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Mar 18, 2011, 06:17 PM
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My first lost-foam fuse


I'm building a smallish pylon plane similar to a Slipso or a Sokol. I decided to get a little crazy and make a lost-foam fuse for it, and I've got my plug all cut, shaped and sanded. Firewall is drilled and attached, and all that's left is ... the glass

Right now I have enough 0.75oz and 1.50oz cloth to fiberglass a small country, but I'm not sure if either of those are the right weight to do this kind of thing. I figure I'd be best off using a denser weave, but will I be ok with what I've got or should I get something else? And how many layers of glass should I use?

Also, I have no epoxy on hand so I'll be picking up some more. I was thinking a slow-cure epookie would be best for this job, but what should I be looking at? 15 minute? Half-hour? 24 hour? I'd like to be able to use leftovers for other modeling purposes, so I'd like to avoid going with super-long-curing types if possible, though I know more time will be better for a first attempt.

Hmmm... I guess what I'm looking for is really just a quick lost-foam tutorial
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Mar 19, 2011, 05:38 AM
Grow old disgracefully!
dickw's Avatar
For building in a mould I use a total of 7.5 oz per sq metre of glass cloth for a fairly lightweght fuselage, so around 4 or 5 layers of your 1.5 oz cloth may be about right if you don't have anything heavier. I use one layer of 6 oz glass and one layer of 1.5 oz glass with an extra layer of 6 oz in the high stress areas (nose & wing mount).
However - for lost foam building you will probably need to do some sanding of the outside of the fuselage, so will need a heavier layup to start with.

Forget curing time for the epoxy, you really need a low viscosity "laminating" epoxy with a "working time" of around an hour to get the glass in place before the epoxy starts to set. Laminating epoxies usually have a curing time of 12 hours or more, but leave the fuselage for at least 24 hours before trying to do anything with it.

You might get better information by asking in the Composites forum:- https://www.rcgroups.com/composites-fabrication-210/

Dick
Mar 19, 2011, 01:01 PM
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Cool. Thanks for the help; I'll be sure to report back with how it turns out

*If you hear any news reports of someone accidentally fiberglassing their arms to a table, you'll know what happened*
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Mar 19, 2011, 01:07 PM
The Kid
Thekid3418's Avatar
In my experience when working with finishing resin you may want to thin it even further then it already is. What you use to thin it depends on the material you're working on. When working on wood I usually use denatured alcohol, but this obviously won't work on a foam plug...

Kid
Mar 20, 2011, 11:37 AM
f5b-uk
Mike Seale's Avatar
Using various brands of laminating resin I've never found the need to thin it but having a warm workshop helps.

Mike
Mar 20, 2011, 10:50 PM
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Quote:
In my experience when working with finishing resin you may want to thin it even further then it already is. What you use to thin it depends on the material you're working on. When working on wood I usually use denatured alcohol
It is a common practice but is not advised. The alcohol will not all evaporate before the reaction occurrs(in fact it is almost imossible to get all the alochol to release from just the straight epoxy part A unless you heat it). The epoxies affinity for the alcohols hydroxl group interference with the reaction and give a weaker product.
It is Ok if you are using the epoxy to seal wood to make fuel proof etc, but is not good if you are using it as the resin in glass/carbon structures.
Mar 20, 2011, 11:03 PM
The Kid
Thekid3418's Avatar
Quote:
Originally Posted by David H
It is a common practice but is not advised. The alcohol will not all evaporate before the reaction occurrs(in fact it is almost imossible to get all the alochol to release from just the straight epoxy part A unless you heat it). The epoxies affinity for the alcohols hydroxl group interference with the reaction and give a weaker product.
It is Ok if you are using the epoxy to seal wood to make fuel proof etc, but is not good if you are using it as the resin in glass/carbon structures.
Well, that is extremely valuable insight! Something to note for the next time I need to glass something

Kid
Mar 21, 2011, 02:01 AM
hul
hul
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I'm not an expert, but have built these lost foam fuses: https://www.rcgroups.com/forums/show....php?t=1392764 and https://www.rcgroups.com/forums/show....php?t=1302684.

I have taped the plug (brown packing tape) to prevent epoxy soaking into it. Need to take care to prevent wrinkles, small pieces of tape (2"x2" or smaller) work best.
I used 160gr/m2 (~4oz) first but that was too stiff, 105gr/m2 (3oz) worked better for me. The smaller of the fuselages (similar size to yours) has 3 layers to behind the wing saddle and 2 behind that and some carbon to stiffen the nose. It is quite soft but plenty strong. I'd remove the plug after 3 layers and see if you like the result. You can add layers if you don't.
Definitely use laminating epoxy.

