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Old Sep 18, 2012, 09:31 AM
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Freddie B's Avatar
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I use clear tape either Scotch 3/4" or cut strips of packing tape.
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Old Sep 19, 2012, 06:44 AM
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Waltjg's Avatar
Crystal River Fl.
Joined Jul 2008
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Bill, I just use the clear packing tape on the exhaust, I don't use anything on the intakes, as fan is usually secured by screws and fit is pretty good. W
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Old Sep 19, 2012, 01:48 PM
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BillO's Avatar
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OK, thanks.
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Old Sep 28, 2012, 03:49 PM
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San Francisco & Santa Cruz
Joined Oct 2004
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Exhaust duct in blue foam

Hi guys, some news from the world's slowest build! I realized that the exhaust duct design wasn't right before I started building it, so it was back to Sketchup. I am finally starting to get the hang of it after many days of practice.

The new design starts with a conical section with the shroud diameter at one end and 100% FSA at the other, long enough to clear the motor fairing. I totally left out that piece on the first design for unknown reasons. Then it splits into 2 half-circles, each with area 50% FSA (for a total of 100%). Each of those transitions to a full circle of the same area. This is the start of the nozzle, which ends with a 90% FSA circle. That's a lot of transitions in a very short distance.

I had to move the fan forward about an inch because the motor fairing is longer than the one on the Detrum unit. Anyway, it's kind of cool to see the part in reality after seeing it for so long on the computer.

The plan is to make the duct from two layers of 1.7 oz Kevlar using the lost foam process.
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Old Sep 29, 2012, 04:35 AM
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United States, WA, Vancouver
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Iam no expert on exhaust ducting, but that looks pretty good to me, nice job cutting that foam out!

Joe
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Old Sep 29, 2012, 02:57 PM
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Thanks Joe -- what do you think about the layup?
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Old Sep 29, 2012, 03:36 PM
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United States, WA, Vancouver
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its been sooooooo long since I have done any glass work, I do remember the last intake/exhaust I did was lost foam too, I used 2 layers of the litest Sig glass cloth I could get, stuff was like tissue paper almost, then I used carbon fiber ribbon to add "hoop" supports and some longitudinally on the sides and top/bottom for torsion support, used polyester resin to lay it up, then let it sit for a week to get good and hard, then dumped lacquer wash in it to get the foam out, came out EXTREMELY lite and very very stiff

Joe
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Old Sep 29, 2012, 09:28 PM
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OK -- was that for a 70mm fan?
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Old Sep 29, 2012, 09:33 PM
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nope, 90mm fan
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Old Sep 30, 2012, 09:13 PM
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BillO's Avatar
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Ahh, so maybe I'll just use 1 layer of the Kevlar then. Thanks!
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Old Oct 07, 2012, 03:08 PM
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San Francisco & Santa Cruz
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Here's my duct, it's only 11 grams! It's really too flimsy so I'm going to add more Kevlar. Hopefully just another 5 or 6 grams.

At this point, I have to go back to some other projects, so it will be a while before I get back to this one. Still, I have learned a lot and it's been fun. Thanks a lot Joe!
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Old Oct 07, 2012, 03:20 PM
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Crystal River Fl.
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Bill, it doesn't have to be super strong as the force works all the way around, I use a .005 Mylar for my exhaust ducting and it works great, but I'm not sure about the bi-fulcral exhaust you have there, anyone have any experience with this?? I know on intakes it needs mto be strong as the suction will collapse it if it isn't. BTW,,, what is your exhaust opening? Is it 85% of FSA??? W.
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Old Oct 07, 2012, 10:37 PM
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Hi Walt, the opening is 1.6" dia. X 2, i'm hoping that is 90% FSA. I must have checked my math a dozen times...
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Old Oct 07, 2012, 10:55 PM
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United States, WA, Vancouver
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hey Bill,
for the exhaust side that should be perfect, for the intake side put the CF ribbon on in "hoops" every 2" or so that should keep it from collapsing from the suction side.

and you are quite welcome, hope to see you finish up on this one soon!

Joe
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Old Oct 09, 2012, 09:21 AM
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Denver CO
Joined Apr 2008
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Billo,
Those look awesome for the first time around!

Im still squeamish about doing glass ducts.
Maybe i should try on the next one.
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