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Comment by jacquesm | Hacker News Reader

I can lift a 200 pound piece of glass with a tiny vacuum sucker. It's the atmosphere keeping that thing up there, and the 2" of ground clearance is what you see around the edge, we don't actually know what the distance is where the evacuation happens. For all you know it as a 3' x 7' plate underneath it that floats just above the surface.

I've done a lot of vacuum picking and it is surprising how large an object you can pick up with a tiny bit of surface.

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Could you pick up, say, a manhole cover?

Sure, why not?

The seal won't be perfect so you'll be running the pump more or less continuously. Apropos manhole covers: I wonder what would happen if this car would drive over one. Or was that your point?

This is why they temporarily spot weld manhole covers before street races.

Yes, and those don't have fans underneath, that's just the ground effect. This is probably far worse. I also wonder how large the intake holes are because you can easily imagine what the effect would be pulling that trick on a road surface that's not perfectly clean.

Mythbusters lifted a 2 ton car using a consumer grade vacuum cleaner. the math is this: the air pressure over 1 sq meter is about 10 tonnes, so if make a box with that area and reduce the pressure by 0.25 atm, you get a force of equivalent to 2.5 tonnes, enough to lift the car.

https://www.youtube.com/live/GbqKwPktCdo?xstg=CAMSBhUDze3xHw...

I'm surprised a vacuum company didn't beat them to it. That would have made a pretty great marketing campaign ("the vac with enough suction to lift a car").

They did

https://m.youtube.com/watch?v=yczxUJLPhkg&ra=m

F1 has taught me: yes, and it will destroy your car.

Atmospheric pressure is around 14psi, at a rough guess a manhole cover is around 200lbs so you'd need just a little over 14sq in to make that work.

There is a racing car at a car museum, it was either BMW or Mercedes, which was mounted to the ceiling because it had a suction fan that would, in theory, let it do that.

Are you sure it wasn’t the Porsche 956?

Oh it might have been! I visited them all, but long ago.

The three famous examples of this tech are:

https://en.wikipedia.org/wiki/Chaparral_2J

https://en.wikipedia.org/wiki/Brabham_BT46#BT46B_%E2%80%93_t...

https://en.wikipedia.org/wiki/Gordon_Murray_Automotive_T.50

I don't know of any others, and it's a horrible idea for anything used on public roads.. even on the race track these cars were notorious for leaving a cloud of debris/dust in their wake

This is not how it works. It’s not sucking against the road, it’s pushing against it with thrusters at the top of the car.

No it’s not. It’s vacuum underneath.

I think we are saying the same thing, and both of us agree that it's not "suckers" like the original commenter said.

No you are definitely not saying the same thing. You say there are thrusters on top of the vehicle, whereas in stead they are sucking vacuum below the vehicle. And the exhaust ports for those fans are not at the top.

Tesla seems to disagree with you as well, they call it a "multi-mode suction system" [1] suggesting that the evacuation under the car is what does the job. And that's far more likely than that the ejection of that little bit of air at the top is what keeps the vehicle planted upside down. But with vacuum that is almost a trivial accomplishment.

[1] https://x.com/Tesla/status/2110907039493038577 ; third slide; caption under the photo.

"Multi-mode fan & ground sealing system pulls air from beneath the vehicle, generating enough suction to hold it upside down while stationary"

Thanks for providing the source.

I'll just note that again, my hypothesis and the actual way it works are very similar to each other, and both are very dissimilar to the suction cap analogy. Suction cap works by passively utilizing atmospheric pressure, this utilizes moving a large amount of air in the direction opposite to the road. The only difference is that it's taking the air from below instead of pushing from above. I imagine that is the case to utilize the same outlets that are used for lifting the car.

The difference is approximately mass counteracting the force of gravity ejected on a continuous basis versus a modest expense in power to run fans. The two are not even remotely similar.

> this utilizes moving a large amount of air in the direction opposite to the road.

False.

The air from the fans is ejected out of rear of the vehicle, not the top. The kinetic energy of that air is neglible at best. The vehicle uses retractible fairings to create a partial seal and the fans create a low pressure zone inside the zone that holds the vehicle to road.

The cold gas thrusters are a completely different system that expels high pressurized air from canisters in the vehicle.

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