Anyone cut a NACA duct into a Givi? - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 9 Old 08-17-2009, 11:48 PM Thread Starter
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Anyone cut a NACA duct into a Givi?

I searched. Nuthin. Just wondering if I could buy a Givi for $112 and cut the duct myself, saving me $88 in the process.

Would anybody be kind enough to make a rubbing of their NACA duct and scan it with a ruler in the picture for scale? or, if you were really clever, list the dimensions?
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post #2 of 9 Old 08-18-2009, 02:25 PM
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More than you will ever want to know:

http://naca.central.cranfield.ac.uk/...a-acr-5i20.pdf

http://ntrs.nasa.gov/archive/nasa/ca...1993085898.pdf

http://www.recumbents.com/wisil/nacaduct/naca-duct.htm

Here is the best one; an Excel spreadsheet that will calculate the form of the duct when you input the dimensions:
http://sports.racer.net/tech_info/ae...calculator.xls

Last edited by Dr. M; 08-18-2009 at 06:58 PM.
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post #3 of 9 Old 08-18-2009, 08:00 PM
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Is the angle of the windshield really ideal for use with a NACA duct?

I thought these were intended for relatively shallow angles of attack. (If I recall correctly, the shape causes vortrices to go into the duct and cause very little interuption of the airflow behind the duct.)

Is there any benefit at the steep angle of a windshield?

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post #4 of 9 Old 08-19-2009, 11:08 AM
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My Givi is working pretty well with a Madstad. Not sure you would need a duct?

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post #5 of 9 Old 08-19-2009, 05:55 PM
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This should be of help...if not helpful, it is pretty interesting. It got me thinking of heading for the garage and giving my Dremel a little exercise.

http://www.chris-longhurst.com/nacavents/


Quote:
Originally Posted by OompaLoompa View Post
I searched. Nuthin. Just wondering if I could buy a Givi for $112 and cut the duct myself, saving me $88 in the process.

Would anybody be kind enough to make a rubbing of their NACA duct and scan it with a ruler in the picture for scale? or, if you were really clever, list the dimensions?

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post #6 of 9 Old 08-20-2009, 06:37 AM Thread Starter
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Woah, Dr. M. You nearly blinded me with science.

Quote:
Here is the best one; an Excel spreadsheet that will calculate the form of the duct when you input the dimensions:
http://sports.racer.net/tech_info/ae...calculator.xls
Do you happen to have this in another form? I don't have Excel.
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post #7 of 9 Old 08-20-2009, 08:31 AM
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Not really

All the NACA ducts I've seen (admittedly, in cars and airplanes) operate at very shallow angles of attack, which is to say that the incident airflow is nearly parallel to the surface in which the ducts are placed. The idea was to induct air through the surface (usually for cooling) without disturbing the relatively laminar flow along the surface, and thus increasing drag. Except for the very thin boundary layer, this is not true of a windshield. So the whole idea of a NACA duct becomes a hole in the windshield, I'd expect. Probably better to enlarge the vent at the base of the windshield, so the fairing directs the air up the back side of the windshield. The 'NACA ducts' shown are vents from the high pressure side of the windshield to the low-pressure side, and are unlikely to generate much flow up the backside, as the sharp edges will separate the airflow from the back surface. Of course, I could be wrong. Anyone got yarn-tuft pictures at speed? Of course, you could add deflectors behind the 'ducts' to attach the incoming air to the back surface.

Last edited by Jimding; 08-20-2009 at 08:34 AM.
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post #8 of 9 Old 08-20-2009, 08:54 AM
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Originally Posted by OompaLoompa View Post
Do you happen to have this in another form? I don't have Excel.
openoffice.org, it's free and it will read Excel (and other office-type apps).
post #9 of 9 Old 08-20-2009, 09:12 AM
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Quote:
Originally Posted by Jimding View Post
All the NACA ducts I've seen (admittedly, in cars and airplanes) operate at very shallow angles of attack, which is to say that the incident airflow is nearly parallel to the surface in which the ducts are placed.
I agree. Givi screens don't have a NACA duct on them, all they have is a NACA-duct-shaped-hole. It could be square or round or anything else and accomplish basically the same thing since nothing is being ducted.

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