Message-ID: <3F8D98D8.2030401@covad.net>
Date: Wed, 15 Oct 2003 11:58:32 -0700
From: James <MadScientist@covad.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: rooster-tail drag
References: <list-2638054@logan.com>
In-Reply-To: <list-2638054@logan.com>
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Hello:

I have frequently thought that  an NACA  turned 180 degrees (front to 
back) would make an excellent low drag outlet vent port.  The air flow 
passing over the leading edge of that configuration would create a 
partial vacuum helping to suck inside air out and the long extended V 
tail would help reduce vortex and turbulence, thus drag.  This is only 
an intuitive explanation.  I would enjoy seeing some experimentation 
with this idea.  Any takers?

James

Eric Rattan wrote:

> I have never seen a NACA scoop used to vent air FROM the aircraft BACK 
> into airstreams.
> I have reviewed all the NACA papers on scoops and have never seen this 
> effect described.  Please point us to any reference on the subject.
>  
> Respectfully,
> Eric
>
>     ----- Original Message -----
>     *From:* JJ JOHNSON <mailto:JJJOHNSON@ACCESSCOMM.CA>
>     *To:* Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
>     *Sent:* Wednesday, October 15, 2003 11:04 AM
>     *Subject:* [FlyRotary] Re: rooster-tail drag
>
>      What is roster tail drag? how and where does it get created? Is
>     there anything about that written up on the net?I'd like to know
>     since I'm in the process of figuring out where to put my radiators
>     in the Long EZ.ThanksMarko
>      
>      
>     Marko, Think of rooster tail drag as drag that's created when air
>     leaves the cowl at steep angle. The air, instead of turning and
>     moving along the side of the cowl like you'd think it would,
>     shoots straight out from the cowl for a small distance [ 6"  may
>     seem small but it will create a huge drag penalty!] Another way to
>     think of it is when your driving and you throw that apple core out
>     the window, notice how it goes straight out for a little bit and
>     then the on-coming air slows it down and it 'appears' to go back..
>     Air leaving the cowl of your plane will follow basically the same
>     sort of path. So if we smooth this exit we'll find that we reduce
>     drag. Its one of the reasons that NACA ducts are soooo  popular,
>     they create a very smooth exit [ the air is coming out parallel to
>     the side of the cowl and then as the duct narrows it is
>     accelerated and gradually pushed out into the normal airstream. So
>     simple yet it took years to understand it all.
>      
>     My 2 cents
>     Jarrett Johnson
>      
>      
>
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