Airfield Models - Installing Robart Hinge Points

Join Wing Panels of a Flying Model Airplane

May 03, 2015

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Back to Joining Wing Panels


Airfield Models ( a Wing Center Section

Many wings are butt-joined and held together with fiberglass tape wrapped around the center joint.  To say I was concerned about the integrity of the wing the first time I built a kit using this method is an understatement.

Nevertheless, no wing I have built has folded for any reason and many were joined using this method.  I trust fiberglass tape for up to moderate aspect ratio wings even wings on aerobats placed under extreme flight loads.

Also see

Cut a piece of fiberglass tape long enough to wrap around the wing with enough excess to make it easier to work with. Fiberglass tape is readily available in various widths through the hobby industry.  Use the width recommended by the kit manufacturer.  If in doubt, use wider tape.

Wrap the tape around the center to get a rough measurement.  Give yourself some extra length to make it easier to work with.

A piece of masking tape wrapped around the tape will prevent fraying.  The tape can be cut with scissors.

Use low tack masking tape to help align the fiberglass tape. Measure half the width of the tape onto both wing panels.  Wrap low-tack masking tape around the wing.

The masking tape serves two purposes.

  • Makes it easy to keep the fiberglass tape centered.
  • Keeps the epoxy from making an ugly, difficult to sand mess.
Tack one end of the fiberglass tape to the wing trailing edge using thin CA. Use thin cyanoacrylate (CA) to tack the fiberglass to the trailing edge and only the trailing edge of the wing.

Using a sharp razor blade or a sanding block, remove the excess fiberglass tape.

Wrap the fiberglass around the wing, pull it taut and tack it with thin CA. Wrap the fiberglass tape around the wing, pull it taut and tack the other end.  Do not pull the tape so tight that the weave is distorted.

Trim off the excess.

Note that if the wing has a large amount of dihedral it is sometimes easier to use individual pieces of tape on the top and bottom of the wing to prevent wrinkles.

The fiberglass should be taut, but not so much so that the weave is distorted. The tape is centered and snug.
Work epoxy through the fiberglass to create a very strong bond. Mix up some slow-cure epoxy and brush it on the tape using an acid brush (also called epoxy brushes).

I like to use laminating epoxy because its thin viscosity saturates the cloth faster and more easily.  Regular epoxy glue can be used instead.

Work the epoxy until it fully saturates the cloth.  If the glue doesn't saturate the cloth then the wing joint will be weak which can result in catastrophic failure of the wing in flight.

If it is too difficult to get the epoxy to saturate the cloth, you can warm it with a hair dryer which will make the epoxy watery thin.

Never thin epoxy!

Heat will also cause the epoxy to begin setting up sooner so ensure the entire tape is coated with epoxy before you warm it.

The wing is shown suspended above the table because both the top and bottom of the wing were fiberglassed in the same operation.

It is easy to see when epoxy has properly saturated fiberglass cloth. Here you can see how the tape should look when the epoxy has properly penetrated the weave.
Remove the masking tape while the epoxy cures. Remove the masking tape before the epoxy sets up.
Wrap new masking tape around the wing to protect bare wood from sanding. Wrap low-tack masking tape around the wing after the epoxy has fully cured.  The tape is to shield the bare balsa from the coarse sandpaper.

Low tack tape is used because sanding will cause the tape to have a stronger bond.  If regular masking tape is used it can actually damage the bare balsa when the tape is removed.

Fiberglass tape has a finished edge to prevent it from fraying.  This edge is thicker than the rest of the tape.

Use coarse sandpaper on a small sanding block to feather the edge of the fiberglass.

Avoid sanding into the cloth everywhere except the edge.  Especially avoid the center of the underside of the wing where the most strength is needed and it is easy to sand into the cloth.

Sand the edges of the fiberglass cloth so that they feather into surrounding areas. A little more sanding is needed if I want the edge of the tape to be invisible under the covering.  This wing is mounted to the underside of the fuselage and the tape will not be seen.

I spent more time feathering the tape on the underside of the wing which is visible but stopped here on the top of the wing.

The wing panels are now permanently joined and properly aligned.  Hopefully this series of articles has demonstrated the importance of joining the wings properly while also showing that it is a matter of patience and technique but not a mysterious skill possessed only by expert model builders.

Feel free to contact me if you anything isn't clear or you have questions.



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Copyright 2004 Paul K. Johnson