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interestedparty
09-07-02, 12:33 PM
I have heard mention of these recently and am curious as to how they work. We all know how a normal fan works, and the idea might seem to apply to the roadwheels of a car. But the wheel is moving sideways to the air that it is trying to pump. I presume the spokes of the wheels are intended to act as fan blades. If this is the case I could see it working if the wheel was turning in air that was still, but when the car is moving then each spoke is moving at the same speed as each piece of air it encounters. Isn't it? Anyway, I look forward to reading an explaination.

John

robert
09-07-02, 12:40 PM
John

The wheel is effective as it will work on the forward side as it is effectvely travelling at twice the speed of the car therefore the vanes will force the air through, theoretically, you could say that it wouldn't work on the return side as the wheel is travelling in the same direction as the airflow, however the forward side of the wheel disturbs the air enough to make it work very well.

Also, the fan is actually in a relative dead zone within the wheel so already has a good zone of disturbed air, so it will actually drag air from both the forward and return.

The wheels are also handed to each side fo the car.

Robert
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interestedparty
09-07-02, 04:13 PM
Thanks for the explaination Rob, though I'm afraid I still can't quite see how it works. I've thought about it some more and it seems to me that the 'fan' is actually turning more slowly than the wheel's progress through the air because the wheel is turning at the rate required by the speed of the car and the circumference of the wheel which of course is greater than the spoked area. If the fan effect did work at all then surely it would be moving the air backwards and forwards.
No matter how much air flows over the brakes, surely it can't cool them more than the ambient temperature, so even if the fan effect works I can't see it making any difference to a car being driven on normal roads.

John

robert
09-07-02, 04:19 PM
John

I will draw a picture later this evening, however please think about the following.

The fan is sitting in an area of traditionally dead air, so the fan will move that dead air which will in turn draw more air through the wheel.

I really cannot see how you arrived at the conclusion that the wheel is moving the air backwards and forwards, as the fans only face outwards from the car.

Lastly, think of the concept of wind-chill, as this will operate on any surface.

Robert
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robert
09-07-02, 04:29 PM
John

The following picture will give you an indication of the actual wheels.


Robert
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robert
09-07-02, 04:30 PM
Or this one.

http://gdcars.com/images/gallery/gdt70/Pic5_800.jpg

Robert
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interestedparty
09-07-02, 04:31 PM
I'm looking forward to seeing the picture Rob. I can see what you mean but it only works if the air in the region of the wheel spokes is dead, and maybe that's the bit I don't get.
Wind chill cannot make a surface colder than the temperature of the air itself. It can certainly feel chilly to a person because of the forced evaporation of the water in their skin, and the heat loss due to the latent heat being demanded, but brake discs are usually bone dry and not subject to this effect.

John

interestedparty
09-07-02, 04:35 PM
Yes, exactly as I suspected. Good looking wheels, though, and a thoroughly desirable car, too.

John

robert
09-07-02, 04:55 PM
>Wind chill cannot make a surface colder than the temperature of the
>air itself. It can certainly feel chilly to a person because of the
>forced evaporation of the water in their skin, and the heat loss due
>to the latent heat being demanded, but brake discs are usually bone
>dry and not subject to this effect.

They are subject to an enhanced cooling effect from the operating temp of anything between 400-650 degrees, and if the ambient temperature is 30 degrees (never that nice in the UK) you will get faster cooling.

If cool air being passed over brakes assemblies didn't work, then why would people duct air to them, or are they wasting their time?

Robert
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interestedparty
09-07-02, 05:03 PM
>
>If cool air being passed over brakes assemblies didn't work, then why
>would people duct air to them, or are they wasting their time?

No, they are not wasting their time. If the brakes are used a lot (as of course they are on a race track) then their temperature rises far above the ambient air temperature and a good flow of air helps to cool them. Quite often this is insufficient and the discs get hotter and eventually radiate heat visibly. On a normal road, especaially a motorway, the brakes will be at or very close to the ambient temperature and even lots and lots of airflow will not lower that temperature.

John

robert
09-07-02, 05:05 PM
That is a given, so where are we going on this thread?

Is your queston does airflow help or is your question do the fan wheels work?

Robert
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interestedparty
09-07-02, 05:14 PM
Perhaps I should not have put my original post in the form of a question. Perhaps I should have simptly stated that in my opinion fan wheels do not work.
Obviously airflow over the brakes is a good thing, but sometimes people can get the feeling that it is possible to overcool brakes where of course it is not. But my original post did not concern desirability of airflow.

John

robert
09-07-02, 05:30 PM
>Obviously airflow over the brakes is a good thing, but sometimes
>people can get the feeling that it is possible to overcool brakes
>where of course it is not.

Ok, so we have clarified that you feel the fan wheels do not work, however you have just said that you cannot overcool brakes.

