HOW TO COVER

WINGS

I am in no way an expert on covering; however, I've had years of trial and error and, now, obtain pretty good results. At the request of a friend, Keith, I developed this page to describe my techniques. The first thing I do is follow the directions for the brand of covering I am using. The rest is practice, practice, practice. For this project I'm using my Sig Somethin' Extra kit.

image01.jpg First and foremost is have a clean area to work. I can't stress this enough. You need cleanliness to keep from damaging the wood prior to and during covering. Oops, looking at the picture I didn't follow my own rules. Well, let's use that old saying, "Do as I say, not as I do."

image02.jpgSand your project carefully. I don't go all the way to 400 grit paper. I normally use 150 grit with a light circular motion to prep the surface to cover. Fill any gaps, voids, etc, with a lite-weight filler (I use lite-weight spackle), let dry then sand smooth. Next vacuum to remove dust and loose particles. Now you're ready to start.

image03.jpg Cut your covering at least 1" larger, all the way around, than the surface you're covering. The extra covering is used to pull, adjust, and stretch while working. Since my wing tips are flat, I prefer to cover the ends first then lay the top and bottom covering. This makes for a smoother job. The foremost advice I can give is get the covering as TIGHT as possible before you go to shrink it, (I'll describe the steps I take in the next paragraph). I overlap the tip covering onto the upper and lower surface about 1/4" to allow a good joint between the different layers of covering. Since this is a solid surface, you MUST permit air to escape while sealing the covering down. I leave a small area unsealed and then, in this case, use the iron to shrink and seal the covering to the wood starting from the furthest end and working toward the 'vent hole'. Once finished, go back and seal down the complete perimeter. (The sock on the iron helps prevent scratching the covering while ironing/shrinking. I only use the sock when shrinking large areas. I go 'sockless' when tacking and sealing down the seams.)

image04.jpg I'm a little out of sequence here. Shown is the top covering being applied. When you do your wing, always do the lower surface first and the upper last. This puts your seams on the down side where any residule fuel, oil, water, will drain off the covering and not try to seep under the seam. Remember what I said, pull the covering as tight as you can before shrinking. I start by tacking the covering on the root about the half-chord mark. I then stretch and tack the covering on the tip at about the same position. Next pull and tack the covering at the leading edge about half-span mark. Now pull tight and tack the same area on the trailing edge. This picture shows my covering '4- pointed'. Now pull and tack around all four corners. This will remove most of the wrinkles. While this is a little tedious, continue to pull, stretch, and tack around the wing about half-way between the previous tacks. Again, your directions will describe this for you, follow them and stretch, stretch, stretch. If it makes you feel better, I normally break something, like sheeting, crack a rib, etc, while pulling and tacking. A little CA and care will fix/minimize this sort of damage. Once you've got it good and tight seal the edges down. Don't shrink yet. I like to cover top and bottom before shrinking. This helps reduce shrink induced warpage.

image05.jpg Okay, back to the proper sequence. I decided to go with a WWII pursuit color scheme for this project. In doing so I wanted to add invasion stripes. When I change color schemes I like to anchor everything down on wood, not change colors over open bays. I applied the white for the invasion stripe between two rib bays using the cap strips as my anchor points. I applied the covering the same way as described above. Note the covering is virtually wrinkle free, with only a slight wrinkle on the lower right side of the open bay BEFORE I use the heat gun. The more wrinkle free you are BEFORE you shrink, the better your result will be. Don't be tempted to shrink each color as you go. Apply your scheme and shrink all at once. Again, this will help prevent warpage.

image06.jpg Now how do you put on other colors and keep the edges straight? Easy, take your time and mark your covering with reference lines. You also want ~1/4" overlap of seams to ensure a good seal that won't allow liquids to seap into the wood. Here the outer yellow covering has been added and the inner section is marked prior to covering. I use a flexible 'sewing tape measure' to go around curves cleanly and a non-permanent felt tip pin to mark my straight edge. Apply the covering in the usual way, making sure the edge of the covering falls alongside the straight-edge mark. Once all the covering is applied, use the heat gun to shrink and seal everything down. I use a soft glove on one hand and while heating with the gun, go behind with the gloved hand to attach the covering to the wood. I work the solid surfaces first and work toward the open wing bays. Once all solid surfaces are sealed, finish shrinking over the open bays.

image07.jpg Now for the black stripes. Since I'm covering over covering, I put a sock back on my iron and reduce the temperature. To much heat and you'll quickly form those unattractive bubbles under your covering. If this happens (and it will) use a sharp pin or X-Acto knife to poke small holes for the air to escape and apply heat to seal down the covering. Again, mark a straight edge to follow and apply the covering. When overlaying pieces like this I use a different method. First tack down one side and hold the other end up while ironing towards it. This helps provide a place for gas to escape before forming bubbles. Go slowly, gently, and with low heat to minimize bubbles.

image08.jpg Ta-Da!!!. One wing panel finished! Cover your ailerons in the same method and using the same care. Carefully match up your trim lines between wing and aileron to present that seamless color scheme.

