Fuse layup bubble problems - RC Groups
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Jul 17, 2012, 12:26 AM
BillO's Avatar

Fuse layup bubble problems

I finally have some time to lay up a few more fuses with my first mold. It's a fairly simple shape about 44" long for a 72" span pitcheron. I've laid up 4 so far, and every one has a number of bubbles that have to be popped, filled, and sanded. Typically there is a very thin layer of resin over the bubble.

I am not using a bladder or press of any kind. This is an unreinforced mold so I'm just doing simple hand layups with a wet seam. Pinholes don't seem to be a problem, most of the fuse surface looks great.

The bubbles are in different places every time, but they tend to congregate in 3 places -- the v-tail flats at the back, around the edge of the canopy step-down, and along the seams.

I'm thinking many of these bubbles may be embedded in the splooge used in these 3 areas. I did a search an came up with this thread that suggests whipping the splooge somehow to reduce bubble size. Unfortunately there is no real conclusion, at least Adam doesn't report success.

Are there any other suggestions, otherwise I'm about to give my old Aero-latte a trial out in the shop!
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Jul 17, 2012, 12:56 AM
Just fly it!
wyowindworks's Avatar
Wow, BillO is alive!

Hmmmmmm....those pesky bubbles. I don't whip the sploog. That never did solve my problem. A few things that might help around the canopy and and stab area:

1) Paint a thin layer of sploog into the area before piping it in.
2) Pipe the sploog into the corner with a baggy with the corner just nipped off. This will often pop larger bubbles as the sploog is pushed out of the hole.
3) Use a brush to "smooth" the sploog into an nice ramp or fillet. This again can pop bubbles within the sploog.
4) Tune your eyes to see those pesky things while your are doing the layup
5) Don't use sploog at all but rather pieces of carbon tow or glass rovings. I usually use about 3 pieces of 12K carbon in the corners. I dip the tow into the resin, squeegee it off with my fingers, lay it into position, and then tap the whole length of the piece twice with the tip of my brush to push out the air. This is more timely but much stronger, more durable, and less likely to leave bubbles behind.

It looks like your seam bubble is sploog related so the above thoughts would apply there as well. If you are getting larger bubbles on the seam then I can give you some time tips to help remedy that.

Who still leaves a few bubbles behind now and then
Jul 17, 2012, 10:23 AM
Composites guy
A couple of questions:
1. does the fabric ply stop near the canopy spooge line or continue up to the canopy opening?
2. do you cut the fabric flush at the parting plane?

1. The jog in the tool where you are putting spooge has a thickness change. If the spooge is attempting to make up that difference, the fabric is not wetting the tool( which supports it) but rather spooge which can allow the cloth to locally pull away from the tool. The fabric when getting trimmed or just due to leverage/weight may slump away from the spooge area since there is no pressure to hold it there and it must fight gravity.
2. If you look at the part from the nose, think of it as a clock face. If the material is trimmed to the parting plane( say at 12 and 6 O'clock), then all the fibers are cut adjacent to the parting plane. IF instead we slightly rotate the lay-up as viewed fromt he front to say 12:30 and 6:30 we will have some open tool face on the OPPOSITE tool where we can make the seam. Clear? Why do this? The cut fibers tend to bleed air and the parting plane is a known gap in the tool where this air will come to the surface. If this happens against the tool, the wetting action of the tool will hold the ply and can supress the void formation. clear?

Jul 17, 2012, 10:52 AM
BillO's Avatar
Hi Adam, well yes it has been a long time since I have done any serious building. Thanks for your suggestions!

On this fuse I did try painting splooge into the corners, but I think the combination of #1,#2,#3 may be more effective than #1 by itself. Using glass rovings is a very interesting idea, but I wonder if that will look OK as the surface layer. Only one way to tell I guess.

If you have some suggestions about the bubbles in the seam, I would love to hear them -- the seam bubbles in the photo look plenty large to me!
Jul 17, 2012, 11:02 AM
BillO's Avatar
Hi Scott, thanks for the tips. Let's see:

1. The fabric does not stop at the corner of the canopy lip, it continues up over the stepdown. I use templates to cut the fabric beforehand so no trimming is done until after the layup is cured and the fuse is removed from the mold. I see what you mean about the fabric sitting on splooge and not the mold face but I thought that was the point of putting it in there.

2. On the seam, I use the "stagger" technique as described by Adam. The first layer is positioned so the fabric is flush or a little lower than the parting plane, with a lap sticking up on the other side. One side has the lap on the top seam and the other side has the lap on the bottom seam. After sliding the two mold halves together, I roll the seam.
Jul 17, 2012, 08:31 PM
Not landing late ever again
threcixty's Avatar
Try "dabbing" the seam, i.e. not pulling lengthwise while setting the seam. Use a flashlight, and try to see if there are any bubbles when you are done from whatever access you have to the middle of the mould, and fix those with something resembling an arrow shaft with a wire clothes hangar that has a small bend on it to push the fabrics back down.

