Wing construction

Foamie: Solid Foam Core, No Skin

Monolithic Molded Foam Construction

Building the whole plane out of one chunk of un-reinforced foam can be a practical labor-saving method when the wings are thick and not very long. Planes like jets, with narrow, stubby wings that are attached to the heavy fuse along a very long chord, are perfect for monolithic foam. A flying wing will also tend to be made of monolithic foam, since every section of the wing tends to support its own weight instead of holding up a heavy central fuselage, and the entire wing is thick enough to provide significant bending strength. Monolithic foam flying wings are also very easy to make with standard EPS insulation foam, which comes in 4x8 panels very inexpensively.

Wings that have a large span relative to their chord and thickness, and which support a central fuselage, will be much less successful. With a brittle foam like EPS, extended wings will crack and fall apart, while a flexible foam like EPP will tend to allow extended wings to flap around without providing useful lift.

Sparred Foam Wing Construction

All large 'Foamie' Wings are internally reinforced, usually with long hollow cylinders made of thin carbon fiber, but sometimes with steel or aluminum bars. The source for the carbon fiber varies from off-label use of fishing poles or arrows, to dedicated suppliers which target RC enthusiasts.

Sandwich: Skin on Solid Core

Foam Sandwich Wing Construction

One of the first things that people do to improve sparred foam is cover it. Tape, in particular fiberglass-reinforced packing tape, is a very popular means of protecting against scrapes and preventing small impactors from ripping chunks out of the wing. The tighter and heavier this is applied, the more a resilient skin forms which not only keeps small impactors from damaging the foam, but strengthens the foam by providing a tensioned surface when it is stressed by flexing. Farther down the continuum, the foam provides enough compressive strength at any one point to keep the tape from collapsing, while the tape provides enough tensile strength to keep the foam from bending or kinking. This sandwich principle has been used not only with tape, but with thicker clear plastic covering material, and with glued-on balsa sheeting as well.

On the far end of the skin strength spectrum, fiberglass or carbon fiber may be applied directly to foam and epoxied in place.

Honeycomb Corrugated Panel Wing Construction

Foam is not the strongest of materials, and it turns out that a series of regular hollow chambers lined with rigid barriers can provide for very strong compressive loads. Again, combine with a moderately strong tension skin and you have a very lightweight structural member. Full-scale airplanes often use an aluminum or carbon fiber honeycomb wherever flat sheeting is required, to make it more rigid without adding the weight of a thick metal skin; Ikea uses this type of design with a cardboard honeycomb and 1/8" laminate sheeting to sell end tables that weigh practically nothing and will support hundreds of pounds.

This method and the foam sandwich variant are popular for heavier hotliners which need stiffness at the expense of weight.

Built-Up Wing Construction: Hollow Skin on Ribs

Thin ribs built of some material that is strong in compression, on the same geometric plane as the vertical stabilizer, provide compressive strength in this building method, while a skin of some strong sheet gives tensile strength. These largely hollow structures tend to be relatively brittle in collisions, but provide both inherent levels of rigidity which are hard to practically achieve with sparred wings, and very light weight. A very high degree of labor is required to build these wings compared to foam construction.

Balsa Ply Wing Construction

This traditional method goes back to before plastics existed, and is still popular among modellers for the ease with which balsa can be sanded down, re-epoxied, and repainted. That said, these tend to be extremely 'crunchy' models. Woods used include aircraft-grade balsa, obeche, and spruce.

Lattice Frame Wing Construction

A lattice of bent wood rather than ribs allows this hollow-core design to maintain a rigid shape with a bit more skin strength than a built-up balsa wing.

• How to make lattice wing skins - Airfield Models

Built Up Foam Wing Construction

Uses a foam skin on foam ribs, or potentially on smaller models a hollow foam skin suspended from continuous formers

Clear Composite Wing Construction

Competition sailplanes typically use carbon fiber ribs and a tensioned clear covering (sometimes brightly dyed translucent), the dominant brand of which is Monokote. With the clear version, one may see straight through the hollow wings. These tend to have stick-on adhesive and are shrunk afterwards using a heatgun to provide tension.

• Monokote How-To

Fiberglass or Carbon Fiber Wing Construction

The professional set tends to use the very similar (except for price and strength) carbon fiber and fiberglass sheeting. This is composite material, that is, braids of fiber woven together, layered with the weave at different orientations, and then suffused with epoxy. These tend to be built in pieces over a mold, and the epoxy distributed in one of two different ways, with a vacuum bag or in wet layup, then assembled. These tend to be much more expensive than balsa or foam, and considerably stiffer. This technique tends to be the most suitable for large model planes of a few meters wingspan, on up through full-size sailplanes.