I’ve been covering RC models for about 35 years. I picked up on MonoKote back in the mid-80’s and tried it for the first time. It took a bit of learning curve but I got the hang of it. Over the years I refined my technique to include fixing errors I made at first and kept improving things up to the present day. Many years ago I tried SolarTex and LOVED using it. I considered it my favorite covering of all. But sadly, 2 years ago SolarTex decided to hang it up and closed their shop. This left a BIG void in the best iron-on covering out there until OraTex came out with a very suitable replacement. They don’t have as many “flavors” as SolarTex did, but hopefully they will continue to expand their line with more colors.
I’ve seen lots of covering jobs at the field and some are good and some not. As always, there are usually a few good builders who do great covering work. But as a rule, I find most ARF’ers simply do not “get it!” One problem seems to be that those doing the covering want to get in a big hurry to finish and their works show it. Covering properly takes TIME and lots of it. One cannot rush thru this job. I will attempt to show how I do the iron-on covering job with OraTex Orange on a couple of pieces of the Top Flite Hellcat Ready-To-Cover model. My final color scheme is a post-WW II drone. Some say that the Orange depicted in some drone photos from that era are incorrect and the real color of the drones was Red. But there were clearly some variations on the Hellcats that might also include a few Orange “Cats” as well. But that’s really beside the point here.
As usual, my articles are primarily written for the newer RC pilots and builders. I realize many words have been spent on this subject, but like Western, War, and Sci Fi movies that keep getting made and remade, there is always a new audience coming into view.
I would also add that having a rather LARGE supply of #11 blades is a great idea. I buy them by the 1,000 blade unit to make sure I don’t run out. It only takes a few cuts to dull a blade. So don’t make yourself work harder over the cost of a few blades. You work will appear MUCH SHARPER when changing blades out after a few cuts. It sounds wasteful but it’s important.
First thing to have for any covering job is a good covering iron that can be adjusted from low to high heat settings. OraTex tends to like lower heat settings so I had to buy a new iron to replace the one I have had 35 years and only gives HIGH heat!
Figure 1. Old and new irons. Old TF MonoKote iron on the left and new Hangar 9 iron on the right. I really like the new iron! Note the heat setting about midway on the scale. Good place to start for OraTex.
Once you have the iron set and while waiting for it to heat-up, you may begin cutting you covering material. In this article I am covering the horizontal tails and elevators, and then the center wing section.
Figure 2. Horizontal tail and elevator of the Hellcat. This is the Ready-to-Cover example which is great for those who want something different from the crowd! Workmanship on these is really nice. They come ready to hinge with Robart pin hinges.
Figure 3. The first step is to cover the trailing edge to include and overlap on both the upper and lower surfaces. This overlap is important to add as it keeps the covering from pulling off the balsa if the covering is simply ironed on the balsa with butt joints. You will see how the overlap comes into play in a bit. The first step is to iron the covering to the trailing edge.
Figure 4. A nice 1/4 inch overlap is suggested. Too little overlap and you won’t get the solid attachment to the covering on the upper and lower surfaces. You should calculate the total width of the strip to include the overlap and cut it on the work table FIRST and then iron it on the piece. That way, there is very little additional cutting to be done and most important, you won’t be cutting into the balsa to trim the overlap.
Figure 5. Take the iron and press down on the overlap all the way around the surface. Make sure not to allow any wrinkles when you do this. Once you get a wrinkle they are hard to erase!
Figure 6. Once you get the Trailing Edge (TE) and overlap ironed on you may cut material for the upper or lower surface. With a small overlap on the TE, iron the upper or lower covering at the TE ONLY and VERY CAREFULLY. The point here is to get the covering firmly glued at the TE and not to shrink the rest of the covering. Then lay the iron FLAT on the surface, but all in one motion, sweep across the surface firmly. Remember that the iron is hot and if you leave it idle it will begin to shrink the covering in an ugly manner. KEEP the iron MOVING. This will glue the covering down to the balsa itself rather than just tacking the edges of the piece and shrinking the top which is not a particularly strong covering technique. Do this sweeping motion all across the surface working toward the Leading Edge (LE). It will take several short passes to do the whole surface.
Figure 7. At the TE, take your #11 blade and carefully slide it down the TE and cut away any excess top surface material. But don’t let the blade dig into the TE covering. It’s a good idea to do this with a new blade. With the overlap you created on the first TE covering, you now have a very strong bond between the two surfaces. Covering-to-covering bonding is much better than just covering-to-balsa as the balsa is relatively porous. Now, not to exclude ironing on the balsa as explained on the previous step, as that is a different situation where you don’t have any covering to overlap.
Figure 8. After ironing the covering down across the surface and around the LE, take the #11 blade and very lightly cut the covering just to one side of the peak so you will have a small overlap. But DO NOT cut with much pressure! You may be weakening the structure by doing so! It’s not so critical here, but on other areas of the covering job, it may be EXTREMELY damaging to structure.
Figure 9. The cut is made and the covering gently pulled off the surface.
Figure 10. The last part to trim is the rounded outboard edge. But first be sure to iron the covering PAST the centerline to the other side and THEN finish the trim cut.
Figure 11. Both Leading and Trailing edges trimmed of excess covering. These cuts do not have to be picture-perfect as we still have more to do.
Figure 12. Last trim cut on this surface is the inboard edge. First, iron the covering over the edge about 1/4 inch or so.
