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Date: Sat, 30 Apr 2011 11:10:02 -0400
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Cooling Inlets
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Ed Anderson wrote:

> For a high speed cruise environment, I would think cooling drag might be 
> of more importance than say perhaps a few pounds of additional weight, 
> on the other hand if you are flying an already draggy biplane for 
> example, cooling drag is probably a very small part of your over all 
> drag, but getting cooling with low airspeed might be the system driver.
>  
> Its all about compromises - space, weight, flow, drag, etc. - oh, yes! - 
> and cooling of course {:>)  all matched to your constraints and 
> operating environment.
>  


I may have read it wrong, but it seems the NACA study that Tracy was referencing said that the cooling drag for the 
Aztec they were testing was about 5% to 7% of total drag.  I've read before that cooling drag is more like 30% of total 
drag.  Big difference there it seems.

Does anyone have any better insight, or is this just an apples vs oranges thing?  We've spent a LOT of time discussing 
cooling drag on this list.  Is it even worth worrying over?  Is it worth stressing over an engine overheating to go 
196MPH instead of 192MPH?