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Author Topic: Covering Tips and Tricks  (Read 55609 times)
Skydanz
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« on: November 23, 2007, 06:36:40 PM »

This is the beginning of a work in progress.
My intention is to share some tips and tricks that I use in covering, repairing and trimming using Monokote, Ultracote and other heat activated covering materials.

I have been asked quite frequently how (and sometimes why) I re-covered my ARFs in a different color and added trim and graphics without those pesky bubbles that pop up.
While the quality of the finish covering of ARFs has improved to nearly professional results, I am the type A person who doesn't want my planes to look like everyone elses. I figure the time and effort saved by buying a plane that is already built justifies a little extra effort to "personalize" it.

That's why in a nutshell!

The following series will show some of my techniques for applying heat activated coverings and hopefully take the mystery out of how to get great results. Let's get started.

It's always best to have a plan. I look at my new plane and try to get an idea of how I think I can improve the looks. Change the color here, add a stripe there or maybe some graphics. I race T-34s and there is nothing more boring than to see 35 planes show up with the same basic white with either red, blue, or yellow trim. It not only makes it harder for the pylon judges to figure out which "red" plane just cut pylon 2 but it's also easy for you or your caller to "misplace" your plane. Huh

By taking an hour or two to strip off the stock covering and replacing with your own color, you've made life easier for many people and added a little class to your world. You don't have to remove all the covering! You can simply add another color or some graphics to set your plane apart.

Many ARFs these days are covered with a film that has a low tack color adhesive that is die cut to fit like a jigsaw puzzle on the particular plane. They are simply placed in the correct spot on the plane, bonded with a iron and then passed through an oven to mass shrink the film. Fortunately, the film can easily be removedby carefully pealing up a corner and then pulling off the film. Before you reapply the new color, it's often a good idea to check for loose glue joints, broken ribs and any small dents while the frame is open.

I like to use a low shrink, lightweight, spackle-like compound to fill any larger dents. Smaller dents can many times be removed by simply adding a few drops of water/amonia mix directly on the dent. Wait a few minutes to "swell" up, then use your heat gun or iron to "set" the wood. A light sanding over the area you are recovering with 400 grit, followed by a quick shot of compressed air and/or a good tack cloth and you're good to go!

Next I'll talk about some tools of the trade that make life easier.


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« Last Edit: January 02, 2008, 01:10:49 AM by Skydanz » Logged

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Skydanz
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« Reply #1 on: November 24, 2007, 11:43:37 AM »

Covering materials have come a long way since the days of silk and dope. After building the balsa framework, a modeler would brush on a coat of clear butyrate or nitrate dope and then adhere pieces of a fine paper-like material called Silkspan or similar material. After that dried, several more coats would be brushed or sprayed over the covering to shrink and seal it. Depending on how shiny you wanted the surface; many more coats of colored dope would be applied until the desired sheen was achieved. Needless to say, this was a very time consuming process!
Nowadays, this process can be achieved with one simple application of a heat activated plastic film that has the color and desired finish bonded to it. The first major improvement I can remember was the introduction of a material called Fascal. It was a clear plastic film that had a heat activated high tack coating that you could stick to the framework and then tighten or shrink out any wrinkles with some sort of heat source. Paint could be applied to the film for color. I remember building fast combat control-line airplanes in my RV on the way down to the 1976 Nats. I was shrinking the Fascal over the gas stove! Not very safe but it got the job done.

Now we have high tech films like Monokote, Ultracote, Solarfilm, etc. To apply these films, we need some specialized tools to make the job a bit easier. In the pictures, I've assembled most of the tools and materials needed to apply the film and achieve an outstanding finish.

Of course, one of the first things we need is a way to cut the material. An X-acto knife is almost essential but I also keep on hand some single edge razor blades and a good pair of scissors. I buy my #11 X-acto blades in packs of 100, as it is very important to have a sharp edge. I can easily go through as many as ten or more blades covering a medium size airplane. There's nothing more frustrating trying to cut a clean straight line, only to have a blade "chatter" or tear the material. Change your blades often.

Measure twice, cut once!
A good, metal straightedge is also important. My arsenal consists of a 48" straightedge/ruler (for the long wing panels), an 18" and a 12" ruler that have a cork backing (it helps keep the film from sliding while cutting). I also keep a small tape measure on hand and a felt-tip marking pen (the marks can be removed later with alcohol). I try to cut the film at least 1" to 2" larger in all directions than the panel I'm covering. While I'm sensitive to being frugal with the seemingly expensive material, it's much easier to have a flap to grasp for stretching the material as much as possible while tacking it to the surface. Save those extra pieces after trimming. They come in handy later.

