[semi-extrinsic]

You can do small aircraft like this, no problem. The trouble is you can't scale it up, due to how quickly the power and energy demands go up. This thing is 560 kW and gets a range of 86 nmi; an A320 is around 40 000 kW and has a range of 3 500 nmi, while an A380 is around 80 000 kW and has a range of 8 500 nmi.

Going from this DHC-2 to the A380 requires an increase in energy storage by a factor of around 14 000x, while the max takeoff weight ratio between the two planes is only 250.

Airbus is developing a hybrid electric jet, the E-Fan X. They've done the math. When their CTO was asked about the possibility of an all-electric A320, the response was

"""

Assuming for a moment that we’d be able to rely on batteries 30 times as energy dense as that of today, an A320 would be able to fly with half of its payload for one-fifth of its current range, 500nm max. So, assuming a battery which today does not exist... It doesn’t work, purely electrical will not work.

"""

[eloff]

We can accomplish the same by producing the jet fuel using electricity. Realistically this will likely involve methane (natural gas) extracted from the ground and water, but it could one day be carbon neutral using captured carbon. The trick is to use clean energy like nuclear of renewables. There was an article on HN just recently about doing that with portable nuclear generators like those used on ships, this could be done right in the airport.

We already have a fantastic dense energy battery called kerosene. All we need to do is make it carbon neutral and our existing aviation tech won't even need to change.

[SEJeff]

Methane can be created via carbon capture entirely. It is in the SpaceX TODO list to create a factory to literally create metholox (methane + liquid oxygen is what they use as fuel for the new Starship / Superheavy rockets they want to use to go to mars) via carbon capture. Elon has already discussed this before. The end goal that the rocket launch is carbon neutral when you are using carbon already captured from the atmosphere.

Here is a good overview of the plan: https://cleantechnica.com/2019/10/30/no-you-dont-have-to-wor...

[hoseja]

The goal is not being carbon-neutral. The goal is Mars ISRU.

[SEJeff]

Elon has explicitly stated in interviews that one of the benefits of the design is that here on earth, it means they can be carbon neutral. I'm just relaying what he's publicly stated already. Yes, Mars ISRU is a HUGE benefit of this design, but it also means they can make their own fuel here on Earth with nothing more than some big machinery and solar panels.

I believe his exact quote was:

""" Sometimes I get criticism for, ‘why are you using combustion in rockets and you have electric cars’. There isn’t some way to make an electric rocket. I wish there was. But in the long-term, you can use solar power to extract CO2 from the atmosphere, combine it with water, and produce fuel and oxygen for the rocket. """

[8bitsrule]

"There isn’t some way to make an electric rocket. I wish there was."

That Musk is no Tom Swift. Tom even had an electric rifle, not just a flamethrower.

which he used to great advantage in colonizing Africa

[WalterBright]

The whole "carbon neutral" think is a crock. Coal is, after all, just dead trees, so coal plants run on "biofuel" and are "carbon neutral".

[m-i-l]

> The whole "carbon neutral" think is a crock. Coal is, after all, just dead trees, so coal plants run on "biofuel" and are "carbon neutral".

The difference is in the timeframes for capture and replacement - with coal it is millions of years, and with wood it is years. That means burning coal releases carbon which was trapped millions of years ago, and it would take millions of years to trap equivalent amounts of carbon with the formation of new replacement coal deposits. Burning wood on the other hand releases carbon that has been trapped within our lifetime, and it is easy to replace with new trees grown in our lifetime. Bear in mind that if we reverse millions of years of carbon capture we would revert the atmosphere to what it was like millions of years ago, and time travellers visiting that era are likely to need breathing equipment.

[ppf]

True, but what is a sustainable level of tree harvesting to feed the world's energy needs?

[eloff]

That's not possible, our energy needs are too great for that now. But nobody would seriously suggest wood (or other biofuels) be our principal energy source anyway.

[ben_w]

Technically correct, but about as unhelpful as saying “solar isn’t renewable because the sun will eventually go out”.

Our biology and our biosphere are not adapted to the atmospheric CO2 levels we would have if we burned all the fossil fuels.

[WalterBright]

My point is calling something "carbon neutral" if it is burning wood is equally unhelpful. Nothing is gained by burning a tree you just chopped down instead of burning a tree buried for a million years - the same amount of CO2 is released.

[mkl]

But the tree you just chopped down got its carbon from the atmosphere just a few years ago. That's what makes it carbon neutral. The coal (/gas/oil/etc.) got its carbon from the atmosphere in the far distant past, so from our point of view it's new additional carbon that wasn't in the system before. It can only be considered carbon neutral over a time span of millions of years, which is pretty meaningless.

[DagAgren]

"Unhelpful"? We have a specific problem we are trying to solve. That problem is: Too much CO2, right now. The term is obviously useful in solving that problem.

