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Old Nov 29, 2008, 09:02 PM
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Question
Genious or Idiot build ideas

Has anybody tried using heatshrink over foam to strengthen it up? I was thinking about the stuff used to go over battery packs. Figured it might add significant strength to the foam as a hard skin. Downside is that it might be too heavy. Any thoughts?
Also, has anybody tried sandwiching foam in between aluminum flashing as a way to strengthen a fuse? Mostly for somehting like a tail boom section that would otherwise be reinforced with bamboo or CF.
Just throwing the ideas out. Trying to think of new ways to strengthen foam without too much weight or cost.
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Old Nov 29, 2008, 09:56 PM
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Mikey C.'s Avatar
Oxford, PA
Joined Aug 2003
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Unfortunately, the heat you need to apply to heat shrink would probably melt the foam underneath. As for Al flashing, that's feasible but I think 1/32" plywood is just as strong and lighter, but I am not sure. Hey wait a minute, I have both, I'll go weight a sample. brb...

Ok, I just weighed equal sized samples, and it looks as if the ply is marginally lighter than the Al, I mean almost no difference. I only had about a 1g sample of ply left over from my latest project though, but it took my scale maybe two seconds to show 1 gram for that as opposed to an instant reading for the Al.

Scientific, I know.

Cheers~
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Old Nov 29, 2008, 10:04 PM
I'm a Registered User
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Heatshrink probably wouldn't work. Standard covering films like Monokote can add considerable strangth to foam though. Even packaging tape can add a great deal of durability.

Aluminum may be an acceptable covering if used on bigger, more powerful planes. You'd need the extra power and wing area to offset the weight gain. Might be good for leading edges of wings and controls for extra durability on smaller stuff. You'd have to be careful not to dent it though as you'd have no good way to get the dents out.
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Old Nov 29, 2008, 10:59 PM
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Thanks
Where might one get 1/32 plywood?
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Old Nov 29, 2008, 11:07 PM
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thewz's Avatar
Temecula
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Quote:
Originally Posted by nikg
Thanks
Where might one get 1/32 plywood?
Michaels craft store has it.
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Old Nov 30, 2008, 08:05 AM
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Kingston, Canada
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Doculam works very well on Depron to strengthen it. Low heat to shrink it and it's sticky back to start with. You can get it at Staples and it's cheap.

Gord.
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Old Nov 30, 2008, 02:00 PM
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Actually heat shrink can work. If you live in the northern regions, you can get heat-shrink material that is used to add another insulating layer to leaky windows and patio doors. I spray the model with 3M super 77, place the film as smooth as you can put some masking tape along the perimeter of the piece ( so that it does not get pulled back while heating) then heat with a hot air gun or hair blower. the stuff is about1-2 mils thick so it does not add much weight. the plane below has increased weight by 1.2 oz on a AUW of 20oz.

Wb
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Old Nov 30, 2008, 03:59 PM
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Sandwiching between .007" CF increased strength 4000% (40x) with only 12% added weight.
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Old Nov 30, 2008, 08:07 PM
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And where would one get CF? I'm assuming that it is a sheet of carbon?
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Old Dec 01, 2008, 12:49 PM
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Quote:
Originally Posted by nikg
And where would one get CF? I'm assuming that it is a sheet of carbon?
I ended up getting .007" and .014" from local speed shop. Had to buy 4'x2' sheets which is lifetime supply. I'm sure you can get it online too. If you want a couple small strips to experiment with PM your address and I'll pop some in a letter envelope.
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Old Dec 03, 2008, 10:59 AM
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1/64 ply from michaels etc...

About as thick as construction paper. Seems a little floppy. Cuts easily with scissors

Should be able to get a full sheet (about 12x20 for $10.00) Awesome stuff. Many uses.

Control horns: Cut out and dab a little glue around the hole for strength

laminating inbetween or over foam for strength. Use PU glue "lightly spread out with popsicle stick. Great for stiffening up motor mounts, making firewall mounts etc...


Cut strips about 4mm wide. Cut all the way thru foam and cover slot with PU (gorilla, sumo, etc...) Only use a little!!! Install strip into foam and once dry it's just as stiff as Carbon tube.

I use the strips for stiffening wings, tails (verticle and horizontal), fuse's.

Also makes great elevator joiners if glued flat at the hinge line.

edit: next post, little guy on right. You can just see the ply fuse stiffner running from canopy back. Hasn't broke yet. Another one hidden in the paint lines thru the wing.
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Old Dec 03, 2008, 11:04 AM
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Got another one for ya.

Buy some colored tissue paper.

Coat the tissue with Water Based Polyurethane using a small sponge.

Place on peeled foam and spread another thin coat on top. Allow to dry and the foam is stiff as a board.

TIP: You can cut out pieces of tissue and spray glue to regular paper. Run em thru inkjet printer and VIOLA, dressed up foamy.

Little guy on left
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Old Dec 03, 2008, 12:04 PM
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"Temper" foam with heat gun til dull surface becomes shiny will approx double stiffness. Learned from Gene Bond.
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Old Dec 03, 2008, 08:27 PM
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Quote:
Originally Posted by DRITCH
Buy some colored tissue paper.

Coat the tissue with Water Based Polyurethane using a small sponge.
I use this method - and add in some of those paints from Michaels (those $1 2 oz cheapo acrylic enamels) to the WBPU. Either that, or I've been known to use the glucohol method that I read about here, and again use the cheapo paints for colour. You won't beat the price (if you're looking for cheap) using either of these methods. You'd be surprised at how little weight is added vs. the strength added. Get the tissue paper from a Dollar Store.

http://www.rcgroups.com/forums/showp...&postcount=492

Brad
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Old Dec 03, 2008, 08:48 PM
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I wouldn't use Al flashing or heat shrink - they are both too heavy (and the heat shrink would probably melt the foam underneath). You can get 1/64" plywood, but that stuff is kinda heavy too. If I need heavy re-inforcement of any foam parts, I use cereal box board laminated on with PU glue. Otherwise I use tissue paper - run the grain in one direction on one side, and the grain in the other direction on the other. You can tell the "grain" of tissue paper by how it tears.

Don't knock bamboo. I bought a window blind that was 48" wide by 64" long, and now have a lifetime supply of bamboo sticks that are 48" long for $13. I'm guessing I have about 600 of them - call it 2mm/ 3/32" diameter (again a guesstimate). Think I paid $13 for it. Use them as longerons in the fuse (all 4 corners) and you'll have a fuse that's incredibly stiff and strong, although not quite as light as one built without the bamboo.

Brad
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