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Comment by jmward01 | Hacker News Reader

This appears to ignore the new technology that electric brings in: Reduced maintenance, (for aircraft) reduced weight in other parts of an aircraft, new propulsion capabilities that increase efficiency of the energy used, new performance envelopes (like flying much higher because the physics are totally different), etc etc. Sure. Take an existing vehicle optimized for burning things and just swap that small part and things look bad but start optimizing for the new way of doing things and the equation totally changes. Additionally, that 60x claim is getting old by the minute. We are getting to 300+ with advancements coming in so fast they are hard to keep track of. That 60x could drop to 10x or lower in just a few years and that, again, doesn't count the reduction in weight that could come from removing a literal explosion maker from an aircraft can achieve.

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There is a cute little two-seater electric airplane used as a trainer.[1] Gets about 50 minutes on a charge. EHang has demonstrated 48 minutes of flight with their flying car (a 16-rotor drone). Expect to see those at the 2028 Olympics, ferrying VIPs around Los Angeles. But energy density is too low for long trips.

[1] https://www.pipistrel-aircraft.com/products/velis-electro/

> reduced weight in other parts of an aircraft

The bigger problem is that the overall weight increases. Rearranging the COG doesn't really matter when most of your energy is spent literally fighting gravity.

This is the first thing that popped up in google when I wanted to compare gravimetric density between gasoline and lithium ion batteries. Gasoline is still approximately 30x denser. That is at least one revolutionary breakthrough in battery technology away, if not several.

https://research-archive.org/index.php/rars/preprint/downloa...

Considering the thermal efficiency of a modern jet engine, the usable energy compared to a lithium battery will be ~15 higher per kg, still bad, but not as bad.

Also some napkin math using common examples gives a range of 0.2 - 1.2 horsepower / kg for gasonline motors, and 8 - 21 horsepower / kg for electric. So even though the batteries weigh more, the motors weigh less.

Doesn't it compound since it costs fuel to carry fuel in a flying machine?

I'm not sure about math but isn't it like 1/15th Isp, even with that maximally optimistic value?

This is not correct for electric trucks. Replacing diesel motor and gearbox with battery pack and electric drive train is close to a zero sum game according to https://youtube.com/@electrictrucker?si=RjdWBQQXansebUyJ

Definitely not a huge penalty.

Fair, but the context here is planes (and boats I guess though that seems less difficult than planes)

Container boats are ridiculously carbon efficient because they move unimaginable amounts of weight (amortizing any fixed costs like keeping the engine running) slowly (low drag) over a perfectly level surface (no loss from going up hill).

Almost any carbon reduction scheme that involves doing anything other than using them doesn’t work.

For instance, the embodied carbon of an apple that goes from China to the US, then is driven to a Walmart in a diesel train / semi is probably lower than the carbon footprint of one from the local farmers market (unless the farmer drives the apples to market in an EV and the local power grid is low carbon).

Right and it's precisely because they can have unimaginable amounts of weight that it's a more tractable thing to solve compared to electric planes.

I don't think the article is debating cargo ship vs car carbon footprint here, it's just the feasibility of electric cargo ship vs bunker fuel cargo ship. (And planes, which seems way harder)

Airplanes don't get to do regenerative braking except briefly upon landing, but you're not going to put generators in the wheels just for that, and you need active thrust reversers, so really there is simply no room for regenerating power in electric planes.

There’s no reason why you couldn’t do regen when descending with an electric-powered prop plane. It would give a steeper descent than normal, and may not be more efficient overall than cutting power earlier and descending more gradually, but it could be done.

Electric will start smaller and build up to big just like everything else. The single and twin engine world is pretty dominated by structure so the gains are easy to see there. As new capabilities and designs are prooven out things will grow or, and this is what I really hope for, we will find that we don't need the massive aircraft to be profitable anymore and we will just get more smaller electric aircraft providing the service in a more point to point nature. One of the biggest efficiency gains we could have is not forcing people into a hub and spoke mega airport model, something that isn't practical with the current massive aircraft tech.

