Model Research Labs

 

Using Myler Covering Materials

There are many good reasons for using Mylar film for covering your models. My favorites are the lightweight, temperature stability, lack of warps, moisture resistance, and speed of application. Mylar is just DuPont's registered trademark for polyester plastic films.

Common polyester resin is a high temperature material that can be injection molded into very strong plastic parts. Polyester resin can also be processed into very thin films that possess excellent electrical dielectric properties At least 99% of all the worlds thin Mylar film is used as electrical insulation in high quality products. It is the material of choice for microelectronics, which is good for us model builders.

Mylar films are sold by the pound and are fairly cheap. Our problem is that the standard roll size seems to be 39 inches wide and 500 pounds long. A 500-pound roll of .00025 Mylar would reach to the moon and back about 2-1/2 times. The hard working staff here at MRL has managed to set up an arrangement with a processor that allows us to purchase old lots of left over Mylar for only about 10 times what the material cost them in the first place. Those prices are still very good for us model builders.

Standard Mylar films range from about .015 thick down to near nothing. The thinness Mylar film I have ever seen, was what is known as 4 gauge, this is nominally .000035 inch thick. Far too light for anything except very light indoor models. We currently stock clear Mylar is thickness of .000059, .000125, .00025, .0005, .001, .0015 and .002. Better yet we also stock metalized silver Mylar in .00025 and .0005 thickness. Soon, maybe by now, we expect to have a good stock of Hologram patterned silver metalized Mylar. This will reflect light, and color, over the entire visible spectrum. Never again will we need to worry about what color the airplane is, It will be all the colors you can see. As you can tell,  I think Mylar was sent to earth for us modelers to use.

Selecting the best choice for your model is simple. The .002 is just too much, too strong, and too heavy for anything less than about a 10 cubic inch engine gas powered model. Incidentally, Monocoat is about .003 thick and about the same strength as .001 Mylar. Our .001 Mylar is good for very large heavy models. Maybe 100" wingspan and up. Details about the special .0015 later.

The .0005 is a good choice for most lightweight outdoor models, as it will usually survive landings in the weeds. This is what is commonly used for Wakefield and Nordic stabs. The .00025 is a bit weak for outdoor use, as it seems to always get puncture holes every time it lands in the weeds. A few of the coupe and Wakefield flyers use the .00025 for stabs and rudders.

For indoor use the .005 is too heavy, .00025 is at the heavy end of what works well, the .000059 is penny plane type covering material.

All of the above pure Mylars will heat shrink a small amount, which allows us to remove small wrinkles and tighten our covering. My method is to run a very hot covering Iron lightly on the surface of the Mylar. Don't count on this fixing major goof ups.

Metalization of the Mylar makes it gas tight, no vapor or gas, not even helium can get through the layer of aluminum that is deposited on the surface of the Mylar. The metalization is accomplished by pulling the Mylar film slowly over a very cold metal platen in close proximity to a small tub of boiling aluminum. The aluminum condenses and collects on the cold surface of the Mylar film. The only reason this works is because it is done in a big machine in a very hard vacuum. Some machines require up to 12 hours to pull down the vacuum, boil the aluminum, and cool the platen, before the machine even starts to process the Mylar. All this just for us modelers. As you can guess, this metalized Mylar does not heat shrink very much.

Adhesives

In your local R/C Toy store you can usually buy adhesives made to be painted on the wood and then the Mylar ironed onto the wood. The ones I am familiar with are BalsaLoc and Balsaright. Both seem to work fairly well but neither is a really high performance adhesive. In such applications I prefer the 3M C77 just because it is so easy and light. There are three other adhesives commonly used by model builders. Probably the most widely used is 3M's C-77, or Super 77 Contact cement. This comes in a large spray can ready to use and its available just about everywhere. The second favorite is 3M's Super Weather-Strip Adhesive, part no 08001. This is available in most auto parts stores but they all know it as yellow snott. This material needs to be thinned about 10:1 with MEK, mix it in small quantities, I use old plastic film canisters. The third and newest choice is 3M's Scotch-Grip, High Performance Contact Adhesive #1357. This is industrial cement that is used largely in the motor home industry; we have to buy it in 24 tube cases for $7.10 per tube. We stock it here at MLR, but your price is $10 per tube.