You'll also need a way to shrink the film to eliminate any small wrinkles that may occur. I use a couple different good, adjustable temperature, heating irons to tack the film down. One is a small iron with a handle and a temperature control on top, like the one made by Top-Flite. The instructions that come with the different films usually have the optimum temp settings for different stages of application. It's important to know what setting your iron needs to achieve those temps, as each iron differs greatly. I use a small surface thermometer to record the correct setting to activate the heat sensitive adhesive on the back of the film. This helps prevent melting the plastic and gives the best adhesion to bond to the wood. Another special iron is a tack or fillet iron. This has a small head with either flat or rounded surface that can get into small spaces. More on its use later.

Other equipment that come in handy for a professional looking covering are a "hot glove" for holding the film while heating and stretching; a trim tool that holds #11 X-acto blades to trim material a certain distance from the edge for clean overlaps; trim solvent to attach graphics without heat; and a tool called "SmartStripe" by Top-Flite that allows you to cut perfect striping tape any size you want out of Monokote type films. Cutting your striping this way allows you to perfectly match the colors of the covering and it is thinner (and cheaper) than the commercially available automotive striping tape.

Of course you'll need a good supply of paper towels (I like the stronger soft automotive paper shop towels), soft terry cloth towels, and an assortment of solvents like alcohol, acetone, and MEK. Window cleaner like Windex, a plastic polish and even Pledge cleaner/polish complete the job.

Next, I'll go into getting started applying the film.


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« Last Edit: March 15, 2008, 01:00:56 PM by Skydanz » Logged

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« Reply #2 on: November 26, 2007, 08:54:48 PM »

Now that I’ve recovered from stuffing myself with turkey and all the fixin’s, let’s get started applying the film.

In my first post, I discussed any dent repair and final sanding of the framework. This is very important. The finish of your covering will only be as good as the framework you put it on. I always spend a little extra time sanding out any bumps from misaligned stringers or butt joints, etc. with a long sanding block and fill any dents with the lightweight spackle compound. There may also be some color residue leftover from the adhesive of the previous covering that will need to be removed. There’s nothing more frustrating than applying a light colored film to your model only to find the dark stains left on the wood show right through! This residue can be usually be removed by light sanding with 120 grit sandpaper, followed by 400 grit to smooth things out. More stubborn stains can be removed or at least lightened to an acceptable point by rubbing with a paper towel soaked with a solvent like alcohol or acetone. If the previous covering was Monokote, Topflite’s Trim Solvent is excellent for removing the stains. Allow the solvent to completely dry before finish sanding. If available, blow off the entire piece with compressed air. Use a clean tack cloth just prior to applying the film.
HINT: Only wipe the wood in one direction with the tack cloth, preferably with the grain.
I’ve found that wiping back and forth tends to pick up the ends of the grain which shows through the covering as little bumps.

The first “Rule of Thumb” is bottom to top, back to front. Whuh?  When a model is painted, it doesn’t have any seams (unless you want the scale panel lines). When a model is covered with film, you end up with a bunch of seams which can be rather unsightly if done wrong. Sunlight can play a cruel trick on your model. Things that go unnoticed in your shop under fluorescent or incandescent light, stick out like a sore thumb when you set it down in the bright sun at the field. There is a way to trick the eye into “missing” those seams by having the overlapped edge of the film facing down. The edge of film coverings will reflect light in the sun and show up as a fairly noticeable line. By having the edge facing down, there is nothing to reflect thereby “blending in”.

HINT: Start by covering the bottom of the parts first, then the sides and finally the top.
This goes for the wing and stab as well. By covering the bottom first, the top can be wrapped around the edge so the seam is underneath. Another way to make seams less noticeable is to add trim or graphics over or near the seams. It’s an old graphic arts way of directing the eye to focus on the things you want and follow a flow to another spot on the piece, away from the more insignificant spots, in this case, the seams.

HINT: It is also important to cover from the back to the front.
The most obvious reason is aerodynamic. Should a seam become loose, and if the overlapped seam were facing toward the front of the aircraft, airflow at 60+ miles per hour would quickly tear the covering off. Unless you’re covering an electric or sailplane, most model fuels tend to attack the adhesive of the films over time and will tend to delaminate the seams when forced into it at flying speeds. Another reason to wipe down your model after every flight with a good spray cleaner!

Time for a turkey sandwich!


