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Old Jul 28, 2014, 12:48 PM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
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What's in the bag, man?

EDIT: Since this thread is becoming a "show & tell" for our vacuum bagging projects, I've edited the title slightly. Feel free to post photos and info about your latest project, ask questions, exchange advice and information....anything goes!

So let's see them....the good, the bad, and the ugly!


3 bums try to rob Clint Eastwood - Dirty Harry scene (0 min 54 sec)



I'm going to try to get my first set of wings into the bag tonight. I have a rare weekday off today, without the wife home, so trying to get organized and mentally prepared. This will be a test run on a pair of extra cores from a 32" foam & lam. film DLG I built a while ago. Although if they turn out reasonably well I'll probably build it out. If you care to comment or correct anything below, I'd appreciate your suggestions.

Simple glass layup: 1.6oz skin and root doublers and leading edge strip, 3oz. tip doublers. Spar will be 12k carbon tow. (or would 6k be plenty?) I'm figuring 2 layers, 1/2 span and full span.

On the mylars, am I correct that they should be just shy of the L.E. and slightly long on the T.E.? And taped together just at the T.E., L.E., or both? (I've read various suggestions here)

I've put these instructions together based on something GT posted on Brandon's HM51 thread. Does this sound about right? I appreciate your comments. Thanks.

- Jim


Prepare the vacuum bag, with bottom bed under the bag.

Prepare the cores: remove dust, apply leading edge strips & hinge strips with 3M77.

Open beer, have a generous sip.

Roll some laminating resin onto the waxed mylars. It will bead up but that is OK.

Lay down dry fiberglass. It will stick to the laminating resin. Skin first, then doublers, then spar.

Roll dry fiberglass onto mylar. This will wet it out. Add a little more laminating resin if needed.

Trim excess glass back to the mylar edge with scissors.

Put two layers of paper towels on one of the mylar/glass assemblies, and put the other one on top, so it goes mylar-glass-paper-glass-mylar.

Put under vacuum for about 4 minutes (or hard roll).

Remove paper towels. If they are rather wet, repeat with fresh ones. The glass will look moderately dry which is what you want.

Take the core and roll a little laminating resin on the edges and at least a half inch all around the perimeter, both sides. Roll a line of laminating resin along the hingeline, hinge side.

Assemble the mylars with their glass, and the core. Tape together with little strips of masking tape.

Surround this assembly with a breather consisting of painters plastic drop cloth to which is stuck a layer of paper towels.

Put in vacuum bag (on bottom bed, which is under the bag).

Put strip of felt along an edge of the breather, running to the vacuum tube.

Close bag.

Pull partial vacuum, while smoothing down the bag over the part.

Put on the top bed, and uniformly weight down, paying particular attention to the edges.

Pull full vacuum.

Relax, smile, finish beer.
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Old Jul 28, 2014, 02:49 PM
Vaci
Joined Oct 2013
102 Posts
Im not sure how .oz translates to grams (i mean surface of .oz unit to gr/m square). Google told me that 1.6oz is 45gr, so i just wanted to tell you that i used 25gr glass and its just fine. Of course there was half disser 1k tow... As for spars, i guess you just gonna use carbon on skins? In that case 12k tow all the way, another one half way, and another one 1/4 way, and triangle glass doubler 1/4 way. I got super light wings that buried 2 fuselages and are still kicking ass.

Just thought maybe this will be useful to you... cheers
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Old Jul 28, 2014, 04:09 PM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
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That sounds about right Vaci.....1.6oz/yd^2 = 54g/m^2. If the wings come out OK they'll probably be used as a light slope plane, so the extra strength won't hurt. Besides, I just cut the skins and doublers already I'm sure on a wing this small the 25g would be fine. But on a 1.5m wing without carbon disser or D-box I think I'd want the 54g.

Your beautiful plane, built on such a tight budget, gives me hope that I can do the same!
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Old Jul 28, 2014, 04:09 PM
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Quote:
Originally Posted by Vaci View Post
Im not sure how .oz translates to grams (i mean surface of .oz unit to gr/m square). Google told me that 1.6oz is 45gr, so i just wanted to tell you that i used 25gr glass and its just fine. Of course there was half disser 1k tow... As for spars, i guess you just gonna use carbon on skins? In that case 12k tow all the way, another one half way, and another one 1/4 way, and triangle glass doubler 1/4 way. I got super light wings that buried 2 fuselages and are still kicking ass.

