Skeptical about electric-powered planes | Hacker News Reader

Skeptical about electric-powered planes

planeandpilotmag.com

99 pointslxm142 comments

There's an area of aviation where a lot of innovation could occur, and people are excited to do it — but the FAA is in the way. Ultralight aircraft, under FAR Part 103, are allowed to weigh up to 254 pounds dry, without fuel. Electric ultralights must weigh up to 254 pounds with batteries, which is practically impossible to achieve, so ultralight pilots who would love to be flying clean electric aircraft are using unreliable two-stroke engines that spew incomplete combustion products like there's no tomorrow. If the FAA would revise the regulations to exclude the weight of batteries, like it excludes the weight of ballistic recovery systems or floats, it would open up a field for innovation and might reinvigorate ultralight aviation, but the FAA doesn't want to even think about ultralights, and ultralight enthusiasts are worried that if they push matters the FAA will shut it down like they did ultralight instruction twenty years ago.

Isnt it because fuel can be dumped in an emergency, if needed? Cant say the same about batteries.

Ultralight airplanes, and any general aviation plane I know of, do not have fuel dump systems. In cases where a plane is too heavy to land, it will often circle for a few minutes to burn off excess.

Not really an option for ultralights or most private aircraft.

But what happens "magically" at 255 pounds of weight that it falls in another category?

The risk is different a large volume of liquid that can spill and is volatile vs essentially a solid (yes electrolyte is liquid/gel).

I think you have to count batteries. That said at least in EU I think there is already a big electric assist / launch sailplane market - is this not permitted in the US?

That said, some of the electric sailplanes are in the 800lbs range - so that is a LOT more.

Why not at least deduct from the batteries' weight the 30-pound weight of the maximum 5 gallons of gasoline? An ultralight has to carry that extra thirty pounds on takeoff, which is probably the point where the higher stall speed matters the most for safety; it seems reasonable to allow at least that much deduction for batteries. Even that would be an encouragement.

Not disagreeing. In my view the reliability / noise (ground issue) / pollution etc make an electric sustainer absolutely fantastic. Sailplanes can slow way down as well, so yes, if they crash its a problem, but these are not GENERALLY stall/spin into ground at high speed. Stall speeds can be down in 40kt range or lower.

I don't follow this area closely though so have NO IDEA of US regulatory rules here. But the electric use cases in this general category seem somewhat clear?

Maybe not possible with ultralight aircraft (those limits are tight!) but certainly possible with the experimental category.

>so ultralight pilots who would love to be flying clean electric aircraft are using unreliable two-stroke engines that spew incomplete combustion products like there's no tomorrow.

This is such a total non-issue, any effort at all spent on this would be better spent on almost any other target from a climate standpoint.

I'm saying these pilots want to do this innovation, not that ultralights are a large proportion of the problem, or even that GA as a whole is a significant contributor to pollution. But the reliability issue is significant: two-stroke engine failure is a frequent cause of ultralight accidents. They require careful maintenance and in-flight handling to be reliable.

I didn't see this as an issue about climate change, but as providing a place for innovation and experience which can later be applied to larger aircraft. If absolutely nothing else, it helps spark more interest in the technology by making it more accessible, and will help with general confidence in electric aircraft ("they've been flying electric ultralights for years now").

It is an issue if you take leaded avgas into account. Not the pollution per se is a problem, but the poison in form of lead in the exhaust gases. Also, any measurable reduction matters, in this case it's even for free, the industry will develop electrical planes for free they just have to allow it. It would be smart to change these policies quick.

Incomplete combination is a poison problem.

There is the "ElectroLight" which is 103-approved, allegedly. https://www.aviationpros.com/aircraft/press-release/21088890...

Better than an ultralight: N540EV, a motor glider kit plane using the engine from an electric motorcycle. Over 700 pounds and it can fly anywhere under day VFR rules.

https://www.youtube.com/watch?v=0jEZrBjHnQg

what if you carried the batteries on your person?

Then you're limited to 100wh?

> but the FAA is in the way

Let's remember that there's a world outside the US, and sometimes focusing too much on what happens in the US is going to make you blind to what's happening elsewhere.

In this particular case, I'd be interested in knowing what's going on in EU (which, combined, is quite comparable to the US economy, and back in 2005 was even bigger than the US one [0]).

[0]: https://statisticstimes.com/economy/united-states-vs-eu-econ...

Most electrical planes flying today will have around 160-200 wh/kg of battery. That's not a lot but somebody is buying them nonetheless. The reason for that relatively modest energy density is that anything flying and certified now would have entered the certification process many years ago. The question is not if those batteries can be improved but by how much.

Tesla already has cars on the road with batteries doing better than that. Their upcoming 4680 battery cells will be around 380 wh/kg, apparently. Then there are several companies working on solid state batteries promising closer to 500-600 wh/kg. Sounds good? That's 2-3 x the range of electrical planes on the market now or very soon. There's nothing to be skeptical about here. Pretty much a done deal. With that type of battery, we'll be seeing planes do 400-800miles; possibly a bit more. If you think that's ludicrous, the Eviation Alice is currently pre-selling a plane that will do 440 miles. Apparently, they use 260 Wh/kg batteries currently. Upgrading to something with 500 wh/kg would pretty much get them close to a 1000 mile range.