I found that cabosil and fillers in a non-pressurized mould that is not on the parting line or 70-90 degree angles in the mould cause more harm then good. The cabosil encourages bubbles in some places. If you use a flashlight and take your time, cabosil is almost not required except for extreme angle changes.

Jul 18, 2012, 12:06 AM
BillO's Avatar
I was wondering about that Jim -- not using cabosil in the seam that is. Today I laid up a tail cone as follows:

1. Painted some unthickened resin over the whole mold.
2. Piped some splooge into the corners using a baggie with a pinhole in it. I could feel and hear 3 good-size bubbles pop as the splooge went through the pinhole.
3. Used a brush to smooth out the piped splooge.
4. Wet out the glass and put it into the mold, trying not to press it into the splooged area.
5. Painted some very runny splooge with hardly any cabosil along the laps.
5. Joined the mold and rolled the seam.

Can't wait to see how it turns out!
Jul 18, 2012, 03:18 AM
Registered User
I think most of the typical solutions have been covered.
-Try to keep bubbles out of the resin, when mixing. Mixing to agressively can add lots of bubbles. Common ways to remove bubbles from the cup is by vacuum, vibration, centrifuge, or heat.
-Try to minimize adding bubbles as you apply the resin. Longer motions usually add less bubbles than many short application strokes. Work fast, since the longer you mess around the thicker the resin gets, making it harder to apply without adding bubbles.
-Remove as many bubbles as you can afterward. Several methods are a stipple brush, rollers, a scribe to pop/pull the bubble out, or a little heat. A vacuum bag combined with heat works wonders, but still best to start with as few bubbles as possible.
Jul 18, 2012, 12:42 PM
Composites guy
On the bubbles in the seam-" I stagger a flush or a bit lower than the parting board"- Try to increase the "bit" lower to at least 1/8" so that the cut fibers in the opposing tail can match up on the opposing tool face. keeps the air which flows from the cut fiber ends from ending up in the parting plane.
Jul 18, 2012, 05:59 PM
BillO's Avatar
OK, I was thinking that low would cause a problem, but I will give it a try on the next fuse based on your advice. I will also try a "seam dabber" rather than a "seam roller" and no cabosil on the seam.

Thanks for the tips!
Jul 18, 2012, 10:32 PM
Not landing late ever again
threcixty's Avatar
Use some 3k tow in the very sharp corners on the outer layer. I always painted the mould with epoxy, let it bead up (water on wax type of thing) then carefully pressed enough tow into the sharp corners to "round them out". Kevlar tow on the front if you are going for a 2.4 thing.

Get a nice bright flashlight to look for airbubbles. I did not pressure mould the nosecones on my planes, or my earlier pods. Using a flashlight, it is fairly easy to spot bubbles, and if you take a long stick with an acid brush and a bit of epoxy, you can remove such bubbles. It takes patience until you get the groove going.

"Push" the brush towards bubbles. DO NOT "paint" the bubbles.

Pressure moulding is definately the way to get rid of bubbles. That in itself is a steep learning curve though!
Jul 18, 2012, 11:55 PM
BillO's Avatar
Yeah, I'm not going to do pressure molding. Probably I need to learn how to eliminate bubbles for the most part anyway.

So I popped out yesterday's tail cone and it doesn't look much different. Some small bubbles on both top and bottom seam. I could live with a couple, but 8-10 is too many on a part this small!

Next one will have to wait until next week...
Jul 19, 2012, 09:54 AM
Registered User
heliwill10's Avatar
Would the torch trick work? I guess it might be hard on the mold. And only work in areas where no fabric would have a meltdown
Jul 20, 2012, 07:30 PM
Twisted and Confused
flyonline's Avatar

how green are you letting it get before joining? I found it easier to let it green somewhat, and I think I ended up with less bubbles, though it might have just been an increase in experience.

Bladders in un-reinforced molds aren't a big deal, I do my rotor with a big open canopy with a bladder and only get really low pressures but it still helps.

Perhaps you are using too much splooge in the corners so that it moves around when you're rolling the seam down?

That's a nice fuse shape anyway, and there can't be too many TWFs

Jul 20, 2012, 11:36 PM
Not landing late ever again
threcixty's Avatar
Cut your acid brushes down a bit, to around 1/2". You can use CA to attach the bristles to the brush if they try to come out. Use a bright light to make sure you do not miss bubbles when you join the moulds. They will show up as an opaque white blotch.

Use as little epoxy as possible. If you are flooding the thing, it can get bubbly. Also, maybe try to paint the moulds first if that would work. Make sure that you are wetting the fabrics from the bottom up, i.e. paint the mould, then lay in the cloth. Even if the epoxy beads up on the mould, it will still work to prevent most bubbles.

Using a bright light will really help with finding bubbles. If you get them during the initial layup, then none should appear later.

Good luck!

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