3M Super 77

Most indoor type models use the 3M 77 spray can cement as it is the lightest way to go. To apply Mylar covering with this cement you first tape the Mylar down tight on a smooth surface. Then holding the model part, (wing, stab, or rudder) in the air, spray a cloud of cement, allowing it to settle over the model part. It doesn't take very much; you will get enough cement on the model surface and most everything else in the room too. Place the model part on the Mylar and press it down around the edges. This is very easy to do on a flat surface like a rudder, but not as easy to do on a cambered surface like a wing or stab. To cover a stab, you touch just the trailing edge to the Mylar and press it down, then start to roll the stab towards the leading edge. As soon as you roll about 50% of the chord you will realize that it is necessary to cut the Mylar loose at the trailing edges and part way around the tips so as to have enough slack to roll the leading edge down onto the Mylar. Continue by pressing the Mylar down good and then trim with a sharp new double edge razor blade right to the edge of the wood. A model knife does not have a chance here. A wing is done the same way and must be covered before any dihedral is put in the wing. After you add the dihedral there will be wrinkle of slack Mylar next to the dihedral rib, Simply slit the Mylar right next to the dihedral rib and push, or blow the loose Mylar up on top of the dihedral rib. Attach it with a tiny strip of clear tape or brush a bit of contact cement under the overlap. Don't sweat it, That's all pretty easy. The only danger is that while rolling the wing to attach the Mylar you must keep even tension on the wing and Mylar or you will acquire a new warp. That is because you put the Mylar on crooked and the Mylar will pull a warp into the wing. It's your fault. I used this adhesive on outdoor models for many years.

3M Weather Strip Adhesive #08001

This adhesive is normally used on lightweight outdoor models. This material comes in a tube and is the consistency of honey. You must thin it out about 10 parts MEK to 1 part adhesive. This adhesive is brushed on the structure and the Mylar pressed onto the adhesive. You need to work fast as the adhesive set up time is never quite long enough. A 10:1 mix will began to loose its tackiness with in about 2 min. and after 10 min. the Mylar doesn't stick well and will need to be ironed down with a very hot iron. This adhesive is generally adequate for most models and the cement does not look too bad after covering.

3M Scotch Grip High Performance Contact Cement #1357

This is 3m's best, and highest temperature, contact cement. Some of the contest modelers have gone to this adhesive because they felt the trim adhesive was letting their Mylar creep under high temperatures. Car trunk temperatures can often exceed 185 degrees F in the warm parts of the country. I have never covered a model using this adhesive, however it is thinned and applied just like the trim adhesive.

The objectionable part to this adhesive is the color. It is an ugly olive drab color and it will show even after thinning with MEK.

I don't use it because I feel there is already enough ugly in my world.

Coloring your Mylar

I think the majority of flyers use a thin coat of cheap spray can paint on the bottom surface of the wing and tail for visibility.

For more class in your models your can use the Rit dye from your local cloth type store.Pick dark colors and allow plenty of time in the bath as the Mylar does not absorb much dye and tends to come our on the transparent side. Some modelers are now using Mom's Crock Pot and leaving the Mylar in for up to 24 hours at med cooking temp. Works well.

Iron on, Heat Shrink, Paintable, Cheap, Light Weight Mylar Covering

Great Stuff

MRL also offers another form of modified Mylar that has a frosty adhesive coating on one surface and is very heat shrinkable with the covering iron. This material is in our catalog as item 019 and should not be confused with the pure Mylars listed above. Item 019 has been modified to provide about 20% shrinkage and the adhesive is high temperature so the shrink temperatures do not affect it. Much easier to use than Monocote. This material is .0015 thick, Monocote is .003 thick. Our material has about 60% of the strength of Monocote but weights only .0009326 per sq. in. This is our most popular covering material where weight matters but is not the all-consuming objective. Commonly used on Free Flight gas models, Electrics, R/C Gliders,

R/C Power models up to about 12-foot wingspan. Also sometimes used to cover wood surfaces as a lightweight surface finish on solid wood surfaces, It really toughens up the wood.

cover all my Quickee 500 models with this film. I recently covered my new Playboy Sr. with it and I must say it does not look right on such an old-timer.

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