STAB

image09.jpg image10.jpg Now that the wings are done I've moved to the horizontal stab and elevators. I covered just like the wings, bottom first then top and keeping everything tight. Because there isn't much place for air to escape, I covered both top and bottom and THEN before shrinking, I drilled a small hole through the TE of the stab and LE of the elevator into the open structure. Now when shrinking the air can escape through these holes and not get trapped inside the structure. I made my holes with a 1/16" drill bit and below the hinge line so they can't be seen. Once the covering was shrunk using the iron and sock I installed the hinges, mated the stab and elevator and, once satisfied with the fit and freedom of movement, I applied a few drops of thin CA to both the bottom and top side of each hinge. Once the CA is set I sealed the hinge gaps. While not always necessary, sealing the gaps gives a much cleaner appearance, can only help improve performance, and only takes a few minutes to do. I used a 1/2" wide piece of covering which was folded down the middle. Attaching one end of hinge seal to one end of the elevator, I pulled the strip tight and ran the sealing iron down the middle (see the left photo). Trim the end to match the the surface edges and iron remaining hinge seal to the stab and elevator. On the right you'll see what it looks like with one side sealed and the other unsealed.

FUSE

image11.jpg Now it's time for the fuse. First a little trick. If you model using faring between the stab and fin, it's best to attach them first and cover along with the fuse. If you cover separately and attach later you'll end up with a tail covering job that doesn't flow well. To support the fairings use scrap balsa to act as fillers where the stab and fin will sit. I've done this with my Somethin' Extra and pinned the filler in place while I cover. You can do the same by either pinning or tack glueing the filler into position. Use this procedure when sanding the fuse and fairing blocks to keep a smooth flowing surface.

image12.jpg As with the wing, cover the bottom of the fuse first and lap up onto the sides about 1/8". Start your covering by tacking front to back (pulling tight of course) then tacking the side about midway. Repeat the procedures as the wing. Once it's fulling attached around the borders of the fuse, trim the excess and shrink.

image13.jpg image14.jpg Now do the fuse sides. Because of the shape of my Somethin' Extra, I was able to do the side and half the fuse top with one piece of covering. If you're model doesn't allow to do this easily, then cover eash side and then the top with a separate piece. Like everything before, tack, pull, tack, etc. On the left is the left fuse side covered before shrinking. On the right is the right side before covering. Because of the stringer turtle deck fuse top, I covered both sides and overlapped the top seam on the top turtle deck stringer BEFORE shrinking. To shrink one side first and then attach the other side, the top stringer would likely get pulled to one side and not proved a straight appearance. If your plane uses a normal 'box' fuse, you don't have to shrink all at once. You can, if you like, attach and shrink each side separately. Remember, no matter how you do it, provide a place for air to escape while you final shrink/attach the covering. Overlap the side covering about 1/8" around the bottom of the fuse. This will provide around 1/4" overlap of bottom-to-side covering which will help prevent fluid sepage onto the structure. The top covering is applied last so it overlaps the side pieces in much the same way.

image15.jpg Lastly the servo access hatch is covering. I did mine with a single piece of black covering. Once all the fuse covering is in place you can fuel proof the firewall, wing saddle area, hatches, etc. I use 30 minute epoxy thinned with a little acetone or denatured alcohol. Thin the epoxy mixture down to an easy painting consistency and brush on. Overlap the mixture onto the covering in the fuel proofed areas to help seal everything up.

PUTTING IT ALL TOGETHER

image16.jpg After covering the tail feathers I temp install and measure for square. Once satisfied with the alignment I mark where they enter the fuse and then remove them. Trim the coveing inside this mark ~1/16". Epoxy and/or CA WON'T stick to the covering, so you need to removed the covering for a good wood-to-wood joint. I prefer using epoxy to glue the feathers with. Apply sufficient epoxy to the horizontal stab and fuse, slide together, check for proper alignment and pin in place. Once the epoxy is set do the same with the vertical stab. In this shot, the tail feathers are already installed along with the control surfaces.

image17.jpg Ta-Da!!! The covering job is done. I cut numbers out of Monokote and used the iron, with sock, on low temp to attach them to the fuse sides. I used my computer to size the numbers to what I needed, printed them out then transfered to the Monokote.

image18.jpg No plane is done without a proper pilot. I hate pilotless planes!!! I found Crash Bandicote (sp) in the local grocery store and he was already done up in flying gear. I cut him to fit inside the canopy and secured him in place with clear RTV. The canopy was attached with RC-56 glue and trimmed with black striping tape. image19.jpg And now we're at the field ready to go. All surfaces were checked for proper direction and amount of movement. Powered by a Super Tiger .51 the Somethin' Extra took to the skies with NO corrective trim required. WOO-HOO!!! My .51 isn't running that well, so I'll replace it with a O.S. .46 for the next flying session. All that's needed is to finish off the wheel pants and add them to the plane. I hope this helps in getting the most out of your next covering job.

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