I consider 2x to be the minimum of what we can expect this decade. That's just a matter of updating these planes with batteries that are either already being produced or will be very soon. More a matter of when than if, really. These are first generation planes too. It's not a question of if they will improve but how quickly and by how much. Designs, engines, wiring, materials, etc. There still is a lot of room for improvements.

Longer term, I'd say 4-6x current ranges should almost certainly be doable based on just battery improvements. My view: 4x would be disappointing. 6x is a good number to shoot for longer term and we can actually hope for more. Like 8-10x. But actually 3x current ranges would already be a game changer. We'll see.

Range is one thing - what is the passenger capacity of these planes?

Wrong metric. Cost per passenger per mile is a better one.

The reason big jets are popular is that jets burn lots of fuel, which is expensive. Bigger jets burn fuel a bit more efficiently so the cost per passenger becomes more reasonable. Big battery electric planes are likely not possible with current battery technology.

But the good news is that small electrical planes are pretty cheap and the electricity is cheap too. So, instead of buying a big Boeing to save fuel, you could buy a few dozen smaller planes, fly to smaller airports that Boeing would not even be allowed to land, and drop passengers off closer to their destinations.

In addition to calling my question 'wrong' - can you also answer it?

Also, if your 'correct' metric were right, then everyone would walk. Does that solve the problems flying does? I don't think so.

[edit]: Also, I guess your metric explains why everyone is only taking the bus or train, and private transportation does not exist?

I'll answer a different question. The major cost of airplanes is engine wear. Engines have a TBO of maybe 2000 hours, which means about a year's worth of flying at 40 hours per week. For a cheap plane like a basic Cessna, the overhaul is the cost of the aircraft.

If electric planes are lower-maintenance, for GA purposes, they could be a lot cheaper. The hobby would go from millionaires to ordinary folks.

Electric motors don't wear out like combustion ones do.

Sure, and an engine that wouldn't need any fuel/power at all would be even better - the question is, what is practically/theoretically achievable.

But I guess the fact that everyone is avoiding the elementary question of 'how much can a transportation system transport' tells me all I need to know about the practicality here.

The Air Force has proven a system that uses renewable energy to power a system that combines water and carbon dioxide extracted from the air to produce E-Jet synthetic fuel. Currently a chemically similar but less environmentally sound synthetic fuel is approved to be mixed 50/50 with regular JP8 in military aircraft and they are doing acceptance testing for full synthetic.

This effectively takes every high efficiency jet engine and makes it carbon neutral, with the added benefit that you don't need to ship the fuel anymore. At that point electric planes are dead.

https://www.afmc.af.mil/News/Article-Display/Article/2820003...

That's one of several possible fuels. What all of those have in common is that they are more expensive than kerosine, which in turn is more expensive than electric.

The big advantage of battery electric is cost. Wherever you can fly them, it will be the cheapest way to do it, by far.

Costs change. Cost of synfuels will only come down, as solar electric continues to do.

How do you get the CO2 out of the air, other than the obvious "grow corn"?

Seriously? Adsorb it. You have to move a lot of air through your system, but that just costs energy. With solar cost still in free fall, it will soon be cheaper to get CO2 out of the air, add hydrogen extracted from water, and deliver CH4 or larger molecules, than to get them out of the ground.

is adsorbing something i can do at home or does it require something on the scale of a refinery?

To do so practically requires scale, but a science fair-worthy demo can probably be done at home, perhaps using distilled water as the sorbent.

There's a few options out there, the most common method is solvent absorption [1].

There's also a YC backed startup, Prometheus Fuels, that's trying to commercialise a process using carbon nanotube membranes for CO2 separation [2].

[1] https://web.archive.org/web/20130508220516/http://www.uk-she...

[2] https://prometheusfuels.com/

Using a sorbent, to absorb the CO2 in preference to N2/O2/Ar (etc.). The 'sorbed CO2 is then de-sorbed in a closed container (for compression, storage, etc.). Selexol is a common commercial solvent for CO2 removal, though for atmospheric removal other tech may be preferable.

Yes, this feels a bit like reading an opinion piece dissing on EVs in CarAndDriver 15-20 years ago. Of which there were many.

How about this for phase-out:

1) use ev motor engines, but power with a fuel cell + methane/hydrocarbons

2) phase in synthetic fuels

3) swap out the fuel cell and synth fuel for batteries when feasible

It's not difficult to imagine electric training aircraft. In fact, they already exist - Pipistrel have delivered 111 of them (https://www.aopa.org/news-and-media/all-news/2021/january/27...). They have swappable batteries and can fly for about an hour.

The total cost of ownership must be super low compared to gasoline engines - there's almost no moving parts, which means no costly engine rebuilds.

I'm very, very sceptical of electric passenger aircraft, but I think it's almost inevitable that electric aircraft will start to dominate at the training and low cost end of the market.

Training makes sense. As usual, range is the big issue.

There was a steam powered aircraft, once, in 1938.[1][2] Looks like it got into the air, went around the pattern once or twice, and landed safely. Unclear what happened after that. The Smithsonian has a copy of the engine.

[1] https://www.youtube.com/watch?v=J1tyRX3bXhg

[2] http://rexresearch.com/besler/beslerst.htm

Agree with the big benefits for training, specially if you can swap batteries like you do with industrial drones.

