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Comment by alexandros | Hacker News Reader

Many of the flaws with the article have been pointed out, but can I just point out the author is so lazy that he doesn't even remove the weight of the fuel from the Boeing 737, nevermind the jet engine and the many other optimisations that can be done when designing from scratch without the ICE constraints. His thought experiment is literally a Boeing 737 with a 25T battery attached to it, and he takes that to be the best case of what Elon is proposing... What makes smart people write things so trivially dumb?

And in case the author objects to me dissecting his rough sketch of an argument and drawing conclusions about him from it, he should have thought of that before taking 5 sentences spoken in a podcast and assuming he understands what the complete idea someone else has in mind is.

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The author replaced the 25 tonnes of fuel a 737 carries with 25 tonnes of batteries, which is generous towards the electric jet (as the fuel burns during the trip).

Edit: It looks like you deleted the post I was replying to, but a 737 with 72 tonnes of MTOW does not carry just 17 tonnes of fuel; you can easily look up the product matrix on Wikipedia.

Also note that landing a 737 with a full load of fuel is... not normal.

The author doesn't really state that he did that, but I ran the numbers, and it seems he's doing that indeed. Not sure how he came to the conclusion that 25T fuel is in the 737, as that doesn't seem to be the case. He still didn't consider the engines that would be almost completely gone weightwise, and of course the main point stands -- the 737 is a specific model, with specific tradeoffs, to handle specific cost variables, including engines and fuel. If one is considering a new design, with drastically different variables, different cost of fuel (almost 1/5th or less) different weight distribution, different acceleration capabilities, different aerodynamics (no more bulky engines at the wings), different takeoff strategies, then this kind of "what if I flipped the fuel on the 737 for a battery" approach cannot be used as proof that an idea is "ridiculous". The author comes to the fight extremely underprepared, and honestly if we all reasoned like that we'd still be in caves. I'm all for calling Elon out on things he's more vulnerable on, but the author tips his hand with shoddy work like this.

I don't think the author is saying the plane has to be like a 737 with the batteries removed; the argument is more like: a 737 with battery replacement is an order of magnitude away from being viable, so the design is going to have to close that gap, and that's a pretty tall order.

It's a fairly lazy argument, but also one that effectively illustrates the challenge.

>The author replaced the 25 tonnes of fuel a 737 carries with 25 tonnes of batteries, which is...

...disingenuous because that's a 35% battery mass fraction, and Musk has already revealed that he's assuming a 70-80% battery mass fraction at 400 Wh/kg[1].

So this 'argument' boils down to, "some numbers that Elon says don't work... don't work."

[1] https://www.youtube.com/watch?v=yx3auTD85Fw

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