Hans
Mar 21, 2011, 08:53 AM
Caution:Makes sharp left turns
Troy's Avatar
TP16, I would go find a small kit of West Systems with slow or fast hardener and do it right from the start or you're wasting time IMHO. I have done small parts with hobby-grade epoxy and it ends up being more flexible than you would want in a fuselage. If you start thinning it with solvents then you're softening it even more. If you store the West Systems well (pumps taken off the cans) it will last you for a couple years easily for many more uses in the future. You can sheet wings, build molds, build more lost foam parts, etc... If the goal is light weight for performance then using a good laminating epoxy will produce stiffer parts that are lighter.
Mar 21, 2011, 12:03 PM
Sure it'll work
Flyextreme's Avatar
+1 on the WestSystems. Back when I used to have time and space to build from scratch, I found WS to be the choice. It's very tough, and you can chooose from (if I recall) 3 or 4 curing speeds. Me and my buddies ran some sample test against 3 or 4 other popular epoxies...all agreed that WS was the best, by far, for our needs which was...a 60" plane at 120-130 ozs that could take alot of abuse, especially on landing.

EDIT: TP16, if you lived with in driving distance, I would give what I have left.

Troy, do you want it?

Peace, Bill
Last edited by Flyextreme; Mar 25, 2011 at 02:51 AM.
Mar 21, 2011, 11:40 PM
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marco_ul's Avatar
Maybe I can share my experience here... I just built a 70% slipso fuselage (nose enlarge to accept 20mm motor) using the lost foam technique. I used what I had on hands and it sucks! I had 2oz cloth from hobbyking and Z-poxy finishing resin. I used 3 layers of 2oz cloth 2 on bias (external and internal) and one layer of 0-90 (middle). Used some carbon tow for the wing saddle.

The fuselage is VERY soft!!!! It's pretty torsion resistant, but all the 'walls' are damn soft. It could fly, probably, but I don't know if I want to invest time to set it up if I think it wont be great. Plus, I ended up sanding through the 3 layer during finishing, making holes in the fuselage...

Maybe I just didn't put enough layers... I'm saying this because the carbon tow got pretty stiff. I might try to add 3 extra layers from the outside to make it more flyable... Next step is to get good finishing epoxy (west system or MGS). A better glass cloth could help a bit too.

Hope this helps
Marco
Old Mar 24, 2011, 11:21 PM
steelersdean
A moderator felt this post violated the following rule: Redacted Content. It is temporarily hidden while steelersdean edits it.
Mar 25, 2011, 02:13 AM
Sure it'll work
Flyextreme's Avatar
Quote:
Originally Posted by steelersdean
tp16. your join date is 8-09. All these questions you ask are very basic. im going to point you in another direction for a hobby. this one seems to be a bit much for you. try bowling, min. golf, or kite flying. This one seems a bit much for you.
What does join date have to do with anything. I have been in and out of the hobby (flying) since 1969, and in it solid for the last 13 years. As I move to different avenue of the hobby, I'm the one asking noob qusetions. I just got into High Performance and I'm a noob there. I was a real noob a few years ago when I delved into helis...a noob when I move from sloping to nitro, and from nitro to Dynamic Soaring, and so on.

Leave the guy alone. He's welcome to ask about anything... help or ignore. More experienced people should encourage, not discourage.

Sorry guys, that just bugged me.

Peace-out, Bill
Last edited by Flyextreme; Mar 25, 2011 at 02:52 AM.
Mar 25, 2011, 07:11 AM
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epwierman's Avatar
Quote:
Originally Posted by steelersdean
tp16. your join date is 8-09. All these questions you ask are very basic. im going to point you in another direction for a hobby. this one seems to be a bit much for you. try bowling, min. golf, or kite flying. This one seems a bit much for you.
Reported to Moderator for Offensive Content / Immediate Ban.

Reason: Causes others to lose interest, not post, and creates bad atmosphere among our group.

Thanks,

Eric
Last edited by epwierman; Mar 25, 2011 at 07:41 AM.
Mar 25, 2011, 07:16 AM
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epwierman's Avatar
Seems like there's bound to be a bad apple we come across once in a while.

It is what it is, and easily ignored while moderators handle it.
Last edited by epwierman; Mar 25, 2011 at 07:42 AM.


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