Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater

Thu, 22 Sep 2016

Building a Biplane: The First Work

Now that I've decided I'm definitely building a plane, and have basically settled on the model (finally, hopefully, fingers crossed), I have actually gotten started on some honest-to-goodness work on the plane.

Well, sort of.

The Marquart Charger plans were drawn up in 1968, on paper, and photostatically reproduced. These plans contain dozens of little metal bracket-y things that are to be produced in quantities ranging from 1 to 20 (based on what I've seen so far). An example is shown to the right.

Rather than bust out my file, or a cutting torch or a hacksaw or anything else, I thought about it for a bit, and realized that it would make sense to investigate having these parts cut out by some variety of CNC machine. That is, a machine that can be programmed to cut a shape precisely, and automatically -- Computer Numerical Control. A bit of looking, and I settled on waterjet, which has the advantage of being very accurate, and unlike laser cutting, creates no heat in the part to mess up the temper of metal parts.

One of the reasons I settled on this "waterjet first" plan was very practical: without a shop space, I couldn't build a "real," physical thing. On the other hand, turning the drawings from hand-drawn to CAD models was something I could do just about anywhere, on my laptop. The CAD models are required in order to get the waterjet cutting done. Seemed like a win-win situation, so I started in.

I decided to use FreeCAD, an open-source CAD program, to do my work. I'm a big fan of open source software, and it ended up being a better choice than using the paid program I already owned. FreeCAD does a thing called "parametric modelling," which was perfect for this task. It took me a few tries before I understood it properly, but once I got it down, it made perfect sense, and worked really well.

The basic idea behind parametric modelling is that you draw out roughly the shape you want, without any real regard for exact dimensions or anything else, first off. It's just the shape. Then, you systematically start applying measurements, or parameters; parametric constraints, if you will: this hole is this many inches from this edge. That rounded area has this radius. This other hole has this diameter. In fact, if you look at the diagram, all that information is already spelled out, pretty much exactly as you'd need to enter it into the CAD program!

So, I started drawing out these little parts in FreeCAD. Some of them were more challenging than others. This part, -201 (apparently pronounced "Dash two oh one"), was actually pretty difficult, but it was also the first one I tried. I went back to it after doing a few others: I ended up redrawing it in 1/4 the time it took on my first attempt, plus it looked way better. I am now able to draw up pretty much any of these parts in less than half an hour, and I've got several dozen done.

I haven't yet sent any samples off to a waterjet company, but I've talked to one, and have an idea of what happens next. I think it will be years before I need the majority of these parts, but one of the things I will do early on will be to go get a couple sheets of 4130 cut up by a waterjet. The price hasn't been worked out, and that's the only thing that might keep me from following through with it. But then, even if I decide against doing it, the parts will be modelled, and I can put up the files for others to use if they want. It also sounds like the setup fees are minimal or zero, so it may make sense to farm out a few of the complex or many-copies-needed parts, and do the remainder by hand.

I'm sure I'll write more about it, but that's the progress I've actually made on building my own biplane so far. I've even been logging the time, and I'm already up to nearly 20 hours. Only three thousand, four hundred and eighty-odd hours to go.

Posted at 22:53 permanent link category: /charger


Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater