REFLECTOR: Cooling

[Velocity Aircraft Owners and Builders list]

I use modified armpit scoops.  They are mounted 3/4" out from the fuselage and have an internal venturi for improved pressure recovery.  I have included a clip from a Flying Magazine article that explains the popularity of misapplication of NACA inlets.

Larry Coen

N136LC



North American's bad experience-and those of others, such as Long-EZ builders who tried to use them for engine cooling air-did not put paid to the NACA scoop. Today we see them everywhere, and they are widely used in precisely the applications-engine induction and cooling air inlets, oil radiator inlets, fuel tank vents, cabin ventilators, all sorts of mysterious apertures on Firebirds and Lamborghinis-for which the original researchers deemed them unsuitable.

Why? Different designers probably have different motives. Many applications require peak performance at only a narrow range of flow rates anyway, and so efficiency losses at off-design points can be tolerated. Even though they are not really drag-free, submerged inlets certainly produce less drag than protruding ones do. They have practical advantages; one is that they're easy to fabricate-much easier than a pitot-style scoop with a boundary-layer channel. NACA scoops are popular with amateur builders, some of whom are probably in the dark about the mechanism of their operation, but assume that if they're used on some airplanes, they must be good for all.

Other reasons are more frivolous. NACA scoops look nice. They don't appear to clutter up the surface of the airplane the way protruding inlets would. They at least seem as if they produce no drag. And that double-ogive with its gently sinking floor is an elegant shape that just feels aerodynamic in an undefined sort of way. Looks matter. When reason fails, follow your heart.


Read more at http://www.flyingmag.com/scoop-naca-scoop#2DDXHD907wXdp5Bi.99


From: Velocity Aircraft Owners and Builders list 
Sent: Tuesday, June 24, 2014 11:21 AM
To: reflector at tvbf.org 
Subject: Re: REFLECTOR: Cooling


Hi Jeff, 

Yes, I had armpits on my STD-RG for many years.  I've got a few pictures of an oil study I did along the way that I can send if interested (the reflector doesn't like pictures).  In net, the issue I saw was that because there isn't any expansion area aft of the armpit scoop to slow the air down, it tends to back up and flow mostly around the scoop. 

My advice - bite the bullet and install the roof mounted NACAs.  Do a good job on the NACA inlet.  You will be extremely satisfied with the results. 

Send me your email address if you'd like some oily pictures.  I'm trying to figure out how to upload them to a photo album on the VOBA website... 
  
Dave

Dave T. Nelson
T/L 553-4327, Voice 507-253-4327, Fax 507-253-3648
Program Director, ISC ECAT NPI & Test Engineering 
      - To: "reflector at tvbf.org" <reflector at tvbf.org>  
      - 
      -Subject: Re: REFLECTOR: Cooling 

- Anyone have experience with VGs on a 173RG with the older armpit scoops? If so please send a pic and explanation. 
- Appreciate it, Jeff 
  
- Thank you, Jeff
- TEAM JEFF Real Estate

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- PRES.-Wasatch Co Association of Realtors
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