Foam RC Planes Add a New Dimension to Model Flight
Electric power and foam RC planes make an ideal match
Model airplane construction in general, and radio control models in particular, have made several evolutions over the years. The first rubber powered free flight model planes flown in the early 1900s were made from bamboo yet turned in some surprisingly good flight times.
Lightweight balsa wood quickly became the model airplane building material of choice. Today, with the rapid introduction of micro-sized RC gear, powerful electric motors and lightweight rechargeable batteries, foam RC planes are an increasingly popular building material.
Using foam to construct RC planes has several advantages. Foam is inexpensive and incredibly lightweight. Foam is typically not as sturdy as a typical balsa wood model airplane structure. Balsa has the advantage of coming in different densities (strength) and can use the stronger wood grains in areas requiring greater strength.
Glues and foam
You need to select with care the glues that you employ to bond foam parts. Foam safe cyanoacrylate (CA) glue usually works well, as does epoxy glue and hot glue guns. As each type of foam can have slightly different characteristics, be sure to test any glue on a scrap piece of material before using on your foam RC plane.
As with testing glue for a foam model, you will need to do the same for paints and other coverings. Foam can melt with the typical temperatures used to apply heat shrink plastic coverings. These heat activated coverings can be applied in certain low temperature cases. Check the manufacturer’s recommendations and test on a sample of the foam.
The same caveats go for any type of paint on foam. Test first on a piece of scrap material before working on your final foam RC plane. Some paints attack the foam, literally melting whatever foam surface the paint is applied on.
The good news is there are several paint products that do not damage foam, yet adhere well. As a general rule, acrylic paints work well with most foam products. Also, any type of paint that can be cleaned with water should be a suitable match for your foam RC aircraft.
One final point on paint, glue and coverings for a foam plane, and this regards fuel proofing. A huge advantage of electric powered models involves the fact that you do not need to fuel proof your airplane. This is especially relevant for foam models, where the foam building material itself may be vulnerable from the effect of fuel used for a gas powered aircraft.
Check that whatever paint you employ for a foam model is waterproof. It would be a disappointment to not consider this aspect of your model’s finish, and notice a ruined paint scheme from exposure to a small amount of moisture.
Foam was never a largely successful building material for gas powered model aircraft. Foam usually could not provide a robust enough structure for the flight loads and stresses employed for these types of mid size to large radio control aircraft. As discussed earlier, foam is generally not resistant to the effects of engine fuel and exhaust residue.
Foam and electric RC models
The challenges of using foam on fuel powered aircraft vanish when used for electric powered models. With the smaller size of a typical indoor RC plane powered with today’s powerful electric motors, the use of foam as a construction material quickly becomes an ideal choice.
The flight loads on these smaller foam RC planes are far less than their heavier fuel powered brethren. Foam for these indoor flyers can be very thin and molded into complex curved shapes. And if additional strength or reinforcement is required, this can be quickly added by the use of lightweight carbon rods and strips glued into place.
There are a wide variety of foam types to choose from as you build your RC model plane. Depron is a popular thin insulation foam that can be formed for curves shapes in smaller RC models. EPP foam is a flexible variant, used for many ready to fly indoor RC aircraft. Foam board and Blucor Fanfold foam is a solid foam, and is used for slightly heavier electric powered RC aircraft.
The key advantage of foam model planes is that the foam is inexpensive and allows for rapidly building model aircraft prototypes. There is little downside to making an experimental aircraft to determine flight characteristics. It is even feasible to employ a simple profile plane design, and make several versions with different types of foam.
As always, seek a light aircraft flight weight, ensure a proper center of gravity location, and use carbon rods or strips as needed to reinforce weaker sections of your foam radio control model plane. Foam, employed properly, is a great addition to your RC model aircraft design and building techniques.
Author: Gordon McKay