I understand downforce and wings and aero doodads on cars. There’s enough of my $$ going to my hobby of tracking my car.
If you’re saying that the McMurty’s wing and other aero features can hold a car in place at much less wind/downforce than other cars, then yes, that’s saying a bunch about the goodness of the McMurty design.
But there was no mention of how much (little) fan speed was needed for the McMurty to stick upside down (or I missed that info). Nor was there a comparison vs. another vehicle not being able to stick at the same fan speed and angles.
Yes, totally ignoring the body shape and rear wing, the McMurtry fan system can generate a more downforce than the weight of the car, and that is at zero mph.
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Really? Are there any other cars that can park (or drive very slowly) upside down? Or any cars that can drive slowly or park on vertical walls? I am no expert, but I know of zero cars that can do this. You are correct, there was no mention of the fan speed. But there was a mention of the weight of the car (1000kg) and the downforce generated by the fan system at 0mph (over 2000kg of force–although Newtons would be a better unit).
Right - and that was my earlier question. Isn’t it being held in place by ensuring a sufficient amount of downforce needed? If the demonstration is that with only minimal (vs. maximum) amount of force, the car sticks. But what’s minimal vs. maximum ?
I think of those “sky diving” simulation things where a person (200lbs?) is floating above an updraft of force from a fan. If you multiply fan force by 15x, can you float a 3000lb car ? If the physics is linear, why not? With enough force can’t anything stick/float?
I mean, yeah? What other cars actually do that though?
Well minimum would be just enough to overcome gravity, and probably not a fun demonstration. And maximum is just a question of how fast you wanna go and how little runtime you want out of the battery.
Yeah, you can stick or float anything with enough $. Fun fact, the indoor skydiving places use a fan that’s 2.4MW. The first order math for how big of a fan you’d need to float a car is not difficult, and I don’t think that fan would package nicely inside a McMurtry
Total aside - my proudest moment of Fermi estimation was after I went to an indoor skydiving place and wondered how big the fan was. I started doing physics in my head, started thinking about drag, and realized it might be easier to instead approach it from a standpoint of how much I paid, how long I got to float, how much power costs, and what portion of operating costs would be appropriate for power. The totally non-physics Fermi estimation approach landed me at 2MW.
“Nobody in 2004 could ever have predicted that the F1 car record would be surpassed, nay obliterated, by an electric car. Think back to 2004 and try to imagine what the world of electric cars looked like. There was no Tesla, no Nissan Leaf even. The idea of using electricity to make a car faster was still a long ways off. The sportiest hybrid available at the time was a Honda Accord. If you took a time machine back 21 years and told them an electric car was quicker than an F1 car around any race track, you’d be carted off to the stocks and pelted with rotten fruit in the public square.”
Aha! Here’s what I was missing. The downforce is generated on-demand, hence “downforce-on-demand”. I was thinking there was giant external fan (like in a windtunnel) pointed at the car to hold it in place.
Or like a typical wing on a car, the downforce is generated by windspeed passing over the wing, while driving. Not from fans that are part of the car itself.
Yup, they use the onboard fans whos force was demonstrated in the video on-demand. Basically when the car isn’t’ going fast enough to generate sufficient downforce such as sharp turns. That is why it performs so well vs an F1 on the Top Gear track. That track has some pretty tight corners that an F1 car can’t take at speed.
Back in the 60s and 70s there was a push to making fan race cars. They all became illegal to race with pretty quickly
The Chaparral 2J was a weird looking race car with articulated side skirts that sealed against the ground and a pair of fans out of a WW2 tank powered by a stroke engine. Together they produced up to 1.5g of vacuum under the car. It ran in SCCA Can-Am in 1970 and was made illegal.
In 78, Mario Andretti won the F1 world championship with a Lotus 78 and 79 that had similar ground effects as the 2J. FIA banned them and said all cars had to have 6 cm clearance.
Also in 78 Brabham - Ecclestone’s team that Gordon Murray designed for - made the BT46 and BT46B. The BT46 had hydropneumatic suspension that compressed under load. The BT46B added fans. They got to race a race before fan cars were banned. Niki Lauda won and took fastest lap in the 78 Swedish GP, it’s only race.
The Chaparral 2J ground effects are totally different than the Lotus 78. The 2J had fans powered by a snowmobile engine that generated a low pressure under the car, in addition to lexan side skirts that sealed the underfloor to keep the low pressure.
The lotus 78 generated low pressure by shaping the floor so that as air moved through it low pressure was generated under the car. This was of course speed dependent and also ride height and pitch dependent, unlike the chaparral and the McMurtry where the downforce was independent of speed.
The brabham was similar to the Chaparral, in that a fan was used to generate the low pressure, but since it was connected to the engine, the downforce was dependent on engine speed, so drivers had to keep the throttle open in turns.
