I’m not a huge petrol-head but I do like cars and recently came across this crazy design: The McMurtry Spéirling
The short of it is the car has an unusual, maybe unique, gimmick…it has powerful fans that draw air through the car providing up to two-tons of downforce even while at a full stop. Normally, cars need to be going fairly fast to get a substantial downforce from spoilers and whatnot. This car has it at zero miles-per-hour. This not only provides better traction when starting it also provides crazy cornering even at slow speeds.
Since this downforce is more than the car weighs you could, in theory, park it upside down on the ceiling. And yes, as you might expect it sounds like a jet is nearby when the fans are on.
The car is a single-seat electric and not really meant for anything at all other than enjoying such a fast and nimble car. It is also quite small. Watching it I keep thinking of it as an oversized RC car.
Thought it was interesting.
You can see it in the video below (the record-breaking run is at 22:25…not sure it is an official record):
All recent F1 cars have more downlift than weight from a certain speed upwards, and that speed is not very high (I remember something around 100 mph, will surely vary by manufacturer and by settings, as the downdrift is set differently for a race in Monte Carlo or in Monza), but this car has it while standing still, which is absurd. But OK, engineers gotta play too.
It is so loud at least you won’t need a horn.
And if its belly is sucking that hard, then it must also blow somewhere. I presume that it vents that big fan out the rear of the car, for yet more thrust? Or does it blow straight up?
Actually, come to think of it, for it to make sense to use the fan for downlift instead of for thrust, you’d need tires with a coefficient of friction greater than 1 (as well as a powerful engine turning those tires, of course). While this is possible, it requires special rubber that usually has a very low durability.
Why would that be? The whole point is to increase the effective force on the tires. If the fans double the effective weight, you can accelerate at twice the rate (assuming you aren’t power limited) for the same CoF on the tires.
Also, there’s no lower bound on how much downforce can be created for a certain amount of fan power. In principle, you could have a perfect vacuum beneath the car that takes no net power to maintain. That’s in contrast to using a fan for thrust, which would actually require significant power at high speed.
Generally the fans are off (and are manually controlled by the driver…in the record run the driver was told to turn off the fans as soon as he finished the run…not sure why though).
I think you only use the fans for those occasional times you want crazy acceleration and handling. Otherwise, 98% of the time they are probably off. Which is good because they are loud. I am sure the car is plenty fast without them.
To create a negative pressure vacuum that would suck the car to the ground, the car featured skirts around the rear three-quarters of the car. Hall approached General Electric to use its relatively new invention, Lexan: a polycarbonate plastic material that was light, flexible, strong, and most importantly, unbreakable. The skirts moved up and down through a system of cables, pulleys, and machined arms that were bolted to the suspension. The result was a near-constant alignment to the road surface. With the fans on, the car would hunker down by two inches.
I watched the video again and the engineer said it can do 300 miles on a charge. Or, one lap on a race track with all the bells and whistles turned to 11 (apparently heat becomes the issue). GT4 pace you can do 20 minutes.
It’s amazing that a group of people would build this as a proof of concept. It’s not like they’re going to build one for sale. It must have cost a fortune.
Ultimately, the point is to get thrust; the tires are just a means to that end. Any given amount of downforce will, through the tires, generate an amount of thrust equal to mu times the downforce, so if you can choose the direction of your fan-force, then if mu < 1, you’d be better off using the fan-force directly for thrust.
What I hadn’t considered, though, which you also pointed out, is that you can’t just freely change the direction of the fan-force. You can get a lot more force out of the same fan by directing the force downwards, where it’s up against the ground and enclosed by the skirt, than you can against the open air, as you’d need for direct thrust.
Though of course, this car might still be using high-mu tires, at least for the record-breaking run, because there are a lot of things that you do for a record-breaking run that aren’t practical for normal use.
They probably will if they get a buyer, but that’s probably not the point. Usually, the business model for supercars like this is to make a handful of the supercar to sell to rich whales, and to use the buzz and media hype generated by those supercars to sell a large number of high-performance but basically normal cars to upper-middle-class buyers.
Well, Jay Leno will buy the first one AND drive the heck out or it. It won’t sit around gathering dust in a private collection. It’s guaranteed free advertisement for the company. It might even unseat his beloved McLaren as the greatest sports car ever made.
I’m not sure Leno could get in to the car. He’s getting old. I’m younger than Leno and I am not sure I could get in and out of the car (it does not have a door as we think of it).
Didn’t the new driver say it was surprisingly easy to get into? Might have needed a shoe horn to get out. Leno would probably order a custom seat if it wasn’t to his liking.
