The Murphy Builders Site

Can someone point me to data or information on
how to size a NACA submerged inlet? I know there
are many NACA inlets. I am thinking of the one
that looks like a Hersey Kiss from the side, low
drag, etc. I'd like to figure out how to size
one given airspeed and airflow requirements.

Scott Hibbs
hibbs@pacifier.com



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Hi Scott,

Tony Bingelis describes and diagrams how to build NACA or NASA vents in his
books "The Sport Plane Builder" and "Sport Plane Construction Techniques." If
you don't have his books you should buy them, they are worth there weight in
gold. He also wrote another book called "Firewall Forward" that is very
helpful before you begin installing your engine.

Bruce G



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Hope these little comments aren't annoying, but FWIW I have the
impression that NACA vents really are not the answer at the speeds we
fly. Yes they look cool but there is not really any performance
advantage for the work involved until you get to a significant
percentage of the speed of sound.

Please share you findings. Sorry I can't recall any references other
than a search of the online NACA files.

Ken

Can someone point me to data or information on
how to size a NACA submerged inlet? I know there

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Ken, they are not annoying at all. That is what
the forum is all about. Let me clarify my goals,
then please comment.

I want air inlets that have very little drag. I
don't mind the extra work or size if I can get
the pressure I need for the engine intake or the
oil cooler AND have low drag. If an external
scoop provides the above and has similar drag
characteristics at the speeds we fly, then I
would just use an external scoop.

Scott

Hope these little comments aren't annoying, but

FWIW I have the

impression that NACA vents really are not the

answer at the speeds we

fly. Yes they look cool but there is not really

any performance

advantage for the work involved until you get

to a significant

percentage of the speed of sound.

Please share you findings. Sorry I can't recall

any references other

than a search of the online NACA files.

Ken

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Hi Scott

OK but remember my thoughts come from observation and reading so they
are somewhat general. A method proven on a Rebel always means more.

I'm aware of some NACA inlets on the sides of cowls and fuselages that
did not work very well. Any intake will tend to work better on the
bottom of the cowl where the pressure tends to be higher. The exhaust is
as important as the inlet though. A nice diverging inlet duct to slow
the air prior to the heat enchanger followed by a converging duct that
speeds up the air and exhausts it into a low pressure area is more
important than the type of inlet for a low drag system. Note that much
of the drag from a cooling system is determined by the speed of the air
past the heat exchanger. In effect this is what a Cessna 172 cowl on a
Lycoming does (in a crude fashion) when you think about the air flow. A
nicely designed system will often let you cut the intake and exhaust
areas in half, which definately cuts the drag. And most heat exchangers
work fine (sometimes better) at lower velocity airflow than our cruise
speed. A scoop will tend to draw in more air and have more drag than a
NACA inlet but neither will work well if the exhaust is poor.

There are also scoops that did not work well even on the bottom of the
cowl until the scoop was moved out an inch or two from the cowl like a
snorkel. Note the famous Mustang cooling inlet. Also you don't generally
want the scoop too close to the propellor as the passing blade may tend
to suck some air back out.

So yes I believe there is generally no advantage to a NACA inlet
compared to a well placed scoop a Rebel for engine and oil cooling.

Ken

scott.hibbs@dcsol.com wrote:

Ken, they are not annoying at all. That is what
the forum is all about. Let me clarify my goals,
then please comment.

I want air inlets that have very little drag. I
don't mind the extra work or size if I can get
the pressure I need for the engine intake or the
oil cooler AND have low drag. If an external
scoop provides the above and has similar drag
characteristics at the speeds we fly, then I
would just use an external scoop.

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HI Ken

I have the NACA vents, 1 per side. If I had to rely on them to keep me cool
in the summer, I would die in there. Best to use an eyeball vent. Bought
one from Van's & the air coming through that device is terrific. One is
great. Don't think you need two. And I like lots of air.

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
klehman@albedo.net
Sent: Friday, June 08, 2001 10:54 AM
To: murphy-rebel@dcsol.com
Subject: Re: NACA inlet data


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Hope these little comments aren't annoying, but FWIW I have the
impression that NACA vents really are not the answer at the speeds we
fly. Yes they look cool but there is not really any performance
advantage for the work involved until you get to a significant
percentage of the speed of sound.

Please share you findings. Sorry I can't recall any references other
than a search of the online NACA files.

Ken

Can someone point me to data or information on
how to size a NACA submerged inlet? I know there

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G'day Brian #328R

Interesting what you have about the NACA vents.

I would like to know just where and how how you fitted the "eyeball" vent

Regards

Ian Donaldson






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Hi Ian

I had some free panel space on the right hand side e.g. the passenger side
panel. I bought an eyeball vent kit from Vans Aircraft & plumbed with SCAT
tube. An amazing amount of air comes through there. I love it.

I suppose the NACA scoops may work well if you find the perfect location but
how many holes do you want to put into your lovely craft before you find the
sweet spot?

Regards

Brian #328R

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
allsure
Sent: Monday, June 11, 2001 9:06 AM
To: murphy-rebel@dcsol.com
Subject: Re: NACA inlet data


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G'day Brian #328R

Interesting what you have about the NACA vents.

I would like to know just where and how how you fitted the "eyeball" vent

Regards

Ian Donaldson



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G'day Brian

Thanks for your reply. I hope you don't mind, but I would like to ask a few
more questions.

What did you connect the eyeball vent up to?
Did you use a NACA vent, or some other scoop arrangement?
Where did you locate the inlet?

Thanks in advance

Regards

Ian Donaldson





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Hi Ian

I ran 2" SCAT tubing right up from the right cowl nostril. I installed 2
air inlets there. One goes to the heat muff & the second directly back thru
the engine compartment to the vent. I did not use a NACA vent just a
standard 2" round flange riveted to the engine baffling.

This really works well. Extremely happy with it. As I stated previously,
the little NACA vents mounted on the sidewalls are really Mickey Mouse by
comparison. I would not be able to fly in the otherwise hot cockpit without
this mod.

Hope this helps.

Brian

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
allsure
Sent: Friday, June 15, 2001 6:16 AM
To: murphy-rebel@dcsol.com
Subject: Re: NACA inlet data


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G'day Brian

Thanks for your reply. I hope you don't mind, but I would like to ask a few
more questions.

What did you connect the eyeball vent up to?
Did you use a NACA vent, or some other scoop arrangement?
Where did you locate the inlet?

Thanks in advance

Regards

Ian Donaldson


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G'day Brian


Thanks for your reply. Now that's a good idea!

We get our share of heat here in Australia and I was concerned at just how I
could get a good airflow into the cabin.

Thanks


Regards

Ian Donaldson
----- >




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