More building on a budget tips

I have been speaking with many people recently about how they build their uav's and larger-scale working aircraft. We were going down the balsa road, which is not so bad. It makes a pretty stiff structure with relatively inexpensive materials. However balsa is graded and strong, light wood is not easy to find nor is it cheap. You can easily run up $300-500/board foot. That is a lot of balsa, I know especially in 3" strips. However, you get the idea that this is not a cheap way to go.

We have been using kiln stabilized wood and it is making a decent product. There have been some issues balancing the stresses in the airframe. Traditional methods more or less work to relax them. My consultations with other people in the community leads me to believe that there may be better construction techniques. The system that we have uses balsa and then fiber glass on top. Our main issue is that balsa takes so long to lay up. To do a good job, it could take upwards of 3-4 weeks of concerted effort to get everything pinned and glued, sanded and filled, sealed and prepped. It is a big job, especially on bigger models with large spans.

OMG the twist, you will make lots of little weights and hooks to untwist your larger pieces as well. In some ways it is a terrifying process for the beginner. It is not hard to do, it can be terrible to do well.Blah blah, no whining. The others use mostly styrofoam cores covered in composites. I have been experimenting this weekend with it too. I have found that you can have a pretty good product with almost no invested time. My realization is that the cheap epoxies available from the hardware store, are easy to handle, water washable, but are way to soft-cured. For these applications, an epoxy chemistry that cures with a hard surface is better than a softer one.

I assume that epoxy chemistries with harder fixing strengths are less easy to handle. We have made several layups and this really is the case. In Florida, it is hard to get away from the humidity and large swings in it. So we lay up outside and bring the layups inside the air-conditioned house. That seems to help even out the handling properties.

The following pictures are using LocTite 60min cure epoxy, 80 oz./yd glass cloth and 3mm depron foam. There are many relief cuts in the foam to help conform to the shape of the fuselage. The pieces are masking taped together, a foam-safe CA glue would work too, but I was trying to limit the number of seams that needed to be joined. Most of the tape is to enforce the shape of the fuselage, not to hold the piece together. Both halves of the fuselage took about 2h to sheet and the glassing took about 20min for one person. It is not perfect, but it is an experiment. My illustrious helpers would assist on the final version for sure.

This model is about 5' (150cm) long and averages 6" (15cm) in diameter.