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« Last Edit: January 02, 2008, 01:08:21 AM by Skydanz » Logged

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Skydanz
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« Reply #3 on: November 27, 2007, 11:56:30 PM »

One of the tasks that worries a lot of modelers about re-covering an ARF (Almost Ready to Fly), or even repairing a plane, is how to cover around those pesky hinges. I have been using a technique that addresses that problem with great success.

Once the surface has been stripped of the old covering, it is important to remove any remnant pieces of covering in and around the hinges. A small pair of hemostats comes in handy for grabbing the little bits of covering that always seem to stick around. It is also possible to use the small sealing iron to press any stragglers back down to the wood. Again, check for any major dents or fractures and repair if necessary.

I’ll use the wing/ailerons covering as my example but the same technique is used for the stab, rudder, flaps, etc.

HINT: It is important to cover the ends of the ailerons and the inside edges of the wing adjacent to the ailerons first. Use the small sealing iron to apply little scraps of the covering to these areas and trim flush with the edge. If the wingtip is flat or beveled, cover these now as well and trim flush to the top and bottom surface.(Refer to the pictures below)

Assuming you are starting with the bottom of the wing, measure one wing half, including ailerons, and add 2” to the chord and 3” to 4” to the span. I prefer to cover each half of the wing at a time with a ¼” overlap in the middle, especially if there is dihedral. Align the leading edge of the film approx. ¼” past the leading edge of the wing so that it wraps around to the top of the wing and tack the film down in a couple places. Now, using a “diamond” pattern, first tack the inboard edge of the wing in the middle and then stretch the film at the tip and tack. Tack the middle of the leading edge then stretch and tack the trailing edge of the wing. Complete tacking and stretching at each corner then the rest of the perimeter in several spots. DO NOT ATTATCH THE FILM TO THE AILERONS AT THIS TIME! Completely seal the inboard edge of the film and seal the leading edge by rolling the film around to the top.

to be continued:


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« Last Edit: November 28, 2007, 12:04:04 AM by Skydanz » Logged

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Skydanz
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« Reply #4 on: December 01, 2007, 01:23:02 AM »

Sorry about the lapse in postings here. It seems like I have a lot on my plate right now and the Holidays aren’t making it any easier. The sewer backed up and the kitchen faucet wouldn’t shut off. I have three aircraft waiting on the workbench that I’m finishing for other people. If the TV hadn’t quit working, I probably wouldn’t have gotten back to this post this soon!

OK What about the hinges? Now that the covering is stretched and tacked down, there should be a flap extending past the aileron hinge line. Make a cut at each corner of the aileron at a slight angle toward the trailing edge. Pic #1 Now, make cuts on either side of each hinge from the center of the hinge line to the trailing edge of the film. Pics #2,3 Slide a corner of each flap through the gap between the aileron and the wing. Sometimes it’s necessary to use a pair of small hemostats to grab the film and coax it through a really tight hinge gap. Pics # 4 Once all the flaps have been pulled through, use the small sealing iron to tack the film to the wing while pulling and stretching. Pic# 5 The trick here is to remove as many wrinkles in the film as possible now. On a hot day at the field, your covering is less likely to relax and wrinkle if the film is tight to start with. Flip the wing over and seal the other side of the gap. Pic #6 Trim the excess flush with the surface. Pic # 7 Seal the covering down at each hinge then cut off the excess by cutting right on top of the hinge itself. Pics # 8,9 Reseal at each hinge if necessary.

Repeat this proccess on the rest of the wing before final shrinking the surface. I'll go there next, if the roof doesn't start leaking.


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« Reply #5 on: December 01, 2007, 07:29:24 PM »

The Ailerons are covered much the same way as the wing. Measure the length (span) of the aileron and add only about ¼” for the film. Measure the width and add at least 1” for the film. Center the film span wise so that approximately 1/8” overhangs each end of the aileron. Align the film with the trailing edge so that the film can be wrapped around at least the actual edge and tack down. (see pic) Tack the film down on the ends of the aileron while stretching. Using the same technique for the wing, cut slits for each hinge. Insert the flaps through the gap and tack down with the small sealing iron.

HINT: As you tack the film down, some wrinkles may occur. Simply use the iron to reheat a previously tacked spot so that the film can be repositioned.

Once you are satisfied with the application, seal around all edges EXCEPT for one end of the aileron. We need a place for the air to escape when the finish shrinking is done. Trim the excess film leaving the open end of the aileron alone until finish shrinking is complete. Cut the flaps at each hinge and seal.