Just thought maybe this will be useful to you... cheers
The unit of ounces per square yard can easily be converted to grams per square meter. You can do the math with the necessary factors here: http://www.worldwidemetric.com/measurements.html or many other internet sites.
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Old Jul 28, 2014, 04:11 PM
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Originally Posted by JimZinVT View Post

Open beer, have a generous sip.

<SNIP>....

Relax, smile, finish beer.[/I]
Jim,

Dude, what a waste of cold beer! Drink the beer, then at the end hit the refrig for another , as your reward.

Chris
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Old Jul 28, 2014, 04:16 PM
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JimZinVT's Avatar
United States, VT, Castleton
Joined Dec 2007
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Or just type it into the Google search window like this: 0.75 oz/sq yd in g/m^2 =
and the answer pops up without leaving your current website.....it's magic

Works for pretty much any units
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Old Jul 28, 2014, 04:20 PM
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JimZinVT's Avatar
United States, VT, Castleton
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There is actually some more "sipping" going on between steps there....that final sip will be small, if there's any left at all

So, do my instructions seem about right? I'm cutting the last of the materials right now, and it's going in the bag after supper, for better or worse.
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Old Jul 28, 2014, 05:54 PM
Vaci
Joined Oct 2013
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Quote:
Originally Posted by JimZinVT View Post
Your beautiful plane, built on such a tight budget, gives me hope that I can do the same!
Thank you Jim! Its easy with enough money, me being poor by worlds standard makes it more of a challenge All you need is clear head and will of steel, and a bit of money of course and you can make anything. Actually vacuum bagging can make excellent wings, but something is pushing me to try molds too. Its a curse.... damn it.
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Old Jul 28, 2014, 06:45 PM
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Originally Posted by JimZinVT View Post
There is actually some more "sipping" going on between steps there....that final sip will be small, if there's any left at all

So, do my instructions seem about right? I'm cutting the last of the materials right now, and it's going in the bag after supper, for better or worse.
Make sure you wax the mylars several times and buff them out.

One thing I do is put the lightly spray 3m77 on the back of the mylars and then put that on 4 mil plastic. I have not seen this done by anyone. When I put the FG down, I cut the LE plastic to within 1/4" of the mylar edge. This allows me to wrap the LE's a bit better when it cures. Another way to do it is to make a plastic sided breather cloth, instead of the paper towels. The paper towels can compress enough to not allow good air removal. When I put this over the wing to bag, to act both as a release from anything oozing out from the mylars and make the pressure more uniform. Also make sure you do not have any ridge overlap of the paper towels as the ridge can be pressed through the mylars onto the cores/wings. Youcan see a line in the skin shine if there is a problem.

One thing I have also tried is taking some polypropylene 1/2" piping and drill lots of holes at all angles radially on the length and insert that in the bag with the breather. The pipe does not crush and the holes allows the air to be removed from even the farthest point form the vacuum bag nipple junction. This helps , I think, when you have a very small vac pump that doe snot pull a lot, but pulls down slowly.

Contrary to what most say, you can get the fiberglass too dry by blotting. That results in poor epoxy skin gluing. If you use CF or Kevlar, you are OK as they hold a bit more after blotting. If in doubt, do a stab/rudder first to get things down. If you are using MGS and are in a hot area, either use the slow stuff or cool down the fast stuff to extend working time.

In some instances, builder have pulled vacuum on the wing, put it in the beds, released the vacuum and then pulled it down again. This makes sure the wing is being cured without any twisting stress.

After curing, do not insert your fingers between the mylars and skins to remove the mylars. You will get slight crushmarks that you will swear not to know how they got there.

The only thing I would say is to bag a smaller less important part the first time, as you do put a lot of work into the wing before bagging, and should experiment as readily on it the first time.

Good luck,
Chris
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Old Jul 28, 2014, 08:07 PM
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JimZinVT's Avatar
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I'm using plastic film between the mylar and the paper towels, per GT's instructions. I've done tails without the plastic film, and the paper towels often end up glued to the edge of the tail by the resin seeping out of the layup. The plastic should help prevent that I hope. And I use a strip of 1/4" thick felt along the edge of the paper towels to give a good vacuum path.

My vac pump is malfunctioning Hopefully I can figure that out and get these in the bag tonight.
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Old Jul 28, 2014, 08:43 PM
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Originally Posted by JimZinVT View Post
I'm using plastic film between the mylar and the paper towels, per GT's instructions.
Good luck with fixing the pump. for small leaks I keep some painters white caulking around as it seeps into leaks.