Nobody is worrying about CO2 on geological timescales. It is simply not relevant to any discussion anyone is having, or any problem anyone is trying to solve.

This isn't complicated? How are you managing to miss the point with such vigour?

[Tagbert]

The carbon neutral part is when you plant another tree in place of the tree you just cut down. The new tree then starts taking up the equivalent carbon from the tree you cut down and burned. That is what makes tree farms somewhat carbon neutral. You can’t do that with coal.

[dboreham]

There's an implicit time window on the sum. Burning fossil fuels is evaporating all the carbon captured in the past billion years, over a few hundred years.

[jjoonathan]

Or biofuel. Plants are good at capturing atmospheric CO2 and the resulting biomass can be turned into fuel using well established technology.

If it's nearly suitable for cars I suspect it's even more nearly suitable for aviation on account of the lower volumes and higher margins.

[munificent]

Now I'm just imagining some sort of steampunk wood-burning airplane.

[rdtsc]

> Now I'm just imagining some sort of steampunk wood-burning airplane.

Almost there https://en.wikipedia.org/wiki/Wood_gas

"Flight attendants will resume service in just a moment, after they throw another tree trunk into the wood gas generator"

[konspence]

Already underway[1]. It's completely viable, it just needs investment and commitment.

[1]: https://www.alaskaair.com/content/about-us/sustainability-re...

[WalterBright]

> Plants are good at capturing atmospheric CO2 and the resulting biomass can be turned into fuel using well established technology.

I.e. burning coal.

[_Microft]

Nope, that's outright wrong (and from other replies you should have learned that by now, so why keep reiterating something false?). Anyways...

The total amount of carbon in circulation is what matters because that part can end up in the atmosphere as carbon dioxide where it shows its heat capturing effects. Trees fix carbon while growing and emit it while decomposing but do not change the total amount of carbon in circulation in the long term.

Digging up carbon that has been locked away for aeons is what is so damaging. There would be nothing bad about burning oil IF that oil were produced by capturing carbon dioxide. We do not do that. We dig up loads of fossil resources and add them to the cycle.

If that explanation was too complicted, here is an easier one: fill a bucket to the brim with water, take a cup and start scooping and pouring back to the bucket. Everything is fine. Now get a second bucket full of water and start pouring into the first (material so far not in circulation is added to it). You see the problem?

If you still insist on your view with burning coal and trees being equivalent, then I challenge you to conduct the water-bucket experiment in the middle of your living room. I mean it wouldn't do no harm, right?

[WalterBright]

Which releases more CO2 into the atmosphere:

1. chopping down a tree and burning it

2. digging up a tree and burning it

Both are the same. Calling (1) "green energy" is outright wrong. Want to be green? Burn less carbon. The source of the carbon you're burning is irrelevant.

[philhippus]

Yes, but it takes 100's of thousands of years for the planet to form fossil fuels such as coal. We can't wait that long.

[WalterBright]

Just stuff the tree into the furnace. It'll burn just fine.

(The only reason the industrial revolution switched to coal was because the landscape was denuded of trees. The Jamestown colony in America was tasked with making glass, glass needs lots of fuel, and England ran out of trees. "Connections" by James Burke)

[blacksmythe]

You have to convert the wood to charcoal to burn hot enough for a blacksmith forge: https://en.wikipedia.org/wiki/Charcoal

I highly recommend a visit to Plimouth Plantation to anyone interested in 1700's era technology: https://www.plimoth.org/

Or Old Sturbridge Village for 1800's era technology: https://www.osv.org/

[hnick]

I don't really know where else to ask, so I'll ask here.

Another topic of research is very rapid sub-orbital passenger flight. Are there any numbers on proposed fuel efficiency for that? I'd expect you gain a lot by removing hours and hours of wind resistance, but getting up to speed and out of the atmosphere probably (gut feel) uses more.

[davedx]

I also haven't seen numbers, but I imagine the energy usage even to reach sub-orbital altitude would be pretty huge compared to a jet plane takeoff -> cruising altitude. Sub-orbital means you also have to bring your own oxygen too (rocket vs jet engine), which can approximately double your fuel mass...

[umeshunni]

No numbers, but you might have seen the SpaceX proposal / video here: https://www.youtube.com/watch?v=zqE-ultsWt0

[mrpopo]

> All we need to do is make it carbon neutral and our existing aviation tech won't even need to change.

Except making it carbon neutral will require enormous amounts of energy, shift the price up, and make aviation available only to the richest among us.

Aviation industry may keep existing, but will need to scale down.

[nine_k]

If the fuel is synthetic anyway, uh can be made better than kerosene.

Also, we have a huge amount of free nuclear energy, daily delivered from Sun, about 1 kW / m². It is nit stable enough for electric baseload, but, depending on the process, may be adequate for fuel synthesis.

North of Sahara may become a primary source of jet fuel, given its vast amounts of insolation, cheapness of the land, and access to seawater. Not exactly tomorrow, though.