Other niche area where there would be a great benefit:

Remote regions like the amazon jungle where a regular trip between villages (no roads what-so-ever) takes hours or days on small powered canoes vs 15 minutes when flying. Electric seaplanes would not only deliver basic modern services (Medical, Police, Business, etc) to these areas but it could do it without the need of shipping expensive fuel from far away.. Solar chargers would take care of that. ( maintenance would be easier too.. )

My small attempt at the technology :) https://youtu.be/zAwpi7VPQTk

And one more niche area.. Electric engines do not care about low oxygen, going up and down from coastal areas to high altitude Andes is economically achievable. Going from a place like Lima to Jauja in Peru can take 12 hours on a road, but barely 45 minutes by plane.

An early attempt with a Pipistrel sinus motorglider * going back down to the coast requires very little engine time :)

https://www.youtube.com/watch?v=UOB8yzieYcs

That's fantastic

Some silly questions if you don't mind.

1. Up thread people talked about electric ultralights as held back by FAA. Presumably your flights are in different t jurisdiction (Lima etc). Are there enough "pro" jurisdictions to compensate for the FAA "anti"

2. Your propeller (mounted behind you) seems to regularly cut out. Is that a planned thing to save energy? just a series of push then glide?

3. What is needed to go from this to something like regular service ? What is missing from this aircraft ?

1. This in Peru, far away from FAA's reach ;) 2. No,It must be a camera sync issue.. I was giving it just enough power to keep altitude 3. This was done just for fun.. To prove it could be done, if you wish. The engine (cheap chineese model) crapped out within 10 hours.. Sometime I'll put a newer/better and use it as a sustainer for when thermals are not available

I think there's a startup (either YCombinator funded or at least they post here) looking to do this with electric blimps carrying freight containers taking products to ports.

I don’t really buy the main counter arguments here.

First, the current tech as stated in the article is short flights, like an hour. That’s actually a niche that’s already marketed—luxury flights to Martha’s Vineyard, Tahoe, Bar Harbor. People are already paying for these flights today.

Second, the heat issue. Batteries do suffer from cold weather but if it’s an hour flight, with the batteries dumping their full charge, between thermal heating and simply insulating your battery it can stay warm.

I think this is the key here: conceptually, there may be some cognitive shear around the word "plane." In the near-term VTOLs aren't going to be airliners or, for that matter, flying cars. Cessnas and helicopters, though...

There's not really a viable path from those short flights to longer ones though and the hype of the industry is driven in part around electrifying airliners.

And those short flights are a small fraction of airline emissions. I haven't run the numbers, but I don't think it can be more than a few percent. If a company or airline actually cared about reducing emissions from aviation they would look at using hydrogen like the Soviet Union did (I'm not talking about fuel cells, the jet engines used hydrogen as fuel).

The path to bigger airlines depends heavily on battery advances, but it doesn’t mean it’s impossible, either. It just means the second market will be Philly to New York. Then New York to Boston. Maybe never across an ocean.

I think there is a handful of airports like London City Airport which could utilize electric to lower noise. Now viable destinations from there is good question. There is probably some others as well, but it's rather limited market.

Consider how much cheaper it might be. The airplane itself would have minimal operating costs —- electricity can be quite cheap, and an electric plane has far fewer moving parts

Shouldn't those short trajets be done by train instead? Any flight less than 2 hours should be a train IMO ( well except if it crosses a sea of course).

The author makes quite some big claims without any evidence, including that "Energy density in these batteries is quickly reaching its theoretical limit". This is misleading bordering on false. Companies like Enovix [1] and Sila Nano have commercialized pure silicon anode batteries for small devices with energy densities greater than the current generation of Li-Ion with graphite/silicon anodes. A whole host of companies are attacking the "battery energy density" problem from all sorts of angles (including Tesla - no mention of 4680 cells in the article, because that would undermine its premise). There is no law of physics saying "350 Wh/kg is the absolute upper limit".

[1] https://assets.website-files.com/6023ee57b22bf2f0c312206d/61...

My understanding is that the 4680 cell doesn't have any better energy density than what Tesla is currently using (the 2170). Yes, it has 5x the energy of the 2170 but it's also 5.5x bigger in volume. In essence, the energy density of the cell has gone down, not up. The battery as a whole could still go up because bigger cells mean less weight in the steal casing, better packing efficiencies and the tabless-ness of the 4680 should allow more efficient thermals. I'm assuming that the claimed 16% improvement in range would come from that. The big improvement of the 4680 is the power (and manufacturing costs), not the energy. In any case, it's sort of a moot point if Tesla won't sell these batteries/cells to anyone else.

Anyway, my take on the article was that the practicality of the electric airplane basically comes down to battery tech. If someone produces a dramatically better battery I assume that putting it into an airplane will be straightforward. So if you want to build an electric airplane what you should really be building is a better battery.

Why is everyone using 4 digits for batteries that are labelled as 5 digits? 18650 are 18650, not 1865 even if it makes more sense that way.

I wonder why the nomenclature changed?

Yeah, you're right - the 4680 is a bigger battery, but my point is battery technology is being pushed on multiple fronts by a host of companies, some of whom have everything at stake to stay competitive.

Also agree that battery tech is what matters. I'm following the space closely. I also made this tool to play with the variables if you're interested:

https://redskyforge.com/electric-aircraft/

We can cite hundreds maybe thousands of references of experimental high density batteries introduced last 30 years. No luck getting them to large scale production.

