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Old Jul 22, 2012, 09:34 AM
Father of Fr3aK, DLG Pilot
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Are you guys using balloons or bladders? I've never gotten anything other than petroleum jelly to work on a 1/4" stem with balloons. I tried soap after Gerald and I spoke a few weeks back... disaster. Maybe with a 1/8 stem but no way on a 1/4" stem.

Molds are jigged up and ready. I forgot how much work they can be. My goal was to go from concept to finished product in a week. Since I started drawing the wing on Tuesday that means I have to get skins in tonight to join tomorrow and pull Tuesday.

I suspect it may not be a week Maybe 8 or 9 days.
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Old Jul 22, 2012, 12:49 PM
G_T
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I put a drop of liquid soap on the end of the fill stem, and slide the balloon on far enough to get to the inflation hole. Then I inflate the balloon. Then the inflated balloon slides easily down the stem. I tried to show it in the pictures a few pages back.

Gerald
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Old Jul 22, 2012, 12:52 PM
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I use an aproximately 1/4" diameter brass tubing stem. Baby powder works great, try it, you'll like it. I tried, very briefly, Gerald's soap method and it didn't work for me. Likely it does work, but I had no incentive to put the time into learning the nuances of the technique. No nuances needed for the baby powder method. Just get some on the stem and the balloons don't stick anymore.
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Old Jul 22, 2012, 01:00 PM
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Aha! Gerald posted while I was typing. The part I missed was the inflation of the balloon before sliding the balloon over the stem. That would prevent the balloon from contacting and sticking on the stem while you slide the balloon in place. So his liquid soap is just lubing the balloon opening which is all that contacts the stem with his method. The baby powder will lube the entire stem without making a big mess and allow the balloon to slide in place easier.

I actually follow Tom's method that he shows in his fuse molding video. I inflate the balloon, stretch it out to help lengthen it, let it sit for a while, then insert the baldder stem while thye balloon is still inflated. With baby powder on the stem, you have the freedom to slide the balloon up and down the stem a bit in case you don't get it exactly right the first time. I guess, in an ideal case, you only need to lube the first little bit of the balloon since that's all that needs to touch the bladder stem, if you get it just right the first time.
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Old Jul 22, 2012, 01:16 PM
G_T
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When I'm doing it I don't pre-stretch the balloon. Actually I don't want to stretch it at all. I figure if you maximize the length you are reducing its ability to expand width-wise or even length-wise as needed in the mold cavity.

I just infate to the end but don't pressurize more than that. Then I slide it down the stem. At the bottom, I roll it over itself (very easy when inflated) to pull it down to the desired length. Then drop pressure, and it mostly clamps itself in place. A little trimming, and tape to taste.

Gerald
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Old Jul 22, 2012, 05:19 PM
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Tom and I are using 2" x 60" or 3" x 50" balloons as opposed to Gerald's 1" x 60" balloons. Tom and I don't worry about the balloons ability to stretch width-wise.
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Old Jul 22, 2012, 05:51 PM
Jim C
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There is a comment somewhere here, but I will just nod.
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Old Jul 22, 2012, 06:15 PM
But I am learning
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I am with Jim.

Brian P.
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Old Jul 22, 2012, 06:26 PM
hot air rises...
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Finally a conversation I can relate to...
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Old Jul 22, 2012, 06:32 PM
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Gerald
I think i have read your explanation on how thats done somewhere else. Hmmmm .....oh ya a condom wrapper .Lol
Gavin
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Old Jul 23, 2012, 01:33 PM
But I am learning
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Quote:
Originally Posted by Gavin Trussell View Post
....oh ya a condom wrapper .Lol
Well we know there is no plagiarism issues then.....

Sorry Gerald, could not resist

Brian P.
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Old Jul 23, 2012, 01:42 PM
G_T
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You never know what people will pick up and pass on...

Gerald
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Old Jul 23, 2012, 02:55 PM
Jim C
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A little eye candy
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Old Jul 23, 2012, 03:38 PM
Father of Fr3aK, DLG Pilot
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USA, OH, Worthington
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Hmm... air fittings, tail molds, drinking straws, and a Fr3aK wing.

Nice
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Old Jul 25, 2012, 10:26 AM
Father of Fr3aK, DLG Pilot
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Cat is out of the bag

So many of you know I'm playing with some new production methods and tooling. One week ago yesterday I made the final decision on airfoil and planform. My goal was to get a molded wing produced in less than 7 days from idea to part in hand. Unfortunately I won't make that goal, but I certainly will make it in under 10.

Here are some pictures of my newest tooling. The first wing from this tool isn't using any carbon in the D-box but rather is just using a tow along the LE and over the drag spar in addition to the main spar. The skins are just bias glass, no disser. I don't think it will be as stiff as the production Fr3aK wings but I think it will be certainly sufficient. I'm trying to see how light I can go while still being stiff enough for a strong launcher. Target weight is 130g, but the inner skins are a pinch resin rich (shiny) so I suspect that 135g is probably more likely. I'll make the next one lighter and prettier

The tooling is much more refined. The corian is doubled up on the top surface before machining to make it stiff enough for solid core compression molding. The frame under the mold surface is engineered much more carefully than the old frame was. The bottom surface skin molds are still separate, but will likely be joined as well after a few pulls. You can see in the pictures that the tips now perfectly conform to the mold, and the tip shape is more gracefully molded than the original Fr3aK allowing easier blade installation and placement. This wing was designed to be hinged from root to tip without tabs. This wing also was molded with the flapperon and TE in cruise position rather than reflexed. This saved a bit of work in finishing.

Tools have been made to bevel the windows in the rohacell where the top and bottom skins meet over the hinge line. Reto brought this up in a separate thread several months ago and most of the production Fr3aKs have been built this way. Getting the two skins together in this "window" keeps launch forces on the hinge line from pulling the skin away from the rohacell, and greatly reduces the possibility of soft hinges down the road. Thanks for the input Reto, and thanks to Phil for applying it to the process.

I'll post pictures and flight reports of this "test" wing as I get it removed from the molds and flown. I anticipate pulling it tomorrow before work, and trimming / finishing / installing servos tomorrow night. Flights will come this weekend and it will be a #2 backup for me at the NATs next week.

Friday evening and Saturday will be busy with finishing up a customer build and packing for the trip.
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