[nradov]

Better than kerosene how? You're not going to get higher energy density without increasing safety risks.

[mrpopo]

Not exactly tomorrow, but we're facing a problem today. What are we supposed to do to reduce CO2 emissions between today and the mythical day we will have unlimited amounts of synthetic fuel available shipped by tankers from Morocco?

[seanmcdirmid]

Well, if we ever figure out fusion, we could get the enormous amount of energy part.

[mrpopo]

Ok; until then, we have to reduce CO2 emissions by 7% each year from now until we reach net zero in 2050. Even if we figured out fusion today (highly unlikely), it won't be deployed at scale by then (a modern fission reactor takes 10 years to build). So there are two choices really: progressively scale down the aviation industry, or ignore the climate crisis and let 100s of millions in poor countries die from climate-related causes.

[seanmcdirmid]

We could actually do that using fission alone, since we have we enough fuel for 70,000 years or so, and nuclear waste is free of green house gases. It would just be very expensive up front, as nuclear plants tend to be.

Anyways, this is the way France is going.

[sansnomme]

If you don't keep the scale, it would never get cheaper. Airlines struggle with profitability as-is, no point imposing additional undue burden.

[alex_duf]

Assuming we have infinite renewable energy supply to produce kerosene from electricity and therefore carbon neutral flights, it still doesn't quite solve the air quality issue.

A step in the right direction, but I hope this doesn't get used as an excuse to fly more.

[Robotbeat]

This is not true. It's easier to scale up. You get more efficient.

Scaling up an electric motor is not particularly hard. Some of the largest machines in existence are electric.

Power is not a challenge for electric. In fact, this electrified seaplane has much more power (560kW) than the original radial piston engine one (336kW), and even more than the turboprop conversion (510kW).

A LOT of very confident people on the Internet post lots of very wrong and/or outdated misinformation about electric aircraft (and electric vehicles in general).

Energy is a challenge, but the answer there is to increase efficiency and increase the mass of the vehicle which is battery. Both of those together give you a usable range of about 1000km. The same motor provider, Magnix, is also providing the motors for the 1000km range Eviation Alice.

Just because a conventional aircraft maker thinks something isn't possible, doesn't mean someone can't make it work. It most certainly doesn't require 30 times the energy density. For the same exact reason why electric cars don't require batteries with 30 times the energy density to compete with gasoline cars.

[semi-extrinsic]

I'm not saying it's impossible to make a 5, 10, 15 seater all-electric work. I'm saying a 100 passenger all-electric will never fly without a revolution in battery tech.

You say "just increase mass of the vehicle which is battery". If you read about this airplane you find that since they are using batteries with an appropriate safety rating for aviation, they've used all the space and mass already:

"this eBeaver isn’t carrying passengers — there isn’t room — and will only have a 15-minute endurance with a 25-minute reserve."

https://www.skiesmag.com/news/harbour-air-makes-history-with...

I tried finding concrete info about the Eviation Alice, but the best I could find was a photo of an unpowered full-scale model. They've been saying the first flight test is a couple of months away for more than one year it seems.

[dmix]

I’m curious if there is some monetary trade off for the sound level:

>> the plane’s four-bladed Hartzell composite propeller generated all of the remarkably quiet takeoff sound — a fraction of the thunder from the legacy Beaver’s radial piston

Maybe they’ll get a special class to be able to launch closer to cities without the noise complaints. Although I’d imagine it’s still pretty loud.

Also the bit after the paragraph about the batteries filling up the back mentions they didn’t use fully efficient batteries... they purposefully chose very safe but underpowered batteries previously used and flight tested by NASA for their own testing purposes instead of the higher end batteries used today in EV cars.

[tim333]

>I'm saying a 100 passenger all-electric will never fly without a revolution in battery tech.

I don't think you're right from an engineering point of view. Just multiply the aircraft size and battery number by some amount. For example:

>In September 2017, U.K. budget carrier EasyJet announced it was developing with Wright Electric an electric 180-seater aircraft to be developed by 2027. https://www.nextbigfuture.com/2018/09/easyjet-and-wright-ele...

Though all battery aircraft whether micro drones or A380 size will have a limited time they can stay up. Electrics currently seem limited to an hour or so whereas jets can do 16 hours now.

There seems quite a lot of potential on short routes <300 miles though using present batteries. (eg. London Paris or LA San Diego).

[leoedin]

There's a lot of mistruth in green technology. You need to get to first principles - the numbers. Look at the power requirements and weight budgets of large airliners, look at the best case energy density of lithium batteries and do the calculations yourself. That's what the parent comment did.

[Robotbeat]

They're using an existing certified battery for the prototype, not for operations. It takes time to certify battery chemistries.

