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This brings me to my final point (promise I won't make anymore points). Use the widest-thinnest radiator you can reasonably fit under the cowl and make appropriate ducting. I guarantee that you don't want to use the thickest-narrowest rad you can fit. That would not cool well at all.
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David Leonard
Hey, wait a minute! Why didn't you take your own advice? I'm sure you could have found a radiator thinner than 3". Did you mean to say widest & thickest? That would be the combination to use to insure the best chance of cooling adequately (but not necessarily the lowest drag or weight). Bernie Kerr did use the widest & thinnest approach on his RV-9 and it had lousy cooling.
Tracy (never promises not to make more points : )
Ok, I have sworn of making any more points here, but I am just answering the question. I did take my own advice. That radiator is about as wide as I can possibly fit without deforming the cowl into the slipstream. When I decided I wanted to beat down my cooling problems with a hammer, I made the rad thicker as the only way to add volume. - but I still contend that is more drag than I would have added if I could have made the rad wider instead.
We ether rad, the goal is to let through just enough air so cooling is adequate. In all this discussion, I have never seen an argument that convinces me that the thick rad would need less air. That I why I keep insisting that we set the initial condition of the same amount of air. It is true that with the same inlets and outlets the thicker rad will flow less air (and have less drag). But the thin rad needs smaller inlets and outlets. That is how it achieves matched airflow and reduced drag.
Theoretical discussion aside, I have not achieved the goal of optimum duct design (which does become more difficult as the rad get thinner) and I am currently letting too much air through my rad. So I have excessive drag. But maybe someday... :-)
I do not believe that useful pressure recovery is a pipe-dream. Some report that the P-51 even gained thrust from the cooling exit (I don't think they mean net thrust from the system thought). Also, both Bill Eslick and I have the same experience that our cowl flaps want to pull themselves wide open by the pressure available at the cooling exit (well into the slip stream).
Oops, sorry, couldn't help myself.
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David Leonard
Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
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