Airfield Models - How To

Create Multi-Part Covering for a Non-Sheeted Structure

May 05, 2015



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Airfield Models (http://www.airfieldmodels.com/)How to Create Multi-Part Covering for a Non-Sheeted Structure Using Iron-On Film

This technique will allow you to create colorful trim schemes for your model while avoiding the excess weight and bubbles created when ironing trim over solid pieces of covering.

Having some graphic arts skill is helpful but is something I'm far from qualified to instruct.  It is important to create a good set of patterns which is not covered in this article.

I have no idea how much time I spent creating the actual trim scheme but it was many hours over several weeks until I was happy with it.

Cutting the patterns, film and applying it took one long day probably about 12 hours taking frequent breaks.

 
 

Graphic created in CorelDraw.Before you get started you should thoroughly clean your workbench, cutting mat, straightedges and anything else that will be anywhere near your work.

Before you begin cleaning, remove your shop foreman so that he isn't actively shedding hair in areas you just cleaned.

You will squeegee the film several times meaning that you'll have lots of opportunites to scratch and dull the film.  Always wet the film with window cleaner before using the squeegee to help prevent scratching.  Ensure the edge of the squeegee is smooth.  Soft plastic squeeges can be wiped across regular copy paper to smooth the edge.  Sand the edge if necessary and finish it off by wet-sanding with fine paper.  Soft plastic or rubber squeegees can be purchased from an automotive supply store.

A wing covered with multiple pieces of iron-on film.When the various pieces are ironed together and ready to be applied to the airframe, clean the adhesive side of the covering with window cleaner to remove dust, lint and other particles.  If you are using a transparent covering then handle it only along the edges that will be trimmed off so that you do not leave fingerprints inside the covering.

I've had no problems getting the covering to adhere to the airframe after cleaning it with window cleaner, but if that concerns you then you can give it a final rinse with water.

While handling the covering be sure not to crinkle it.  The best way to remove the backing is with the covering upside down on the bench.  Pull the backing straight back over itself rather than straight away from the covering.  The static in the covering will hold it down and prevent it from wrinkling.

Joined covering for the BMJR Models Splash-E rudder.The minimum that covering should overlap is 1/4" unless the part to be covered is particularly small.  For wings I normally make the overlap about 3/8" so there is no danger of it coming apart while I'm tugging the covering around wing tips.

I overlapped the covering for the BMJR models Splash-E rudder about 1/16" which worked fine, but I don't think that is enough for larger components.

Make a good set of patterns from heavy paper stock.  I use 11" x 17" cardstock when it's large enough.  Otherwise I use poster board.

If one poster board isn't large enough then you can butt additional pieces together using tape along the seam on both sides of the boards.

The outlines drawn on the board are the actual outlines of the wing.  Note that I accounted for excess covering around the perimeter so that I have something to hold while applying the covering.

Always ensure the covering is flat and smooth on the board before working with it. Throughout this process you always want the covering to be as flat on the surface as possible.

That includes when tracing the pattern, when cutting the finished piece and especially when sealing pieces together.

When the protective clear backing is removed from the covering there is a strong static charge which we will use to our advantage here.

Use a bench brush to smooth the covering.

If necessary, use weights to prevent the pattern from moving while tracing it. If the pattern is large then you may want to place weights around the edge to prevent it from moving or lifting while you trace it.
Sharpie markers work well and can be removed with alcohol. I always use a Sharpie marker.  It cleans off easily with alcohol.
Use a straightedge for straight cuts. Use a good straightedge for straight cuts.  I always protect the piece I'm keeping with the straightedge.  If I slip or cut away from the straightedge then the mistake is on the waste side.
If you're careful, curves can be cut freehand. I can cut along a curve well enough that I don't bother trying to use a template to cut around.

By the way, the edge will be smoother if you spray window cleaner on the cutting mat and then squeegee the covering down.  Wipe up excess cleaner before cutting.

Again, whenever you use a squeegee, wet the surface first to avoid scratching the covering.

After the film is cut to size, remove the marker with with alcohol. Remove the lines drawn with the marker when you have finished cutting the film

The coverings I have used are not affected by alcohol on either side.  Wipe from the center off the edge and use alcohol sparingly to avoid it seeping under the covering to the adhesive side.  Even though alcohol doesn't seem to affect it you still don't want to be rubbing it into the covering adhesive.

Test fit the pieces together. Test fit the pieces together and make any corrections necessary.  The white will be on top of the red and blue.  I've placed it underneath to check the fit because I can't see through it.

One thing I didn't mention is that whenever possible seams should face away from the airflow.  That means they should be to the rear and out.

In this case, the red is the bottom-most piece followed by blue and then white.

Clean your glass thoroughly.  Spray window cleaner and place the first piece of covering on it. I have only attempted this technique on glass.  It will probably work on smooth, clean metal as well.

Clean the glass one final time and inspect it closely.  You don't want to iron crud to the covering.  Use a soft, lint-free cloth to remove the cleaner.

Spray the area for the first piece of covering.  This will be the piece on the bottom of the stack.

Wet the covering with more window cleaner.  Squeegee the film smooth and flat. Wet the covering with more window cleaner and squeegee it smooth and flat.
Spray more window cleaner for the next piece of film. Spray the area for the next piece of covering.
Iron the two pieces together. Float the second piece into the correct position and squeegee it.  Work from the center toward the edges.

If the covering isn't aligned correctly then remove it, spray some more cleaner and try again.  It's not too difficult, but sometimes having a helper makes it easier.

Iron this piece down.

Practice on scraps first to find the proper setting on your iron.

I found out that I've been doing this the hard way.  In the past I tried to use only the tip of the iron so that the covering would not become distorted by heat.  In this example I'm using Oracover Lite which irons on at about 210 and shrinks at about 230.

These temperatures will not even begin to bond the covering together when it's on glass because the glass extracts a lot of heat.  I gradually turned up the iron until I could peel up the blue and the red came with it.  The iron was over 325 before that happened.

What I also found out was that I didn't have to use just the tip of the iron.  I could place the shoe flat on the seam which not only sealed it better but it didn't shrink or distort the covering at all.  It had absolutely no affect yet the pieces were firmly bonded to each other.

You should always try to peel the covering apart before you actually remove if from the glass.  You need to know if it's actually stuck together or not.

Continue adding the rest of the pieces ironing each one down before adding the next. Add remaining pieces using the same technique.

Again, check that it is bonded well before removing it from the glass.

Apply the covering just as you would a single piece. All that's left to do is to iron it on the airframe as usual.

This wing is thick having tips with extreme compound curves.  They are a challenge to cover even when using a single piece of covering.

I covered this wing by myself and applied a lot of force while using a heat gun to get the covering to conform to the tips.  In other words, I was pulling very hard on this covering.  The seams never gave any indication that they were even thinking about coming apart.

I used a heat gun to shrink the covering after it was adhered around the permiter of the wing.  I did have to use the gun along the seams to fully shrink the covering but I kept the gun moving and stopped as soon as it tightened so that the seam wouldn't come apart.

If I have time, I will also write an article about making the actual covering patterns using computer software instead of a drafting table.

 
 

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Copyright 2006 Paul K. Johnson