And small general aviation aircraft like these usually only have a small portion of their takeoff weight as fuel, maybe 20-25%. But passenger aircraft may have 50% of their takeoff weight be fuel (for instance, 777 on long haul flights). Electric aircraft like Eviation will need to go further (55%). This is something you can do with a cleansheet design like Alice, but can't with a mere conversion designed literally over 70 years with manufacturing and materials from 70 years ago.

And you can apply the same principle of increasing take-off weight fraction for kerosene-powered aircraft as well. The Virgin GlobalFlyer was 82% fuel on takeoff. It flew around the world and then some. Kerosene is much better than it needs to be to enable modern flight.

You're absolutely right about Alice being late, but the design concept is a good example of what is possible. You combine state of the art but existing lithium ion chemistry (which needs some work for aviation certification but IS used on the ground already) with state of the art lift to drag ratio (and perhaps additional innovations, like wingtip propulsion to reduce losses from wingtip vortices) with efficient enough structural mass to enable 55% of the takeoff weight (as well as landing weight, of course) to be battery.

These things multiply together to enable long range.

[manigandham]

Cars are not airplanes. Electric cars are much heavier but weight isn't a big problem on the road. That's why they work, and they're still catching up to traditional range expectations.

With airplanes, you have to lift that weight using the same energy stored within. In that case, energy density is the absolute issue. Nothing else matters.

There's no magical solution, a high-school physics class will teach you how to calculate the potential energy requirement to lift up a certain amount of weight, and dividing by energy density and volume of current battery tech does not lead to a working jet any time soon.

[mcsb4]

> the potential energy requirement to lift up a certain amount of weight, and dividing by energy density and volume of current battery tech does not lead to a working jet any time soon.

E=mgh

E=(1kg * 9.81m/s^2 * 10.000m) / 3600s = 27.25Wh.

Tesla currently is at around 260Wh/kg thus roughly ten times the amount of potential energy needed to get to 10.000m altitude.

I'd assume that till 2030 we get to ~500Wh/kg by improving current technology. And maybe some quantum leap to 1500-2000Wh/kg within 20 years.

An A320 or A380 will likely always need a fuel cell but a 15 seater with 1000km range is only a question of time.

[variaga]

>Tesla currently is at around 260Wh/kg thus roughly ten times the amount of potential energy needed to get to 10.000m altitude.

That's the energy - assuming 100% efficient conversion of battery power to altitude - to lift _only_ the battery to altitude (and then immediately fall back down).

Actual engines are nowhere near that efficient and you'll presumably want to lift the rest of the airplane too. Then you have to keep using power to keep the plane aloft and land it safely.

Your hypothetical 2000Wh/kg future batteries still have a specific energy less than 1/5 that of aviation fuel (Jet A = 11950Wh / kg). A 15-seater electric with 1000km range based on those magic (7.5x better than state-of-the-art) batteries would instantly upgrade to a 5000km range if you tore out the batteries and replaced them with a gas tank of equal weight.

Batteries need a ~40x improvement in their specific energy density to make sense as an energy source for aircraft that depend on thrust for lift.

Tragically, physics doesn't care that battery powered planes would be cool.

[Dylan16807]

> Batteries need a ~40x improvement in their specific energy density to make sense as an energy source for aircraft that depend on thrust for lift.

I don't know how I can say "no" strongly enough.

If you only need 500km of range, it does not matter a single bit that jet fuel would increase your range from 1000km to 5000km. (Or 100km/180km/5000km respectively, if you want to talk about more contemporary batteries.)

Two things matter. Is the range good enough? How much does it cost? Jet fuel should not even be considered when answering the first question.

[Gibbon1]

A good way to think of this is as a venn diagram. If an electric plane has 1000km of range then it overlaps with jet aircraft. And probably also cars, buses, and trains. I think of friends that live in the middle of Nebraska. If you want to take a plane first you drive three hours to Omaha. If electric aircraft were cheap enough perhaps they would come out ahead flying to Denver instead.

[leoedin]

Potential energy is only one component of the power required by aircraft. If you want to actually go somewhere, you need speed, which means drag.

Drag increases the square of the velocity. That means going at 500knots (as an airliner does) uses a lot more power than going at the 150knots this seaplane might fly at.

You can calculate an approximate power requirement for the aircraft based on its glide ratio [1] or look at the power based on engine thrust [2]. In all cases you get figures in the 14-80MW range (engines don't tend to be full throttle during cruise)

That means your 260Wh/kg battery would need to weigh somewhere between 54 and 308 tonnes to sustain an hour of flight. That doesn't include takeoff, which is only a few minutes but might reach towards 200MW.

For reference, the 737 (low end power calculation) max takeoff weight is 62 tons and the 747-400 max takeoff weight is 397 tons. So in both cases you're looking at basically 30 minutes of useful cruise with current battery tech.

The range loss is additionally confounded by the fact that current aircraft lose fuel, so lose weight, during the flight. This accounts for a not-insignificant portion of the range.

