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Author Topic: Some questions about mylar  (Read 1729 times)
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pedwards2932
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« on: January 27, 2018, 08:59:52 AM »

I have started using mylar covering and am getting pretty good results.  The only issue I have been seeing is getting clean cut edges.  I have been using a scalpel which cuts pretty good but I am not steady enough to cut exactly on the edge.  When I use tissue I usually sand the edges to get them smooth and get the stray pieces that aren't cut.  Mylar doesn't seem to sand that great just wondering if anyone has experience with it.  I just did a Guillow P51 in mylar and painted it black then silver and I think it came out pretty good just the tail surfaces could have had cleaner edges.   Also when using mylar on flying surfaces do you only use glue on the outside edges or on all contact points?
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Bryanair
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« Reply #1 on: January 27, 2018, 09:29:33 AM »

I use a soldering iron - just run it quickly along the edge of the wing etc.
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pedwards2932
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« Reply #2 on: January 27, 2018, 10:16:28 AM »

Interesting that makes sense.  I will try that next time.  How do you handle seams?  I glue seams but the glue doesn't work well with the trim iron as it makes it want to stick.  I am using glue stick to stick it to the frame and it works great.  I tried some of the heat activated stuff and it was much harder to use and the results weren't as good.
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Bryanair
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« Reply #3 on: January 27, 2018, 10:30:37 AM »

I use neat heat activated Balsaloc for sticking the mylar to the structure and on the seams.  A domestic iron to activate and shrink the Balsaloc  On flying surfaces I only put Balsaloc on the outside edges.
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RalphS
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« Reply #4 on: January 27, 2018, 11:16:41 AM »

To tidy get tidy edges I use a snapped double edged razor blade to cut then run the hot iron along the cut edges to shrink them back to the framework. 

I have only ever used very thin contact adhesive to stick the mylar.  I usually coat edges and top of ribs.  Use a sharp needle or modelling pin to put a hole in ribs, etc., to allow air to escape between cells to stop the mylar ballooning.

Have a look at Flyguy's covering jobs for perfection.

Keep at it.

Ralph
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pedwards2932
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« Reply #5 on: January 27, 2018, 11:41:39 AM »

Yeah Flyguy is where I got the notion to try mylar.  I have a KK Ace that I have covered with it but am waiting to get my servo/reciever set up before I finish the covering.  I used balsaloc but I didn't like it as well as glue stick....I think Flyguy uses Uhu.  Like anything else with this hobby you get better as you do it and ask questions from those that have been there.  The soldering iron will probably solve my issue and I like the idea of final sealing edges with some glue. 
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faif2d
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« Reply #6 on: January 27, 2018, 02:35:01 PM »

We used to use Doculam to cover combat models years ago.  The mylar had an adhesive on one side but it was not fuel proof.  I used to run a seam of glue along the edges to keep it all together.  Those only had to last about 4 or 5 flights so I have no idea how long that covering would have lasted.  The 1/4 mil mylar that I used on A2 tails was adhered with weldwood contact cement thinned.
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fred
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« Reply #7 on: February 13, 2018, 01:07:24 PM »

No idea what a mylar covering is. 
Familiar with tissue,  silkspan, airspan(s) and doculam types though.
Modge podge has proven a superior heat activated Glue than Balsaloc (which is essentially  regular White glue) in my uses.
 It's label claims it as dishwasher safe .. which suggests a fairly determined bond.
 Never ever put a model into a dishwasher to test this tho.
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michellehughes
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« Reply #8 on: March 20, 2018, 06:39:15 PM »

I prefer to use soldering iron. It is light and durable
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lincoln
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« Reply #9 on: March 20, 2018, 09:29:20 PM »

My favorite covering adhesives are Stix-It, from Sig, and Fab-Tac, which I got from Aircraft Spruce. Stix-It can be obtained in smaller quantities. I had the Fab-Tac for fixing a fabric boat. I'm pretty sure Stix-It will work on mylar.

