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10-27-2009, 03:26 AM
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Join Date: Jul 2009
Location: New Zealand
Posts: 54
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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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10-27-2009, 07:25 AM
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Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
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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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10-29-2009, 08:04 AM
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Join Date: Jan 2005
Location: Sedona Arizona
Posts: 349
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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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11-04-2009, 12:36 AM
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Join Date: Nov 2005
Posts: 1,256
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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
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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__________________
Steve "Flying Scotsman"
Santa Clarita, CA
PP-ASEL, ASES, Instrument Airplane
RV-7A N660WS flying!
#8,000
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11-04-2009, 10:54 AM
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Join Date: Nov 2008
Location: Kansas City, MO
Posts: 120
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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
Last edited by N54SG : 11-04-2009 at 05:25 PM.
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11-04-2009, 11:24 AM
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Join Date: Jul 2009
Location: New Zealand
Posts: 54
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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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11-04-2009, 12:34 PM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Quote:
Originally Posted by N54SG
... 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...
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Good point that is lost on most people. NACA ducts have to have sharp edges to maximize efficiency/air flow.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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11-10-2009, 04:20 AM
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Join Date: Jan 2005
Location: England
Posts: 1,087
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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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01-08-2010, 09:58 PM
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Join Date: Dec 2006
Location: Kalifornia
Posts: 466
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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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01-09-2010, 07:05 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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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?
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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