Ferrari Rear Wheel Lip

[Reca]

This is what I had in mind...

That’s different from the Ferrari design (besides, you indicate the air flows in both ways thru the spokes and that doesn’t make sense, that’s what I was pointing out in previous post)
As I said at the front the duct is wrapped around the disc (and also around the caliper), at the rear it’s not :
[IMG:150:128]http://img223.imageshack.us/img223/7752 ... lu1.th.jpg[/img]
At the front all the air out from the disc holes is channelled straight thru the wheel spokes and never touches the rim.
At the rear the disc holes aren’t covered while on the outer side of the disc there’s sort of “donut” just like previous years that matches quite closely the rim inner shape and also covers big part of the area of the wheel spokes, leaving just a limited gap where air could flow out from disc holes thru the wheel spokes. How big the clearance actually is, hence how much air could pass from there I can’t tell.

Notice anything about the wheels? Rear in particular!

That they are quite thin and enclosed in the bodywork

[manchild]

That’s different from the Ferrari design (besides, you indicate the air flows in both ways thru the spokes and that doesn’t make sense, that’s what I was pointing out in previous post)

No, no... sorry you got such impression. Those red lines with arrows on both ends are to indicate pressure of hot air within the rim.

Williams had ducts is wrapped around the disc on rear whees last year so I thought it is so on Ferrari too. Not having ducts wrapped around the disc doesn't change essentialy what I've imagined.

[RH1300S]

I think the picture is misleading Manchild. It appears to show an inlet and outlet on the inside of the wheel as well as the wheel cover detail on the outside.

From Reca's pictures it appears that there is only a rear facing outlet to the duct - this is on the inside of the wheel.

Surely the flow is from the outside of the wheel - through the wheel cover then passing through the brake as required and then exhausts into what must be a low pressure area just ahead of the wing end-plate.

Looking at the brake duct - the detail around the wheel nut looks very like the mouth of a jet engine - ideally shaped as an intake? It makes sense that the wheel covers probably affect the intake area of the duct.

EDIT: I love the section detail of the wheel - it is beatifully shaped to create a path for the loads, yet still very delicate.

[Reca]

No, no... sorry you got such impression. Those red lines with arrows on both ends are to indicate pressure of hot air within the rim.

Ok then, do you think that something like this would work as you intend ?

[IMG:150:128]http://img45.imageshack.us/img45/2310/f ... sr4.th.jpg[/img]

[Ciro Pabón]

So, next time I race along a Ferrari in the rain, should I try to splash the wheels laterally as much as I can with my car, for it to "suck" the water to the brakes?

[ginsu]

I like your picture Manchild, but I think that the hot air doesn't flow through the wheel rim, but stagnates and gets sucked out by the low pressure of the exit duct on the inside of the wheel.

Also, I was thinking of why Ferrari would want to exhaust hot air towards the inside of the wheel and came up with an interesting idea. What if the heat from the brake ducts causes the carbon fiber to become more flexible? Then, during the race the lower wing (which holds the endplates and upper wing surfaces) could flex, allowing the whole rear wing assembly to tilt back, reducing it's angle of attack, and drag. When the car is being inspected everything is cold and stiff, but during the race with all the rejected heat things start flexing.

I know it's far-fetched, but it would be ingenious.

[ss_collins]

BTW, Racecar Engineering had an interesting article about this, and I sent them an email regarding our findings...hopefully they will be checking out our forum very soon!

Indeed...

great forum - best I've seen yet. I'd like to speak to its owner.

[manchild]

I like your picture Manchild, but I think that the hot air doesn't flow through the wheel rim, but stagnates and gets sucked out by the low pressure of the exit duct on the inside of the wheel.

When they are using fairing with smallest hole carbon dust can be seen exiting sideways. For example, try finding clip with Ferrari braking in turn one at Turkish GP.
I'm sure that rim is "pressurized" a bit since inlet duct works as ram-air system and hot air can't exit as fast as cold air enters and if so than hot air fills whole space reaching fairing wall and partly exiting outside. It could be said that aperture in fairing has some sort of BOV function - when outlet duct can't swallow as much as inlet duct bites than aperture in fairing prevents overheating by letting some of hot air out.

[manchild]

Sorry for double post it was an accident.

[Reca]

So, next time I race along a Ferrari in the rain, should I try to splash the wheels laterally as much as I can with my car, for it to "suck" the water to the brakes?