If that's a rubber powered model, keep in mind that you won't be able to enter it into Flying Aces contests. They consider mylar covering heresy, although I think some CD's might be a tiny bit heterodox. Or at least want to be.
--------
What thickness of mylar are you using? For the thicker stuff, I've found a really good pair of scissors useful, as well as the sharpest Xacto blade I can find. The thin stuff is much more cantankerous, and easily shredded. If you're using a soldering iron to cut it, it's best if it has thermostatic control, or some other way to turn it down until it can't burn anything. I've used a cautery for trimming the stuff, but I have to be careful it doesn't get too much voltage and burn the wood! (Basically, this kind of cautery is just a thin wire heated by electrical current from a couple of AA batteries.)
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pedwards2932
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« Reply #10 on: March 21, 2018, 06:56:16 AM »

I am using 6 micron that I got off e-bay. It was called Electrostatic Speaker Membrane and I got 40m for about $30.  I just fly them for my own entertainment so I am not worried about contests.  The glue sticks have seemed to make a pretty good bond.  I do notice that occasionally the Mustangs covering sags a bit with temp change....not sure if this is because of the paint as I have a larger model that is unpainted and haven't noticed any sagging, just as tight as when I put it on.  I use a scalpel to trim.....I find them to be sharper than the exacto and cheaper.  Seems like no matter how I trim it still leaves a bit on the edges....with tissue I would just sand the edges off.  That doesn't work with mylar.  When I cover my next one I am going try the soldering iron trick to see if that helps
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gman
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« Reply #11 on: March 21, 2018, 11:39:14 AM »

I am fascinated by reference to speaker membrane.  On EBay it all looks the part except for the very low (2%) shrinkage quoted. Perhaps when you're making a speaker you don't get it as hot as we do. Clearly Pedwards has success with it, anyone else used it to good effect?
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NormF
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« Reply #12 on: March 21, 2018, 07:24:55 PM »

I am fascinated by reference to speaker membrane.  On EBay it all looks the part except for the very low (2%) shrinkage quoted. Perhaps when you're making a speaker you don't get it as hot as we do. Clearly Pedwards has success with it, anyone else used it to good effect?

I just covered a P-30 rudder with the 6um speaker mylar. I used solvent based contact cement thinned with MEK. For trimming, a new single edge razor blade worked fine. Shrinkage was similar to regular plastic coverings. Thanks to Manuel Cisneros for the source.
BTW - for us Calif folk, MEK is not readily available, I used Famowood putty thinner.

Norm
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lincoln
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« Reply #13 on: March 21, 2018, 08:57:58 PM »

That's relatively light, which is probably good for a rubber powered model. I calculate that it's around 8 grams per square meter, if it really is mylar. That's about 2/3 the weight of bare japanese tissue. (The good stuff, not the faux "japanese tissue" you get at the gift store.) The REALLY light stuff is 0.9 micron, but you'd only want to use that on indoor models.
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gman
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« Reply #14 on: March 22, 2018, 09:58:13 AM »

 
[/quote]

I just covered a P-30 rudder with the 6um speaker mylar. I used solvent based contact cement thinned with MEK. For trimming, a new single edge razor blade worked fine. Shrinkage was similar to regular plastic coverings. Thanks to Manuel Cisneros for the source.
BTW - for us Calif folk, MEK is not readily available, I used Famowood putty thinner.

Norm
[/quote]
Thanks for the comment Norm, clearly it's the right stuff. I would have thought 6micron is fine for everything up to say an F1A stab, and ideal under jap tissue. A lifetime's supply for $30...hmmm, problem is that I've got most of a life's worth already! Now who can I share some with? I echo your thanks to Manuel Cisneros though I don't know the gentleman.
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jamesf
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« Reply #15 on: March 25, 2018, 12:56:16 AM »

I have been building RC models since 1959, rubber and free flight before that.  Along with everyone else I switched to the plastic coverings when they became widespread.  I still prefer the look and strength of silk and dope as well as the ease of repair that silk and dope offers.  A problem that occurs with silk however, is that the first coat or two of clear dope drips through the silk and makes a mess of the silk on the other side. 
I wonder if covering the open areas with thin doculam first would stop the problem?
Wet silk and thinned dope would stick to the doculam easily enough.  It would take fewer coats to seal the silk as well.
Any opinions?
James
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3view
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« Reply #16 on: April 09, 2018, 03:06:51 PM »

James,

This is an interesting method of avoiding puddles of dope on silk...

http://www.antiquemodeler.org/sam_new/p%20covering/assets/Ramon%20Alban%20covering%20with%20silk%20using%20the%20miniscus%20method.pdf


Steve
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jamesf
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« Reply #17 on: April 09, 2018, 03:47:41 PM »

Steve,

Very interesting article. Something that I would never have thought to try.  I will build a framework and try it out soon.
I have 40 or more yards of silk that I have bought over the years, all pristine in their plastic packages.  I know that it dates me but I still like colored silk clear dope finished wings best of all.  Thanks very much for the web URL.

