When building RC planes with foam I think it is safe to say foam has become one of the most important materials for because of the ready availability and wide variety and use of low-cost electric power. It is much more economical for commercial suppliers of RC ARF aircraft to use foam than labor-intensive built-up balsa structures. In addition, the price for balsa wood, the traditional RC building material has continued to reach higher levels due to demand in other larger markets and limited supply.

 

There are a few Foam types available for scratch building RC planes with foam:

EPO / Expanded Polyolefin beads

EPS / Expanded Polystyrene beads (ice chests, cups, packaging, etc)

XPS / Extruded Polystyrene sheet (foam board core and other foam sheet applications)

XPS / Extruded polystyrene (blue and pink home insulation foam sheets)

EPP / Expanded Polypropylene beads

DEPRON - Depron is actually polystyrene (EPS/XPS) plastic and the (EPS) means expanded while (XPS) means extruded. For our purposes, we’re only interested in the stronger, denser

XPS Depron which also happens to be closed-cell foam.

 

When building RC planes with foam the simplest models are flat 2D foam models like :

Micro Extra

Micro Wing

Honda SU 26

Gee Bee R3

Shuttle-X

Paper Airplane

Fighter Combat

 

A bit more complex is a combo of the flat fuselage with airfoil wing or an airfoil flying wing :

Team Legit Forty

Rite wing Drak

Slice & Dice

Slice Flying Wing

Hurr-E-cane flying wing

 

Cutting Foam sheet when building RC planes with foam :

Make sure to use a new Xacto #11 blade

Xacto Razor Saw

Hacksaw (results in rough-cut edges that must be sanded to final dimensions so a bit of extra material must be accounted for

Hot Wire

The finish of foam edges by sanding and after sanding apply a thin layer of Elmer’s glue on the edge to help keep the paper edges tacked down.

 

Gluing of parts when building RC planes with foam :

3M-77 spray adhesive can be used to laminate paper-covered foam part

Use Foam Safe CA for all polystyrene-based foam

Regular CA is preferred on EPO and EPP foams but Foam Safe can be used

Epoxy, white glue (Elmer’s) can be used on all foams

 

Equipment mounting when building RC planes with foam:

1/8" plywood is usually adequate for motors in the 28mm to 35mm (and smaller) range. Add side supports to the ply mounting plate if the edges overhang.

1/64" plywood is recommended as underlayment directly to flat foam sheeting for mounting servos, speed controls, receivers, and especially the Velcro strip for the main battery. This requires carefully cutting just barely through the paper and removing it for an area the size of the 1/64" ply piece. When building RC planes with foam 3M Extreme Mounting Tape (thin black sponge-like) is good for small servos, receiver and speed control mounting. Hot glue can also be used if preferred for attaching parts like servos

 

Choosing a model when building RC planes with foam:

When building RC planes with foam pick an existing aircraft/model type & shape you like and find dimensional information and/or photo views on the Internet and then scale up (or down) to arrive at the dimensions for the desired model size. Using the scaled dimensions, then create line drawing outlines of the fuselage, wing, and vertical and horizontal stabilizers.

 

Determining CG  (center of gravity) when building RC planes with foam:

When building RC planes with foam If the model is not based on an existing design with CG information already established, then calculate the proposed design layout CG. If the wing is a simple constant chord design use a distance of 25% back from the leading edge as a good starting point. If the wing is a swept-back or tapered design then there are basic, easy to use CG calculators on the Internet.

 

Basic stability considerations when building RC planes with foam:

When building RC planes with foam If the design is not dimensionally or proportionally based on an existing one, then some consideration should be given to basic lateral stability (sometimes referred to as rudder moment arm). The ratio of the distance from the back edge of the prop to the CG to the distance from the back edge of the prop to the rudder hinge line should be in the range of 0.28 to 0.34. Typical is 0.30 - 0.32. Lower value results in the long tail moment and more stable better tracking. Higher value results in a shorter tail moment, less stable, and more snappy maneuvers. When building RC planes with foam other considerations are the vertical stabilizer area (includes rudder and fuselage area below the vertical stab and rudder) in the range of 10% to 12% of the wing area should be adequate for most electric powered foam RC aircraft. Another stability consideration referred to as “Static Margin” regards horizontal stabilizer (including elevator) area and placement. Some online CG calculators include

 

Choosing a power system when building RC planes with foam:

The basic considerations for the power system when building RC planes with foam are watts (power) per pound of model and KV. Make sure the power is adequate for your model when building RC planes with foam.