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- Hacker News
- The maths of the flying is a little puzzling to me.
Back of the fag pack, let’s say it is light for an electric car and weights 1000kg. I’ll also go on a limb and guess the air flow is actually subsonic - 200m/s would make it 0.6 Ma (still insanely fast!). Even then, that requires 50 kg of air every second. Or 40 m^3. Using everyone’s favorite metric, this empties an Olympic swimming pool in 1 minute. It also requires a MW of power. I mean… that’s a lot??? Though admittedly, only about as much as accelerating 0-60 in 1 sec (50% of that in fact). So the flying would draw as much power as accelerating at full throttle.
Power requirements would go down a lot with slower exhaust speed, but then you need to shift more fluid. 40 m^3 already seems like a lot to me.
I get it’s a neat little demo and they have to get SpaceX into the picture somehow, but still I don’t understand how it’s supposed to add up. Also, what do I know - just a humble physicist.
by rich_sasha - So, are we just going to ignore that the man is literally asking for YEARS of deposits aka free loans, for a car that literally might never come to fruition?
This is insanity. How are shareholders still supporting this man?
by jdelsman - I don't want flying cars.
I want clean water. I want a stable climate. I want bees to survive.
by chunkyslink - I simply won't believe they'll sell a version that leaves the ground until I see someone who obviously isn't working for Tesla with one. I'd be surprised if the FAA didn't have something to say about it. I just don't believe for a second that a stiff wind or a low ceiling or a power line (public road or not) or a very obese driver with nobody in the passenger seat isn't going to turn a very expensive car into a very expensive upside down piece of scrap. SpaceX has had enough explosions resulting from COPVs that I can't imagine these actually getting into the hands of people with more money than sense. It's a compelling marketing gimmick that can't be real.
But practicality aside, you have to be an absolute fool to believe any promises Elon makes at this point. Whether it's the automatic charging cable snake, or your car picking you up and dropping you off at the airport, or renting out your car as a self driving ride share, or your cybertruck also being a boat, or the dozens of other empty promises that he's made, there's just no reason to think he's telling the truth about anything until you can try it for yourself.
by bastawhiz - This is one of the coolest marketing stunts/demos that I have ever seen. In fact, it's the second coolest, only after SpaceX/Tesla's Starman.
However, the COPV-powered reaction thrusters could shred anyone on the wrong side of the vehicle. Even in the non-invite-only 0 to 60 in .6s version, that is also a problem, correct? Meanwhile:
> Tesla 'Cannot Guarantee' Your Roadster Pre-Order Will Ever Be Delivered
https://insideevs.com/news/812247/tesla-roadster-preorder-de...
by consumer451 - So this is a really neat technical demo, using spacecraft cold-gas thrusters and guidance hardware/software to do crazy stunt stuff in a car, but what's the relevance to an actual product that can be sold, even as a small-volume exotic? These are pressurized gas thrusters, so either the tanks, valves, and piping take up most of the interior of the car, or it has a low-single-digit number of seconds of thrust before recharge, probably both. Also the tanks for these things tend to use incredibly high pressures and are apt to explode spectacularly in any sort of accident.
This is sort of like demonstrating a car that softens the asphalt in front of it with lasers to get a better grip; difficult, technically impressive, and zero chance that it will ever be allowed on a public road.
Edit: According to this Motor Trend article, it uses a big carbon-fiber pressure vessel at 5500psi, so basically an enormous fragile bomb. And the one that did all the stunts had two of the pressure vessels which would have filled most of the interior.
https://www.motortrend.com/news/tesla-roadster-thrust-system...
- Everyone's focusing on the cold gas thrusters, which of course is very cool, but not actually shocking that it technically could be done (economically is another question).
But can we talk about the just casually driving straight vertical or sticking to the ceiling? I didn't think that would be technically possible for a 1000kg+ car with probably at least 2" of ground clearance.
There's presumably very limited stores of compressed gas, so you might get one hop or a couple 0-60 boosts per charge. But with electric fans, suction is a feature with much longer duration (minutes?), so you could feasibly do the batman driving on the tunnel ceiling past traffic trick.
by mNovak - Ok, so it actually flies. That was unexpected.
It's an incredible engineering achievement to build in massive fans and rocket engines into a high performance car. It's truly wild.
It's being sold in two modes. One with cold gas (no combustion) seemingly just for extra forwards acceleration (no flying) and one with real combustion rocket engines, the latter was in the video and is "invite only".
Wild that they devoted so much effort to an economically completely infeasible model. I wonder if the combustion version will even break 3 figures sales.
Even just the cold gas variant seems like a nightmare for production, there's a high pressure COPV in that thing and that's gonna make crashes much more.. exciting, and Tesla doesn't have a great record anyways. But very few of these are ever getting sold anyways.