[1]: http://large.stanford.edu/courses/2013/ph240/eller1/ [2]: https://aviation.stackexchange.com/questions/19569/how-many-...

So basically for electric passenger aircraft with even remotely comparable performance, we need a battery revolution. It definitely won't be by 2030.

[ben_w]

All depends on what you want. You can have “infinite” range with “no” battery — gliders are a thing, you can rise on thermals and turn the potential energy into kinetic to get wherever.

But if you want to go as fast as a chemical engine and sustain that for as long as a chemical engine, you either need at least the energy density of a chemical fuel or some way to refuel in-flight.

Fuel efficient often means “slow”. Great for cargo, not so much for passengers.

Edit:

Just to add, I’m looking forward to a future of short-range electric personal aircraft, I’m just not expecting pure electric intercontinental for anyone other than hobbyists — unless there’s a big breakthrough in density or wireless power transmission.

[Robotbeat]

The longest range conventional chemical aircraft flew around the world without landing. It's not necessary to equal that range for any commercial application. Kerosene is better than it needs to be.

Fuel efficient for aircraft doesn't necessarily mean slow, however (unlike ships). What matters is cruise lift to drag ratio. As long as you can adjust cruise altitude for peak efficiency and as long as all the flow is fully subsonic, then lift to drag ratio is mostly independent of speed (as you can increase altitude where the air is thinner to compensate).

So yeah, electric aircraft might stay at Mach 0.5 or so, but they don't need to be slow. Mach 0.5 is still much faster than any passenger high speed rail service and MUCH faster than car or bus or boat.

Pure electric intercontinental may be feasible for near-term chemistries like lithium-sulfur if you continue to push efficiencies (both structural and aerodynamic). Very long haul, like LA to Tokyo, will need lithium-air technology which is a few decades off.

[cjbprime]

Electric motor gliders should be great! You only need the battery/prop for takeoff and occasional sustaining flight and the glide ratio is ~4x better than general aviation planes.

[leoedin]

It's almost like you didn't read the comment you're replying to. It makes the absolutely valid point that the power requirements of a small jet airliner are many orders of magnitude greater than the power storage capabilities of any current battery technology. I don't really see how you refute that. Nobody's arguing you can't make a small electric plane work (clearly - the article is about one which works). Big ones are another thing altogether.

[deepspace]

> This thing is 560 kW and gets a range of 86 nmi

Not even that. I believe an 86 nmi range is what they are hoping to achieve by 2025. Current range is a fraction of that. The technology demonstrator has a theoretical flight time of 15 minutes and no ability to carry passengers because all the room/weight is taken up by batteries.

[WalterBright]

"Kelly was now so desperate to save weight that he upped the ante to one hundred and fifty bucks to anyone who could save him a measly ten pounds. I suggested we inflate the Blackbird's tires with helium and give each pilot a preflight enema. Kelly tried the helium idea, but helium bled right through the tires. The enema idea he left to me to try to promote among the pilots."

   -- "Skunk Works" by Ben Rich

[Robotbeat]

30 minute flight time, not 15. Should have approximately 86 mile range with this one.

There's plenty of room for passengers in this concept. Where are you getting this false information?

[deepspace]

See: https://www.skiesmag.com/news/harbour-air-makes-history-with...

From the article:

> What certainly hasn’t been done before is to fill a Beaver’s cabin with lithium-ion batteries, taking the plane to its gross weight. As a technology demonstrator, this eBeaver isn’t carrying passengers — there isn’t room — and will only have a 15-minute endurance with a 25-minute reserve.

[beefield]

Sorry, you seem to be quoting a bit selectively. From the same article:

> These are batteries that NASA is using, but they’re not batteries that we’d use if we were going to try and make it economical to fly today, because they’re very low in watt-hours per kilogram

[semi-extrinsic]

On the other hand, it's not like NASA was trying to get the lowest energy density possible. They were trying to get a li-ion battery pack with acceptable safety margin. And for this I understand one of the biggest factors is to have sufficient space between cells that a thermal runaway in one cell cannot spread.

[ct0]

Imagine the headaches when the airport tells these guys to hover for a while wile delays clear out. This is a niche product, albeit a cool one.

[Robotbeat]

It's a seaplane, it lands on the water, not an airport. Additionally, the total flight time including reserve is 40 minutes in this prototype and will be at least 60 minutes on the operational one (with Tesla-like-energy-density batteries).

[walrus01]

It seems to me that they have two somewhat separate engineering challenges. The electric motor and throttle control system, all the drive train stuff forward of the instrument panel in a Beaver. Plus however they retrofitted the cockpit engine control. Which might be quite a bit lighter than a pt6 turbine retrofit to turn an old Beaver into a turbo Beaver.

And then the other much harder problem which is achieving sufficient Wh per kg energy density in batteries, and Wh per litre of volume. For which they are dependent on global factors for r&d of batteries and improvement in density.