> One of the biggest efficiency gains we could have is not forcing people into a hub and spoke mega airport model

The airlines have already switched from that model.

That would be terrifying.

Wheeled vehicles have lots of opportunities for braking, but airplanes and boats not so much, so even if you could do regenerative braking (which you probably can't) it'd not be enough to be worth doing. It's a loss compared to wheeled EVs of 30%-50%.

And then airplanes typically need to be lighter when landing than when taking off, and jet fuel has the nice properties that a) as you use it up what you've left weighs less, b) you can toss enough jet fuel to get to landing weight if need be. Batteries have neither of those properties, which means that electric airplanes would have to be built much sturdier (i.e., heavier, therefore more expensive and less efficient) to handle heavy landings, or would have to carry less cargo / fewer passengers per unit of stored energy (i.e., less efficient).

I'm afraid that no matter how good wheeled EVs get, it's going to require a whole new kind of battery before you can ever get to practical. large electric airplanes.

The point was the other parts of the plane. No lines moving all that gas around and the pumps and the plumbing in and around the engine and the bleed air piping and the and the and the.... There are a lot of potential places to shave weight when you go electric. An aircraft optimized for electric will be massively different if done right.

The way jetliners scale shaving the weight of those things (and note that you're not counting the weight of electric cables that can carry hundreds of amps) is nothing. It might be something for tiny airplanes, but that's it.

"Additionally, that 60x claim is getting old by the minute. We are getting to 300+ with advancements coming in so fast they are hard to keep track of. That 60x could drop to 10x or lower in just a few years"

What was a Tesla Model S power density 10 years ago? Today? Hardware moves slower than you think. All your points have some basis of consideration but the potential performance improvements they represent are tiny compared to the single huge downside of having to fly a giant, heavy battery everywhere and that is not going to change anytime soon.

Battery density doubled in the last ten years:

https://www.westchestercleanenergy.com/post/lithium-battery-...

Density is going up exponentially in the graph because it has been improving 18% for every doubling of the number shipped. Global EV market share is projected to cross 25% this year, so we should expect two more 18% improvements as it approaches 100%. That should improve density 39%. Then (ignoring batteries sold so far, and assuming there are no new markets for lithium batteries), we’ll see another 18% in 2 years (164% of current density), 4 (193%) 8 (228%), and so on until some theoretical limit is hit.

In all likelihood, some other technology will replace lithium batteries at some point. That further improves the density numbers.

There are physical limits to Moore's-like laws for chip densities and chemical power densities. We can't be too far from those for lithium.

And that's great, lets assume that continues, which there is no guarantee of, when would batteries be in the same ballpark as jet fuel?

Lets call current batteries 300 Wh/kg and jet fuel 12,000 Wh/kg, that means, according to you, development would look something like:

Battery Density: 2035 - 600 Wh/kg 2045 - 1200 Wh/kg 2055 - 2400 Wh/kg 2065 - 4800 Wh/kg 2075 - 9600 Wh/kg

So in half a century we may see batteries approaching the power density needed.

Other than potentially reducing maintenance costs, I'm not sure any other part of this stacks up. I don't see how electrification would allow you to save weight in other parts of the aircraft. I don't think electrification adds any new propulsion capabilities that are more energy efficient, not for airplanes or boats anyway. For boats, the electricity would still be turning a screw and for airplanes the only method of propulsion that would work is an old-fashioned propellor. That last is the same reason you can't fly electric planes in new performance envelopes: prop planes can't get that high and wouldn't work if they somehow found themselves up there. Even turbo-prop planes (which have gas turbines that enable them to work more efficiently at high altitudes) are limited in altitude by the fact that the tips of the propellors are going very nearly the speed of sound.

Storing and producing aviation grade fuel is a considerable expense and logistics chain (unleaded AVgas replacements are still not generally approved - if you live near a small airport you've been getting dusted with lead fumes for decades).

An electric plane dispenses with that: it can functionally be charged up anywhere there's any sort of electric service.

Lithium cannot get much denser in energy storage, sorry. Even 10x denser than jet fuel is still way too heavy.

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