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Comment by elmerfud | Hacker News Reader

The impressive thing to me is the level of traction needed to do something like this. It seems they're taking old tricks and building a "sucker car".

https://www.roadandtrack.com/motorsports/a32350/jim-hall-cha...

Still neat stuff.

Race sanctioning bodies will need to update their rules or these will just be one off bragging rights.

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In Micromouse (https://en.wikipedia.org/wiki/Micromouse) - a competition where autonomous devices solve a mouse maze - the fastest competitors are all using fans to increase traction (and thus speed).

radicalbyte, you're absolutely right that the use of fans in Micromouse increases the traction, and therefore the speed at which the maze is solved. Suction allows for impressive performances.

However, a small caveat that might be worth considering is that while the suction indeed increases speed, it might be more accurate to say that it primarily improves acceleration instead of car speed: The issue often lies with achieving rapid acceleration rather than with maintaining high speed. Even systems with relatively low traction can reach high speeds given enough time and distance, but the ability to accelerate quickly is crucial in competitions like Micromouse.

Speed = ∫(acceleration) dt

Sure, but once you have speed you can use aerodynamics to get grip (e.g., F1 cars). So this is really only relevant if you need acceleration from low speed.

F1 has featured a car that used a fan to generate downforce.

https://en.m.wikipedia.org/wiki/Brabham_BT46

An issue with aero features (other than not producing their effects at low speed) is their ability to stall. Ground effect was especially dangerous (back when high-ground-effect designs were allowed) because if it stalls during a high speed corner (say from driving over a bump, like a kerb maybe) you can instantaneously lose a huge amount of downforce, which is obviously quite dangerous.

Exactly, thus you can simply integrate over a longer time span.

But if you want to increase the acceleration you need traction, your tyres need to be glued to the asphalt. Since you don't have aerodynamic pressure at those speeds you need to suck the vehicle to the ground.

Derivatives of relative displacement as defined by a distance metric in a [e.g. metric tensor] space:

  Length = Point2 - Point1
  Length * Time^-1 = Velocity or Speed
  Length * Time^-2 = Acceleration
  Length * Time^-3 = Jerk
  Length * Time^-4 = Snap or Jounce
  Length * Time^-5 = Crackle
  Length * Time^-6 = Pop

Displacement (geometry) > Derivatives: https://en.wikipedia.org/wiki/Displacement_(geometry)#Deriva...

Fourth, fifth, and sixth derivatives of position: https://en.wikipedia.org/wiki/Fourth,_fifth,_and_sixth_deriv...

Something weird about this is that humans very often ascribe the sensation of d^ns/dt^n, to feeling d^n-1s/dt^n-1.

So people will say that something which accelerates quickly is 'fast'. Or they will say, when they feel themselves initially being pressed back into their seat as a plane starts its takeoff roll, that they are experiencing 'acceleration' when what they are experiencing is actually jerk.

The thing is, you can't actually feel motion at a constant speed - so the only thing that tells you you are acquiring speed is your body's experience of acceleration - so when you feel yourself accelerating, you associate that with speed. Likewise, your body also can't really tell the difference between constant acceleration and just... being at a different angle, and maybe a bit heavier than normal. So it's when you experience changes in the apparent direction of 'down' and the overall 'weight' you're feeling that you think 'oh, we're accelerating'.

My favorite way to get a sense of what acceleration, jerk and snap feel like is to focus on what happens when you're in a car that's braking hard. You're decelerating at a relatively constant rate while the brakes are applied - it feels as if 'down' is pointing slightly forward, meaning you'd be sliding off the seat if it weren't for your seatbelt holding you back. When the car finally stops though, there's a very abrupt change in acceleration - a 'jerk'. 'Down' switches to pointing straight down again, very quickly. You're pulled back into your seat. That's jerk. And specifically the sudden onset of that swing in what direction 'down' is pointing, and then its rapid disappearance is snap. Your body feels like it's being 'jerked' around when the car stops precisely because that motion has high snap - you experience a sudden high amount of jerk, then the jerk ends.

>The thing is, you can't actually feel motion at a constant speed

In a vacuum. If you roll the window down, or if the atmosphere starts ablating you into a hot plasma then you may realize you're going very fast.

Or the air's going very fast past you. Who can tell?

Unless you’re in a wind tunnel or a hurricane, you can be pretty confident in the reason for the fast air.

Well, if you're on a 2D plain, it's pretty easy to tell. If the solid plain is stationary to your motion, then the air is fast. If the solid plain is moving, then it's a little tricker to figure out.

Oh cmon, who rolls down the windows in an airplane? ;)

Then you're experiencing acceleration, just in the opposite direction.

Not if you’re moving at constant speed. The air molecules are experiencing acceleration.

Please define "drag" in a way that somehow contradicts what I said...

The setup for our thought experiment here is someone traveling at constant speed.

By definition they are not experiencing any acceleration.

If they are experiencing a drag force they are also experiencing a thrust force that is equal to it because they are traveling at a constant speed.

‘Feeling the effect of a force’ is not the same thing as ‘experiencing an acceleration’.