[beefield]

Do you have a source? (Not trying to be snarky but seriously interested. Haven't seen any technical details anywhere...)

[manigandham]

Also batteries weigh the same at landing and takeoff while jets rely on the reduced weight from fuel burn for safe landing.

[SahAssar]

No, not for safe landing. If a jet couldn't land safely while fully tanked then they would not be able to land in emergencies happening early in the flight.

They rely on the plane being lighter from fuel burn and therefore more efficient to extend their possible flight time, but not for safety.

[jseutter]

I guess it depends on what you call a safe landing. For large airplanes the maximum takeoff weight is typically greater than the maximum landing weight. If an airplane lands overweight it can no longer fly until it has been inspected and repaired. Most emergencies will involve flying around for long enough to get the aircraft within the acceptable weight limit. Some older aircraft have the ability to dump fuel, although I don't know of any new ones that have this capability.

Needing to land before getting under weight usually means a crash landing. In modern times, very few things like fire or an engine self-destructing will require immediately getting out of the air. It is usually better to fly in a straight line, figure out what is going on, figure out where to land, then land. This lets you get underweight, lets you communicate with air traffic control, lets emergency services prepare, etc.

[totallyabstract]

It isn't an issue for smaller planes (A320, 737), but larger planes (such as 747, 777, A340, A380) usually have a lower maximum landing weight than their takeoff weight. If an emergency happens early in flight they usually have to dump fuel to reduce weight before they can land. https://en.wikipedia.org/wiki/Fuel_dumping

[manigandham]

An emergency overweight/crash landing is the opposite of a safe landing.

Airliners will dump fuel or keep flying to get below maximum landing weight if possible. If they're still overweight and manage to land without issue, the plane will need to be inspected and repaired before it can fly again.

[smileysteve]

Isn't fuel vapor more dangerous than liquid fuel though?

Contained vapor creates an explosion, while liquid must evaporate first.

[catalogia]

The strain the weight of the fuel places on the airframe during landing is the issue, not a risk of explosion. Furthermore fuel tank inerting systems can greatly reduce the likelihood of any problems.

[manigandham]

Sure, but I'm not sure what you're asking in context. It's not about fuel vapor but overall weight on the airframe at landing. The bigger jets are not designed to touchdown at the fully loaded weight.

[apendleton]

That's all undoubtedly true, but fortunately, most flights don't require the capabilities of an A380, and in fact, demand for that specific set of capabilities is apparently low enough to stop building them altogether. Even for A320 flights, most are not 3500 miles, even if the aircraft is capable of it.

If we could make progress targeting just short hops targeted by DASH-8s or CRJs or whatever, we could still make significant progress, even if it meant leaving the longer-haul flights alone, or targeting their emissions with different technologies (synthetic fuels from carbon capture, maybe).

[0xffff2]

All electric with this century's technology might work for 8-16 passenger short-haul aircraft, if that market can be created (think, many flights from various regional airports between the SF Bay Area and LA area). Nothing bigger is going to fly without a massive breakthrough in battery energy density.

[anongraddebt]

I agree. But can you explain why this is? For me, it's just a hunch.

[0xffff2]

It really just comes down to energy density and the fact that batteries weigh just as much when you land as when you takeoff, whereas you burn off most of your fuel over the course of a jet-powered flight. Those two things together mean that as you increase the size of your aircraft, batteries take up a bigger percentage of your available weight budget.

It's pretty much a smooth curve, with the breakeven point depending primarily on energy density of your batteries. Until very recently, the electric aircraft weren't possible at all. We're now at the point where two seat trainers with short (but long enough for a typical lesson) endurance are possible and in production. If you look at where battery tech is going, we can probably push that up to 8ish seats and a somewhat longer endurance within a few decades. When you look at the size of even a small regional jet, it doesn't seem likely that current battery tech is ever going to get us to the energy density necessary to make it work.

[fragmede]

Pedantically, the batteries do weigh less when depleted. Not enough to make any sort of difference, but E=MC^2. We're talking micrograms for a battery the size used here. Doesn't invalidate the point that electric airplanes can't work effectively with current lithium-poly battery technology though.

[0xffff2]

You're right, that's so pedantic it's really not worth mentioning.

[chris_va]

I could see a non-rechargeable electric battery (but refillable, ala jet fuel) such as aluminum-air maybe working.

The round trip efficiency would be similar to diesel (since you are re-smelting rather than recharging), but the effective energy density on the plane could actually be much better than jet fuel.

[davedx]

> Going from this DHC-2 to the A380 requires an increase in energy storage by a factor of around 14 000x

First of all: citation needed.

Secondly: it's a disengenious argument to say "you can't scale it up", then give the largest passenger aircraft in operation as your first scale up target.

What about scaling up to the size of the propellor aircraft regularly carrying people between Amsterdam and many cities in the United Kingdom every day, or thousands of the other short haul routes? Indonesia is another example.