For anyone else like me wondering why hydrogen is difficult for airplanes (not mentioned in the OP article):

from https://www.bbc.com/future/article/20210401-the-worlds-first... --------------

Hydrogen has higher energy by mass than jet fuel, but it has lower energy by volume. This lower energy density is because it is a gas at typical atmospheric pressure and temperature. The gas needs to be compressed or turned into a liquid by cooling it to extremely low temperatures (-253C) if it is to be stored in sufficient quantities. "Storage tanks for the compressed gas or liquid are complex and heavy," says Finlay Asher, a former aircraft engine designer at Rolls-Royce and founder of Green Sky Thinking, a platform exploring sustainable aviation.

And there are other challenges. The energy density of liquid hydrogen is only about a quarter of that of jet fuel.

Probably you will want liquified H2. So, we need volume manufacturing of aerogel, for the tanks. If we don't go to wholly new airframes, we will need to sling the LH2 tanks in nacelles under the wings, like the engines, because the needed tankage volume won't fit inside normal wings. (With a new airframe with more internal space, the tanks could be inboard, but maybe you don't really want big tanks of LH2 inboard.)

The LH2 would be electrolyzed on demand at the airport, using power delivered by transmission lines from all over, banking LH2 when the sun is out or the wind is blowing, when it is cheapest.

Once these planes start flying, it will become impossible to compete with them, because the smaller mass of fuel needed translates to substantially more freight, both total capacity per flight, and per unit-cost of fuel. But there are still things to work out, so there will be an interim need to synthesize jet fuel from atmospheric CO2 and H2, which should soon get cheaper than extraction.

It would be helpful if somebody were to come up with a good use for all the waste oxygen everyone is going to be producing.

> Probably you will want liquified H2.

More likely to use solid adsorbed hydrogen. Room temperature, room pressure, less mass in the tanks.

Adsorption has been experimented with for several decades at least. But modern computer power and modern processes for controlling material surface properties make it more likely than ever before.

https://en.wikipedia.org/wiki/Adsorption - not specific to hydrogen

Random PDF of study: https://www.cambridge.org/core/services/aop-cambridge-core/c...

https://www.youtube.com/watch?v=U7CCq4oBgw4&t=464s - latest "breakthrough". One day, one of these will be real.

Less mass than what? I promise you, adsorbed hydrogen along with whatever it is adsorbed onto will not weigh less than the same hydrogen, liquified. LH2 at atmospheric pressure does not need a heavy tank. If they can get it to adsorb to an aerogel, they might have something, but you still have to get the H2 back out.

The best solid adsorbed hydrogen is currently running about 5% the density of liquid hydrogen. Most solutions use either graphene or heavy metals too rare to meet mass demand. It's not a promising technology.

As you say, we've been working on solid adsorption for a long time now. Nothing has left the lab. The video presents an optimistic future, but we don't even have the basics yet.

Firstly, there is a fundamental issue - H² doesn't really give you anything to work with. The vast majority of compounds have two protons, two neutrons (rare isotopes have more protons). [They're distributed in the most boring orbitals, just spheres with no real edge to gain leverage.](https://winter.group.shef.ac.uk/orbitron/atomic_orbitals/1s/...)

This lack of leverage makes surface adsorption tricky. The molecule gives us nothing to grab. You won't carefully craft a surface that can hold H².

I think right now there's a focus on activated carbon. That's become a bit of a synonym for 'graphene', with it's well known limitations.

When I studied the subject, metal-organic complexes were the focus. These would be extremely customisable, but if they worked we'd probably have seen by now. They tended to use heavy metals. I wasn't optimistic at the time, I thought anything using materials past the 4th row of the periodic table was unrealistic. As the metals get heavier they get expensive and sometimes rare. If we want to solve a common problem, we need common components. If your solution has lanthanoid, it won't scale.

I was right btw. The research group closed when funding was reallocated. Each experiment ran the research budget of another group. MoC's don't really get much love any more.

Anyway, we should probably think about what makes a good hydrogen adsorption material. I think it's pretty simple, you want a material that: stores a high density of hydrogen, is reusable, quickly picks up hydrogen, and quickly releases hydrogen.

The latter 2 categories is the 'kinetics'. Of the materials we know, all (literally all) that have 'good' kinetics are either single use or low density. Conversely, all that are both multi use and relatively high density have poor kinetics. Additionally, most of those with good kinetics have unrealistic conditions, like requiring 400˚C temperature to release the hydrogen.

From a realm of sustainability, it'd be cool to dream up a way for having bioships [1], so that the energy would be accumulated in the structure while still on the ground, then metabolised while in-flight.

Well, SkyMoos [2] would also be nice to have around.

[1]:https://en.m.wikipedia.org/wiki/Bioship

[2]:https://aliens.fandom.com/wiki/Skymoo

LENR scientists are using palladium and nickel to compress hydrogen up to 100k atmospheres (90 hydrogen atoms per 1 atom of palladium) at room temperature and pressure.

No?

LENR is not a particularly active field of research. The most recent noteworthy paper is a well funded, failed, replication. It is a pipedream. There are almost no LENR scientists.

