Airfield Models - Apply Fiberglass Cloth to a Model Aircraft Wing

December 19, 2021

How to fiberglass a model aircraft wing

This is Part 4 of a multi-part article describing how to apply fiberglass cloth to a model aircraft.

Part 1 of this series describes advantages of using a fiberglass base and recommended cloths to use.

Part 2 describes resins and squeegees.

Part 3 describes the fundamentals of applying the cloth.

You should have a good understanding of all previous parts before continuing.

Fiberglassing the wing

As is standard for most finishes, fiberglass is applied in several pieces from bottom to top. In this example, I use a single piece for the bottom and another for the top.

Normally, each the top and bottom use two pieces. Each piece goes from the tip and overlaps the center past the wing saddle on the opposite side of the wing. This method adds tremendous strength to the center of the wing.

Each piece must be allowed to cure fully so that it can be feathered before adding the next piece. Otherwise, the second piece will be sanded through where the first piece ends which will negate the advantage of having them overlap.

Normally two pieces of cloth are used on each the top and bottom of the wing with the cloth overlapping several inches in the center. In this case, a single piece is used because the additional strength of an overlapped joint is not necessary.

The standard method of glassing a wing is to use two pieces on each the top and the bottom of the wing. These pieces should overlap a healthy amount — at least past the opposite side of the fuselage.

Glass feathers beautifully, so the seam will never be seen. The overlap adds a lot of strength to the center section.

In this case, the wing is more than strong enough, so to save weight and time I am using one piece of cloth.

Pour a liberal amount of resin on one half of the wing.

I am using 1 hour epoxy. It is actually still workable well after an hour. In fact, this particular brand is about as thick as normal epoxy glue after about 4 hours. It takes over 24 hours to fully harden.

To make the job easier, I have applied resin to only one half of the wing. I will spread it out to cover the entire panel using a squeegee before continuing to the other half.

Before going on to the other half, I will remove most of the excess epoxy, but I am not going to spend too much time at it. When the entire wing is glassed, I will go over the entire wing removing as much epoxy as possible.

Again, the only job the resin has is to adhere the cloth. Any resin beyond that is unneeded weight.

Spread the resin with a squeege before moving on to the other half.

One half of the wing having the cloth full saturated.

More resin can be removed, but I will apply resin to the other half of the wing before removing the excess.

The entire wing panel is fiberglassed. Now go back over the wing and remove excess resin.

The wing is completely glassed. Now I am going to spend a fair amount of time scraping up as much glue as possible.

You will notice that the glass does not go over the trailing edge of the wing. I did this deliberately to ease the application.

What I will do when the top and bottom are both glassed is go back and glass the trailing edge and the inboard edge of the wing tips using a strip of cloth. That will complete the wing glassing process and from there it is a matter of sanding and finishing.

Fiberglass cloth goes around compound curves very easily.

Note how easily glass cloth can negotiate compound curves. Getting the cloth to lay over this wing tip required almost no effort.

The cloth stuck to the underside of the wing will remain there. It sands easily when the resin is cured.

The trailing edge is glassed with a separate piece of cloth.

The wing is fixed in place so it will not move while applying glass to the trailing edge.

The wing is blocked up to make it easier to work with.

I glued the dowels in place even though I shouldn't have. As I stated in the Wing Construction article, they should be left out until the finish is done because they get in the way.

That turned out to be true, so when the wing was jigged up I used a couple pieces of balsa to prevent the wing from rocking on the dowels.

I probably could have cut the glass on the bottom of the wing to cover the inboard side of the wing tips and the glass on top of the wing to cover the trailing edge.

I chose not to do this because the wing has a lot of area to cover. There are a lot of areas to check such as the leading edge and wing tips to ensure the cloth is down. Eventually there comes a point where it is easy to miss something, so I minimized this by using a separate piece here.

Prior to applying any fiberglass to this wing, it weighed 10.1 ounces. It is approximately 600 square inches. After glassing the entire wing it weighs 12.0 ounces. A digital postal scale was used for measurement and I wish I would measured in grams instead of ounces... too late now. Weights given are after trimming excess cloth but before sanding.

I mixed 3/4 fluid ounce of epoxy for each side of the wing, but used only about 1/2 ounce each. Therefore, the total wing used about 1 ounce of epoxy.