I think that there’s a misunderstanding here Ciro. The difference in the Ferrari design compared with others is not from where the cooling air enters, the intake is on the inside of the wheel just like in any other car. The difference is that in Ferrari case at least part of that cooling flow is exhausted from a duct on the inside. How big is the % exhausted on the inside compared with the % going out on the outside I don’t know (that depends by dimensions of all the gaps, pressure differences and a quantity of variable we can’t know) but I’m quite convinced the former includes all the carbon dust from disc and pads, just look at how clean were the wheel spokes at the end of the stint compared with front ones and then look at the dirt on the wing endplate.
In the pic I posted of my model the intake wasn’t visible but it’s on the inside :
[IMG:150:128]http://img53.imageshack.us/img53/2164/f ... hi5.th.jpg[/img]
Basically manchild schematic is conceptually what I always had in mind since the start and what I tried to model, the differences are in the details (when I said that I didn’t agree with his explanation was because of the mistaken interpretation of the red arrows in his drawing).
The problem is I’ve yet to find a pic good enough of the rear duct from behind and without wheels to have my idea of the design confirmed (for example I’ve yet to see also if the outer face of the airfoil shaped part is entirely open or it’s closed with just an hole for the driveshaft). I know that previous year cars had a duct covering the open side of the caliper, just like I made on the model. I assume, but I’m not sure, it’s the same on the 248F1.

[ginsu]

Reca, great model of the wheel! But, how would the flow from the edge of the disc get to the exit duct? There needs to be some kind of passageway, so the hot air wouldn't just bleed out from the edge around the upright.



If the rear is anything like the front (Bahrain 06), then it would be very easy to route air back out towards the inside of the wheel.

BTW, everybody should buy the Jan issue of RaceCar Engineering...there should be some discussion on this topic.

[zac510]

There must be some lower drag benefit, otherwise the amount of effort being expended just to redistribute the braking heat across the width of the rim is quite enormous.

[mini696]

These are all 'low-drag' vehicles:

Notice anything about the wheels? Rear in particular!

Remember the rear wheels dont steer, so they can have more 'covering' than the fronts.

[DaveKillens]

The front wheel assembly has a full duct that channels all the hot brake air away from inside the wheel rim. The rear is very different, obviously leaving a lot of the hot brake air to come into contact with the wheel rim. Why? Well, it's always nice to have an understeering car rather than the opposite. With the Ferrari system, you can almost guarantee under all circumstances that the rear tires will have more heat (and thus, more grip) than the fronts. A very desirable situation on starts and close racing. The front brakes do so much of the work, that it takes little time to bring them up to temperature, so much that only heat dissipation is the only issue.
But it's possible to imagine scenarios where the rear wheels cool off too much when entering a corner, such as entering the tight chicane turn one at Monza.
If your rear wheels have cooled a bit too much, it would be easy to spin out at that corner. Testing has proven that tires have a time delay between the time they are asked to turn, and bring heat into the carcass. It may be as little as .25 seconds, but it's nice to know the rears have retained some heat along the straight, and when braking, some of the brake heat has already been at work re-heating the rear tires.
I believe that is one reason for their existance.

[Reca]

If the rear is anything like the front (Bahrain 06), then it would be very easy to route air back out towards the inside of the wheel.

The rear brake duct is different from the front, I tried to make my model conceptually similar to it (at least, to what I believe it looks like).
That’s the 248F1 :
[IMG:150:128]http://img437.imageshack.us/img437/3678 ... lr7.th.jpg[/img]
Unfortunately in this pic just like in all I found the rear side isn’t visible so I’m not sure it’s like the previous years cars, I assume it is (this is the F2003GA but also on F2004 and 2005 was similar) :
[IMG:150:128]http://img441.imageshack.us/img441/6785 ... ek8.th.jpg[/img]
If the assumption is correct and the 248F1 is similar to previous years cars then the air exiting from the outlet on the inside is most likely taken from the duct covering the caliper (and the pads), it’s obvious that it includes consequently all the carbon dust generated by disc and pads wear and would explain why the endplate is covered with dust at the end of race.

The doubt is about the air exiting from other part of the disc circumference, the non covered ones. This air is hot but, relatively, clean (meaning it doesn’t include much carbon dust) so it doesn’t leave noticeable traces to identify its path. Most likely it goes out thru the wheel spokes, but I can’t tell how big the clearance between the “donut” and the inner side of the rim is (the only thing I can tell is that the transversal section of the “donut” on the 248F1 appears to be slightly less “rounded“ than in the previous years). It’s also possible that part of cooling air goes out from the other gaps, for example the upper part of the rim on the inside, where the upper wishbone passes, isn’t completely closed, maybe a fraction of air leaks out from there too. If that’s the case or not it depends by the clearance between the donut and the rim inside face, the size of the other gaps etc etc.

I'm sure that rim is "pressurized" a bit since inlet duct works as ram-air system and hot air can't exit as fast as cold air enters and if so than hot air fills whole space reaching fairing wall and partly exiting outside. It could be said that aperture in fairing has some sort of BOV function - when outlet duct can't swallow as much as inlet duct bites than aperture in fairing prevents overheating by letting some of hot air out.

First question.
Imagine you are the passenger in a car going at 200 km/h and you have a toy balloon that you want to inflate. You open the window and put the balloon outside, keeping the open end straight against the incoming flow. How much time does it take for the balloon to be inflated ?
Second question.
How much “hot” do you believe the cooling air becomes after passing thru the disc ? 50°, 100°, 300° ? We know that the disc reaches often temp in the order of 800-900 °C, but what about the cooling air ?