[ppf]

If we are looking at an energy-conscious (or energy-scarce) future, then we really have to consider what forms of transport are feasible at all. For these kind of short-hop journeys, flight is probably not efficient enough.

[SECProto]

Power (kW) determines takeoff weight (ie plane size/passenger count), energy (kWh) determines range. This article doesn't have all the info needed to say how this would scale. For instance, if the energy storage of the batteries doubled but the power stayed the same, you couldn't make the plane capacity any bigger but you could extend the range to more than double.

[darksaints]

Fuel cells are a possibility. There is some pretty high power densities (2.5kw/kg for SOFCs, 10kw/kg for less efficient PEMs). Electric motors are now reaching 15kw/kg. For comparison, a GE90 is about 10kw/kg, and older turbofans down to 2kw/kg. Running on liquid hydrogen presents some problems that are definitely solvable, but SOFCs can run on pretty much any hydrocarbon fuels at extremely high efficiencies (50-60%, 80% with combined cycles, compared to the ~45% that jet engines get).

I actually think the future may be a lot more simple than we're making it out to be. With some slight modifications to design, we could run existing turbofans on liquid hydrogen fuel. The biggest objection that most people have is the storage of hydrogen...but liquid hydrogen doesn't actually need to be stored in cryo tanks as long as the fuel is being used at faster rates than it evaporates. That's not a problem with jet engine consumption rates...low tech insulation may be sufficient.

[avmich]

There reportedly is an additional threat to the climate coming from inversion traces (modifies enough of Earth albedo?), so if we're delivering water to high altitudes, it's still not good.

Electrical motors would solve this; if we'd be able to avoid dispersing water from fuel cells up high, that could work.

LH2 has storage - and safety - issues still not solved. Toyota Mirai approaches it from a different angle, with some other shortcomings.

[WalterBright]

Burning kerosene also delivers water to high altitudes - the result is contrails.

[m-i-l]

How about using battery powered aeroplanes for shorter trips, and solar powered airships for longer distances? Bear in mind that the first electricity powered flight was an airship: "In 1883 the first electric-powered flight was made by Gaston Tissandier, who fitted a 1.5 hp (1.1 kW) Siemens electric motor to an airship."[0] And we also have solar powered airships which can stay in the air for 6 months at time now[1].

[0] https://en.wikipedia.org/wiki/Airship

[1] https://www.sciencealert.com/this-gigantic-chinese-airship-f...

[rklaehn]

Why would it matter how big the plane is? For a certain battery energy density and battery mass fraction, you should get a certain range, no matter what the size of the plane is. If anything, large planes should be a bit more efficient.

I think hybrid would be a great compromise. Short range jets spend a lot of kerosene just during taxi and takeoff. If you could just do launch and climb on batteries and then replenish the batteries from a jet powered generator during cruise, that would already be huge in terms of not just CO2 but also ops cost.

[DagAgren]

I think people aren't quite willing to face up to the consequence of this, though: This means that commercial air travel, as we know it, is going to go away. We can not afford to keep burning fuel at the rate we do for flights today, and we won't even have that fuel available at some point. And if we can not develop electric or renewable alternatives, which we very well may not, we will just have to stop doing it.

[riazrizvi]

According to my numbers an electric 747 would get more people further.

1. DHC-2 takes 6 people 86 miles ~= 500person/miles

2. 747 potential battery payload ~= 200,000kg (fuel capacity)

3. Power capacity of 200,000kg lithium-in ~= 25MW hours

4. Power required to take off, assuming 2.5 minutes to reach cruising altitude ~= 90MW * 2.5 / 60 ~= 4MWh

5. Power to cruise at about 600mph ~= 1/4 power to take off = 22MW (waves hand)

6. Time available to cruise ~= 1hr

7. Distance cruised ~= 600miles

8. Electric 747 takes 600 people 600 miles = 360,000person/miles

Maybe the power to cruise is 1/2 of power to take off, they'd still get 120,000person/miles.

[jacquesm]

It takes a 747 quite a bit more than 2.5 minutes to reach cruising altitude. 30,000 ft at 5000 fpm is 6 minutes, and engine input is a lot higher than 90 MW because engines are not even close to 100% efficient (neither are electrical ones).

Also, the weight on landing is critical not on takeoff, and you can't exactly shed battery weight because empty batteries weigh roughly the same as full ones do, so you will need to take maximum landing weight into account.

Finally, you need to take reserve fuel into account, alternates and headwinds.

I think you should re-do these numbers with more realistic inputs.

[riazrizvi]

Reserve fuel? I didn’t even allocate any fuel to land, I am assuming passengers won’t mind the bumps at their destination, you know for the planet.

[catalogia]

There are more practical ways to reduce the population than cratering airplanes into runways.