I can't see any noteworthy papers for PdNi as a hydrogen storage mechanism. It's capability to absorb (hold within its structure; not adsorb, to hold on surface) hydrogen has been known for a century, if it had utility we would know by now.

https://patents.google.com/patent/US10507452B2/en

I'm glad I prompted an expert to comment! Thanks.

For those who, like me, got confused: Hydrogen requires more volume for the same energy as jet fuel, but even with that larger volume, it is lighter than the smaller volume of jet fuel.

Much lighter. The difference is quite a lot more than you might guess from the raw numbers, because the LH2 doesn't need to loft the weight of the jet fuel, but only its own, lesser weight.

Since it doesn't need to loft that weight, that lifting capacity can be used for cargo instead, thus also increasing the top-line income for performing the flight. Finally, locally produced LH2 will be cheaper per joule delivered than jet fuel, moreso after its carbon is taxed, and the carbon burned in transporting it to the airport.

It will take a while to get there, because it needs both new (or maybe retrofitted?) airframes, and new airport infrastructure, initially only at key international airports.

Not injecting CO2 directly into the stratosphere will be a side benefit.

When hydrogen is used to power aircraft, it will be in the form of liquid anhydrous ammonia. Safer than elemental hydrogen, already mass-produced for its regular use in agriculture, more energy-dense, doesn't embrittle, etc.

Anhydrous ammonia makes a better fuel for ships. They can use the existing engines, and just replace tankage and plumbing. ("Safer" is hard to quantify. Less explosive, but overwhelmingly more toxic if vented.)

Tankers may carry ammonia synthesized in the tropics to northern ports where local solar is impractical, to burn in existing gas plants in competition with long-distance transmission lines. Or, synthetic CH4 from captured CO2 might win. Either way will need massive H2 production.

Well, sure, it's good for ships too. In general powering a large ship has a much more generous performance envelope. Thus, "bunker oil". Ammonia is better than bunker oil and it's also better than compressed elemental hydrogen, for powering any machine that moves.

I don't know of anyplace where compressed elemental hydrogen would be a good choice.

You'd use LH2 or ammonia rather than compressed H2. All else being equal, cruise power for an aircraft is linear with mass, and LH2 has 1/10th the mass for the same volume. For a 40% fuel fraction, an aircraft with liquid hydrogen comes in at 65% of the weight and 25% of the energy content for the same volume of fuel. This will get you a bit under 40% of the range of the kerosene jet, if both jets are equally efficient. Ammonia is fairly similar, maybe a few percentage points higher. You could probably get more than 50% of the range of existing designs using fuel cells that are more efficient than jet engines. More likely we're looking at a rethink of how we design aircraft to accommodate larger volumes of fuel. If we did this, we could approach currently used fuel mass fractions with LH2, and potentially go further than we do with current aircraft.

Keep in mind the effective energy density of ammonia after taking efficiency into account is still ten times the energy density of today's state-of-the-art lithium ion batteries (by mass). LH2 is of course much higher than that. I find it hard to see batteries replacing anything other than short hop flights for the foreseeable future, if that. Fuel reserve requirements alone make it a tough proposition.

You cannot use in-wing tankage for LH2, so calculating with the same fuel volume is a pointless exercise.

Keeping similar (or retrofitted) airframes, the tankage would probably need to be slung in nacelles under the wings. There, the extra volume is no problem, and being closer to spherical minimizes tank wall insulation. You might guess the extra nacelles would be a huge drag problem, but fluid dynamics is a deeply unintuitive science.

The mass efficiency is amplified by not needing to loft as much fuel mass, which capacity can be used for extra payload, offsetting any drag losses. And, LH2 produced from solar will be a lot cheaper per joule delivered to the engines.

Pax airlines over oceans etc using batteries is a bad joke. It's pure garbage hype.

Some fantastic value around reliability and maintenance (two huge issues in GA market) with electric.

If EPA bans leaded fuels (which they should immediately) there may be additional demand here.

But it's going to have to be SHORT flights - think 30 - 45 minutes. Even then the payload (useful) is going to be pretty poor I'd imagine.

I likewise don’t get the breathless exuberance over the prospect of electric airplanes. Weight matters a little bit in cars. Weight matters one hell of a lot in light airplanes.

Fuel and Maintenance costs, they're about 10-20% and 30% of total costs (flight/ground crew, landing/taxes, and amortization make up much of the rest) respectively. Combined they are a huge portion of potential cost reduction.

If it's too heavy to fly the cost reductions don't matter. There are no proposed designs that use batteries that can carry anywhere near the weight of the current generation of airliners.

I don’t think that long range jumbo jets are the target here. I’m also doubtful that batteries will be the dominant power source. I think it’s speculative, but there are certainly DARPA funds/projects available, and they (and FAA) actually do care whether these can fly.

Because of this, there are a number of companies working on synthetic aviation fuel generated by renewables.

I gather enough people would like to commute to climate-change symposiums via private jet without having their lifestyle choices made mockery of that they'd accept an electric airplane with all its drawbacks.

This limitation will help motivate advances in battery tech.

This is an industry we will be trying to improve for several hundred years from now at least. Very good chance electric airplanes are not feasible today, or tomorrow, but this is a long game. Maybe it won't be typical batteries, and very likely not lithium ion batteries.

In this case the game is not building 'electric airplanes' but 'better batteries'. If you have the power plant at a reasonable power output / weight building the airplane is not such a challenge.

