, internet says 17-21, to make the math easy I'll take 20%. 1Kg of gasoline then produces 9MJ of usable mechanical power, and produces 2.3kg of CO2 to do that.

For Al-air electric, let's take drive train effy of 85% (this is battery losses, inverter losses, e machine losses and friction etc) so to get 9MJ of mech power you need ~360g of Al, and to reduce this 360g of Al from bauxite produces about 3.8kg of CO2.

So per usable MJ of (mechanical) power the Al-air battery produces about 2x the CO2.

 

[mfb]

On the positive side: The CO2 is produced in a fixed place, making capturing and sequestration an option. Splitting the CO2 to carbon and oxygen again (using CO2-neutral energy sources) is an option as well. All these things are not possible with internal combustion engines in vehicles.

 

[essenmein]

On the positive side: The CO2 is produced in a fixed place, making capturing and sequestration an option. Splitting the CO2 to carbon and oxygen again (using CO2-neutral energy sources) is an option as well. All these things are not possible with internal combustion engines in vehicles.

If the CO2 is split back to O2 and C, then I would agree.

However with sequestering, there is another insidious side effect there not considered, esp if there is large scale global roll out. If sequestering, this process takes oxygen, and carbon out of circulation.

At least with the biological Carbon cycle, its well, a cycle, where CO2 is constantly produced and consumed, ie the oxygen is released as part of the cycle and the same molecules basically just do the rounds repeatedly.

But with sequestering and metal air batteries, you take carbon and bauxite, produce aluminium and CO2, you bury the CO2 (ie its gone now), take the Al and oxidize it with new oxygen. Then you go back, take that oxide with some new carbon to get the Aluminium back and make new CO2, which you bury again.

Which now means every time that 1kg of aluminium does its loop, 10.4kg of CO2 disappears from circulation, ie since by mass CO2 is ~30% carbon and 70% oxygen, ie we're literally loosing 7kg ox oxygen and 3kg of carbon to use 1kg of aluminium to make a meager 29MJ.

Imagine the effect of reducing O2 concentration in the atmosphere, I doubt good things would be the result...

A lot of these things sound good till you zoom out a bit and consider other effects.

Then this really is just an energy storage mechanism, you somehow still have to supply energy to do this from somewhere.

 

[essenmein]

Because I like perspective, I went and roughly calculated how long it would take to consume half the atmospheric oxygen if 100% of todays global transportation energy was delivered with metal air batteries (~0.65TW), at that consumption rate it would take about 125k years to take half the oxygen out.

So maybe not such a big deal if the energy source is clean, at least not in the first thousand years or so!

(ref: dry mass of atmosphere 5.1e18kg, prop of O2 23% by weight, 309W av per person, 7.1B people, 28% total energy consumption (in US) is for transportation)

 

[mfb]

So maybe not such a big deal if the energy source is clean, at least not in the first thousand years or so!

I don't know what we will use in 1000 years, but I'm highly confident it won't be anything we use today.
The timescale gets even longer if you limit it to air travel. Cars can make more frequent recharging stops.

 

[member 656954]

Also, as far as I know, there's no such thing as an electric jet,

There is at least one, Lilium. It is a VTOL design that has undergone test flights - unmanned, I think only for the moment - and has a planned 300km range (and seems to have around a 300 km/h speed). The prototype is a two seater, which obviously is not very practical, so it will be interesting to see if they can scale up to bigger designs.

 

[russ_watters]

There is at least one, Lilium.

Cool looking plane, but calling it a "jet" is just a fun-sounding fiction. It isn't.

 

[member 656954]

Cool looking plane, but calling it a "jet" is just a fun-sounding fiction. It isn't.

Yeah, many people have said that. And I wonder whether if we were to have this discussion in 50 years, anybody will be disputing Lilium's definition

Still, if a jet requires an engine that burns fuel to produce thrust via the discharge of heated air and exhaust gases then we'll never have an electric 'jet'.

But there is one electric engine that I'm not sure has been mentioned, the ionic plane. I used this concept in my sci-fi novel, love the idea of a plane flying with its own lightning storm flickering over the wings!

 

[russ_watters]

Yeah, many people have said that. And I wonder whether if we were to have this discussion in 50 years, anybody will be disputing Lilium's definition

Certainly yes. It's not a jet, it's a ducted fan. They are very, very different things.

Still, if a jet requires an engine that burns fuel to produce thrust via the discharge of heated air and exhaust gases then we'll never have an electric 'jet'.

It doesn't. You could have an electrically heated Brayton cycle; it was proposed (not sure if tried) with nuclear power, for example (using the heat, not producing electricity).

 

[member 656954]

You could have an electrically heated Brayton cycle; it was proposed (not sure if tried) with nuclear power

Wow! Was that one of those crazy 50's ideas when nuclear was being proposed for trains and such? But would a Brayton cycle generate enough thrust? I don't know much about them.

 

[russ_watters]

Wow! Was that one of those crazy 50's ideas when nuclear was being proposed for trains and such?

Yeah, but crazier than a train - one was literally an air cooled nuclear reactor:
https://en.m.wikipedia.org/wiki/Aircraft_Nuclear_Propulsion

But would a Brayton cycle generate enough thrust? I don't know much about them.

The Brayton cycle is what jet engines use:
https://en.m.wikipedia.org/wiki/Brayton_cycle
https://en.m.wikipedia.org/wiki/Jet_engine

 

[essenmein]

Wow! Was that one of those crazy 50's ideas when nuclear was being proposed for trains and such? But would a Brayton cycle generate enough thrust? I don't know much about them.

