Hi all, I am building a plug for a small f-18 which will be my first time doing a fiberglass fuse. I know you have to do the mold in two halves but I don't know if I need to do it in top/bottom halves or left/right halves. The thing that is causing me problems is the wing/fuse fairing... it slants down a bit so I would think if you did the left/right halves the layup would get trapped in the mold and top/bottom halves I think you would need a very curved skert to follow the lines of the fairing. Anyone know how to go about this?
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Joined: 3/1/2002 From: Rancho Santa Margarita, CA, USA Status: offline
My solution isn't anything special. It's simple b/c it's been done by so many people.
You can do a left and right half and have the wing/fairing nub very short. There might be a small undercut when molding, but it should be able to pop out no problem. I’ve done larger molds with some pretty good size undercuts and the parts popped out no problem.
If you don’t want to do this, do a top and bottom. Use a Sharpe and mark the parting line on the mold. The parting line does not have to be straight. It can be as curved and wiggly as you want. You then need to attach a parting board to that line. See [url]www.ctsales.com[/url] for a tutorial on how to do this. Wax and PVA the mold. Then lay down a surface coat of resin. Use something to thicken the resin up just a little (like Microballons). Make sure you push the mixture into all the corners (including the corners where the mold intersects the parting board). Let this begin to cure until it is tacky. Then lay a piece of light oz cloth over it. Let fully cure (couple days). Then start building up the layers until it is pretty darn thick (3/16”-1/4”). Let cure a couple days. Then remove the parting board. Wax the other side, including the lip of the glass that was created from the parting board and repeat. Then let the whole thing set a week or so. Then pop the molds off.
It’s really not that hard. There’s a lot of other guys on here that have done this as well. There’s also a wealth of information as to how to do it. Research a little and you’ll find it. Email me if you have any questions, suggestions, or corrections.
Thanks for the info, it is going to be for the Toki .18 unit and the size is 35.5 span by 50 length. another thing I noticed with doing the right/left mold is at the bottom of the fuse near the tail cone and where the front fuse meets the belly the mold will curve in towards these grooves which I think would lock in the fuse in the mold... do you know what I mean and is this a concern? Thanks again for the help.
Posts: 263
Joined: 3/1/2002 From: Rancho Santa Margarita, CA, USA Status: offline
If you could email me a sketch, CAD model or pict I could better help you out. Also, I'm interested in what you're doing. Email me and let's talk about some possible opportunities, if you're interested.
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Joined: 2/16/2002 From: Palm Bay,
FL, USA Status: offline
Do a top and bottom mold for the F/A 18 your seem should run from the nose to the lex and follow the lex to the tail straight. You will have no problems pulling parts from this.
Posts: 263
Joined: 3/1/2002 From: Rancho Santa Margarita, CA, USA Status: offline
I've done both. Personally, I think you can get a better surface if you use the foam. Make sure you use a high density foam though. It's easy to cut to get the shape close to the formers, then sanding it exact. When you're done, do two layers of a 3oz fiberglass cloth and sand that surface.
If you use the wood, I found that if you don't sand it perfectly, you'll see the edges of the planks in it. Even if you glass over the wood, it's hard to get the edges out.
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Joined: 1/19/2002 From: Anchorage,
AK, USA Status: offline
One detail you may want to investigate, if you're doing top/bottom molds, instead of left/right molds....
The shape of most of these jet fighters is roughly cylindrical, but I've noticed when doing CAD models of these things, that relative to the center "waterline" of the plane, the noses tend to slope downward from roughly the cockpit area to the tip of the nose.
What this means is that, to avoid getting your plug (and later, parts) trapped in the mold, the parting board must slope downward in the front. I recently did a large Long EZ, which has the same trait.
Here's an image of the molds, where you can see the slope. Basically, you want the parting board to stay on the centerline, (or let's say the widest part of the structure) and that's why mine had to be cut, then angled down at the nose.
< Message edited by Mike James -- Jul 31 2003 12:31PM >
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Mike James RC Design and Building - www.nextcraft.com
Thanks guys, I am doing the top/bottom mold and I'll make the parting board curved to match center line. I also got some pink foam yesterday and glued the pieces in place[what kind of glue do you guys use for this?] after some thought I figured it would give a better finish as well. Today I will sand the foam back so it should start to look like something but I do not have a digital camera yet so I can't post pics, I do have a couple of people who take pictures for me but they are both on vacation right now until next week. I will post pics as soon as I can though. Do you think it would be better to do an all composite jet or have the wings and fins foam/balsa? Also retracts or no retracts?
Posts: 2464
Joined: 1/19/2002 From: Anchorage,
AK, USA Status: offline
Sticking foam blocks together:
I use epoxy for this job, mixed with microballoons, but I'm careful to only glue the "centers" of the blocks, so that when I sand the blocks to shape, I'm not sanding any epoxy seams.
PS on the parting board "curve"... I didn't actually "curve" mine, but instead I scored it, propped it all up (on the plug) at the right angle, and then used some hardwood blocks to bridge the scored area, so it would retain the shape.
Can't wait to see your results. Good luck. (and hey! Buy a digital camera, with some extra memory... It's worth it.)
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Mike James RC Design and Building - www.nextcraft.com
Thanks, the plug is going well and I have the sanding very close, it actually looks like an F-18 now and is getting me excited! What would a guy do if he got to excited and sanded a little to much in one spot Do you fill it up before you glas it and what kind of filler do you use...dry wall filler?
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help with f-18 plug - 
help with f-18 plug - 
Do you fill it up before you glas it and what kind of filler do you use...dry wall filler?