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From: "Ed Anderson" <eanderson@carolina.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-2500067@logan.com>
Subject: Re: [FlyRotary] Re: Naca Report on Radiator Thickness
Date: Wed, 21 Nov 2007 20:19:36 -0500
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 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