Cooling fan (or not)
Posted By : Andy Vowell, 23-Mar-2004, 08:16pm
Hi Mik
I have one, but only fit it on really hot days. Most of the time it is not needed but on a hot day sat on the grid waiting for the go, temperatures can get a bit critical. On cooler days it is fine. Fans are heavy and draw power so leave it off as much as possible.
I just have an old Austin allegro fan that I zip tie to the rad when needed. If you look at the photos on your own website you took at mallory last year you can see it pretty clearly. (Though as I blew a head gasket there I obviously forgot to turn it on!)
http://www.friendlydragon.co.uk/classic/2003/03071...
Tour the scrappy and get one for a fiver.
Cheers
Andy
PS If you move your rad forward a bit then you can fit a fan behind it and avoid all the airflow blocking problems.
I have one, but only fit it on really hot days. Most of the time it is not needed but on a hot day sat on the grid waiting for the go, temperatures can get a bit critical. On cooler days it is fine. Fans are heavy and draw power so leave it off as much as possible.
I just have an old Austin allegro fan that I zip tie to the rad when needed. If you look at the photos on your own website you took at mallory last year you can see it pretty clearly. (Though as I blew a head gasket there I obviously forgot to turn it on!)
http://www.friendlydragon.co.uk/classic/2003/03071...
Tour the scrappy and get one for a fiver.
Cheers
Andy
PS If you move your rad forward a bit then you can fit a fan behind it and avoid all the airflow blocking problems.
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Cooling fan (or not)
Posted By : Richard King, 23-Mar-2004, 08:36pm
>PS If you move your rad forward a bit then you can fit a
>fan behind it and avoid all the airflow blocking problems.
How so? Surely it just blocks the air coming out the back of the radiator instead and you get pockets of still, hot air in betwixt the fins?
I'm no aerodynamicist, but I did a course on it at college and it all looked like dv-dt^3/(dx/dy) etc.-
Cooling fan (or not)
Posted By : Michael Davis, 23-Mar-2004, 08:55pm
Yes, I've never worked that one out either although many people have said that it works.
Surely the air has to flow right through the radiator and out the other side in order to provide cooling. If a lump on one side blocks the core, how does moving it to the other side make it less restrictive. I can see that there might be a slight gain due to heated air escaping arounf the blockage rather than cold air never making it to the rad but not a big difference to my mind.
Then again, I never was any good at dx/dy stuff!
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Cooling fan (or not)
Posted By : Andy Vowell, 23-Mar-2004, 10:14pm
All good discussions, but I think I prefer the fan behind as the actual motor is away from the blades so not blocking if well behind. Swings and roundabouts really.
Besides, using Richy's very valid point about a fan behind restricting airflow through the rad, if the rad is in the standard as built location then I think having the engine a couple of inchs behind it does a excellent job of stalling airflow!
Just a thought.
Cheers
Andy-
Cooling fan (or not)
Posted By : Andy Vowell, 23-Mar-2004, 10:22pm
Another thought (brain started working now)
Fan behind, air enters rad in clean(ish) flow direct from front of car so is the purest charge of air you are going to get, perhaps with some laminar flow. Air is then dragged through by fan creating a low pressure behind where it gets all mixed up and messy after it has been used.
Fan in front, nice clean flowing charge of air is turbulated (is that a word?) before the rad, so enters the rad at higher pressure but all messy and swirly so probably less efficient.
Does that sound scientificly right?
Andy V-
Cooling fan (or not)
Posted By : Nigel Gibbins, 23-Mar-2004, 10:48pm
Yes - the air is messy, swirly and turbulated.... very scientific
A bit discombooberating this eh?
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Cooling fan (or not)
Posted By : John Davies, 23-Mar-2004, 11:38pm
All,
I fully agree with Andy about fan position, but even more about the effect of the engine. As important in promoting flow into the radiator is flow away from it. The engine ruins this flow, which must find its way out under the car, promoting lift on the way.
A duct/ducts leading heated air cleanly away from the rad and out into a suitable exit point can reduce cooling drag by 50%! Look at many rear engined, front rad cars such as the Lotus Elise.
The Spitfire engine is probably far enough back from the rad to allow such an extractor duct, out into the low pressure area towards the front of the bonnet. Not so, six-cylinder cars.
Here's another idea. No fan, but a mesh container in front of the rad. Fill with ice cubes. Cooling from the melting cubes while sitting on the grid, free air flow once racing as all the cubes will have gone. Even better - dry ice!
