Received-SPF: none
 receiver=logan.com; client-ip=140.172.240.2; envelope-from=bdube@al.noaa.gov
Message-Id: <5.2.1.1.0.20041021101039.025c10a8@mailsrvr.al.noaa.gov>
Date: Thu, 21 Oct 2004 10:21:06 -0600
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
From: Bill Dube <bdube@al.noaa.gov>
Subject: Re: [FlyRotary] Re: Cooling version 2.2
In-Reply-To: <list-481369@logan.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"; format=flowed

Steve,

At 06:49 AM 10/21/2004 -0400, you wrote:
>Bill,
>
>Actually, where the scoops are located, they are outside of the fuselage,
>and the only thing in front of them are the wing strakes.

         It was hard to tell in the photos, but are they 3 or 4 inches away 
from the fuselage?

>   I didn't measure
>from the strake leading edge to the scoop inlet, but I would estimate that
>it is between 3 to 4 feet.  I guess that would mean that there is a boundary
>layer of about .6 to .8 inches present at that location.
>
>If the boundary layer air becomes an issue, I will either put a small air
>dam ahead of the scoop, or as I did with the NACA, install a vortex
>generator ahead of the scoop.

         The problem is the difference in pressure/velocity between the 
boundary layer and the free air stream. The free air stream turns around in 
the scoop and air comes OUT in the portion of the scoop next to the wing. 
It's just like making a big slot in the back of the scoop, but results in 
much more drag.

         A scoop like the one on the bottom of the P-51 is what you want to 
have.


         An air dam will not be as effective as spacing the upper lip of 
the inlet away from the bottom of the wing.


>I thought that I might have a photo that shows the scoop in relation to the
>wing, but looking at the ones that I took, none really show it very well.
>
>Regards,
>Steve
>
>-----Original Message-----
>From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On
>Behalf Of Bill Dube
>Sent: Wednesday, October 20, 2004 8:19 PM
>To: Rotary motors in aircraft
>Subject: [FlyRotary] Re: Cooling version 2.2
>
>
>At 05:55 PM 10/20/2004 -0400, you wrote:
> >Attached are a couple of photos of my lower cowling. It is minus 2 small
> >armpit scoops, and plus 2 larger scoops.
>
>          I notice that these scoops include the boundary layer with the air
>they scoop in. Isn't this a problem, especially near the fuselage?
>
>          The boundary layer grows at something like a 0.2 inch per foot of
>length. This rule of thumb would imply that you would need to space the
>side of the scoop about 3 to 4 inches from the fuselage. The upper lip
>should be something like 1.5 inches off the underside of the wing.
>
>          If you don't space the scoop away from the surface of the
>airplane, you create a lot of drag and you don't take in much air.
>
>          Perhaps there is some key point I'm missing.
>
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html