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  #1  
Old 10-27-2009, 03:26 AM
Dragonfly Dragonfly is offline
 
Join Date: Jul 2009
Location: New Zealand
Posts: 54
Default NACA type airbox intake

Not directly RV related but thought there may be a few people here who had done this or seen it done or had an opinion on the idea.

I am looking at using this NACA style scoop as an intake to a filtered airbox (its actually for a Pitts Special - carburated O-320).



It will be placed in the usual place, about 1ft below the spinner with the narrow portion towards the top, the intake hole is 2.5". With the slope of the cowling the intake hole is essentially facing directly forward.

Just wanted opinions on if it is likely to work well or if I'm wasting my time.
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  #2  
Old 10-27-2009, 07:25 AM
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F1Boss F1Boss is offline
 
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Default Well, maybe

It might work (only sue to its location) -- but this type of intake does not generally produce any MP increase on piston engine intake systems due to 'ram effect'. You would be better off with a scoop sized to about 2x the fuel controller throat area, and try to include an expansion area that allows the air to slow a bit, but it would seem to me that this won't be possible in this particular installation...

That is a nicely done part indeed!

Carry on!
Mark
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  #3  
Old 10-29-2009, 08:04 AM
Randy Randy is offline
 
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Location: Sedona Arizona
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Default

I recently installed a similar inlet up towards the front of my RV7A. Results are not great but I do think I am getting a bit of MAP increase from it. I was able to form mine in such a way that the opening is straight in, the air does not have to turn.

I plan to experimt with the installation of a "helper scoop" to see if it increases the MAP any. I have seen 30.5" down on the deck at speed.

My inlet air foes through a K&N Appollo then in the engine..

Randy C
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  #4  
Old 11-04-2009, 12:36 AM
Flying Scotsman Flying Scotsman is offline
 
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I like the looks of this for use in place of the white plastic Van's NACA scoop...would it fit as a direct replacement in the appropriate locations on the side of the fuse in a -7? (That is, are all NACA scoops identical, I guess?)

Quote:
Originally Posted by Dragonfly View Post
Not directly RV related but thought there may be a few people here who had done this or seen it done or had an opinion on the idea.

I am looking at using this NACA style scoop as an intake to a filtered airbox (its actually for a Pitts Special - carburated O-320).



It will be placed in the usual place, about 1ft below the spinner with the narrow portion towards the top, the intake hole is 2.5". With the slope of the cowling the intake hole is essentially facing directly forward.

Just wanted opinions on if it is likely to work well or if I'm wasting my time.
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  #5  
Old 11-04-2009, 10:54 AM
N54SG N54SG is offline
 
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Default

If you look at the fast guys, the real fast guys, (Relentless, Nemesis) all of their engine air intakes stick out from the cowl. I assume to get away from the boundary layer generated by the spinner. My cowling is the same way. I think the only way to get a NACA duct to work properly is if it is mounted on the side of the aircraft in a way that the pointy end it facing the relative wind. Even then, it has to be done perfectly. That carbon NACA duct looks good, but it seems to have rounded edges on the "ramp". That I think can defeat the entire purpose.

For a good read on induction inlets..

http://www.n91cz.com/InductionSizing...izing_rev0.pdf
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Last edited by N54SG : 11-04-2009 at 05:25 PM.
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  #6  
Old 11-04-2009, 11:24 AM
Dragonfly Dragonfly is offline
 
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Default

I'm starting to agree and will probably change the way I attack this not. Its not a true NACA duct in the sense of the word.

I will probably go to a protruding intake as you mention above, tried and true method which works and is easy enough to do.
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  #7  
Old 11-04-2009, 12:34 PM
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N941WR N941WR is offline
 
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Quote:
Originally Posted by N54SG View Post
... Even then, it has to be done perfectly. That carbon NACA duct looks good, but it seems to have rounded edges on the "ramp". That I think can defeat the entire purpose...
Good point that is lost on most people. NACA ducts have to have sharp edges to maximize efficiency/air flow.
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  #8  
Old 11-10-2009, 04:20 AM
penguin penguin is offline
 
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I started my career at Hawker Siddeley in Kingston, one chap who was very knowledgeable on air intakes dismissed the NACA duct as a way of getting significant amounts of air inside an aeroplane. His view was that any intake worth its name must stick into the airflow and grab some air - otherwise you just don't get any mass flow down the intake. If he was pushed further his opinion was that most 'NACA ducts' that he had seen weren't really as they did not correctly implement the required shape - (see here). My guess is that the person who moulded the duct in the picture copied something else not very well and didn't look at the original spec. For an engine intake I would get something out into the airflow!

Pete
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  #9  
Old 01-08-2010, 09:58 PM
RVadmirer RVadmirer is offline
 
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Location: Kalifornia
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Default That Chap....

....must never have seen Rutan's canards. Over half of those flying, and certainly the most efficient ones, have NACA inlets for engine cooling. They work really well when done properly.
Very true that it has to be shaped correctly to do what it is designed to do and many have butchered them up and wondered why they didn't work, including me.....
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  #10  
Old 01-09-2010, 07:05 AM
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DanH DanH is offline
 
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Default

You'll get some dynamic pressure recovery with most any hole below the spinner just because of location...see a fuselage CFD pressure plot.

As for canard cooling intakes, most with NACA ducts are in the armpit area?
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