The arguments presented here are logically sound and I agree that we won't be replacing a Boeing 747 with electrical. I also agree there are a lot of companies (not just electric planes) fleecing investors for money for products they have no idea whether or not they can build but claiming they absolutely can; but taking risk is baked into the idea of investing and is why profit is justifiable for investors so I think this is a moot point.

That being said, I absolutely think we will see EV planes in short haul -- and short haul flights are a HUGE source of emissions. This is good.

Here's a link -- local seaplane company is moving it's fleet to EV planes and has been flying test flights for almost a year: https://www.harbourair.com/harbour-air-magnix-and-h55-partne...

A number of years ago I read, I believe on this very site, that, in general, the main product of many of today's tech startups is no longer the product itself, but the idea of that product, and their customers are not the people who buy the actual product, but investors. And I think it's fair to say that investors are often easily affected by hype.

It's probably a bit dismissive of the passion of many founders[0], but I have found it a useful perspective in many cases.

[0] Honourable mention goes to the CEO of the ten-person company I work for. He really does believe in this ish.

Electric on short haul flights really doesn't make sense to me either in most real-world scenarios given the energy densities possible from current batteries. Although you may be able to pull off the flights themselves without any issues, you will be unable to use the plane continuously because of the time you will need between flights to recharge. Of course, in scenarios where the plane is in use for only a small fraction of the time, this isn't a problem, but that does not apply to most commercial situations

The most realistic way to attain "green" flights seems to me to be some variant of a high energy density fuel such as hydogen produced from green electricity... so-called "green hydrogen". This also solves the range limitations of batteries, besides charging time. There are however significant problems with using hydrogen too, as other comments in this thread point out.

Airplane engines are really expensive. If the electric plane is significantly cheaper, it could be beneficial to eat the lower utilization. Also bigger batteries don't necessarily charge slower. If you have more cells, you can force more power into the batteries. The charging cable will be massive, but that might be acceptable.

well... when they start doing all their flights on electric engines in 2022 I guess we'll see if it makes sense... did you read my link?

> you will be unable to use the plane continuously because of the time you will need between flights to recharge

Couldn’t a battery be swapped so that the plane wouldn’t have to wait? (I’m sure it’s tricky, but that seems like the clear solution to charging taking along time.)

The batteries would then need to be more easily accessible and a more standard shape. You probably couldn't have batteries in the wings.

I would imagine commercial planes would take a hybrid approach. They would have their own primary batteries hidden throughout the plane, and then they would have range extender swappable batteries in the cargo area.

I'm optimistic about electrical. Here is a high level analysis of power and energy density required for some electric vertical takeoff aircraft, compared to some existing batteries: https://www.pnas.org/content/118/45/e2111164118 (h.t. kittyhawkcorp twitter). The necessary power density is achieved, the energy density needs to improve by about 2x for these vehicles to attain their intended range.

The article also compares the range and energy efficiency to electric and ICE vehicles, accounting for the distance reduction by flying in a straight line versus driving on the road. If I recall it doesn't apply any extra value for time savings. The overall energy used in flying could be as little as 2-3x the energy used driving a terrestrial electric vehicle. Combine that with vertical takeoff and no traffic and we're looking at something pretty compelling.

And how much does it really need to cost compared for example to a Tesla? The weight will be more optimized and the safety regulations I assume are much sterner. The technical complexity seems similar but the volume will be much lower. I don't think it really works if you need a pilot's license so full autonomy is probably also a prerequisite for an everyday application.

I think EVTOL will still be embryonic in 2 years, but impressive in 5 years.

Autonomous vehicles can't drive in a tunnel yet, and you're imagining flying autonomous cars in 5 years?

Flying cars already exist, they're called helicopters, and they are not a promising consumer technology, and never will be. Flying heavy materials (such as human flesh and bone) is far too energy intensive and inevitably produces too much noise. It is also far too dangerous to become a consumer technology.

1. Autonomy in the air is far easier than on the roads

2. Helicopters have a much lower L/D ratio in forward flight than the tiltrotors being proposed for eVTOLs.

1. Yes, but autonomy in a fixed tunnel would be easier still, and yet the Vegas Loop is using human drivers.

2. Helicopters have the advantage of actually existing in many varied form factors and designs, in common civil use, unlike tiltrotors.

Yes, in the air I'm expecting a very different scenario than on land. No pedestrians just an element of collision avoidance for birds, all vehicles legally required to be broadcasting their position to an automated air traffic control, probably maintaining 100 meters between vehicles versus road traffic being 1 meter from oncoming. In the air it would be almost a pre-planned route with a 50 meter collision avoidance corridor. Plus an emergency landing site selection process, potentially the ability to land on water or an emergency parachute.

Part of the reason I found the paper I linked to be persuasive is that they predict the EVTOL aircraft only needing 2-3x the total energy of an EV. The energy cost in dollars could be less than gas for an ICE vehicle making the same trip. There are very light aircraft with 100HP engines, I'm picturing something light and birdlike.

I love this comment because it’s true of a lot of hardware startups I’ve seen lately.

While they may not be very good at building airplanes, they are absolute savants at issuing press releases

"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." - Clarke, A.C.

This guy isn't even a distinguished scientist. He's a just a bitter investor that lost money to a snake-oil start-up, and has a penchant for logical fallacies.