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« Last Edit: December 01, 2007, 07:36:26 PM by Skydanz » Logged

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« Reply #6 on: December 02, 2007, 08:21:41 PM »

Now that everything is covered (right?), its time to do the finish shrinking.

Trick: Now is the time to do a final check for any wing warp. An incidence meter is indispensable for any modeler. I use mine on every plane, including ARFs. This can be done without the wing attached to the fuselage by setting the wing on a block of foam or a large towel, folded several times, and then weight the top down firmly. However, a good hand level that is about as long as the chord of the wing can be used to do a rough check for incidence. We are only checking for a difference in incidence between each wingtip. If you have a flat bottom wing, do this with the wing inverted. Place the hand level on top of one wingtip so that the end of the hand level is vertically aligned with the trailing edge of the wingtip. Use a small block to prop up the level at the trailing edge. Now look at the bubble on the hand level and mark one end with a felt pen. (If the bubble is not somewhere near the middle of the hand level, adjust the angle of the wing until it is and then mark the bubble.) Transfer the hand level to the opposite wingtip in the same way and block up in the same place. Look at the bubble again. A straight wing will have the bubble in exactly the same spot. If it is not within a bubble length then you have a warped wing. You may be able to take some, if not all, of the warp out by twisting the wing, opposite to the warp, as you apply heat to the film.

I almost always use a good heat gun to do my finish shrinking. The iron, even with a “Hotsock” on it, tends to leave fine scratches and dents in the film. Start at the center section of the wing and work towards the tip. I try to heat a large section first to soften the film in all directions and then pinpoint the gun to shrink. It takes a little practice but when you see the film shrink, follow closely with a soft cloth or mitt to make the film adhere and then move on. Shrink the film on the ailerons from the sealed end to the open end. As you reach about 1” from the end, reduce the amount of heat and go ahead and seal the end. Doing this way helps eliminate bubbles that pop up when there is no where for the air to escape.


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« Last Edit: December 02, 2007, 11:51:28 PM by Skydanz » Logged

Time spent flying is not deducted from one's lifespan.
Skydanz
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« Reply #7 on: January 02, 2008, 12:57:09 AM »

Now that the aircraft is covered, it’s time to put on some trim. Almost every kit, even ARF’s, come with instructions and usually a picture of the plane is printed somewhere on them. If you’re lucky, they’ll have a three-view of the plane. I will scan and print a couple copies of the picture so that I can layout a trim scheme on it. Colored pencils or even Crayons can be used to get an idea of how the colors will look together. Once you’re satisfied with the trim scheme, layout the design on the trim covering film. If the design is complicated, like scallops or a freeform design that needs to be mirrored for the opposite side, I’ll cut the design on some heavy paper and trace it out on the film.

The secret to getting bubble free trim is to use a solvent to adhere the trim to the covering. There are several products that work well with most covering films like Top-Flite’s Trim Solvent for Monokote or another product called No Heat that works well on Ultracote and Econocote. I’ve even used a commercial cleaner called Cinch that will soften the backing on many films. Another item that is essential is some sort of transfer liquid that allows the trim to be positioned or repositioned exactly where you want it. I’ve used a spray window cleaner with some success but a product called Rapid-Tack, available at TAP Plastics, has yielded excellent results for me. Originally, Rapid-Tack is designed for applying vinyl decals by softening the adhesive and allowing the air trapped under the decal to be squeezed’ out.

HINT: Make sure the covering is clean and dust free before applying the trim. Also make sure the covering has been heat shrunk and any wrinkles ironed out.

Generously apply the trim solvent to a clean, lint free cloth or shop towel and wipe the covering in the area where the trim will be applied. Quickly spray the transfer liquid directly over the area you just wiped with solvent and give the adhesive side of the trim a light mist as well. Now lay the trim down on the covering and position. Spray a little more on top of the trim. Use a soft squeegee or even a credit card to work the bubbles out, working from the center out to the edges. Remove the excess liquid with a paper towel as you go. Allow the trim to set undisturbed for at least an hour or more so the transfer liquid can completely evaporate. Do not use an iron or heat gun as it will cause any moisture under the trim to turn to vapor and create a bubble. I will let the trim set overnight before handling; just to be sure the adhesive has completely bonded with the covering. Now any striping tape can be applied, if needed.

Trick: Wipe the covering with Pledge furniture polish for a beautiful shine. Plus, it repels dust!

By using the techniques I’ve described above and a little patience, anyone can achieve professional looking results in their covering that they will be proud to show at the field.


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