Ray’s Rant #3
What we ended up talking about last Rant is really called wing loading. It is calculated by multiplying the wing span by the chord (width) and dividing that by the weight of the aircraft, that will give you it’s wing loading. Thankfully, most quality plans and kits have figured all these things out, so we just have to follow the plans in building an airplane that we can fly.
This time I want to look at the materials we use in building the models, and the good points, and bad of the materials.
This is probably still the most common, but is being replaced quite quickly by newer materials. Most people are knowledgeable about wood, and the different types of glues we use. The wood most commonly used is balsa wood, which comes from Ecuador in South America. It is a very light soft wood, and comes in many grades, the top grade being triple A balsa. Good balsa is not easy to get these days, but still is usable although expensive compared to many types of wood available locally.
Wood’s good points are: we are used to working with wood, and it can be used in many ways. It comes in strips, sheets, and blocks, depending on what use you need it for.
Wood is strong in the direction of the grain, not so strong across the grain. To a point it can be bent to the shape you need without cutting. Sheets can be cut into many different shapes, and when working around a bend, can be softened by wetting it, and bending while wet, and allowed to dry in the shape you need it.
Blocks are handy for areas that need to be filled, and it is easy to shape with a knife, and is easy to sand.
There are many types of glue available to bond the pieces together.
Some of the disadvantages are: Wood rots over time, can soak up water and oil.
It can also warp and twist unless handled carefully. It takes time to build an airplane out of wood, but not as labour intensive as some other materials we will mention. There are other things, but these are the main ones.
We have newer woods available now, and one that is very useful, and speeds up building time. Light ply gives us a plywood that is slightly heavier than balsa, but has the better strength of the two. It is three ply, and is also easier to cut than regular ply. A lot of our ARF’s use this type of material, and can be made into a light and strong model.
We also have our regular aircraft ply wood, of several thickness and number of plys. We use this for firewalls (1/4 is 7 plys), undercarriage attachment points, and wing spar doublers.
Foam has really set off a splurge in park flyers, and indoor models. Molded foam airplanes are allowing larger airplanes, and well detailed scale models to be available as RTF’s. Most modelers don’t have the tools or knowledge to make these types of models. Foam is fairly forgiving in a crash, and can be glued back together, although moderation has to be used, as weight can quickly be added, and so lose the advantage of its light weight.
Styrofoam has been used for many years to make wing cores, and if care is taken, you can cut wing cores a home with a hot wire, and some help from another pair of hands. Once you have the cores cut, you can quickly make up a strong wing. Just be careful in what adhesives you use, because many of them will dissolve the foam.
We use this material in many applications in a model, one of the most impressive is the high quality fuselages that can be turned out, with external details molded right in. In a larger model in can be made light weight for its size, and comparable to most other materials. It is repairable, and broken areas can be built up and reinforced by another layer of cloth and resin. Its biggest drawback, is the time needed to make a mold, and lay up the fuse sides. If you are only making one model, it is going to be a long labour of love, but makes sense when a number of models are made from the mold. Also, not many of us are familiar with the resins and cloth and procedures to make up a fiberglass fuselage.
I am going to include in this section a number of materials we can use that are manmade materials that are useable in making a model.
One of the new ones that I think will be used more once builders figure out how to best use the material. Coreplast is a material new to many, and is used mostly in combat planes, because it is a light and strong material. I call it plastic cardboard, and as modelers get used to using it, that it will be used in many more applications as time goes on. It has a lot going for it, and with some imagination I think we will see it used in models a lot more in the future.
Carbon fiber, and this type of material is coming into more use as well, and is strong and light.
The point to be made is that most planes are a combination of all these materials, and next rant we will look at how we can incorporate them into our building of models that can produce a strong light flying model.