Figure 13. And then trim the covering in a neat overlap. You don’t want to fully cover this edge as it is generally epoxied to the fuselage here. So, never use epoxy over 100 percent covering – recipe to disaster!
Figure 14. One side done and one side to go!
Figure 15. With the opposite side covered like the first side and trimmed, you can (just barely) see how the two coverings meet at the LE and blend together nicely! But we are not done yet!
Figure 16. To keep the two surface coverings from pulling apart in the heat of the day at the field, I add another “overlap” of about 3/4 inch material to keep the two surfaces locked tight. Start at the inboard edge and glue it down.
Figure 17. Making sure you have the overlap even on both sides, continue down the LE with the iron. Where the curved edge starts, be careful and slowly work the covering around the curve. Small wrinkles will be smoothed out with the iron and won’t show. I generally taper the last couple of inches of any curve with a small scissors to keep the big wrinkles from forming.
Figure 18. Final overlap is almost invisible if you work slowly to keep wrinkles out of there. Last trim is at the inboard edge. This final overlap also protects the LE from any fuel that gets leaked out of the engine or fuel tank. Once your covering gets gas or glow fuel between it and the balsa, it will start to peel apart.
Figure 19. One horizontal tail is finished. Almost looks like it’s painted if you work carefully.
Figure 20. Now comes the elevator covering. The elevator is done slightly different from the stab. First step is to cover the LE with a large overlap!
Figure 21. Cut and add the top or bottom covering to the LE first and then pull it tight and tack it over the TE. You don’t want it guitar-string tight here, but try to keep the material snug as you can without warping the elevator. Once you have it tacked to the TE, run the iron on top of the TE to secure it tight. Continue around the curved end of the elevator, pulling the covering snug as you go. DO NOT SHRINK the covering at this time! Wait till you have both sides covered and THEN shrink it carefully. You can still warp the piece by too much shrinking.
Figure 22. Back side of the elevator after covering one side.
Figure 23. Iron the material over the inboard end and then trim as shown.
Figure 24. As with the horizontal stab, trim the excess off the elevator with a new blade. Elevator should be as shown at this point. Note that the covering has not been shrunken. Continue to cover and trim the opposite side and THEN you may shrink the covering on both sides. But, do not go crazy with the iron! Just a quick pass or two on both sides at first. Then allow to cool a minute and see if it has any sags. Touch it up as needed with the iron. And I should have mentioned at the first, use the iron for the whole covering process, not a heat gun. Heat guns can burn thru the coverings before you know it!
Figure 25. When you have both parts covered it should look “clean” like the parts in the photo.
Figure 26. And then do the same thing on the other horizontal tail!
Figure 26. Here we have the center wing section. Large parts are done somewhat the same but with larger strips of covering. But there is a limit to how big each strip should be as too large a piece can be hard to handle without ruining it. First, cover the cutouts for the flaps. Then move to the upper or lower surfaces.
Figure 28. I laid out the material in 8 inch wide strips. This makes covering more simple. As with the horizontal stabs, you iron the covering on the bare balsa for most of the surface. You still have the overlaps around the edges. Make sure you have the covering straight across the wing and not cock-eyed.
Figure 29. With another 8 inch strip, add it on top of the previous strip but with a 1/4 inch overlap. Always move from aft to forward with the covering. Continue to iron the covering to the balsa as you go. Start with ironing the overlap seam making sure you are straight across the wing and then iron the material to balsa.
Figure 30. With the last 8 inch strip, cover the forward part of the wing with the same overlap as before. Trim out the openings carefully and leave some excess covering to be used as shown in the photo below.
Figure 31. Excess covering left around the openings to iron onto the wheel wells, in this case. You can go back and trim these more evenly if you like, but they won’t likely be seen later. Or paint the wheel wells green Zinc Chromate to blend it all in as one color. But the important thing is to ensure that the ends are glued down well. You may also mix a bit of Z-Poxy finishing resin and paint it over the ends to really lock them down.
Figure 32. Trim the edges like before. Then move to covering the opposite surface.
Figure 33. Top side of the center wing covered and done. Top side was done exactly like the bottom side in three sections applied from aft to forward.
The end of the tour!
That is the nickel tour of my iron-on covering techniques. There are always going to be different techniques required when moving to other parts of your model, especially the fuselage. The fuselage is one area that you DO NOT want to trim off covering around certain areas over balsa using a #11 blade! Cutting into balsa on certain fuselage parts can lead to structural failures. So, plan ahead with your coverings over sensitive spots to finish with a straight cut (made on the work table) and end with just ironing it on without any trimming.
Perhaps the most important feature of my covering method is always using an overlap (where possible and practical) to keep the pieces from pulling away from each other when the model is in the heat of the Sun. This can be with a simple 1/4 inch overlap of two sections of covering or by adding a separate overlap like I did on the leading edges. Either method works well.
When using other coverings such as MonoKote, they tend to require slightly hotter iron settings, especially going around curved surfaces. Adjust your heat settings until you get one that works, but try to keep from using more heat than is actually required.
Take your time. No need to be in a hurry. This material is fairly expensive, so think-through each panel’s covering completely – measure twice and cut once. Also, keep in mind that craftsmanship is important; NO, it’s EVERYTHING!
TEXT & PHOTOS BY LANE CRABTREE