John
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Cooling fan (or not)
Posted By : Andy Winterton, 24-Mar-2004, 07:51am
Ah, but does one really want laminar flow through the rad, where the air next to the surface stays next to the surface, and so gets hot.... or turbulated (great word) flow, where fresh, cold air rubs against the fins?
Still think I'm gonna leave my fan off altogether...
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Cooling fan (or not)
Posted By : Richard King, 24-Mar-2004, 08:13am
Crikey, eh?
I didn't realise that this was such a hot topic... I've got a fan and it's useful to prevent the car boiling over in parc ferme, it's off when I'm racing and I don't have any real problems with overheating.
Oh, and it's a turbulating fan and not a laminar fan
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Cooling fan (or not)
Posted By : John Davies, 24-Mar-2004, 08:15am
Andy,
Definitely laminar flow!
Turbulent flow has a much higher drag, so that flow through the rad matrix will be reduced. In fact it will 'stall', just like a wing that has lost laminar flow. Heat extraction will be less efficient.
Look at any F1 car. The intakes for the rads are smaller than the rad dimensions, so that air entering the duct slows down before it meets the rad matrix. Slow air is not only less likely to be turbulent, it has more pressure (Venturi effect). Then they put the rad air exhaust in the rear diffuser, in a low pressure area, so the pressure gradient across the matrix is greater. Comes back to my point about air extraction.
John-
Cooling fan (or not)
Posted By : Richard King, 24-Mar-2004, 09:45am
>Look at any F1 car.
There is that, but sidepods and diffusers break the silhouette regulations...-
Cooling fan (or not)
Posted By : Michael Davis, 24-Mar-2004, 10:31am
yeah, but my air intake grille is still smaller than my rad and I have a duct between the two to try to promote exactly the effect John was talking about
I haven't worked
out an extractor duct yet but I had thought about it.
Thanks for all the advice people. I've decided to go with a fan that doesn't cover the entire radiator (in fact about half of the area) so hopefully reducing it's air blocking effect whilst still allowing some forced cooling when it's needed.
The fan will have to go in front of the rad for now as I've already made up all the mountings and an intake duct and I'm not about to start re-engineering all that to move the radiator forwards (besides which I have an oversize radiator and it only just fits under the bonnet where it is now).
Many thanks
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Cooling fan (or not)
Posted By : Andy Winterton, 24-Mar-2004, 10:44am
Agreed John..... spent a bit of time over the winter on ducting air.
What have you done on yours?
PS. Still undecided whether I can get away without a fan at all! How long will we be held on the grid? Will it be me doing the holding up? Do I feel lucky?-
Cooling fan (or not)
Posted By : Michael Davis, 24-Mar-2004, 10:51am
Exactly the questions I was asking myself the other day (and eventually asking other people here too). I decided to start off with a fan and if it causes more problems that it solves, I can always take it off again.-
Cooling fan (or not)
Posted By : Mark Hadfield, 24-Mar-2004, 12:58pm
If your worried about your radiator and cooling why not try this radiator and if everything goes wrong and you overheat you could pull over and make a cup of tea Maybe you could set up a mug with a tea bag in as your catch tank then there would be no delay in getting a nice cup of tea after the race
Cooling fan (or not)-
Cooling fan (or not)
Posted By : David Thompson, 24-Mar-2004, 01:50pm
I like the mug of tea idea - would have been good at Mallory and Snetterton where the races were stopped and we all had a chin-wag on the grid for 20 mins whilst the unfortunates who crashed were shovelled up off the track.
Trouble is I don't drink tea - I wonder if I could adapt a swirl pot to act as a coffee perculator?
Perhaps the 'bread van' could come round with some nice cakes too?-
Cooling fan (or not)
Posted By : Richard King, 24-Mar-2004, 07:44pm
>Trouble is I don't drink tea - I wonder if I could adapt a
>swirl pot to act as a coffee perculator?
Mind if I join you for an espresso? Tea is the drink of the devil
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Cooling fan (or not)
Posted By : Andy Vowell, 25-Mar-2004, 01:21am
Well for an expresso you'll need to see me as I'll be going expressilly fast. yo ho ho.
Andy V
(going slightly dodgy after 3rd wake up for 16 day old mechanic)
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Cooling fan (or not)
Posted By : Andy Winterton, 23-Mar-2004, 09:00pm
Only ever used mine when held on the grid on a hot day, so planning to leave it off for now.....
I prefer the in-front position (oo-er missus) .. as the fan is then pushing itself away from the rad rather than pulling itself into the rad. Could be important with my scrapyard -challenge fan mountings!
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