Covering The Wings
Poly Fiber System


The following is a Poly Fiber, Poly Tak covering job of the wings. We will also present an AFS system wing covering job in another web page. Please remember, there are usually several ways to complete any job, the following information is just one of these examples.

Tapping Down Edges

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Prior to taping the gusset edges, it is recommended to first use a plastic mallet to tap down the edges as close to the aluminum tubing as possible. This should be done on "ALL" gussets and sheet aluminum edges throughout the plane. This will help in the long term effect of reducing the gusset edges from cutting or wearing through the covering or skin of the plane after the plane is flying.

Taping The Edges

The best tape to use for taping off the gusset edge and rivets is a Dacron First Aid tape available at WalMart in 1" X 10 yard rolls. The covering is also made of Dacron, so if it ever gets wet, it will not mildew or decompose. For all the edge and rivet taping throughout the plane, you will need to buy about 5 to 20 rolls, depending on how many layers of tape you use. Only one layer is needed to protect the fabric from sharp edges. However, for a more professional look in hiding edges and rivet heads under the fabric, you may wish to use up to three layers.

Aircraft Spruce also sells a simular tape. A roll of 1" X 60 yards sells for $7.30 and may actually be the better deal, price wise.
(Pricing as of 10/2006)

Some builders have successfully used sports grip tape, such as used as a grip aid on bat and hockey stick handles, while some others have used just plain masking tape for the taping of edges. However, masking tape wears very quickely and would not be the choice for this job.

Any of the above mentioned tapes seem to do the job of stopping the fabric from abrading on the rivets and sharp edges and eventually wearing through the fabric.

         
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Be sure to apply three (3) layers of the Dacron tape over all rivets and sharp edges, like the gussets and aluminum sheeting edges.

         
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Adding Quilt Batting To Aluminum Sheeting

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Although not required, adding a quilt batting to all aluminum sheeting surfaces will keep the fabric from unevenly sticking permanently to the aluminum when painting. This also gives a much smoother surface and look to the fabric after painting. A standard quilt batting and double sided Scotch Tape was used for this purpose. Both products are available at WalMart and many other stores.

         
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First, lay out the quilt batting, then cut the size needed to completely cover the surface of the aluminum sheeting. Apply the double sided Scotch Tape on the aluminum sheeting along its inside perimeter, then diagonal strips about 4 inches apart down the length of the sheeting.

Now, just lay the cut batting onto the aluminum sheeting and press down to adhere the batting to the double sided tape. That's it!

         
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Masking For Straight Glue Edge

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When getting ready to apply your glue to the spars and wing tips, it is best to use an inexpensive masking tape to create a "straight" glue edge. The glue edge about 1/8" after where the covering fabric starts to wrap around the wing spar. You will need to cover the "BOTTOM" of the wing first.

         
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Before applying any tape or glue, be sure to lightly sand off any corrosion and completely clean all aluminum surfaces to be taped or glued with MEK. (DO NOT USE STEEL WOOL)

See MEK Warning Information before using.

Another Tip!

Concerning "old" Poly Fiber - Poly-Tak glue. It is said to throw it out if it becomes dark in color. Depending on how the glue is stored, this can happen after a year or two of sitting in the can. When the glue begins to darken with age in the can, it loses some of it's ability to create a strong bond between the metal and the fabric. I know some guys take a long time to complete their build. You should be informed about using old dark glue if you wait too long to finish with the fabric covering.

After the masking tape has been applied, you will need to apply two coats PolyTak glue from the glue line and extend around the spar to about the middle of the inside of the spar.

The photo to the right shows this process after the bottom covering has been finished and the top is ready for covering. However, the gluing process for both top and bottom are very similar.

         
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Use a small paint brush to apply your glue. Wait until the first coat of glue has fully set up before applying the second coat. Once both glue coats have completely dried, remove the masking tape by folding the tape back onto itself and slowly pull the tape off.

What Glue To Use

There are two primary types of gluing systems, Poly Fiber's Poly-Tak with MEK and AFS bonding system, using CecoBond Cement with AFS Heavy Duty Cleaner. We will be using the Poly Fiber system for this process.