Fuel is a major expense for commercial airlines, they don't burn it just for shits and giggles. Airplanes use fuel when landing because destroyed aircraft and piles of corpses will quickly cost more than any fuel they'd save by trying to glide every plane to the ground.

[jillesvangurp]

Big aircraft are a thing because small aircraft are very expensive to operate. In GA there's a thing called the 100$ hamburger which is basically pilots doing short flights to grab a burger and spending about 100$ on fuel to get some air time. These are short hops and the handful of companies operating flights commercially for this kind of distances charge similar amounts (or way more) for the privilege per passenger. The main reason that this market is so small is the fuel cost. If you drastically cut that cost, you create a new market.

What electrical flight will do initially is enable the 5$ hamburger flight and create that market. Same distance, same speed, fraction of the cost. GA is currently prohibitively expensive mainly because of fuel. Operating that kind of flights commercially offers similar advantages though you still have to account for the pilots.

And while pilot cost is a factor, their availability is a much bigger problem. There simply aren't enough of them to operate the tens of thousands of mass produced electrical planes that on paper could out compete commuter jets on cost, scale, noise, flexibility, ability to land just about anywhere, etc.

The solution to that is self flying planes, aka. drones. This will likely happen long before we train up hundreds of thousands of new pilots. Like self driving cars there are challenges for this and like self driving cars those challenges are increasingly of a legal rather than a technical nature. It's technically feasible but getting permission to actually start doing this will take time and is happening very slowly despite e.g. Waymo 'drivers' actually needing to touch their controls is now becoming a once every few tens of thousands of miles kind of thing.

The list price for the Eviation Alice (projected to hit the market in 3-5 years) is around 3M and flies 9 passengers. The list price for an A319 is around 90M and flies about up to 160 passengers. So, ballpark it's not unthinkable to fly similar amounts of people using 20-30 mass produced self flying electrical planes competing on most 1-2 hour hops that these jets are typically used for. That will take decades to happen but it is entirely feasible with today's level of technology.

Small planes are not fundamentally hard. Cessna nailed mass production decades ago and electrical planes are vastly simpler (way less moving or combustible parts) And as Tesla and other battery manufacturers are showing, there's nothing fundamentally hard about producing a few hundred kwh of battery at a reasonable weight. A small plane with 500-1000khwh of battery will have a very usable range. With increasing energy densities, that will eventually extend into longer ranges as well. The Eviation Alice manages close to 600 miles on 900 kwh of what is essentially similar to the current energy density of mass produced EVs i.e. hardly the state of the art in battery tech. They are holding back here to get this thing certified ASAP instead of opting for already existing newer battery tech.

The impressive thing about this particular announcement is that it is a cost effective conversion for planes that are 60+ years old with a very well understood mission, which is very short hops. The reason that is economical is because combustion engine economics for that are so spectacularly bad and always have been. Electric flight is going to kill that market first and very soon because it hardly was a market to begin with. Small electrical planes crossing the Atlantic is going to happen at some point in the next decade or so. From there to that becoming a routine thing will take more time. But once that happens, it's likely to challenge the economics of dong the same in a 747. There's no fundamental need to scale electrical planes to that size even though that will probably eventually actually happen as well; but that will indeed require decades of improvements in energy density in batteries.

The only questions around electrical flight is when, not if.

[Gravityloss]

How would planes would look like if fuel prices increased a few fold? I would assume probably less jets and more turbine aircraft, at least on short trips. Straight wings and slower speeds. Boeing and Airbus might lose some market share. Boeing never had a turboprop, Airbus owns 50% of ATR.

[Gibbon1]

> How would planes would look like if fuel prices increased a few fold?

Like High speed rail

[ericpauley]

> less jets and more turbine aircraft

Assuming you mean turbofan vs. turboprop here, since both of these are turbine-driven.

In either case, my understanding is that turboprops don't present a substantial gain in efficiency, as turbofans allow for higher and faster cruising altitude, which reduces drag on the airframe.

[bamboozled]

I’m sure you have your valid reasons for doubting the feasibility of such a plane, yet here we are in 2019 talking over a network which was completely inconceivable at one point in history.

I just read your message as, “Can’t be done yet, will most likely be done somehow in the near future”.

[notatoad]

the scaling problem might be real, but it's not really a problem for harbour air, whose primary routes are ~50km from vancouver to victoria or ~80km from vancouver to whistler on nothing bigger than a twin otter.

[0xffff2]

The scaling problem is real. There's no electric plane in the world that can do that route with passengers right now (including this one). The scaling problem is probably surmountable for this particular use case, but it's far from trivial.

[cma]

Shouldn't it be easier to scale up at least to a point? Cross section increases slower than interior volume.

Scaling up on range is different, but just scaling size/passenger count I would think would be easier.

[gok]

Jets consume an unusual amount of energy and you don't run them at full throttle all the time. You'd probably use propellers and/or ducted fans for any electric airliner.

[copperx]

Is this battery limitation how we get flying cars?