Matronics Email Lists :: View topic

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

naca inlets

Matronics Email Lists Forum Index -> Kitfox-List

View previous topic :: View next topic

Author Message

icubob(at)newnorth.net
Guest

Posted: Thu Aug 07, 2008 2:41 am Post subject: naca inlets

hi all,

  anyone had any experience with turning a naca  vent ''backwards'' to ''pull air'' from the cowling? does it work?

                                  bob noffs

    [quote][b]

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Thu Aug 07, 2008 3:33 am Post subject: naca inlets

 	  Quote: 	
		   From: bob noffs [icubob(at)newnorth.net]

  anyone had any experience with turning a naca vent ''backwards'' to ''pull air'' 

 from the cowling? does it work?


	


I am sure it will work and create a Venturi effect since it goes from a smaller to a larger volume, Bob. But there might be even better designs. It could be fun to experiment with e.g. cardboard shapes and water in a transparent tube hold in an air stream, like the window of your car, to see which shape works best.

The 'lip' at 45 degrees that I moulded under my cowling to cool the Jabiru works extremely good; I probably have the coolest engine installation. But with aerodynamism, it takes very little to see things go wrong. For example, I was told of another very similar installation where the bottom of the aft end of the cowling has a L-shaped bar and that was enough to invert the flow of air.



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200 ... grounded

<pre><b><font size  color="#000000" face="courier new,courier">

_________________
Kitfox 3 - Jabiru 2200

lcfitt(at)sbcglobal.net
Guest

Posted: Thu Aug 07, 2008 7:12 am Post subject: naca inlets

I doubt it.  There was an article on NACA vent design in one of the 

magazines a time back when I was working on the Lancair.  It described the 

shape for optimum performance - sharp edges at the surface inlet junction. 

This got me thinking that there is more to the shape than the curvy outline. 

I think the shape is designed to draw air from a rapidly moving laminar flow 

airstream.  As it crosses the edge, it rolls into the duct and actually 

compresses the air passing through the duct.  I don't think you would find 

that same efficiency moving air from the cowling to the outside airflow.



A solution might be suggested by looking at a lot of airplanes - 

professionally designed and see what they have done.  I have never seen a 

backward flowing NACA duct on any airplane other than an "experimantal.



Lowell

 	  Quote: 	
		   From: bob noffs [icubob(at)newnorth.net]

  anyone had any experience with turning a naca vent ''backwards'' to 

 ''pull air''

 from the cowling? does it work?

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Thu Aug 07, 2008 9:55 am Post subject: naca inlets

Maybe also look at some Nascar applications...I've seen NACA ducts  

used there, but it seems like it was always on an "ingoing" air  

application.

Lynn Matteson

Kitfox IV Speedster

Jabiru 2200

Status: "Condition grounded, but determined to try."  (Pink  

Floyd..."Learning to Fly")

On Aug 7, 2008, at 11:08 AM, Lowell Fitt wrote:

 	  Quote: 	

 <lcfitt(at)sbcglobal.net>

 I doubt it.  There was an article on NACA vent design in one of the  

 magazines a time back when I was working on the Lancair.  It  

 described the shape for optimum performance - sharp edges at the  

 surface inlet junction. This got me thinking that there is more to  

 the shape than the curvy outline. I think the shape is designed to  

 draw air from a rapidly moving laminar flow airstream.  As it  

 crosses the edge, it rolls into the duct and actually compresses  

 the air passing through the duct.  I don't think you would find  

 that same efficiency moving air from the cowling to the outside  

 airflow.

 A solution might be suggested by looking at a lot of airplanes -  

 professionally designed and see what they have done.  I have never  

 seen a backward flowing NACA duct on any airplane other than an  

 "experimantal.

 Lowell

> From: bob noffs [icubob(at)newnorth.net]

>  anyone had any experience with turning a naca vent ''backwards''  

> to ''pull air''

> from the cowling? does it work?

>

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

bigboyzt0yz

Joined: 29 Jan 2008
Posts: 29
Location: Centeral Maryland

Posted: Thu Aug 07, 2008 11:47 am Post subject: Re: naca inlets

The placement of mine might be in the wrong place right now. I looked at several photos of Doug Kelly's Kit fox and put them where they did. 

 The other week someone pointed out that there was a outline on the cowl painted over that was directly in line with the area where the front half of the engine cowl had a attachment point and no exit for the engine air( hot air). On a normal day below 80 degrees it is just fine but on the high air density days the air coming in is warm that is till you get to 3K ft. I just free handed my vents and molded them in place. 

 I spoke to John King and he said that he just opens the door 3/4 of a inch and it is plenty of air. So maybe the next person will not go through putting them in and just open the door a little (KISS).

IMG_8503.JPG

Description:

Duct Rt Side

Filesize:

1.92 MB

Viewed:

466 Time(s)

_________________
Lee Fritz in Owings Mills Md. 2002 KitFox-IV Classic/912UL/Warp drive taper tip/100% Complete ( Extras Strut fairings08, Grove gear09,) 300 hrs since Aug 07 "Have your feet on the Pedals and keep reaching for the sky".

mikeperkins

Joined: 22 May 2007
Posts: 123

Posted: Fri Aug 08, 2008 8:02 am Post subject: naca inlets

Bob,   

   

The NACA submerged duct will not work backwards. The 1948 NACA report on ducts discusses a pressure build-up based on vortices produced by the edges of the inlet that energize the slow-moving boundary-layer air. The vortices increase in size from front to fore to aft (with the serpentine shape of the edge aiding in that). Turning it around does not allow the vortices to form.   



 One note to everyone installing a NACA submerged duct - - the edges of the duct should be as sharp as possible. Many builders round off the edges. But since the duct is based on vortices, rounding them off reduces their effectiveness.   

   

The NACA report is available at http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930093809_1993093809.pdf  

   

Mike Perkins  

      [quote][b]

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Fri Aug 08, 2008 10:10 am Post subject: Re: naca inlets

I made really snazzy NACA Ducts for my cabin ventilation, never 

could get the cabin cool enough. So I popped in some Snap Vents

in the side windows which pop open and act like great big air scoops.



Can adjust from no air to hurricane in the cabin now, so I'm happy.



Moral of the story, super slick high tech isn't always the best solution.



Regards,

Jeff

icubob(at)newnorth.net
Guest

Posted: Sat Aug 09, 2008 3:49 pm Post subject: naca inlets

---

lkc(at)juno.com
Guest

Posted: Sat Aug 09, 2008 6:37 pm Post subject: naca inlets

Not to be dence, but what is naca?   



____________________________________________________________ 

[url=_blank]Earn ATM Machine Profits While You Sleep. Simple and Easy. Click Now.[/url]

  [quote][b]

propellerdesign(at)tele2.
Guest

Posted: Sat Aug 09, 2008 8:34 pm Post subject: naca inlets

National Advisory  Committee for Aeronautics

 [quote]   ---

Display posts from previous:

	Matronics Email Lists Forum Index -> Kitfox-List	All times are GMT - 8 Hours
Page 1 of 1

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum