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Composite part plugs and foam

Old 07-20-2007, 09:58 AM
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ByLoudDesign
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Default Composite part plugs and foam

I need to get someone to tell me what is the best foam to make plug for the landing gear(Wheel pants & struts) and the cowling. It will be removed after the part is completed. I also was thinking of making molds by using them as plugs before removing the sacrifical foam. There seems to be a wide range of them from beadboard to heavy structual foam with good sheer qualities. I have build things from 65' commercial fishing boats to dolphin hose cones, so the fiberglassing is not the problem. Although I think I will opt to go more into the carbon fiber and epoxy lamination. The plane is the Curtiss Goshawk (F11C-2 / BFC-2) in 1/4 true scale, plans ready now tieing up lose ends like engine selection, and vendor / manufacturer sources for hardware, like wheels, tires and brakes. Most vendors want to help up from but then you try and pin down how much and they get REAL iffy. I think it may be that they have a hard time with telling people how much for fear of them bolting away. Lets face it big projects take commentment of time and money. When you strat something like this a estimate it double or tripple the figure you come up with. I would have never bleived that it would take me two years just to do the plans.
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Old 07-20-2007, 10:08 AM
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DMcQuinn
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Default RE: Composite part plugs and foam

I use pink foam that I get from Home Depot. I can get it in 2 inch thickness (4'x8' sheet). I laminate thicknesses together to make parts thicker than two inches. I use a 3m 77 spray adhesive to join the two sheets as it sets up instantly and does not interfere with the sanding later. It shapes up pretty easily using saws and sandpaper and the resulting surface is fairly smooth (as compared to beaded foam). I cover this part with 6 layers of 6 ounce glass to make the male plug. This makes it strong enough to put a really hard finish on the plug. Then I make the female mold from this and then the final parts from the female mold.
Old 07-20-2007, 02:42 PM
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ByLoudDesign
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Default RE: Composite part plugs and foam

Thanks so much! I have been looking at that pink insulating foam wondering if it would work. Is polyester resin compatible or do you need epoxy?
Old 07-20-2007, 04:02 PM
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Default RE: Composite part plugs and foam

I always use epoxy resin (west systems), so don;t know about the polyester.
Old 07-20-2007, 04:12 PM
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Bill Jennings
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Default RE: Composite part plugs and foam

G'Day.
What a great project. Could you tell me a little more about the model you intend to build please? Thanks for your time.
Regards.
Bill.
Old 07-20-2007, 08:47 PM
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soarrich
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Default RE: Composite part plugs and foam

ORIGINAL: ByLoudDesign

Thanks so much! I have been looking at that pink insulating foam wondering if it would work. Is polyester resin compatible or do you need epoxy?
Polyester will dissolve the pink foam, or the blue or white, you'll need epoxy.

You might want to look into using UltraCal30 for your molds. You make the plug out of blue/pink foam, coat it with polyurathan paint, pour the UltraCal30 on it, remove the foam, you got a mold. Terry Luckenback did a video on it, google it, I did a thread on this or the other rc forum on a mold I made for my flying wing's fuse. I think I used about $7 worth to make my molds. If you go this was buy the video, lots of info.

Old 07-20-2007, 09:24 PM
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Default RE: Composite part plugs and foam

I can second Ultracal 30 for small molds. I even once cloned a BVM Bobcat fuse with ultracal 30. Beware though, the bigger the mold, the heavier it gets!
Old 07-21-2007, 10:47 AM
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Default RE: Composite part plugs and foam

Thanks for all the great input, I have made production molds for every thing between a dolphin(the animal) to Coast Guard 30' utility/surf boats, yes solid mold that hold their shape get heavy fast. I have worked with the West System t-88 and poly cloth on a little 17' run-about! So do you get the finish you need on the plug or polish the UltraCal30 mold?
Old 07-21-2007, 11:15 AM
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Default RE: Composite part plugs and foam

I always work the plug to exhaustion, and then work it more. Once I do a layup for a mold, I don't want to have to do anything else.

I use PPG K38 primer and then wetsand with 400 and then 600. Some people go further, but that's what I do.
Old 07-21-2007, 11:54 AM
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Default RE: Composite part plugs and foam


ORIGINAL: ByLoudDesign So do you get the finish you need on the plug or polish the UltraCal30 mold?

Ultra Cal 30 is like Plaster of Paris, but it gives you about 30 minutes working time, the mold is so hard it rings if you tap it. After you have the mold you let it dry for about 3 days, you think its dry in 2 hours, but it's not, then you wipe epoxy into the mold. After you wipe the mold with epoxy you wipe it all out, the UltraCal 3o absorbs some, after you do this three time you wax it then spray on PVA and make parts. Very good finish.
Old 07-21-2007, 12:14 PM
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Default RE: Composite part plugs and foam

Bill
I have for the past 2 years in my spare time developing a set of full scale plans for the Curtiss Goshawk originally designated the F-11C, put in production as the BFC-2. I spent a vast amount of time and several hundred dollars rounding up as much data on her as I could. There are only two known planes left in the world out of several thousand built. I have developed the model in ΒΌ true scale. Conventional construction; ply basswood and balsa with fiberglass cowling, landing gear covers and forward fuselage that is aluminum is real life. I and several others have guess-ta-mated her weight to be in the 40-50# range with a top wing span of 94-1/2” and over all length at 68”. I am planning on using a ZDZ 120 B2RV engine, but there are several that would work, especially on of the several radials in that same displacement range. Have w functioning tail hook, I dreamed up. Plan to offer the plans for sale when completed, and kits from just structure part all the way up to everything present to build the whole model. Have a vendor for the laser work on parts and a fiberglass outfit ready to make mold and part. I would not have believed that it would take so long, most of the time is on the enormous amount of details of construction need if you intend on marketing it. Its easy if you have the basic plan and do the rest in you head for your self, but want to make a 100% project out of it. If you would like to get further info or maybe a set of preliminary plans it could be arranged

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Old 07-21-2007, 12:30 PM
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ByLoudDesign
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Default RE: Composite part plugs and foam

Well the wheel pants are 15-1/2" x 6-1/2" x 2-3/4", can a thin shell be made and beef it up with glass on out side, How much UC30 would it take? The cowling is about the same size 14" dia. We would go to a mirror like finish on the plug if we did not want to post process the mold, and then it was a heavy coat of tooling gel then hand layer up 3/4 oz. chop, one layer at a time to make sure the heat stayed ata minimum. Bend up used water pipe and chop and fab-mat these like ribs and stringer, some time we got quit a surprise when it came time to turn it>
Old 07-22-2007, 03:50 PM
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Bill Jennings
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Default RE: Composite part plugs and foam

Thank you very much for your kind offer I would like to stay in contact and watch you progress with this project, At the moment I am up to my (you know what) in projects but I would love to follow you on this one.

Regards.
Bill.
Old 07-23-2007, 07:58 AM
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Default RE: Composite part plugs and foam

Sounds good to me, Bill. You have my off net email so email me and we can stay in touch!
Charlie

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