Exactly this. One of the bigger “fans” of them — Gordon Murray — is actually producing a road legal one. The T.50, which is Gordon Murray’s attempt to “revisit” the McLaren F1 and do everything he couldn’t do (or hadn’t yet realized was possible) back in the 1990s: https://youtu.be/NT8PMXCMrsM

For those who aren’t aware, Harry Metcalfe was the founder of EVO magazine and had an outsized behind the scenes influence of Top Gear’s new format in the early 2000s. While Gordon sticks to some of his script, the two get VERY nerdy at points digging into all sorts of non-obvious minutiae and detail. 53 minutes is a lot, but by far it’s the best interview about the car by a large margin.

Harry is also a very big EV and renewable electricity nerd, and loves digging into those topics with tons of research.

"is actually producing a road legal one"

The one at Goodward FOS was cleared by DoT and is road legal. The driver announced it in an interview on TV.

that'd be lovely to drive behind -- you can see the dirt cloud that it's constantly sucking off the ground loom a few inches aft at all times during the Goodwood run.

I presume the fans must be turned off on public roads?

aside : how does one engineer a fan blade that's going to suck in rocks all day under normal use?

You don't. You design the intake or ducting with inertial separation. The inertia of any debris dense enough to cause damage can't make it to the fan.

In the PT6 turboprop engine, the system forces air to go around a bend, and also opens a trap door. It's actuated by the pilot for landing/takeoff.

https://aviation.stackexchange.com/questions/16206/how-do-in...

There is no need to run the fans at all or at least not nearly at full speed on public roads. So I would expect the dust cloud to not be there during operation on public roads.

Also the output it filtered so there are no rocks or other debris thrown into the car behind. That was already the case on the prototype raced at Goodwood.

the T.50 has a fan, and it is used for aerodynamic benefit, but it does so by helping speed up air through the under car diffuser, which allows them to use a more aggressive diffuser than would otherwise work. It all adds up to a modest downforce improvement and/or drag reduction.

The McMurtry by comparison is more like the old F1 fan car, in that it is literally sucking itself down to the road, with tons of force, with a skirt and so on.

Yep. As Gordon said about the Brabham, the McMurty is, “more of a blunt instrument.”

When I watched it do the hill climb I was thinking of all the drivers they might’ve approached, and thought that if Mark Webber hadn’t hung it up a few years ago he would’ve, “noped out” of that conversation immediately given his history of flying for Mercedes in the beginning of his career.

Plus that time when he flew his Red Bull at Valencia. Definitely the F1 driver with the most air time... so maybe the idea of a car that is actively pushing into the ground (instead of passively with wings/diffusers) would appeal.

I know that the "spacex package tesla roadster 2.0" is a running Elon hype joke, but the discussed thrusters would be revolutionary in extreme car design. Fan cars can only suck downward, but thrust vectoring would be a whole different ballgame: it can push down, directly thrust, push counter to the g force in a tight curve, brake faster.

Thrust vectoring could serve as a safety system to dynamically produce downforce in case a high speed car starts to go airborne, can counter spin-outs, etc.

While not full thrust vectoring, more like unthrust vectoring, McLaren did this:

One further famous example was the so-called “fiddle brake”, given its name much later by Ferrari technical boss Ross Brawn, but known within the team as “brake-steer,” that McLaren ran in the latter half of 1997 and into 1998. This simple concept allowed the rear brakes to operate on either the left or right side only, providing a clear benefit under acceleration in corners – and an instant lap time advantage.

https://www.mclaren.com/racing/inside-the-mtc/mclaren-extra-...

iirc, F1 cars today all use brake steering.

Brake steering by applying different pressure left/right is not allowed.

11.1 Brake circuits and pressure distribution

11.1.1 ... all cars must be equipped with only one brake system. This system must comprise solely of two separate hydraulic circuits operated by one pedal, one circuit operating on the two front wheels and the other on the two rear wheels. ...

11.1.2 The brake system must be designed so that within each circuit, the forces applied to the brake pads are the same magnitude and act as opposing pairs on a given brake disc.

https://www.fia.com/sites/default/files/2022_formula_1_techn...

As do road cars with stability control.

Along similar lines, there exists the e-diff.

Basically a standard diff using brakes to shape power output. Basically a brake limited version of a limited slip diff.

> Fan cars can only suck downward

This doesn't really seem like that big of a disadvantage to me. You can just keep increasing downforce until the tires are able to give you the traction you need for any maneuver. It seems like that should scale as far as you need it to, and be way more efficient than rockets. I guess the limits would be in the tires and suspension.

Increasing downward force on a pneumatic car tire without increasing tire pressure causes the tire's contact patch to deform, and you lose grip. This can happen in driving due to weight transfer.

You would need something other than pneumatic tires, or some sort of dynamic tire pressure system.

Either one seems more practical than rockets on a car. And modifying pneumatic tires to minimize this problem might be possible, if it's something that just hasn't been prioritized because it wasn't that big of a problem before. Also, a sophisticated fan system might be able to make the downforce larger, yet less variable than natural downforce.

You actually increase grip but lose traction overall.

