Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater
Mon, 03 Dec 2018
Building a Biplane: The Many Steps to Actually Make a Part
I've been impressed by the seemingly countless steps necessary to actually make a part for this biplane build. I'm currently in the middle of making the drag and anti-drag strips, which will go inside the wings as crossing "wires" to keep the wing structure from racking forward and aft.
At first glance, the drag strip idea makes a lot of sense -- no special tooling required, sheet metal is widely available (and probably more available or cheaper in the late 1960s than 4130 wire of the appropriate size), it's easy to cut on a sufficiently beefy shear, etc. However, on reflection and having accomplished 90% of the construction of the strips, I think I would have been happier buying wires.
Here's what it takes to make a batch of 36 drag strips:
- Acquire sheet metal. $80 at Online Metals for a 2x3' sheet of .063" normalized 4130. This was by far the simplest part of the process.
- Find someone with a big enough shear to tackle 1/16" 4130. I managed to find someone through the Biplane Forum who offered to do it for free at his shop. We cut my sheet into about 40 1/2" by 36" strips.
- Polish the edges of the cut strips. I finally figured out that I could hit multiple strips if I was careful by using the belt sander that has served me so well making ribs. This process alone took over 2 hours between finding the right procedure and actually doing it. I started out with draw filing individual strips clamped in the vise, which doesn't count the 2+ hours I spent making perfectly smooth vise jaw covers. Such a simple operation that took so much time and head-scratching.
- Bend the teardrop end of the drag strip (see the above picture). 4130 is no slouch when it comes to the strength department, and I wanted to get these bends perfect the first time. The solution I eventually came up with was to build a bending jig out of beefy 1/4" thick angle iron and 1/4" plate (7.3 hours, not counting driving around hardware stores for a couple hours, looking for 1/4" angle iron). This can be used in the 12-ton el-cheapo hydraulic press I got back in my engine rebuilding days to get the strip most of the way bent, then it's off to the vise with a hunk of 1/4" round to close the end of the loop, but keep the teardrop open.
- Weld the edges of the loop's tail. For all my initial fears of welding, this was among the simplest operations in this process. It still took 3 hours to weld all 36 of them.
- Cut the slot into the teardrop. This process was the subject of much heartache for me. My first idea was to use my milling machine with a very tiny endmill to cut the slot before the strip was bent. This worked, but was very slow, and ran a substantial risk of breaking the cutter, for it was ever so wee. Then I had the idea to use a slitting saw in the mill once the loop had been bent. Much better, but I discovered that after welding, the slot would expand a bit, and the plans are very particular that the slot should be a particular size. So I thought it better to weld first, then cut the slot to eliminate welding as a possible source of error. I welded up the first 17 strips, and tried to cut the slot in one of them, only to be horrified to find that welding modified the strength of the metal such that the saw (which had worked perfectly before welding) suddenly sounded like it was about to explode. Finally someone on the forum suggested using an abrasive cutoff wheel, which worked well, and was the method I finally used to cut the rest of the strips. I spent nearly 5 hours just figuring out how to cut slots and then slotting all the strips. I'm glad I didn't have to use a hacksaw and file to do the job, as someone suggested when I asked how Ed might have expected the average homebuilder to do it.
- Clean up the welding scale. I started out by hitting the strips with sandpaper to clean up the scale, but it didn't do a very good job. I finally switched to a wire brush and had much better success. I also destroyed two partially-used wire brushes in the process. If I have to do any more of that, I'm getting the wire wheel set up on my bench grinder again. I need to do that anyway, as long as I'm welding parts.
That's the process so far. I'm not done yet, but that's as far as I'm taking it until the wings are built, and I can see exactly how long each strip needs to be.
By contrast, the steps necessary to deal with wires would be:
- Buy wire. This requires an order from Aircraft Spruce, and costs more than the sheet metal ($128 + shipping vs. $80 for sheet metal).
- Cut wire to length. Hacksaw and file to clean up the cut.
- Thread ends. Time-consuming, and requires a left-hand threading die for one end, but a well-denfined problem with a well-defined solution.
That's it. If I had it to do over again, the extra $50 would be 100% worth it. I think the turnbuckle situation would be a bit cheaper too, by at least half. If you find yourself building a Marquart Charger, may I humbly suggest that you don't follow the masochistic "Do it exactly per plans" path that I have, at least for this particular situation.
For your edification and edumacation, I also filmed much of the process and turned it into this moderately interesting video:
Posted at 23:06 permanent link category: /charger
Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater