The output end of the Apstar High Graphic Rotary Die-cutter (above left). This is equipped with UV driers to instantly dry inks on the surface of clay coated


board would be oriented along the span of the wing, or along the length of the fuselage. Because the flute runs this way on the wing or on a rounded part of the fuselage, it is easy to manipulate a curvature by creasing the cardboard parallel to the direction of the flute, without losing any strength. As a mat- ter of fact, the camber helps increase the strength.


Obviously, a plane with a fair amount of compound curves wouldn’t lend itself to the use of cardboard. That’s why a quick perusal of some of Chuck Felton’s designs will show planes with relatively straight lines that are far more suited to cardboard. And even with those the plane becomes a bit of a hybrid with parts like cowls, canopies, or fairings carved from balsa or foam blocks. Glue is an easy matter as Chuck has al- ready pointed out in the Caravan article. Since it’s a paper product white glue, an aliphatic resin, canopy glue like Pacer’s, or even hot glue works really well. In the Sutherland plant there is an automated glue machine that spreads beads of glue when joining the packaging. A single bead of hot glue could be flanked on either side by a white glue. The hot glue provides a quick cure and tack that allows the white glue to soak in and cure over a longer time for a stronger bond.


Then there’s the question of weight. There is a lot of “air” in this material. In one of the pictures you’ll see Joe holding a 4 × 8-foot piece of ¹⁄₈-inch something called “kemi” kraft paper. That’s the regular corrugated with clay and white mixed into it. At that size it was a little cumbersome to handle but it didn’t weigh more than 7–8 pounds. And it was easily large enough to build two of the Cessna Caravan Chuck shares with us this month.


Being a paper product it will readily ab- sorb moisture, much the same as balsa, so it does need to be sealed like balsa if some sort of paint is applied, and more especially if a glow or gas engine is in the nose of the mod- el. Unlike balsa with its microscopically un- even surface, and its occasional minor or major dings and dents, cardboard doesn’t need a filler coat, only a sealer—if it’s to be painted. Chuck likes dope finishes for their extremely light weight and his long famil- iarity with the technique involved. Hard to change what’s always worked well, even if the new “thing” offers all kinds of miracu- lous claims and advantages.


So what other things to use for sealer then? Water thinned (about 50:50) white


FLYING MODELS


board. It imprints vibrant colors for display and brand work. Another look at the size of the machine (above right). Could even print colorful models!


glue brushed on very evenly dries quickly, seals well, doesn’t raise any paper grain and is compatible with almost any kind of paint. As long as a very thin coat is evenly brushed on, weight gain will be negligible. And it won’t curl or warp the surface.


Same can be said about Minwax Poly- crylic Protective Finish, though this is more expensive, and it does leave a sheen if the semi-gloss or gloss finish is used. One of the best features of either technique is that cleanup can be done with water. No thinners needed.


From this point on any paint could be used. Thinned acrylics sprayed on with an air brush or acrylics from a spray can seems a good choice, especially since they can be eas- ily cleaned up with water. Latex house paints have also been used in a technique perfected by Roy Vallaincourt, which can be found on his website www.vaillyaviation.com. MonoKote, or any of the other opaque heat shrink films also work well as Chuck points out in his article. But, he says, don’t apply a sealer. The bare surface will provide extra adherence of the film’s adhesive. One concern with applying a paint finish is the “bleed through” from the brown of the regular kraft paper corrugated. Light col- ors? Absolutely, there is bleed through. That’s where two other types of corrugated may be preferable. Both have a white liner on one or both sides. The first is a kraft pa- per that has gone through a bleach to make the paper white. This has the same surface texture as regular kraft paper.


The other white corrugated is the “kemi”. The surface finish on this comes from the clay and white that is mixed into the slurry. The resulting paper will be used for the lin- er, not the flute. It offers a surface that actu- ally has a bit of sheen on it and Joe Suther- land suggested that this might offer the best option for a paint finish.


Unfortunately, but realistically there is something else to consider: repairs. Acci- dents will happen. Each material that’s been used over the years for modeling has its own repair techniques based on the severity factor from 1 to 10. Balsa, fiber- glass, or foam generally use methods unique to themselves. So where would cardboard fit in?


Most likely the techniques used wouldn’t be very different from balsa. Say a leading edge is bashed in. First the damaged section would be cut away using a template of the replacement “skin”. The balsa leading edge would be spliced into the existing one and


In honor of FM’s visit, Joe created this corrugated bipe with some preprinted graphics. As long as he gets the c.g. right, it should fly! All we need is the plan.


47


some thin balsa “shelves” glued under and around the perimeter of the remaining structure. The “skin” template of cardboard could be glued in place to the shelves and edges. Of course, it might require some filler to smooth things but all that would be left to do is some patchwork paint.


Can’t say if all the foregoing has tipped your personal scales from mere curiosity to a “let’s try this once” but there’s one more thing for consideration, a good source of the cardboard satisfactory to building models. One place to try for the appropriate size would be a furniture store, or a dealer for things like snowmobiles or lawn tractors. A better source is a cardboard packaging company like Sutherland’s. It was pure chance that the company was so nearby, but in the interview Joe said that packaging companies like his are not a rarity. They won’t be in every town, or even county, but they will be regionally close by that won’t in- volve more than an hour or two’s drive. Even better than that many will gladly sell or give you what Joe called sample sheets, the sheets large enough to build mod- els. Companies like his often support the lo- cal community and provide the large sheets of cardboard used in community projects like the scenery backdrops in a school play. It may not be the miracle material but cardboard is worth consideration. It may not rank quite as high in advantages as balsa but there is a lot to be said in its favor. It is much cheaper than balsa. It is comparably strong and resilient, and it is reasonably available in the sizes needed. Perhaps a for- ay into a “paper” airplane may be a captivat- ing and thoroughly enjoyable experience.


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