Hmmm, from a Newtonian perspective I would have argued (or at least my personal impression is) the only thing we actually perceive is force (i.e. acceleration). All the situations you described are just (higher-order) changes of acceleration and even if you give them a name: At the end of the day, the only thing that matters to our bodies is the force.

Sure, but my argument is that you only really take note of changes in the acceleration you experience. Yes, your internal sense of ‘which way am I accelerating’ is the sensor you’re using (also ‘which way and how hard are my limbs being pulled’ and ‘how much force am I feeling in my joints and on the parts of my body that are touching the objects around me’) - but when those all indicate a generally constant vector with a magnitude close to 10m/s^2 your body just intuits that that direction is ‘up’. If that vector is changing your body figures you must be moving because ‘up’ normally doesn’t move.

So it’s changes in acceleration that create movement sensations, not acceleration itself.

Interesting thought but I'm not entirely convinced yet: 10m/s² down (along your body axis) is not the same as 10m/s² in any other direction. I would assume the body is perfectly able to distinguish between those.

Yes, you know if you are standing up or lying down. But your body doesn’t interpret either of those sensations as movement.

If you flip from one to the other suddenly, your brain figures out ‘we’re rotating’ pretty quickly though.

Interesting topic. A pretty good video about this: https://www.youtube.com/watch?v=ZMQbHMgK2rw

That's where I heard about it in the first place :)

Gordon Murray was ahead of his time: https://en.m.wikipedia.org/wiki/Brabham_BT46

Then there's the Brabham BT46 "Fan car" that actually raced in F1. Once. Before it was banned. :-)

https://youtu.be/B294RfWj1QE?si=jxYpIgwtH44at6Bq

...and it's current spiritual successors The McLaren F1 and now the GMA T.50 https://en.wikipedia.org/wiki/McLaren_F1 https://en.wikipedia.org/wiki/Gordon_Murray_Automotive_T.50

Huh, never knew that the F1 had floor suckers!

From a Youtube interview with Gordon Murray I saw, the T.50 has fan-enhanced diffusers, the fan ingesting the boundary layer to prevent flow separation.

It's not able to produce extra downforce at zero speed.

The McMurtry Spéirling is more akin to this, with a 1.4s 0-60mph run.

Huh the Nick Mason credited with being a McLaren F1 owner is the drummer from Pink Floyd.

Suddenly I remember a Top Gear episode where Nick Mason drops off his F1 (maybe it was a Ferrari Enzo?) at the test track, then his personal helicopter lands on the strip, picks him up, and flies him out of the scene, all while "Money" by Pink Floyd plays in the background.

Enzo. That was a good episode.

https://youtu.be/f7jsauspMmU?si=MDEr2B1uHq4FT-oh

The interview where they talk about his book is entertaining as well.

I forgot about the book! Clarkson subtly-not-so-subtly promoting the book was such a riot. And to think that's not even close to the most ridiculous thing they did in the show's heyday.

Nick Mason has a pretty significant collection of cars. Back in the day he used to take his kids to school in his Ferrari 250 GTO. These days the car is so valuable I got the impression he has to call his insurance company to get permission to take it out on the road. Years ago he published a book called "Into the red" with some of his cars. The book had a companion CD of the engine noise made by a selection of the cars. They took each car to the track to record it.

Perhaps the most intense car he owns must be the BRM V16 which, to quote someone who saw it race back in the day "would make your ears bleed". https://youtu.be/fZMPDCNyQxE?si=e97ihEFRW7DU_UcC

It was "voluntarily" withdrawn after one race, even though it wasn't contrary to the rules

You are correct.

Fans (no pun intended) of sucker cars are likely to be interested in the Goodwood record setting run by the McMurtry Speirling car.

https://www.youtube.com/watch?v=5JYp9eGC3Cc

These cars stem from the Formula Student, which since 2022 has re-allowed the previously forbidden "powered ground effect".

But this car has an upgraded battery and powertrain beyond what the rules allow and they maybe also use tire warmers and potentially rubber/glue on the launch surface/tires

A photo shows them using tire warmers and they're running Hoosiers, which are incredibly sticky tires.

I have no idea what you're on about with "rubber/glue on the launch surface/tires." That's not a Thing.

It is a thing.

https://en.m.wikipedia.org/wiki/PJ1_TrackBite

Interesting. This is a Formula Student car, the european version of the Formula SAE. Powered ground effects were banned a long time ago in Formula SAE, but it seems like Formula Student does allow them.

It was disallowed for many years but is re-allowed since the 2022 season

Had the same thought, 0-100kmph in 3sec gives so much wheel spin. Must be a whole lot of electronic trickery ever invented from launch control, traction control to power management plus the mechanical stuff sticky tyres, down force.

It amazes me how much faster we have got the last 6-7 years.

Racing rules are not generally updated because ground effect (powered or not) is a safety concern because losing traction through a corner suddenly when it fails can be catastrophic. This is why it was banned in F1 in the 80s, damage or getting lifted up and the car will suddenly fly off the track.

Another modern electric fan car which holds the goodwood record: https://youtube.com/watch?v=TptzkkbC1vE

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