Ahem, human ingenuity at its best...
https://en.wikipedia.org/wiki/Supersonic_Low_Altitude_Missile

 

[russ_watters]

...let me expand on my issue with this:

There is at least one, Lilium. It is a VTOL design that has undergone test flights - unmanned, I think only for the moment - and has a planned 300km range (and seems to have around a 300 km/h speed).

As I said, this is powered by ducted fans, not jet engines. But does that matter? Well, maybe/maybe not. Using the term "jet" implies high speed - I'm not sure why else they would say it. But 300km/h is really slow for a jet - it's even relatively slow for a propeller plane.

Ok, so how about judging it for what it is? Well, it looks like it is intended to be a small, personal transportation vehicle - the proverbial flying car. Just looking at the prototype, while it looks cool, fan efficiency is a function of size: fewer bigger fans would be more efficient than more larger ones. But if they are ok with a very short range for a niche application - say, replacing a helicopter flight from the airport to your house or company <100 mi away, maybe that's ok.

 

[RonL]

This puts life into an old idea of an electric jet engine :)

https://en.m.wikipedia.org/wiki/Aircraft_Nuclear_PropulsionIndirect Air Cycle
Indirect cycling involves thermal exchange outside of the core with compressor air being sent to a heat exchanger. The nuclear reactor core would heat up pressurized water or liquid metal and send it to the heat exchanger as well. That hot liquid would be cooled by the air; the air would be heated by the liquid and sent to the turbine. The turbine would send the air out the exhaust, providing thrust.
The Indirect Air Cycle program was assigned to Pratt & Whitney, at a facility near Middletown, Connecticut. This concept would have produced far less radioactive pollution. One or two loops of liquid metal would carry the heat from the reactor to the engine. This program involved a great deal of research and development of many light-weight systems suitable for use in aircraft, such as heat exchangers, liquid-metal turbopumps and radiators. The Indirect Cycle program never came anywhere near producing flight-ready hardware.[8]

 

[jrmichler]

Pipistrel just announced a larger electric airplane capable of carrying five passengers: https://www.avweb.com/news/pipistrel-unveils-801-evtol/. It's designed for short flights, but they believe there is a market for such a plane.

 

[diogenesNY]

Not exactly a pure electric airplane, but a hybrid combustion/electric aircraft... actually a retrofit of a 50 year old design.

From today's Wall Street Journal:

https://www.wsj.com/articles/electr...t-makeovers-in-race-for-the-skies-11563200318

that _may_ be behind a paywall... here are a few other articles on the same plane:

https://www.dw.com/en/ampaire-test-flies-worlds-biggest-electric-plane/a-49098126
https://www.msn.com/en-us/news/technology/ampaire-test-flies-worlds-biggest-electric-plane/ar-AACxoIr

https://www.aviationtoday.com/2019/06/06/ampaire-hybrid-electric-cessna-flight/
diogenesNY

 

[mfb]

The twin-engine plane will be able to carry seven to nine passengers and boasts a range of up to 100 miles (160 kilometers).

Can serve some remote places and island chains.

 

[member 656954]

Not exactly a pure electric airplane, but a hybrid combustion/electric aircraft... actually a retrofit of a 50 year old design.

Good catch, @diogenesNY, I heard an interview with Ampaire CEO, Kevin Noertker, recently, and he noted that once cruising altitude was achieved, the energy requirements of fixed-wing flight lend themselves to electric motors. This forms the basis of their hybrid design, which complements a traditional engine, rather than trying to entirely replace it. It seems a reasonable bridging technology until (if?) batteries reach fossil fuel-like energy densities, though I not sure how it would work in a large passenger jetliner.

 

[RonL]

Here is some good information for anyone interested in fuel/electric design, as for my thinking electric/electric assisted by wind friction of a plane in flight, is the possible holy grail.
I believe the videos below are well worth someone's time to watch, should be a help in setting up a test platform, (I learned a couple of things)

https://hackaday.com/2019/07/20/designing-compact-gasoline-generator-prototype-for-drone-use/

 

[A.T.]

There is an effort currently in the UK to convert a small passenger commuter transport to electric power.
The aircraft flies an island hop route involving very short distances, so the range deficiency of electrics is less problematical.
A BBC report on the project is here:
https://www.bbc.com/news/uk-scotland-north-east-orkney-shetland-45876604

This is a reasonable next step in this development effort.

Similar plans for short distance flights in Norway:

http://www.bbc.com/future/story/20180814-norways-plan-for-a-fleet-of-electric-planes

 

[russ_watters]

"Plans" are easy when they don't involve/require plans.

 

[etudiant]

Now in flight test in Vancouver. Details here:
https://www.pprune.org/rumours-news/627880-electric-powered-commercial-aircraft-here-we-go.html

Short hop sea plane conversions, trade fuel and maintenance costs for substantially lower range.
There is a real niche here with considerable room for expansion imho.

 

[mastermechanic]

There is Solid State Battery technology currently developing and its main problem is the cost to manufacture. They've 2.5x higher energy density than li-on types.

But I, personally, don't see the electricity as the main power source of the world. Considering the current battery tech. flying a 70 tonnes of 737 requires tremendous amount of energy and if that much of energy is packed in a battery form it would weight too much compared to fossil fuel. Specific energy of gasoline is incomparable high compared to batteries.

Second problem with electric powered vehicles is electric motors have low operational life compared to IC or Jet engines. Their maintenance is easy and low cost but in terms of operational hours I think they would require frequent maintenance when they are used in an aircraft.