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

Wed, 15 Apr 2020

Building a Biplane: Back In the Build

My last entry was pretty brief, with the simple aim of showing you my build log. Looking at the log, and at this journal, you would be correct in guessing that there was some kind of an interruption.

In late 2018, it was becoming obvious that I'd have to move soon, which would mean giving up the shop I'd put together for my Charger build. It would mean an unknown delay until I could find another house, ideally with a shop, and resume thinking about this insane plan of building my own full-size biplane.

And yet, here we are. I've found my new house, and I managed to find one with a 2-car garage that was ripe to be converted into a workshop. That process has taken far longer than I wanted it to, but is nearly coming to an end as I wait for the new garage door to be installed -- the whole COVID-19 situation means I'll probably be waiting for a while, though.

When I left off on the project, I felt that my next logical step was to profile the spars, and start assembling a wing. I had the ribs built, and all the compression tubes. I hadn't yet ordered the cross-brace wires, but I've still got that shopping cart loaded up at Aircraft Spruce and ready to go. I had found all the internal wing brackets in a Ken Brock kit on Ebay.

However, there was a significant piece missing. The wedge blocks.

Long story short, the Marquart Charger has a very classy-looking 10° sweep to the wings, but all the ribs and bits that go inside are arranged parallel to the fuselage. This means that you have to make up that 10° difference somehow. This is where the wedge blocks come in.

The use of the wedge blocks is pretty obvious. For instance, in the diagram below, you can see how the wedges, in green, are used to make a 90° surface against the wing spar, shown in blue:

So, that made a lot of sense to me. Wedges, cool.

Then my eye would always trace back to this cyclopean horror:

I had no idea what this thing was trying to tell me. For years, I would see it, and immediately get confused. It looked for all the world like a single piece of wood, that I was somehow supposed to cut up to form all those wedges, and it just boggled me to no end. How do you cut that -238 piece from the corner of the -239 piece? Wouldn't it leave a huge gap? How are you supposed to cut all those angles without the saw taking out its kerf and leaving you with undersized pieces? It just absolutely confused me.

Finally, shop nearly done, but not quite done enough to go around cutting thousands of dollars worth of spar material and assembling wobbly half-completed wing structures which might need to be moved (inviting any number of broken wing ribs), I decided to bite the bullet and ask for help with this wedge horror. Not that I have been shy about asking for help before, but it's always a bit of a struggle to admit that I don't understand something that everyone else seems to get.

So I fired up a graphic editor and cut out the section of plans I'd be posting about, but something about it made me pause. Suddenly, out of the blue, the picture that had for all time looked like a white vase on a black background snapped around, and became two human faces, facing each other with a white space between them.

It wasn't showing a single piece of wood. It was showing all the wedges overlaid on top of each other. My brain felt like it was going to explode.

Instead of drawing out six side profiles and six face profiles, with the attendant measurements for each, Ed Marquart had done the sensible thing and drawn them together to save space and drawing effort. This sudden understanding was, I must say, a huge relief.

Here is an annotated diagram with improved dimension lines, which shows in red how to interpret the dimensions for making a -239 wedge:

Looking over the plans and dimensions, it looks like I've probably got enough off-cut spruce to make most of the larger wedges, though I'm going to order some 1/4" thick stock to make the -238 wedges, since there are so many of them.

Now, I just have to figure out how I'm going to cut all these extremely sharp angles. I've started on a sled for the table saw, similar to this design. I don't have any MDF lying around at the moment, so I'm starting with some not terribly good plywood as a base. I'm pretty sure a sheet of MDF is in my near future, but it's good to experiment with the technique for the moment.

Honestly, I'm just excited to have something I can do during COVID times that doesn't require a helper, like the spars, and can be accomplished with the shop in a relative state of disarray while I wait for a new door. Progress is finally being made again, and it's a gratifying feeling after such a long delay.

Posted at 13:37 permanent link category: /charger

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