Now that is a completely false comment, as to operate efficiently brakes need to be between a specific temperature range, which is nowhere near the normal ambient temperature of a normal day in the UK (12-16 degrees).

Why does EVERY brake manufacturer provide an optimum operating temperature? Is this just for the hell of it or is this for a specific reason.

http://www.auto-ware.com/techref/brakepads.htm

Robert
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pcoghlan
09-07-02, 06:11 PM
Robert,

You made a recent reference to the fact that you may have your ncar in the MIRA wind tunnel at some point soon. Do they have a rolling road in there too? If so then could you not have the wheels tested in there to quantify the impact of the fan desing?

Maybe insert some dye into the windstream and watch the effect to see how effectively the wind is sucked into the wheels/pushed out.

I am no aerodynamics expert or engineer but I would think that the wind would be disturbed but nevertheless heading from the front of the car to the rear with a potential dead area within the dish of the wheel. Any air in the region of the blades would be pushed/pulled to the outside of the car by the blades, no? This would in itself create a low pressure thereby pulling more air in.

I for one know that it is possible to have brakes overheat on a road and my old Mustang used to suffer from it frequently in the twists. (Sub)-standard brakes, heavy car, energetic driving and twisty roads = overheating brakes. ;)

Paul

PS As I am going for the fan wheels myself I am please to see them at long last, 6 weeks and counting!!

robert
09-07-02, 06:24 PM
The facilities within MIRA are something to behold.

They have the wind tunnel with a combined rolling road, which can be used to evaluate the cars actual motion, however it will only operate to 130km/h http://www.mira.co.uk/fluids/ftfswt.htm#Hire

I will firstly be looking at doing some computation fluid dynamics as that will give me an appreciation of the issues we will face.

Robert
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robert
09-07-02, 09:15 PM
> Perhaps I should have simptly stated that in my opinion fan
>wheels do not work.

John

Firstly, the fan wheels do work, as I have used them in a real world environment. I went on a track day last year, and after 3 laps was experiencing brake fade to the extent that I had to do a cooling off lap after every third lap. At the time I was running 350hp, 16 inch Image wheels and Pagid fast road pads.

This year, I went on the same circuit, however I had 550hp, 17" fan wheels, and the same Pagid fast road pads. I was able to keep out on the circuit and was only forced to come in when I noticed the fuel level was low.

I have not bothered to draw a diagram, however will describe how they work in words.

The wheels are effectievly masked from airflow by the body, and the internal face of the wheel is in a zone of dead air (not really moving). Internally to the wheels, we have the engine bay, which is also an area of dead air.

The fan wheels direct air from within the body outwards, and by moving the dead air, they will actually move the air through their full rotation as the airflow over, around or under the car has no bearing on the dead air captured within the wheel immediate environment.

If any of this doesn't make sense, then either I am not explaining this correctly, or not conveying my message well enough.

To summarise, I have used both standard wheels and fan wheels in a real world environment and will never go back to the standard wheels as they work very well and the concept, excecution and design are sound.

Robert
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pcoghlan
09-07-02, 09:23 PM
They look a lot easier to clean than the GTD5's too!!

:+ :+ :+ :+ :7

interestedparty
09-07-02, 09:27 PM
Robert

I am going to have to assume that the effect of the wheels being masked from the airflow is something that only applies to Cobras, seeing as the makers of every other high performance car I can think of haven't bothered with fan wheels.
However, I am happy to acknowledge that in your case they definitely work.

John

interestedparty
09-07-02, 09:37 PM
I missed this one earlier, I'm not used to this style of forum where it is possible to reply to a specific post even if it is not the last one.
Let me re-explain my position on this-
Let's take the case of two chaps driving on the motorway and not using their brakes as per normal motorway driving. One has fan wheels and , for him they are working and blowing air over his brakes. The other has conventional Halibrand replica wheels and no fan effect. What I am saying is that both sets of brakes are at the same temperature.
In a situation where the brakes are being used a lot, eg track day, then extra airflow will help cool the brakes which will be far above ambient temperature. Obviously brakes have an optimum temperature range, and equally obviously this has to be higher than ambient because if it wasn't they would immediately start to fade as they warmed up. This would make descending a long steep hill dangerous.

John

robert
09-07-02, 09:41 PM
>Robert
>
>I am going to have to assume that the effect of the wheels being
>masked from the airflow is something that only applies to Cobras,
>seeing as the makers of every other high performance car I can think
>of haven't bothered with fan wheels.

Major Manufacturers like Volvo http://www.swedespeed.com/features/project_cars/854/part1.shtml

Or Alfa Romeo http://www.erebuni.net/wheels/alfa.htm

Yep, no major manufacturers have utilised this.

Robert
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interestedparty
09-07-02, 09:47 PM
I wasn't really thinking of Volvo and Alfa Romeo, more Ferari, Aston Marin, that sort of thing.

