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Re: RAdiator fans and H2o cooled engine

dmp@TmedBSD.MCG.EDU wrote:
> 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.

That's the benefit of having an Indy-Car cooling guy Ron Davis (I don't
know him, BTW) calculate and build your radiator. 

> > 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.

It's BETTER than that: Charles Airesman article said [on test stand, not
in the air] he's getting -1.0" H2o column gauge reading at idle and at
4000rpm pegged his gauge at 5", which he equates to his Vari-Eze
positive cowling pressure at 200kt.

> > >  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

I don't agree with variable in or out either. The whole point is once
you get it right, your augmentor will simply work, and one of it's main
benefits is already drag reduction, the other totally effective cooling.

I could see restricting the inlet to facilitate warm-up on really really
cold days, and that's only if for reliability and flow performance (or
maybe that's the only way to go for aircraft) one were to remove the
heat-sensitive thermostat in the coolant system, and that's a (lopsided,
IMHO) trade-off against removing a simple automotive part that runs
everyday for years on end in most cars (and can be checked & routinely
replaced) versus augmentor complexity/reliability/possibility of an
inlet flap getting stuck shut.  And that's really overkill, cuz if it'll
start, it'll heat up, regardless of ambient temp and what are you going
to get at 12k ft anyway ?  A major benefit of keeping a thermostat is
you don't have to over-design inlet flaps/etc to avoid OVER-cooling the

ON THE OTHER HAND, a simple set-screw operated ground adjustable inlet
may be the simplest 'build-once, tune until rite' method for setting up
the augmentor, with added benefit of possible adaptability to later
engine swaps.  By that I mena, if new engine's displacement,  etc are
roughly equivalent, use same expensive radiator and labor-loved
augemntor and just adjust air-flow.

Jeff Barnes