In that video, Gordon mentions that the McLaren F1 already had fans for downforce.

Paraphrasing: https://www.whichcar.com.au/news/mclaren-f1-secret-downforce...

I think he was the one that developed the original concept for F1 racing in the '70s with Brabham, the BT46B car, I think? Supposedly to counter Lotus's lead in ground effect research on their car.

That's exactly right, the term usually refers to cars that use fans to generate vacuum for better grip rather than propulsion to go faster. Cars today can easily go super fast in a straight line, the hard bit is putting that power down in corners.

> the hard bit is putting that power down in corners.

Or even just getting it from tyres to ground. Traction control exists to avoid the car just spinning its wheels in place as it’s completely lost grip.

At high speed downforce can do the job, but at low speeds not so much.

How scary would it be to be in one of those 1,400+ horsepower supercars and to hit the gas just to immediately see all four wheels start spitting smoke as they spin in place and start abrasively cutting through the asphalt?

Four wheel burnouts from a roll aren't that impressive from inside the vehicle. It's basically like being on "high traction" ice but with more noise. The vehicle mostly continues doing whatever it was already doing before you stomped on it.

> How scary would it be to be in one of those 1,400+ horsepower supercars and to hit the gas just to immediately see all four wheels start spitting smoke

Not very, unless the car suddenly gets a patch of grip and launches you into a tree.

> to hit the gas just to immediately see all four wheels start spitting smoke as they spin in place and start abrasively cutting through the asphalt?

You'd have to wear down the entire tyre first, which isn't going to happen unless you're already at the thread (though supercar tyres do wear down very quickly).

Tyre rubber is much, much softer than asphalt, and for good grip you want pretty soft rubber. By the accounts I've seen, even cold F1 tyres feel sticky. And drag tyres outright crinkle on takeoff.

Based on experiences with 72hp Suzuki SV650 all you need to do is grip the front brake and give it some gas. Digs asphalt at about 5mm/sec just fine. The tire gets totalled pretty fast too. So it's not rubber being too soft.

Apparently you've never walked on hot asphalt or been a hooligan doing donuts and/or burnouts in asphalt parking lots. The tire rubber and asphalt binders/tar basically become one and the gravel comes along for the ride caught in the crossfire.

I've seen both (as I work in civil engineering). That is all dependant on the asphalt mix. Parking lots are usually not done with a proper performance graded asphalt, so they'll deteriorate very easily under strenuous loading conditions. Roads (in well-regulated jurisdictions) use strong asphalt mixes with a lot of large granular aggregate and a lot less asphaltic content (and asphalt that's stable at higher temperatures). This makes roads a lot tougher in these loading conditions, but also tough (and therefore expensive) to put down - need to roll it fast while its still hot, with both steel drum rollers and rubber tyre rollers.

Not saying they can't be damaged, just that a parking lot is a poor comparison

It's scary enough in a 400hp/3600lbs RWD car. Even with traction control enabled, the car likes shaking it's ass any time you tap the gas and turning the wheel on anything remotely slick with power in will break the traction wheels loose.

Hence the fans sucking it to the tarmac giving it more traction

Ken Block Hoonicorn : https://www.youtube.com/watch?v=C7Tl7Zn-KRE The V2 version of the hoonicorn is about 1400hp and he does spend most of the time smoking tyres.

But the asphalt is mostly fine. It's a lot tougher than rubber.

It would be scarier if the tires didn’t break loose. Have you ever seen a top fuel dragster in real life? It’s a surreal sound and site.

Thanks for that. I'd taken it to mean it was propelled by fans and couldn't figure out how that could possibly work. This linked article on the road legal version confirms what you say in one of the image captions:

https://www.autocar.co.uk/car-news/new-cars/mcmurtry-launch-...

"It will feature a track mode, which will turn on the downforce-creating fan"

Gran Turismo 5 players will remember the Chaparral 2J Race Car '70 (a real race car with two giant fans on the back which was immediately declared illegal after protests of other car makers) and the fictional Red Bull X1/X2014 fan cars.

I’m impressed that this video game technology comes back!

This kind of fan was F1 technology back in 1978.

Check out the Brabham car that won on its debut at the Swedish Grand Prix.

The 3rd paragraph in the link also explains that.

Ah! I somehow missed that paragraph!

If you’re not going to use grip on the road for propulsion you might as well make an airplane.

From an engineering perspective, racing cars are much closer to aircraft than they are to road cars; they just have their wings upside-down.

With the difference that they are typically not allowed to have mobile aerodynamic surfaces.

That's why fan cars can be considered cheating. The fan is made of mobile aerodynamic surfaces. The Brabham BT46B try to circumvent the rules by saying their fan was a cooling fan, it didn't work.

If you allow mobile aerodynamic surfaces, indeed, you are going to have aircraft. It is easy to imagine a car with actual wings, with flaps, ailerons and elevators.

Not to be too much of a pedant, but the Brabham BT46B's excuse that the majority of airflow was used for cooling did stand, which was why Lauda's one race win wasn't taken away. It was protests from other teams, Ecclestone's personal interests, and rule changes after the fact that meant it only raced that one race.