John

wilf
09-07-02, 09:58 PM
All very interesting scientific stuff, but my point is, (and of course you would expect no less of me) that those there wheels have NO place on a car which purports to be a Cobra.

Only two types of wheel belong there - rusty old donor wheels during the build and halibrand (or sunburst) types after.

Now, for a track-oriented car that just happens to look a bit like a cobra, fair 'nuff.

Wilf}>

robert
09-07-02, 10:05 PM
Oh, and Speedline and OZ made a range of fan wheels, so they definitely don't work in any other application than a Cobra or T70, basically nothing else with a GD badge!!!!!

MAybe the aerodynaics of the GD badge make it work.

Robert
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robert
09-07-02, 10:15 PM
No John, this is what you actually said.

"but sometimes people can get the feeling that it is possible to overcool brakes where of course it is not."

You stated that it is not possible to overcoll brakes, however what you don't take into account is the braking configuration of any given car.

Take for example a typical Cobra Replica. It will have Jag discs and calipers which were DESIGNED to stop a 2ton plus car, and if the car is used on a circuit, then it will have some form of fast road pads. Those particlar pads will only operate properly between a given temperature range, which means that if the owner was cruising and not using his brakes, then the actual brake temperature would equalise with the ambient temperature.

Now to operate effectively, the brakes would have to come up to a specific temperature, which wouldn't happen until that person had applied the brakes and the kinetic energy had heated up both the pad and the disc.

OK, now lets go to the another extreme, the owner has race pads, slotted and vented discs. His brakes will have to get to a far higher temp to be able to stop.

Now do you still feel that it is impossible to overcool brakes??????

A braking system needs to be configured with the intended use in mind, otherwise you will either not be able to stop because the brakes have not reached operating temp, or you will not be able to stop because they have cooked and you have brake fade.

Robert
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dave
09-07-02, 10:29 PM
Robert.
For what it's worth coming from me, I know what you mean.;-)

interestedparty
09-07-02, 10:36 PM
Robert, I realise you feel strongly about this, but you are reading an awful lot into what I said earlier. When I talked about 'overcooling brakes' this is the kind of thing I was referring to-

"In terms of brakes, I run standard jag calipers and discs with pagid fast road pads, and the car stops with no drama whatsoever. In conjunction with the GD fan wheels which work very very well, sometime too well. There have been a couple of instances where I have been tanking up the motorway without using the brakes for 30 minutes and have then had some rsehole pull out on me only to find the brakes are too cold!!!"

This chaps brakes would have been no cooler than if he were using conventional wheels

John

interestedparty
09-07-02, 10:47 PM
Is that irony?

John

robert
09-07-02, 11:03 PM
What chap are you talking about??????????????????

I was detailing an aspect of MY car, no one elses, and yes it is a proven fact that you can overcool brakes.

WHY DO THE MANUFACTURERS OF THE BRAKE PADS PROVIDE AN OPERATING RANGE IF COOLING DOESN'T HAVE AN IMPACT, I AM SURE THEY HAVE BETTER THINGS TO DO THAN MEASURE THE OPERATING TEMPERATURE.

I have had enough of this now.

Robert
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robert
09-07-02, 11:06 PM
Yes.

Irony - A literary style employing such contrasts for humorous or rhetorical effect, also a synonym of wit which is the better cousin to sarcasm.

Robert
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robert
09-07-02, 11:07 PM
Thank You!!!

Robert
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robert
09-07-02, 11:08 PM
Oi But out big nose, this is a private conversation. :D :D

Robert
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wilf
09-07-02, 11:10 PM
John - actually I thought those GD bagdes were more stainless-steely than irony.

Wilf :D

wilf
09-07-02, 11:12 PM
Typical - can't take a little constructive criticsm!!

Wilf }>

robert
09-09-02, 09:14 PM
Yes, air is pulled out.

Robert
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pgoodrum
12-10-02, 09:40 PM
Robert

I'm not saying they do or don't work, just curious :-)


have you done any actual tempurature measurements with/without your fan wheels to see just how much brake temperature is affected?

Pete

ps who makes them, how much and do they do 15"??

Kelvin
12-10-02, 11:06 PM
Hi all,

don't forget cavalier sri's had a fan on the wheel trim ;)

Kelvin

nicklouse10
07-11-02, 08:40 PM
judging by the angle of the blades on that crazy blue thing above, the air is "pulled" from the car side of things, not "pushed" through from the road side of things, is that correct?
they look pretty wicked, were they very expensive? I am currently putting away the pennies to get a set of wheels, and havent decided what to go for. I will hopefully be spending lots of time at track days next year and was a bit worried about overheating brakes, this seems like a step in the right direction.
you can see why I need new rims, these are pretty horrific!