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In the video they claim the air is supersonic at exit, and point out the mach diamonds -- and I think they said 60 kilonewtons of thrust max, which is really a lot. So I think the volume of air would decrease roughly 60% from your estimate? I'm not a physicist.

I'm imagining this in two phases: phase one - you drive around, and excess energy goes to compressing air. Phase two - you use that compressed air which takes very little additional power, so you get to double up on force. I guess likely a 'running mode' where it's using some power to keep suction on.

I'm curious how much time you get at full blast vs 'just' enough to keep the car pinned to a wall, e.g. 1 vs 2 g.

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So let’s double the speed - 1.2 Ma. You need half the mass now - 25kg/sec. If you want to have 10 seconds worth of hover - that’s 250kg of gas. Plus the weight of the storage tank. Plus - this is the amounts for hover. Not for any extra force on top of that.

It still doesn’t make much sense to me. And that’s before considering what happens when you get rocket stream hitting a tarmac road. Never mind public roads, this sounds like a major hazard anywhere. Plus the quantity of compressed gas son board (if that’s how it works)… not a pretty crash. At these numbers, imagine 10MJ released all of a sudden - apparently that’s about 2.5kg of TNT.

Surely I’m missing something… as I say, I can’t make sense of it.

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Your math is pretty good, Tesla actually gave the storage tank capacity as 250kg

ETA: this is a horrifying amount of energy to be sitting on top of.

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Can't wait to see the crash test video.
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I guess on the plus side SpaceX has been trucking much worse around in and out of orbit verrry reliably for years now in tough conditions.
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1% failure rate for space rockets might count as very reliable, but if 1% of all cars explode then we are in for a ride.
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what's there to miss? if these ever make it to market their only purpose will be conspicuous consumption for vice-signalling ding dongs
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The "pin to a wall" part uses fans, not the cold gas thrusters. It can probably stay there until the battery runs out. The gas thrusters are only needed if you want to go 0-60 in .8s (with the Thrust version), or if you want to fly (with the Rocket version). Probably those only last a few seconds before the air tanks need to recharge.
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Mach diamonds in a compressed air jet aren’t surprising. You can get them from a canned compressed air duster: https://hackaday.com/2024/02/18/canned-air-is-unexpectedly-s...
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> phase one - you drive around, and excess energy goes to compressing air.

It's an electric car - unless you've got an incredibly long charging cable, there is no "excess energy" when you're driving around.

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You have the answer in your calculations, you just need to take to its logical conclusion. I say its was balsa not cartoon...
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It _does_ go supersonic, otherwise the converging-diverging nozzle doesn't make sense.
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Back of the what ? Shame on you
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> Back of the fag pack,

napkins, and envelopes at least kind of make sense.

Who was ever writing on the back of cigarette packs?

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> Who was ever writing on the back of cigarette packs?

British officers planning trench raids in the front lines during WWI. Or, at least, that's where I've been told the expression originates.

Really, though, is it impossible to imagine no one, ever, using a cigarette pack to jot something down? It's a colloquialism. It doesn't even have to be taken literally to make sense. What is gained by questioning it on that level?

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cigarette packs have not been blank on the back since the commenter has been alive
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> is it impossible to imagine no one, ever, using a cigarette pack to jot something down?

Wouldn't the back have printing on it? I could imagine someone ripping the pack open and writing on the insides, which are blank.

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In quite a few countries they were rather blank, not like today!
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I don't know what cigarette packaging looked like at the time, but can imagine they were possibly government provided in a very simple paper package.
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> Really, though, is it impossible to imagine no one, ever, using a cigarette pack to jot something down? It's a colloquialism. It doesn't even have to be taken literally to make sense. What is gained by questioning it on that level?

I took the OP's question to really be a question about the origin of that phrase, and with your answer, I learned something I didn't know before. So I, for one, am happy the question was asked.

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I'm glad it was asked too and enjoyed the answer.

The OP's question was clearly skeptical though:

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napkins, and envelopes at least kind of make sense.

Who was ever writing on the back of cigarette packs?

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Implication being that writing on the back of cig packs does not make sense. I'd agree with your reading if not for the "at least kind of make sense" bit.

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My father taught me times tables, each one written on the back of a fag packet, in 1972. And we used matches for addition and multiplication before that.
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Bike shedding.
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this is funny because I know so many people who always note down phone numbers and such for the day on cigarette packs. sometimes even carrying a few with them all the time.

in india.

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Smokers who didn't have napkins or envelopes handy, presumably.
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