Received-SPF: pass
 receiver=logan.com; client-ip=66.133.182.164; envelope-from=canarder@frontiernet.net
Message-ID: <435695D6.1070405@frontiernet.net>
Date: Wed, 19 Oct 2005 13:52:06 -0500
From: Jim Sower <canarder@frontiernet.net>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7) Gecko/20040514
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: NACA scoops
References: <list-773629@logan.com>
In-Reply-To: <list-773629@logan.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

<... Half of somethin' will always be greater than nothin' ...>
True as far as it goes, but even NACAs are more than nothin'.  A lot of 
the serious speed merchants in the EZ community are going with downdraft 
instead of NACA and getting good results.  As I said in an earlier post, 
there's more to it than just frontal area or inlet efficiency.  I would 
surmise that a good downdraft setup buys you back more drag than it 
costs by enabling you to do important things with the lower cowl and get 
more/cleaner air to the prop disc.

At least the heavy hitters seem to believe so ... Jim S.

Ernest Christley wrote:

> Ed Anderson wrote:
>
>> Hi Thomas, afraid not exactly an old wives tale.   Here is an extract 
>> from an  old NACA report that appears to take the position that 
>> submerged (NACA?) ducts are not the best suited for radiators or 
>> anything requiring much diffusion or pressure recovery. 
>
>
>
> Ed, I took my lunch break to read the 5I20 report.  What FUN!!
>
> I think we're tripping over semantics here.  There is a subtle 
> difference between "supplying air to a radiator" and "using a NACA 
> inlet for pressure recovery."  The subtlety is the root of the 
> argument.  Just because it isn't good a pressure recovery doesn't mean 
> that it will make a bad cooling inlet.  It only means that you will 
> have to do some pressure recovery in some other way, like a 
> streamlined duct.  "We don't THINK it will work for radiators, because 
> there isn't enough pressure recovery" IS a long way from "it can't 
> supply air to a radiator and you shouldn't waste your time trying 
> ***because the inventors said so***".  I'm only objecting to the very 
> last clause.  The authors might fully agree that a submerged inlet is 
> a perfect compliment to a streamlined duct. The submerged inlet 
> collects air in a low drag manner which it does well, and the 
> streamline duct is responsible for pressure recovery which IT does 
> well.  But we don't know that, 'cause they don't make any attempt to 
> speak to it.  I think it would be appropriate to assert that the 
> authors would agree with the statement that sticking a radiator 
> against the back end of a NACA inlet is only marginally better for 
> cooling than hanging it out the bottom of the fuselage.
>
> Having said all that,  Thomas' original statement is spot-on.  The 
> report authors did indeed recommend against using the NACA inlet as a 
> pressure-recovery device.
>
> Jim, the report Ed and I are discussing has a section on drag.  As I 
> read it, they didn't bother with a drag study because it is so low 
> with a submerged inlet.  All the losses due to drag end up as pressure 
> where it's needed.  If those NACA guys are to be believed, even though 
> the downdraft scoop was half the size, it will still have more drag.  
> Half of somethin' will always be greater than nothin' 8*)
>