This NACA paper discussion is interesting but has almost nothing to do with our installations using standard automotive rads rather than the flat plate rads in the paper. Radiator frontal area is almost irrelavant in our installations because they are totally enclosed within a streamlined body. Too bad, because if frontal area was a significant factor, it would end the argument about thick vs thin :-) The thin rad would look terrible in this respect.
Keep everything in perspective!
Note that the NACA paper indicates that the rads we use (tube & fin type) have no application in aircraft. If that were true it would mean all our discussions and work on installations so far have been a total waste of time!
Tracy (should be working on RV-8)
On Nov 21, 2007 9:20 PM, Ron Springer < ron2369@sbcglobal.net> wrote:
Well, engineering judgement tells me that your drag
increase is still too low. Now I'll just have to prove
it by looking at that report, or elsewhere.
Sounds like a good project for the long holiday
weekend, or I could just work on my Cozy ... it will
be a tough call!
> Ok, Ron, I went back and looked at the drag aspects
> again. It looks like
> the calculation was accurate, however, I think this
> will put it into a
> better perspective than before.
>
> The frontal drag at 120 mph for the 1 square foot
> radiator (using just the
> frontal area - no drag coefficient) was
>
> 37.63 lbf/ft^2, the "internal skin" drag of the 4"
> thick radiator was 6.7
> lbf/ft^2. The skin drag for the 1" thick rad was
> 4.28 lbf/ft^2. So
> comparing the 6.7 with the 4.28 was where I came up
> with the 58% increase in
> skin drag.
>
> However, adding the frontal and skin drag factors
> for the "total" drag, I
> get 37.62 lbf/ft^2 + 4.28 lbf/ft^2 = 40.98 lbf/ft^2
> total drag for the 1"
> rad. For the 4" rad 37.62 + 6.7 = 44.32 lbf/ft^2,
> so based on that it
> appears that the total drag was increased by
> 41.90/44.32 = 5.5% more total
> drag for the 4" radiator than for the 1" radiator.
> It might be a tad bit
> less than that due to the 5% decrease in mass flow
> on the frontal area of
> the thicker rad.
>
> At least that is the way it appears to me.
>
> Ed
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