James Fuller
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sspresdavid
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« Reply #18 on: April 09, 2018, 09:57:59 PM »

Silk expands when wet and should always be applied wet. Having covered more airplanes then I care to count, here is my technique. Dope the structure. In the case of a rubber powered fuselage, dope everything. Wings and stabs only require the perimeter. In the case of an under cambered wing, dope each rib with straight dope. Apply enough coats so the surface is starting to shine. Wet the silk with a sprayer or even dip it in a pan of water. Let the excess water drip off and then lay it on the structure. The wet silk will cling very nicely to the doped structure. Gently pull out any wrinkles. Keep a sprayer handy and if the silk starts to dry, spray it. Brush a mixture of 50/50 clear dope on the perimeter. The silk will grab very quickly, but can be easily re-positioned by loosening with thinner. The dope will blush, but that will go away later. Trim with a sharp razor after everything is dry.

Start doping with a good quality foam brush. I know that the brush says " not for lacquer " but don't worry, it's a throw away. Start out with 50/50 and brush on a couple of fairly dry coats. If a puddle should appear, you can pull it right out with a dry brush. Once the silk is sealed, you can continue finishing with any technique you like.
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mkirda
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« Reply #19 on: August 13, 2018, 02:05:36 PM »

I am fascinated by reference to speaker membrane.  On EBay it all looks the part except for the very low (2%) shrinkage quoted. Perhaps when you're making a speaker you don't get it as hot as we do. Clearly Pedwards has success with it, anyone else used it to good effect?

I just covered a P-30 rudder with the 6um speaker mylar. I used solvent based contact cement thinned with MEK. For trimming, a new single edge razor blade worked fine. Shrinkage was similar to regular plastic coverings. Thanks to Manuel Cisneros for the source.
BTW - for us Calif folk, MEK is not readily available, I used Famowood putty thinner.

Norm

My indoor Coconut scale 54" Comet Taylorcraft is covered in the 2um stuff. Painted on the inside with floral spray.
Recently did a P30 with the same stuff, came out well.

Regards.
Mike Kirda

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duration
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« Reply #20 on: August 13, 2018, 03:40:49 PM »

My dad always covered large models (control line and free flight) with tissue first, shrinking with water and doping a coat or two. Then the wet silk was laid over the tissue, positioned, and doped in place. (This is similar to the tissue over Mylar technique.) The idea is the same: the first layer (tissue in my dad's case) seals the underside of the silk so the amount of dope required is much less than covering with silk only. He swore that silk over tissue ended up lighter than silk and lots of dope.

One of the early Zaic Year Books mentions filling the pores in the silk with Knox clear gelation from the grocery store. (This was a powder that was mixed with water or juice to create gelatin deserts.)

Louis
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« Reply #21 on: August 14, 2018, 10:32:37 AM »


If that's a rubber powered model, keep in mind that you won't be able to enter it into Flying Aces contests. They consider mylar covering heresy, although I think some CD's might be a tiny bit heterodox. Or at least want to be.


Mylar is acceptable in the FAC under one condition - it MUST be covered with tissue paper (and that tissue be the external surface).  Bare (or painted) plastic covering is not acceptable in the FAC.

I purchased the 2um and the 6um speaker membrane off ebay after talking with Mike Kirda about it.  I have done one test - 2um on the rear portion of an Embryo fuselage.  I used glue stick as adhesive and a trim iron.  It shrunk up very well and then I covered with tissue.  I brushed the tissue on with Future as the only adhesive for the tissue.  That seems to work just fine.  I did not do any weight measurements and the rest of the plane has now been destroyed (but the rear fuselage still is solid)!

Next I will be trying the 6um on the rear of a large OT Rubber model that has had the tissue blown out.  I will cover in the same manner.

--george
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