Covering The Bottom

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You can either tape the fabric into place or use something to weight the fabric along the edge to hold the fabric flat and without major wrinkles for gluing.

         
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Making sure the fabric is as free of wrinkles as possible, liberally apply about 10 inches by 1 to 1-1/2 inch of MEK with a small brush to the surface of the fabric which will soften the glue below. Using your fingers, immediately work the glue on the spar into the fabric until the MEK has evaporated.

For safety reasons, it is recommended to use MEK resistant chemical gloves.


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Now, repeat this process for securing the fabric to the wing tips by 2" and the inboard covering which wraps around the most inboard "BRACED" rib.

The factory recommends leaving the inboard section uncovered.

         
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You can either turn the wing over or leave it as it is to trim the edge of the fabric to accommodate and pass by the wing ribs to finish gluing to the inside of the wing spars with MEK as described earlier.

         
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After you have covered the bottom, you will need to open any bolt or rivet holes in the fabric on the spas which are under the applied fabric. If you do not do this before covering the top of the wing, the holes will be very difficult to locate under two layers of fabric.

Using a standard, inexpensive soldering iron, burn or melt the fabric to open the holes "now" before continuing.
         
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Shrinking The Fabric

Cooking Thermometer
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Start with a household iron set at about 225F to 250F or 107C to 121C. Most builders will use either a $10.00 cooking thermometer or the far more accurate $70.00 Raytek Minitemp MT4 laser, infrared thermometer, available at www.infrared-usa.com.

         
Raytek Minitemp MT4
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After allowing your glued material to set and harden for a while, you will need to shrink the bottom wing fabric before proceeding.

Using a household iron and either a candy thermometer or laser temp. gun, adjust your iron to about 250F degrees and shrink the material slowly until it is taught. You will not do the final 350F degree shrinking until both top and bottom fabric gluing have been completed.

         
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Covering The Top

When applying the glue edge masking tape, start at about 1/8" after where the covering fabric starts to wrap around the wing spar at the top and end about 1/8" prior to there the bottom fabric leaves the spar. This will give you about a 2" glue surface to work with for gluing the top fabric to the spars. Wait until the first coat of glue has fully set up before applying the second coat.

Prior to applying your glue to the spars, first apply about a 1/4 inch coat of Poly Tak glue to the top portion of the ribs from one end to the other. You will need to reactivate this glue "after" ironing the fabric to full tightness with MEK and before applying the reinforcing tape on the fabric above the ribs. This will take place in the next article, called "Securing & Riveting The Wing Ribs".

The builder of this Challenger used a personal technique. What was done was to apply two coats of Poly Brush to the glue area, then two coats of Poly Tak on top of the Poly Brush coats. This is the reason for the "pinkish" coloring in the glue. Although this works, Poly Fiber only gives directions for the use of just the Poly Tak.


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Again, you will need to apply two coats of Poly Tak glue between the two masking tape glue lines.

The photo to the left shows the two coats of glue applied with the masking tape removed. The photo to the right shows about 1-1/2" area glued down using MEK to reactivate the glue below the fabric.

         
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Use a small paint brush to apply your glue. Wait until the first coat of glue has fully set up before applying the second coat. Once both glue coats have completely dried, remove the masking tape by folding the tape back onto itself and slowly pull the tape off.


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Using a single edge razor blade, fold the loose excess fabric back onto itself and place the razor blade in the fold. Hold the fabric snug while holding the razor blade "FLAT" with the spar surface, cut off the excess fabric by carefully sliding the razor blade along the spars surface. This will give you a nice "straight" cut at the glue edge line.

Once you have finished gluing the top fabric and the glue has fully cured, it is time to start shrinking the fabric.

First, set your iron at 250F degrees to take out all the loose wrinkles and bring it all slightly taught. This lower temperature will keep you from shrinking one end of the wing fabric more then the other. Once this has been done, reset your iron to 350F degrees and iron again to bring the fabric to full tightness.

         
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Now, turn the wing over and iron the bottom at 350F degrees and you are done with the wing covering process.



In the next section, we will go over attaching the top fabric to the wing ribs with reinforcing tape, rivets and finish tape.


That's it, you finished one wing. Repeate the above processes for the remaining wing.