Building Foam RC Planes
Foam is an ideal building material for electric powered RC models
Foam is has been in existence for several decades. Only recently has foam found widespread use for building lightweight radio control model airplanes.
Since the dawn of practical RC flight in the mid 1960s, all models were powered by gas engines for outdoor flight. Balsa and various other hardwoods were used to make just about every airplane built, as these construction materials had adequate strength for the engine vibration and stress loads of these larger aircraft.
Foam for non-structural aircraft parts
Foam was used for non-structural sections of numerous RC model aircraft, such as a turtle deck, fuel drop tanks, or portions of a nose cowl. Foam is lightweight and easily shaped, making it a very suitable material for these sorts of modeling tasks. But it was the lack of structural strength that made building a foam RC plane a difficult goal to achieve.
This concept for RC aircraft design changed with the advent of micro radio control systems for model flight. Starting around 2005 or so extremely lightweight electronics, rechargeable lipo batteries and powerful tiny electric motors for the first time allowed for practical micro RC flight.
This changed everything for the RC hobbyist. One could now fly year round in colder climates. The low cost of these control systems combined with numerous ready to fly airplanes and helicopters, caused RC model plane designers everywhere to rethink old assumptions about building foam RC planes.
For starters the existing limitation of the low strength of foam could now be addressed. Lightweight RC models produce very little stress on the airframe. These models usually fly slowly so that any crash or hard landing has a minimal chance of damaging the airframe. For the first time foam can be widely used as a primary construction material for radio control models.
Foam can be reinforced
It now became an easy matter when building foam RC planes to include some reinforcement to prevent wing flexing or add fuselage strength. Carbon rods, strips and tape can be glued on the foam surface of a model aircraft, or cut into channels in the wing. Carbon rods provide very effective bracing and reinforcement of thin foam wings for indoor flyers, just as wire bracing was used to strengthen World War I aircraft. This bracing concept can be used for model monoplanes as well as smaller biplanes such as the 4-Site.
If carbon reinforcement is not available, wooden dowels or strips of plywood work well as substitutes. This concept of combining a lightweight material (foam) with a reinforcement material such as plywood can be applied to all your lightweight model building tasks. Note my use of 1/16 inch plywood to reinforce the balsa wing dowels in the Blackburn and the Chickadee.
The use of electric power precludes the need for any type of fuel proofing for a foam model plane. You do not need to cover or even paint a foam RC model.
An inherent advantage of building foam model planes is the fact that you can design and build an airplane very quickly.
Foam is ideal for rapid prototype model construction to test different model design concepts. Foam allows a modeler to try various wing sizes and placement, tail layouts and nose moments to achieve your desired flight performance. Once the design is finalized, you can then prepare a final set of construction plans and make the final version.
Experiment with different types of foam
There are different types of foam used for model airplane construction. The best way ahead is to see what others have accomplished with the various types of foam either at your local flying site or on one of the internet forums.
Foam is inexpensive enough that you can obtain samples and test them on your own. Depron is a popular thin and lightweight foam used on smaller models. EPP is a flexible foam used in many ready to fly models. Foam used as insulation for building construction is available at home improvement stores, and comes in brand names as Blucor Fanfold, or a generic name with pink foam board.
In summary, foam has always had potential as an inexpensive, easy to work material for building foam RC planes. The need for structural strength required by larger gas powered aircraft precluded the widespread use of foam.
This has all changed now with the widespread use of small flying model aircraft. Foam is the ideal construction material for these aircraft due to their light finished weight and low flight loads. The ability to selectively reinforce foam structures with carbon or wood allows for even more innovative use of foam as a foundation building method for today’s micro RC model aircraft.
Author: Gordon McKay