4 replies to this topic

[John Clayton]

The accepted wisdom appears to be that the best cooling comes from using 2x Twin blade fans, or the 6 blade export fan. However, these fans are geared to provide adequate airflow at tickover (say 1000 rpm) in a traffic jam, but for motorsport use I reckon they will probably generate a lot more airflow than you really need -and also generate huge drag at normal motorsport rpm i.e. 4000-6000 rpm. Given that "drag is proportional to speed cubed", there could be a lot of power lost here.

Has anyone dynoed to see how much power mechanical fans lose, compared to an electric one (or tested fans with an Airflow meter)?

Do read the stuff on this thread before posting below -the posts from May 25 2011, 05:11 PM onwards cover a number of the issues on this topic:
http://www.theminifo...howtopic=192069

Here's the car's spec
http://www.theminifo...x...=129848&hl=

I've got a Dowty Aerofan on the way which is worth a try. As always though, its difficult to quantify its benefits without proper scientific testing i.e. a before/after rolling road test and also an airflow meter behind the rad

Edited by John Clayton, 05 June 2011 - 09:24 AM.

[Big_Adam]

the best cooling comes from using 2x Twin blade fans, or the 6 blade export fan

*puts on choker*

GATHER ROUND PEOPLE OF THE CONGREGATION, I SHALL NOW READ FROM THE BOOK OF VIZARD,

"The moulded plastic fans have more aerodynamically shaped blades and thus, they absorb less power and move more air than the early metal fans"
~ David Vizard - How to Tune the A Series Engine (3rd Edition P505)

[John Clayton]

Interesting. I looked at my metal 4-blade fan yesterday and it is certainly rather crude (and the blades aren't too aerodynamic)

[Ivor Badger]

Interesting. I looked at my metal 4-blade fan yesterday and it is certainly rather crude (and the blades aren't too aerodynamic)

But they are curved and less likely to depart at high revs than plastic. Since the engine in a competition car rarely sits ticking over, you simply adjust the fan to suit at the rpm you are using and that is normally 2x2 blades on a 1300.

[John Clayton]

Sorry -I said 'Aerofan' but I meant 'Dowty Autofan'.

I've received it now and the blades are 'cranked' i.e. the portion of the blade behind the pivot point (i.e. where it is attached to the hub) is at a greater angle of attack than that forward of the fulcrum. Therefore, as it goes faster the blade will twist against the spring pressure and thereby feather itself somewhat (reducing the overall angle of attack of the blade). Thereby, it decreases the airflow that it pushes per revolution at higher revs. That said, the amount of flex the blades have look like they will give only a modest reduction in airflow/revolution.