Fan Wheels??

[interestedparty]

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]

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
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[interestedparty]

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]

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
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[robert]

John

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


Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[robert]

Or this one.

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

Robert
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[interestedparty]

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]

Yes, exactly as I suspected. Good looking wheels, though, and a thoroughly desirable car, too.

John

[robert]

>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
Forum Admin

http://www.cobraclub.com/flags/UK.gif

[interestedparty]

>
>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