Comment by manfredo | Hacker News Reader

Comment by manfredo | Hacker News Reader

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Batteries are fundamentally unsuitable for aircraft. The energy density is easily an order of magnitude lower than thermochemical fuels: https://en.m.wikipedia.org/wiki/Energy_density#/media/File%3...

Furthermore batteries don't get lighter as their charge is expended, as opposed to fuel that gets burned off. This means a plane powered by batteries has to land with the same mass of fuel as it does when it takes off. Many aircraft are worse at decelerating themselves than accelerating. This means they can actually take off with more mass than they can land, thus extending their range. This can't happen for battery powered planes.

Hydrogen powered planes is less far fetched than it seems. The Soviets built a prototype: https://en.m.wikipedia.org/wiki/Tupolev_Tu-155

Cryogenic storage of hydrogen is less difficult than it seems. Because the engines are constantly drawing fuel from the fuel tank, the tank's pressure is constantly dropping which cools it down. Most of the difficulty around hydrogen storage is in long term storage where hydrogen permitting through the vessel is a concern. The main challenge for applying it to aircraft is being able to make a vessel light enough and in a form factor suitable for planes, namely fitting it in the wing.

Let's just use RTGs instead! A gram of Polonium-210 produces 140W of heat. It's also an almost entirely alpha emitter, which means that little shielding is required. At about a 10% efficiency of an RTG you could effectively get 14W out of a single gram of it. A 737-300 seems to require about 7-10 MW of energy at level flight. Put 1 ton of Pu-238 onto a 737-300 and you can run the aircraft (probably) for 6-7 months without refueling. Okay, you probably need a smaller aircraft, because takeoff takes more energy, but still!

While Polonium-210 is incredibly toxic, it does have a half-life of 138 days. If you do have a crash then in <8 years you'd only have about a gram of it left.

The main tricky part is that we produce about 100 grams of it a year. But what's a little scaling up for a startup anyway?

(I'm sure I made a calculation error here somewhere.)

There might not be any math problems, except on how are you going to reject 10MW of thermal heat from inside the airplane at all times

You need 4 engines. After you land, you run 2 engines forward and 2 in reverse.

Note that you will only have 1g of polonium, but dispersed in 1T of lead, which is less toxic, but not really environmentally friendly.

I could make the argument that fuels that burn are unsuitable for automobiles which crash into each other frequently.

But yeah, I think it would need lots of development to get battery technology to do something like a ny-tokyo flight. It might only work for short hop service.

I guess that's how it has worked for battery electric trucks. The first one basically did short, known routes around town with lots of stop/start. That controlled the parameters and made it feasible. I don't know if battery powered trucks will ever replace long-haul trucks unless batteries get lots better or charging gets really fast.

> I could make the argument that fuels that burn are unsuitable for automobiles which crash into each other frequently.

Lithium ion batteries don't like crashing into each other either. The article mentioned that lithium sulfide batteries degrade differently than lithium ion, so fires as a result of heavy use may be reduced, but fires as a result of unscheduled disassembly seem likely, and could be worse than fuel --- you can dump fuel or circle to use it up, but you can't (probably) dump batteries, so you're always going to have lithium available. Not sure if the lithium sulfur compounds are less flamible than the compounds found in lithium ion.

Look at some yt videos of li-ion or li-po fires, this will change your mind

You're correct that batteries are much more suitable for cars, especially commuter vehicle and things like garbage trucks that have relatively limited routes and sit idle for much of the day. There's why were seeing electrification take hold in cars, way before it takes hold in planes (if ever).

Diesel fuel won't burn as gasoline does. Gasoline is ok here to, if compared to a hydrogen-oxygen mixture explosion ;)

Ah, simply have separable battery modules that you drop from the plane as their charge is depleted. Put pop-out wings on them and use gps guidence so that they glide back to recovery centers on the ground, which you've had the foresight (and funding) to build in sufficient density along any likely route your plane might operate. Problem solved.

I'm joking, mostly.

Periodically they would fall over landing on the recovery barge and explode, but that's to be expected. :)

(and your idea is brilliant, it should jokingly be called "blue ice")

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