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.

As If You Thought I Have Not Been Working

So I have been trying to get some interesting pictures of the layup of the Big Baby fuselage. However, the pictures that I do have are not as demonstrative as I would like. I guess I will have to get down there and take some myself. All in all, the mold concept worked and the internal, integral structure also seems to be pretty successful.

Our idea, is to mold a certain amount of internal structure into our composite molds. The interest is to reduce production time of aircraft to the limit of curing and finishing time. More advanced resins could be used in the future. Our experiments are with normal 60 and 90min set air-cure epoxies. We also used a male mold to reduce our total investment. Surface finish is less than important to see for these experiments. They are about the viability of integral structure composite lay ups. I have said that last bit a few times, but I have received several comments about this.

The next step is to relief the wings so that they make a pocket, lift system that will effectively create a similar cross-section to the metal equivalent airframe.

Adventures in Composites: Two Bogans and the Art of the Lay... Up

After a year of sitting, our polyester resin had spoiled. So we contacted some people and they said you could do it with just about any medium cure time epoxy. Out into the proper disposal container for petro-chemical waste. Yeah, I went there. Off to the local hardware shop for some epoxy. We bought several batches of 60 min epoxy. Some of the information that our friends told us suggested that we could use isopropyl alcohol to help keep the viscosity of the epoxy down as it is laid up.

Information like this is when it gets exciting. We found out a few things. You can paint the alcohol onto a layer to help flow the epoxy and to reduce the bubbles and flatten wrinkles. I would suggest that pour some alcohol into a cup and paint it on where you need it. Each layup will be different so it is hard to say where you would have issues.

There were some bubble generators in the seam where the semi-mold met the backing. This is probably pretty obvious, but it was due to training air under the resin laden cloth. Our mold also had several regions with nearly perpendicular sections which were hard to wet. In areas like that, I would suggest liberally pre-painting. Be careful not to pool the resin in the bottom since that is not where you want the part to be strong. Another observation was to make sure that when each layer is put down, both people should work in the same direction. Do not work the resin from the nose and the tail. It makes wrinkles and other defects.

It is very important to make sure that each layer has as much of the resin out, or at least even distributed as possible. This means that all of the bubbles, wrinkles and puddles need to be worked toward the edge of the layup. A roller and brushes are the weapons of choice for this work. The handle edges are great for wringing out excess resin from tight radii.