Re: RAdiator fans and H2o cooled engine

[dmp@TmedBSD.MCG.EDU]

> From:          Jeff Barnes <jcbarnes@ibm.net>

> > I think i will try the spritzer when I get my new radiator. 275 cubic
> > inches was definately not enough for 230 HP. Im pretty sure the one Ron
> > Davis in building now will be too large 528 cu.in.
> 
>   Was the safe 15 minutes on a test stand with the 275 cu.in ?  
> 
>   I don't know how cu.inches factor in; the CSA didn't mention
> cu.inches. Nor did it mention total system coolant requirement, which of
> course is weight. If that's actually radiator frontal surface area as

If you assume that the coolant cores are 1" and the fins are 1.5", 
then you could have radiators that are 1.5, 3.0, or 4.5 inches thick, 
depending on how many rows are in the rad. If you double the 
thickness, then you can halve the frontal area, so cubic inches are a 
factor.

Except. As you add layers, the ones behind see warmer air coing in,
so they can't expell as much heat, so you have diminishing returns 
with thickness. So the tradeoff is large frontal area drag with a 
large area rad vs. higher internal drag with a thicker rad and 
somewhat less than halved, third frontal area drag.
 
> x 9"H x 12"W (15"W including tanks), 14 fins per in, with inlet size
> recommended by Ron Davis at 15% radiator AREA (I get 108sq"), and

Wow. That would give a pressure increase of better than six and and a 
half times! At 130knots, that's 5.4 inHg, or almost 3 PSI. AT 108in2, 
that's 286 lbs pushing on the rad, so it needs to be well secured and 
sealed.

> >  but a variable inlet should reduce the drag penalty.

I'm not sure I like variable inlets. Too much mechanical stuff to 
disrupt airflow. Better to have a variable outlet, like the P-51. In 
fact, one person I've been chatting with says you don't even need a 
inlet diffusser, just an exit diffuser to control the flow. (Not sure 
I totally agree with that one.)

---
David Parrish