alt Hacker NewsThe 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.
Replies
You have the answer in your calculations, you just need to take to its logical conclusion. I say its was balsa not cartoon...
It _does_ go supersonic, otherwise the converging-diverging nozzle doesn't make sense.
Back of the what ? Shame on you
> Back of the fag pack,
napkins, and envelopes at least kind of make sense.
Who was ever writing on the back of cigarette packs?
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.