Practical Composites: Fiberglass Over Wood

We are putting together some good pieces for everyone see how we are doing it. The big tip that we can tell everyone is hair spray. It is too funny to think of either of us ever sing hairspray. One has been bald for half of his life, and I have never been a big coiffure kind of guy.

The pictures that I am including are of a model that is 57" (143cm) x 6" (15cm)  wide and 4" (10cm) tall.

                       

The glass sued is standard s-glass, 2oz per yd glass from Aircraft Spruce . Our experience shows for fuselages, two plies is more than enough for fuselages. Make sure that your plies are pig enough to cover all of the piece and hang over about an inch (2-3cm). More than that makes it hard to support the piece, the fabric keeps pulling away from the edge  or it gets tangled.

Apply the hairspray liberally to wet the surface of the cloth, then use a foam roller to spread the spray and wet all of the glass. It takes a few minutes to work the whole surface. When it dries, it will feel more like paper than silk.

Having learned the hard way. You can let these dry for 15min or so, until they are not tacky to touch. However, do NOT let them dry for lunch and a trip to the hobby shop. The hair spray dries too much and coats the glass so that the resin does not stick. That is bad, it will just wreck your finish and everything will look all orange peel or like bubble city.

I hope this helps with your projects.

Building on a Budget

So we are working out our system to build giant-scale planes on a budget. We build mostly our own designs. It is far more challenging to wing it. I have to say that building from forms is pretty challenging, and worth it for those of you who like to do it their way.

One suggestion that I have for you guys is, lattice. Maybe that is not an obvious description. We have the most luck building complicated curvatures, when we lay out a regularly spaced net of 1/16th inch (1.5mm) balsa strips x 1/4" (6mm) . The spacing is what ever makes sense for the model. I mean, you will need to work out some of this for yourself. We find that wings are good with 6"(15cm) pieces cord-wise and 20- 25% spacings span-wise. That way there is a reasonable pitch and still a good amount of coverage. Onto this, you glue your actual skin down.  This helps reduce the actual curvatures involved, but also allows for the skin to be supported without the need of a foam internal block. Use wood glue if you are working on a Styrofoam base or CA if you are working on a compatible base. CA will eat Styrofoam, even the vapors will destroy it.

We get all of our balsa from local suppliers. Our favorite supplier is www.solarbo.com .

Big Baby Developments... Daddy's Building a Brand New Plane

I am not ready to reveal the Big Baby just yet. It is going pretty well, symmetric and no smeared blood or anything. No blood this late in a project is a big relief.

The airframe for the next version will be a bit different. This time, I was careful to build the skin by wetting and pinning the skin to as closely as possible match the model curvature. Besides the 10s of pins that were used, the technique was pretty effective. 

Use masking tape along the down side of the board so that there is a basic joint between the pieces. Then just use a wet sponge to wet the downside of each of the planks. Lay the plank onto the surface of the model to be copied. Work from one end and pin along the edge every inch or so about a 1/10th of an inch from the edge each time. Do this for one inch rows along the plank. Depending on the curvature being copied you may need more pins or to pin in specific directions to keep the balsa layer in contact with the curve.

After the part has dried, overnight or after a few hours, adjust the pins to fit the planks as closely as possible to the curve. The planks may have to be rewetted to relax them into place. Then use a foam-safe (in my case) glue in the joints. The tape will be removed before you install internal structure. Once it is dried and the seams are glued. You will want to remove the pins and the part from the form. I cut simple cross-sections to support the structure. Then used CA glue to glue the seams and to bond the internal structure to the skin.