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Old 20th June 2006, 01:41 AM   #1
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Lightbulb Making Flared Ports

Im planning on making 6" Flared ports. My question is what is an optimal curve for air flowing at a maximum of 80ft/sec. Im not looking for quiet ports, im looking for maximum efficency. I would assume a parobalic curve. My Plans are to heat PVC up in oil then push it over a mold of clay with the aid of a scafold type frame around it, controlled weights, and a heat gun.

I figured this would be the best place to ask this kind of question.

If you are thinking "80ft/sec, that is fast" this is an SPL install, im doing dual 6" ports on a frainken incriminator audio death penulty that i am building from an elemental designs e12a's TC9.

I have a goal of 147dB on term lab if you are wondering. I will be compeating dB Drag Street B.
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Old 20th June 2006, 05:17 AM   #2
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Quote:
My Plans are to heat PVC up in oil then push it over a mold of clay with the aid of a scafold type frame around it, controlled weights, and a heat gun.
This sounds like an uncontrollable mess, I seem to remember pvc getting stringy when melted. Also, once you have a clay mold you can simply lay fiberglass or carbon fiber around it.
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Old 20th June 2006, 07:00 AM   #3
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You might be interested in the work I've done on flared ports.

I only used a circular profile for the flares, but the writeup on using a heat gun over a mold could be useful, as could the test results.

Follow the links at
http://www.users.bigpond.com/bcolliso/port-flares.htm


For 6 inch PVC pipe I found that 30mm flare radius was the best I could obtain before splitting became a problem. Here's a photo of it....
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File Type: jpg 6in-2piece.jpg (15.8 KB, 580 views)
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Old 20th June 2006, 01:00 PM   #4
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Very informative link.

Molding PVC is actually not a hard process if you take your time, and i want to use PVC becase then I can use PVC fittings and ends and lots of duct tape so when tuning for SPL I can swap port tuning frequincies with ease.

Fiberglass would probably cause problems, i would do that IF it where a fixed port. But I have some-what unlimited acess to a Term Lab pressure sensor so i can do a sweep, change the port and let the coils cool, then do anotehr sweep.

I could also make the fiberglass ends work with the PVC but it would be so expensive i may as well use PVC.
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Old 20th June 2006, 03:08 PM   #5
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Have a look at these by Guillaume Pellerin, Jean-Dominique Polack and Jean-Pierre Morkerken, from the 112th AES (Munich - 2002) and 116th AES (Berlin - 2004):
http://www.haliaetus.com/AES_112th.pdf
http://www.haliaetus.com/AES_116th.pdf
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Old 20th June 2006, 06:08 PM   #6
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what a FREAKING excelent read.

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Old 20th June 2006, 06:50 PM   #7
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Sure do wish i understoo the advanced college calculus though...i got the gist...i just dont get all the equasions. which is ultamitly all i need. Ill probably save thoes to my computer and give my self a crash course in advanced calculus over the next few weeks to see if i can better understand it.
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Old 21st June 2006, 12:46 AM   #8
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Or, go down to your local model rocket hobby store, take measurements (carefully) and expand them to your requirements. You'd have to a bit of experimenting with regard port length, but thats what plumbing supply stores are for. You'll probably find it's the same deal as flared ports - your 'flare' adds a specific length to the lenght of the port and calculations can be done via Unibox or WindISD after that.
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Old 21st June 2006, 01:43 AM   #9
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Or i could do that, but some of thoes formulas optimized the nozzle for certian velocities...but yeah.
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Old 21st June 2006, 05:05 PM   #10
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I don't live in spaces big enough to need ports on my subby. I just use cone area and a bit of oomph and room gain does the rest.

Correct, for your needs (dB Dragging) you'll probably need optimisation. But the actual length and volume should be able to be determined on length and volume of the port. The shape can be formed to account for these parameters - in essence, the shape of the outer areas on the nozzle is very close to parabolic and the volume can be calculated as such.

I found some easier to read references on the design of rocket motors (they are, after all, trying to get gassed to flow in a straight line - without vortices - as you are). The gist appears to be that most efficient is whe pressure at the exit of the nozzle should be the same as amient pressure. Shape is determined by the best way to get the gases to flow along the walls of the nozzle - and it's not a parabolic, maybe hyperbolic? It's been too long since school (and I have watched too much soccer this month).
http://www.braeunig.us/space/sup1.htm
http://exploration.grc.nasa.gov/educ...et/nozzle.html
http://members.aol.com/ricnakk/th_nozz.html
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