I'm much more excited about manufacturing gasoline using renewable energy and captured carbon. That would provide the energy density planes need while being legitimately carbon neutral.

Near carbon neutral fuels look to me as reasonable solution. Specially if the production is something we could ramp up and down easily and fast with renewable supply of electricity. Ofc, efficiency isn't great, but still seems much simpler thing to solve.

The author of this piece[0] has a fairly strong background in starting and running companies, so his opinion is worth more than the average commenter's.

[0]: https://commons.erau.edu/ntas-bios/27/

Here's a video that's making a basically the same argument (although with a more sarcastic tone) that electric batteries don't have a sufficiently high energy density to power an economically competitive plane https://www.youtube.com/watch?v=dMmaG_3NnGs

he writes: "watt/hours", so ymmv ...

The busiest air routes in the world aren’t the transatlantic ones but short routes in Asia. If you could make a 30 or 50pax plane that could fly for 1 hour you could serve a lot of the busiest routes to/from Seoul, Taipei, Jakarta, Singapore, Bangkok.

They are electric plane routes that aren’t replacing normal flights, they are replacing routes that should have been short-ish train rides (but weren’t, typically because of water). It’s crossings of very busy and narrow bodies of water between very populated areas.

Replacing even one of those top routes with electric would be a huge success.

Even if there is no viable path to 300 passengers or 8 hour flights, this has to happen.

Worth comparing with battery trains. Just a few short years ago these were considered impractical, people were waiting for hydrogen or complex electrification projects.

Now, (thanks mostly to cheaper batteries) the numbers pencil out for longer distance transport (as long as you include carbon and pollution costs) but just having a bunch of batteries you can connect to the grid (and move around by rail) could possibly pay for the whole thing by itself. Combining the two is looking pretty sweet.

For planes, I imagine the ability to use these to offset the emissions from longer flights will be a potential driver of adoption.

I'm also surprised that assisted launch isn't talked about more, but maybe the physics just doesnt work out. Just saw a company that is trying to launch satelites by throwing them from the ground. The 10000G would kill humans, but is okay for other uses. Feels like they could possibly branch out to terrestrial cargo delivery.

I have mostly questions...

Are we at the theoretical limit of energy density in current batteries? How much more progress can we make, in theory? Could it be that in 20 years we find drastically better materials for batteries? Materials which would make electrical flight feasible.

Assuming high energy-density batteries are coming, shouldn't you start now with developing electrical airplanes to be one step ahead of competition?

jumping on with one more question: would there be an advantage to lining the wings/flat surfaces with solar cells and patching them into the powertrain, helping drive even higher efficiency gains during optimal weather?

I did the math for that one, though not exactly for an airplane, but for a boring land vehicle (think Ford Traffic). I assumed futuristic photovoltaics with 40% efficiency, a factor of 0.7 to account for angle-of-incidence inefficiencies, pretty much all of of the van covered in panels, for an area of about 16 square meters, similar to the wing area of a glider Schleicher ASW 22 (I couldn't find the wing area of a Cessna 172).

The result I get is somewhere from 3 to 8 kilowatts. A quick search in the Internet shows that a typical car has engine power starting at 130 horsepowers, which is 95 kilowatts. A van the size of a Ford traffic probably uses twice as much, and the Cessna uses 132 kilowatts.

So, no, I don't think we are getting aviation as it exists today with solar panels and batteries, but one hour twenty minutes in good weather will be enough for some recreational pursuits.

I also did the math for sailplanes with solar panels. That looks better, if all you are looking for is activating the propeller for a small fraction of the total flight time, or having an aircraft that can go very slow (that, in fact, has been done). I'm just an amateur, but my opinion is that, without solving the energy density issue, about 98% of the aviation we enjoy today will be gone.

I spreadsheeted this out a few months back for a plane. It is absolutely not worth it.

Assuming that higher energy-density batteries are possible is an extremely big ask. Yet somehow, plane companies are valued as if there is a commercial business case. I think long-range (over 2000 km), big airplanes are as far away as fusion power plants. Maybe even further, as fusion does not require any theoretical breakthroughs. You don't see big valuations for companies purporting fusion power generators, but for some reason, you do for electric planes..

> plane companies are valued as if there is a commercial business case. I

Perhaps that is because there is a large number of passengers who wish to fly shorter distances than 2000 km. In most countries all internal flights are considerably shorter than that.

I wonder if culturally we need to change if we even need to travel. After all it is very recent phenomenon outside migrations. After all most of the history vast majority of population stayed or travelled very little.

> After all most of the history vast majority of population stayed or travelled very little.

That doesn't make it inherently desirable.

> Are we at the theoretical limit of energy density in current batteries?

Yes and no.

Using air for the "ox" part of the redox reaction makes it possible to dramatically increase energy density (gravimetric and volumetric both).

The tricky part of that is making the battery rechargeable. Lots of research attention is focused on it.

If you want your battery totally enclosed (e.g. for use in vacuum or corrosive environments), than we are closer to the limits. Probably within a factor of 5, maybe within a factor of 2.

> Could it be that in 20 years we find drastically better materials for batteries?

No, the periodic table is fixed.[1] Maybe, if you are prepared to consider using nuclear "batteries".

