"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.