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Balsa Vs. Foam

  • Written By: Peter Goldsmith
  • Posted: 2005-03-16

Twenty-five years ago there were only a few materials used to produce model aircraft. There were some plastic control line models and the occasional foam free-flight aircraft, but the majority of models were produced from a combination of balsa and ply. In fact, there were not many kits available, and almost no ARFs or RTFs. In the '70s, more and more kits were becoming common in the hobby store. The '80s brought with them two-income families, and increased the value of people's time, or lack thereof. This caused ARFs and RTFs to blossom in the field of radio control aviation, allowing the modeler to enjoy the building and flying experience in a shorter time period. One of the by-products of this industry shift was an increase in the variety of models on the market and a somewhat shorter lifespan for each model. No longer did the modeler have to spend six months building his dream; it could be done in a few weeks.

With the growing interest in park flyers, there has also been an explosion in the number of unique materials used to produce these aircraft. With improved electric power systems, airframe weight has decreased. And with the recent development of Lithium batteries, the weight savings afforded by the batteries' lighter weight has allowed for stronger, somewhat heavier materials to be used for airframe manufacture.

The question posed to me was, "What's the difference? Which is better, balsa or foam?" A simple enough question, but the answer stimulated this article.

The ParkZone F-27 Stryker is an uniquely shaped "foamie".

"Foamies"

The best way to get the discussion started is to understand why certain materials are used. Foam is widely used in park flyers because of its lower weight and its ability to produce virtually any shape imaginable. Most of these "Foamies" are manufactured using polystyrene type foam. They are produced using an injection molding process where the foam is injected as a liquid, and allowed to cure following the contours of the mold. Many of you may have seen the aeration holes in your own foamies that result from the molding and curing process.

If you're a modeler that is actively involved in park flyers and small RC aircraft, you are typically driven by two needs: variety and speed. I call park flyers "fast food modeling." We all have our major projects: a scale aircraft, new IMAC aircraft, sailplane, or even a jet. But when laboring away on these bigger projects, we still need to fly; we still need our modeling fix. Park flyers, just like fast food, answer this hunger. You can assemble them quickly and fly them anywhere, making foam easy to use and fast to manufacture. Fast manufacturing leads to my answer to the consumer's need for "variety." "Wow, I built this thing in two hours, and it flies great." I know this has been one of my thoughts. And the next thought that usually crosses your mind: "I might get another to build next month." You can probably start to see the pattern that is developing here. There are many foamy-type park flyer aircraft on the market so you have a wide selection to choose from and can build your new model in a shorter amount of time.

One of foam's biggest assets is its ability to produce almost any shape. There are, of course, some shape examples where foam may not be optimum; wing trailing edges, small thin protrusions, etc., but in general, all of the full-size aircraft you see flying can be reproduced fairly accurately in foam. Another popular use of foam is in the profile model, meaning it has a full shape outline but there is no width to the components. The models are simply cut out of a flat sheet. Basically get your favorite 3D-view and enlarge it to the appropriate size. Then trace the outline onto the thin foam laminate and presto, you have made an entire aircraft. The next step is to glue the pieces together, add the radio gear, and typically a small electric motor, and presto-you're flying. There are many kits available, and prices are competitive for these profile type models. E-flite produces a range of profile models where all the work is done for you. Just glue the parts together and you're ready to fly in hours. Most of these kits come with attractive decal sets or in some cases the scheme is printed directly onto the foam. The typical foam types used in these models are called Depron. It is slightly higher in density than the injection molded foam (styrene) but is manufactured in a similar manner. Like all foams it starts out life as a chemical, which then expands, aerates and produces the final lightweight material.

Special adhesives need to be used when gluing most forms of foam. There are some exceptions, but most will react to cynoactrolate type glues unless they are "foam friendly." Most epoxies will work with no effect on the foam, and hot glue and most water-based woodworking type glues are also acceptable.

To summarize, the value of foam park flyer aircraft seems to be variety-driven; the quality is acceptable and the assembly time is fast. Repairs are easy and in most cases durability is quite good. Many modelers see a foam model-affectionately known as a "foamy"- as a kind of low emotional debt type situation. Not much time is invested, therefore not much value is perceived. They have their place and supply us with our weekly aero modeling fix.

The E-flite Mini Funtana.

The Value of Balsa

The more traditional materials in the park flyer world are making inroads into the segment as well. Quality balsa/ply and covered models are popping up all over. For example, E-flite has produced the Mini Funtana, responding to this growing segment with a familiar method of manufacturing that is somewhat new to the park flyer market.

For the flyer looking to spend a little more money and a little more time, new balsa and ply park flyers are the perfect option. Consider these planes as less like fast food and more like cuisine food-still eating out, but higher quality. So instead of fast food, we may spend a little more money on the finer cuisine, yet still save time on preparing at home. I know most of you don't eat your models but I think you get my point. The balsa/ply type models are definitely higher quality in most examples I have seen. They have a higher perceived value, and they do also cost a little more. So what do you get for this extra investment? Time spent preparing these little miniature beauties is much the same as foamies, and in some cases a little faster as you are working with materials and glues you are used to using with your more traditional modeling projects. For some reason, we all feel comfortable using balsa and ply; it just seems right that models are made from these materials. Many of the ARF models come pre-covered in some pretty cool schemes. Most use the popular brands of covering and trim, so repairs are as easy as matching the color scheme with a simple trip to your local hobby store. In my experience the balsa-type models seem a little lighter and have better flight performance. More accurate airfoils can be produced, and wing loadings are less due to the more weight-conscious materials. These models are probably more fragile but typically are not flown in high-risk areas. Most are flown in parks, local fields, back yards and so on. Some make it to the indoor activities, but due to the congested flying space, risks of mid-air collisions are increased. As always the emotional debt factor seems to drive all of our decisions in modeling. The amount of time and money we invest in our models seems to be directly related to our preparation and flying attitude. Unlike foam, the balsa/ply planes seem to have a preferred place in the heart of the modeler. It's a statement of quality to purchase these. If you like nice stuff and appreciate workmanship, you're going to love what's on the market now. Miniature versions of all your favorite pattern-type models, 3D aircraft, and in some examples scale models, are starting to appear.

And The Winner Is...

So, which is better, balsa/ply or foam? It really depends. Like everything in life it's all about the context. If you are a traditionalist, a connoisseur of model aviation, or just appreciate familiar and quality materials, I would say you're going to lean towards the balsa and ply type models. If you're a go-getter, a compulsive flyer, have little time, live on the edge, or like variety, then foam is your friend. Fortunately Horizon tries hard to appeal to all of the wonderful personalities and preferences in this great sport. It's not easy sometimes reaching everybody, but it's a challenge we all enjoy.

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