> The drag increase of 58% sounds way too low. You
> increased surface area by 300%. Unless mass flow
> decreased a lot (it didn't) or drag coefficient
> dropped a lot (it shouldn't), then this can't be
> right.

Well, there is no change in frontal area between the
radiators, so the old 1/2pV^2*A drag factor remains
essentially the same for all  - discounting the
small 5% decrease in mass flow which would (by
itself) help decrease the frontal drag some.  So the
question is would the increase in skin friction be
proportional to the increased internal surface area
( I would presume it is)?  And if it is? Then what
is the absolute amount of drag per square inch based
on.  Is the  internal core drag  a small part or a
large part of the overall core drag.????  I know -
it probably depends........ {:>)

Ed,

This is a very good point. I am thinking flat plate
drag equations and infinitesimally thin fins. That is
not true. The drag is probably dominated by the
stagnation of air on the frontal area of the fins and
anything else that produces frontal area. That frontal
drag will probably dominate the internal skin friction
drag. So, even though the internal skin friction drag
should go up 260% for the thicker case (see other
email), the frontal drag will be only be slightly
reduced due to the lower mass flow. The net effect
could very well be only a 58% increase as your
equations show.

I've been schooled!

Thanks,

Ron