I found that you can get cheap fabric batting from a fabric store, instead of paper towels.

Chris
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Old Jul 29, 2014, 12:34 AM
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JimZinVT's Avatar
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OK now it really IS in the bag

My home-brewed fridge pump vac. system has "issues". If it tries to cycle back on too quickly the motor won't start. But if it rests for about 45 seconds between cycles it's fine. While testing it before I started the layup I wasn't getting a good seal on the hose, but once I cured that it worked fine. Now that the bag is closed it's cycling every 5 minutes or so, for about 2 seconds. I need to get a "real" vacuum controller for it. The one I'm using was scavenged from a Food Saver. The whole system was built from stuff I got free. For the bag, I'm using the plastic drop cloth and latex caulk method. It works great.

Do you guys usually do both wing halves at once, or one at a time? I did both at once, since it's a small wing. It was a rush to get it done and in the bag in 50 minutes. Just shy of the 60 min. working time for the EZ-Lam epoxy. I'll probably do one half at a time when I do a bigger wing.

I cut my fiberglass wing skins oversize and then had to trim them to the mylars before they went in the bag. Is this how most people do it? I don't really see another option....it's so easy to deform them while positioning on the mylars, I'd never get them lined up straight.

In my rush, I didn't tape the mylars together over the cores. I hope everything stayed lined up while the vacuum came up. Hard to tell with everything hidden between paper towels.

One thing I discovered is I really don't like working with carbon tow for the spar. Even though I pre-rolled it to flatten and smooth it out, I still made a hairy, crooked mess of it while getting it positioned. I'm sure it will look horrible. I'll have to look into other options....uni-carbon? rods or tubes? Suggestions are welcomed. I guess if I painted the mylars then the ugly mess wouldn't show. I added pigment to the epoxy for a transparent yellow color. Over the blue foam it may look green We'll see tomorrow night.
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Old Jul 29, 2014, 12:37 AM
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United States, WA, Kennewick
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Good luck Jim! The steps you have written out sound right. If your paper towels have a pattern, though, consider using toilet paper to blot excess resin instead- it will debulk the layup more evenly. I generally tape the mylars together at three points along the LE, once or twice on the TE, and sometimes once at the wing root. The LE is the most important though.
I am excited to see the finished product!
-David
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Old Jul 29, 2014, 12:47 AM
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United States, WA, Kennewick
Joined Sep 2011
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Looks like I replied just after you finished bagging the wing!
I have tried to answer some of your questions below in red:
Quote:
Originally Posted by JimZinVT View Post
Do you guys usually do both wing halves at once, or one at a time? I did both at once, since it's a small wing. It was a rush to get it done and in the bag in 50 minutes. Just shy of the 60 min. working time for the EZ-Lam epoxy. I'll probably do one half at a time when I do a bigger wing.

I usually do both wing halves one after the other, with separate batches of epoxy.

I cut my fiberglass wing skins oversize and then had to trim them to the mylars before they went in the bag. Is this how most people do it? I don't really see another option....it's so easy to deform them while positioning on the mylars, I'd never get them lined up straight.
I do it this way as well. Another option is to attach the fiberglass to some wax paper with spray adhesive, then lay it down onto the wetted mylars.

One thing I discovered is I really don't like working with carbon tow for the spar. Even though I pre-rolled it to flatten and smooth it out, I still made a hairy, crooked mess of it while getting it positioned. I'm sure it will look horrible. I'll have to look into other options....uni-carbon? rods or tubes? Suggestions are welcomed. I guess if I painted the mylars then the ugly mess wouldn't show. I added pigment to the epoxy for a transparent yellow color. Over the blue foam it may look green We'll see tomorrow night.
You could probably precure the tow with some epoxy thinned with alcohol. I have tried both uni and rods, and prefer the uni as I can taper the spar, and it is faster to prepare.
I'm looking forward to see the wing out of the bag tomorrow! Have fun resisting the urge to crack it open early.
-David
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Old Jul 29, 2014, 01:04 AM
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Originally Posted by DavidZ1 View Post
I generally tape the mylars together at three points along the LE, once or twice on the TE, and sometimes once at the wing root. The LE is the most important though.
-David
Do you cut the mylars to match the core size exactly, or run them a little long over the T.E.? I've seen both mentioned, but seems like exact size would be easier to keep them positioned over the core?
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