1. https://en.wikipedia.org/wiki/Reduction_potential

I think a lithium ion battery is only about 6-7% lithium by weight. So primary physics isn't blocking. If you could double that you'd be able to increase flight time from current roughly 90 minutes to 3 hours.

No we're not. The next step forwards in energy density for Lithium Ion batteries is likely to be 100% silicon anode Li-Ion. This is a very difficult manufacturing/engineering challenge but significant progress has been made (look up e.g. Sila Nano and Enovix). These give us a significant step forward in energy density.

Then there are solid state batteries. These are more difficult. But again multiple companies with lots of funding are attacking this from all sorts of angles.

The OP making this claim as if it's a law of physics is simply wrong.

The contrarian in this case would be making Elizabeth Holmes' argument "first they say you're crazy...the you change the world." Of course, the folks delivering such an argument are either peddling vaporware or actually on a path to changing the world. Sometimes, perhaps even the speaker does not know the side of the divide on which they fall?

While we're dreaming, I'm dreaming of fusion power or solar power being used to synthesize 100LL or Jet A from the atmosphere, but I'm not holding my breath.

That would solve the climate issue though it wouldn't solve the air pollution problem.

Jet A from solar has been demonstrated. And will be used in huge volume, for a couple of decades, as LH2 aircraft and infrastructure are built out.

Not true at all:

- no loss of power with insulated batteries

- heat generated in battery pack and motor can heat the cabin with a heat pump

- energy density in batteries is steadily increasing

- price of batteries steadily decrease

All of this would work with the tech from a current Tesla, but flight time will get acceptable in a few years.

Car and truck are going to be 90% electric in a few years

Planes are going to follow after, but not before.

Did you know "avgas", short for "aviation gasoline", in its most common use, is still using lead as a countermeasure to engine knocking? It means, the aviation industry continues to poison the world by spraying lead in the form of exhaust gases everywhere.

The sooner this is stopped, the better.

The article mentions this indirectly, but the leaded gas issue is actually orthogonal to the question of the practicality of battery powered aircraft. Aircraft can and do work without leaded gasoline. The unleaded aviation gas issue has already been discussed to death here. It gets brought up every time there is any reference to anything to do with any aircraft that runs off gasoline.

The FAA in the US just approved a list of about 600 aviation engines to use unleaded, so that welcome change is progressing.

Jet aircraft use jet fuel, not avgas. Avgas is really only used by small GA aircraft and the FAA recently approved many of them to use unleaded avgas.

Leaded gasoline is bad, but the worst part about it was that its use was concentrated in cities. Dose makes the poison, and kids in cities were getting a lot of tetraethyllead from all the motorized vehicles driving around. That isn't an issue with avgas, which is typically used while flying thousands of feet above relatively unpopulated areas.

> In contrast, the internal combustion engine on a 172 makes enough heat to keep the cabin warm whenever needed

Right, and it's always making that heat whether you need it or not. So it's a good thing your avgas has a shit-tonne more energy density than my batteries because you're going to need it to waste all that heat.

Look, physics is physics, you can't cheat it. Which means pure electric is only good for short air trips (energy density), but there's plenty of room to make airplanes more efficient (internal combustion = waste machines).

So those who are busy saying it's impossible should get out of the way of those who are doing it.

If you want to take a plane without constant heating, be my guest.

My Zoe keeps my toes warm all winter long, and it does it 30 seconds after I turn it on in -20 c weather. My diesel needs 10 minutes to warm up the cabin.

Heat pumps rock. Internal combustion engines suck. Fight me.

Heat Pumps work best above 40F (4C), and after that they are not very efficient. I don't believe that would be a good fit for an energy starved system such as an electric plane.

> Heat Pumps work best above 40F

[citation needed]

Have you ever experienced cold weather?

For year-round heating and cooling comfort, heat pumps work great in areas of the country with moderate temperatures. This is especially critical during the heating season. Once the outdoor temperature goes below 25⁰ - 30⁰ F, a heat pump can continue to provide heat. However, it will use more electricity to do so, which means higher utility bills. This is because there simply isn’t as much heating energy available as the outdoor temperature drops and the system will work longer to achieve the same indoor temperature. That’s why many air-source heat pump systems are installed with a supplemental heat source. Source https://www.carrier.com/residential/en/us/products/heat-pump...

Why do people seem to care about electric planes? If the fuel is synthesized through a clean process isn't an energetically dense fuel better?

Seems like a pretty big IF there. What is the carbon net of that process?

Is zero good enough? The process would bank fuel produced using solar and wind during the parts of each day/night when each is cheapest.

Here's a half-baked idea. The big problem with many next-generation electric cells like lithium-airs is that they have a short lifespan, right? But aircraft, unlike domestic cars, already have a fairly intensive maintenance schedule. Might it be feasible to just completely replace the batteries a few times every year? Obviously the manufacturing cost of the batteries, net of whatever you recover from recycling them, would have to be not too crushing.

You would swap out the batteries after every flight, and charge them while waiting for the plane to come back. Replacement is an inventory maintenance problem divorced from flight dynamics.

“Ultralight” and “electric” don’t go well together - and it will stay this way.

Good. With that out of the way, time to build some trains.

And tracks too, don't forget the tracks! :-)

I'm skeptical about 2.62 MB pages with dozens of ad/tracking dependencies for a 1700 word article.

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