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  #11  
Old 10-09-2018, 10:37 AM
BMC_Dave BMC_Dave is offline
 
Join Date: Mar 2017
Location: Seattle, WA
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Interesting to learn a bit of history of the NACA scoop and the (non) reasoning it's used in GA.

https://www.flyingmag.com/scoop-naca-scoop
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  #12  
Old 10-09-2018, 10:39 AM
terrye terrye is offline
 
Join Date: Feb 2010
Location: Vancouver, BC, Canada
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Default NACA Inlet

Quote:
Originally Posted by Volumex View Post
So to paraphrase, they are great for air-breathing engines but don't use them for vents.
The original goal of this NACA AR 5I20 investigation and report was to find the suitability of low drag inlets for jet engines, so it is no surprise that the summary specifically mentions this. For example, see figure 38, second to last page where the inlets are shown on the fuselage sides just ahead of the wings. In this position they do not recover much if any ram pressure and you never see them employed in this manner. However, numerous smaller NACA vents are used on the nacelles of pod mounted jet engines for various purposes. They are also used as general purpose low drag inlets.

An earlier post mentioned they should be placed in an area where the fuselage cross section is increasing. A more general statement would be they should be placed in a flow field with a positive pressure gradient. If placed in a flow field with a negative pressure gradient they will act as an exit vent (and not very efficiently). There are lots of examples of poor placement like this on race cars and some aircraft.

To the OP's question, the NACA inlet is not drag free, but I don't think you could measure the difference in speed of your aircraft between one NACA inlet and two.
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  #13  
Old 10-09-2018, 10:45 AM
lr172 lr172 is online now
 
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Location: Schaumburg, IL
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Quote:
Originally Posted by Marc Bourget View Post
To obtain the design benefit of a NACA scoop you should put it in an area where the fuselage cross-section is increasing. Also pay attention to the "bar" across the aft end of the opening. Proper design requires a substantial radius (compared to most installations seen).

FWIW
Is this "radius" in the 90* corners or a radius'ed edge to the vertical oriented cut in the skin?

Larry
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  #14  
Old 10-09-2018, 10:49 AM
lr172 lr172 is online now
 
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Thanks for all of the input. It is much appreciated!

Larry
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  #15  
Old 10-09-2018, 10:51 AM
rdrcrmatt rdrcrmatt is offline
 
Join Date: Oct 2014
Location: Milwaukee, WI
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We have them in both sides, no drag difference (same TAS at a power setting) before and after them.
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  #16  
Old 10-09-2018, 12:40 PM
lr172 lr172 is online now
 
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Good data to know. Sounds an extra scoop may be in my future.
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  #17  
Old 10-09-2018, 09:19 PM
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vfrazier vfrazier is offline
 
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Location: Mount Vernon, IN
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Put the scoop under the wing if possible.

While I only have 2 firm data points, my RV-4 and my F1 Rocket had 11 degree F HOTTER air coming in the fuselage sides than from under the wing. The thermometer doesn't lie.

Believe me, on a 90+ degree OAT day, the fuselage scoops were downright HOT!

YMMV!
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  #18  
Old 10-12-2018, 10:15 AM
cholladay cholladay is offline
 
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Location: San Antonio
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For the over head console. I am not sure it matters but I put mine on the left side behind the baggage door. I also have a valve on a servo to help to control airflow. I have tons of air. I sealed up the Vans rear vents during construction. The back seat passengers only use the overhead console. They have never complained about benign to hot.
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  #19  
Old 10-13-2018, 08:41 PM
Marc Bourget Marc Bourget is offline
 
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Quote:
Originally Posted by lr172 View Post
Is this "radius" in the 90* corners or a radius'ed edge to the vertical oriented cut in the skin?

Larry
It's the inlet edge that's perpendicular to airflow. The "corners" where the curved side edges is 90 deg.

FWIW
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