Totally, but I still got downvoted a bunch... Using air for propulsion only makes sense if you're saving weight by which point you're better off cornering with wings instead of dragging wheels around with you.

These fans are to create _down_ force to increase the "weight" of the car.

Wings(/flaps/ailerons) are great for that, too, depending on their orientation. And arguably simpler. More effective at high speeds, but then apparently so are these fans.

I am very much aware. I was pointing out why using fans for propulsion would not be a good idea.

Right and it’s specifically used for cornering downforce, since the coefficient of friction isn’t high enough to justify generating downforce like this in a drag race.

I went to the article wondering if it was about a record using a class of cars driver by fans (thinking cartoon style giant fan on the roof :D)

That is also the purpose of the wing on the back of the car. To generate more downwards force at speed.

Right, but the wing doesn't start to work until you hit serious speeds, whereas the fan gives the car extreme traction at launch, which is pretty important in a race that only lasts 30 seconds, especially when your electric car has ~infinite torque.

Aero also has the issue of creating a ton of drag. An f1 at 300kph will decelerate around 1g if you lift off the throttle.

Did you see Pastrana's ridiculous Subaru with active aero? It puts the wings away when they're dragging and they pop back up when the downforce and/or drag is wanted.

Thanks for this, I had just seen a couple highlights, just watched it and it is absolutely ridiculous. Amazing :D

> the wing doesn't start to work until you hit serious speeds

I don't know what you consider "serious speeds", but wings can produce meaningful downforce at pretty low speeds. Check out the various unlimited class autocross cars which carry giants wings for downforce, even though autocross events are typically very low speed events (2nd gear most of the time).

"Meaningful" on order of 100lbs at 60mph. Which isn't nothing, but a Viper ACR has a peak downforce of 2000lbs@177MPH, or basically half the total weight of the car.

Plus, with extreme aero, there's a top-speed vs downforce tradeoff to be made. The big fan trick doesn't have that issue.

If you drill into published specs for wings, it's generally true they only really start to work at silly speeds on most road legal cars. The far more important effect is upon the emotional response of the owner when they look at it... There are exceptions, but virtually all rear spoilers only start to do their work meaningfully at well over 100mph.

Example: Porche Cayman GT4 RS, extremely potent track-day Porche with giant wing.

> https://newsroom.porsche.com/en/press-kits/718-spyder-cayman...

> "At the car’s maximum speed, there is a total of 122 kg of rear downforce."

Yes, thats right, you get 122kg of extra downforce once you hit 196mph. Really helpful in 2nd gear... The reason manufacturers generally only quote wing downforce on road cars at incredible speeds is because the number is not very impressive at lower ones.

> Example: Porche Cayman GT4 RS

That's a street car. You need to look at race cars to see where wing development can go.

For an example of race cars which generate downforce at autocross speeds, take a look at cars like https://www.autoxandtrack.com/a-mod-acme-special-fastest-aut...

that's a street car though. what about actual GT3 cup cars or GTD class cars?

i couldn't find any numbers, but they do put them in the wind tunnel.

The wing starts to work immediately. Just not much. This is a pedantic but important point. Even low speed motoring events aero can be very very important if sufficiently large wings are allowed. Aerodynamic gear for cyclists is advantageous even if you are a slow cyclist, etc.

Popular "wisdom" in cycling is that aerodynamics are not a factor below 10 mph and not much of one at 15. It becomes pretty noticeable in the 15-20+ mph range (increasing with the cube of speed, or something like that).

Yes, but the physics is that the amount time saved over a fixed distance is actually more for the 15mph cyclist than the 20mph cyclist.

However the percent of time saved for the slower cyclist is less, but only a little.

Basically at cycling speeds the aerodynamic curve is pretty flat so it doesn't really matter if you are fast or slow.

The main issue is more so that they produce incredible downforce at the cost of incredible drag.

Infinite torque...?

~ much more torque than can practically be delivered between the tires and the ground, which is why using a vacuum to improve the traction and eliminate the transient squatting motion of the vehicle is so important in a short race.

Drag racers have had this problem for a long time; those races last less than 5 seconds. This hill climb is interesting because it's only a bit longer, half a minute, which really changes the equations for electric race cars vs. something like Pikes Peak which is 8 minutes to the top (and is now also totally dominated by electric cars).

Probably thinking of https://en.wikipedia.org/wiki/Jerk_(physics)

If acceleration were an instantaneous off-on step, that would be a https://en.wikipedia.org/wiki/Dirac_delta_function

This is a weird car guy myth that gets tossed around. The thinking is that, electric motors make uniform power output at any RPM, and torque = some_constant * power_output / RPM. Thus, as RPM goes to zero, torque goes to infinity.

Obviously, this is wrong in the real world for so many reasons, but that doesn't stop this from getting repeated.

Repeating it is a great way to paint yourself as one of those dolts that likes to act like they care about EVs for the virtue points.

Everyone who's ever used a drill knows that while speed and torque are inversely related in most of a motors normal operating range you don't get insane torque at low speed. Of course you can wind a motor differently to mitigate this somewhat but still, not a huge improvement. You wouldn't see reduction gears on all sorts of things if this were the case.