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Date: Wed, 21 Nov 2007 18:20:06 -0800 (PST)
From: Ron Springer <ron2369@sbcglobal.net>
Subject: Re: [FlyRotary] Re: Naca Report on Radiator Thickness
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-2500116@logan.com>
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Message-ID: <111670.85765.qm@web81313.mail.mud.yahoo.com>

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!

Ron

--- Ed Anderson <eanderson@carolina.rr.com> wrote:

> 
>  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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