A couple of really productive days in the shop this past week, but not many photos to share.
Started the final fit-up of the upper strut fittings. The plans call for the strut fittings to extend 107mm from the lower wing skin. To make fit-up correct, I scribed a line 107mm from the rounded tip:
With the strut pickup held in position against the angle, it's a simple matter of lining up the scribed 107mm line with the bottom of the spar. The skin is 020 here, so the line is very slightly past the spar:
I drilled the strut/pickup interface hole as per the plans, but the plans don't really define the spacing of the mounting bolts that attach it to the strut angle. Base doin what I see in the plans, it appears to be evenly spaced, so that's what I went with. It started with A3 pilot holes in the pick-up:
Clamping the strut pick-up tp the strut angle in the correct position. The camera angle makes it look like the scribed line is inside the spar line, but it is actually where it needs to be. From here, I drilled through the strut pickup and into the angle. Once I had a couple of clecos in place, i removed the strut angle from the spar and took both to the drill press to enlarge the 3 pilot holes up to AN3 bolt size (sorry no pictures). The bolts will be added after everything is deburred/primed.
The next step was to take off the strut assemblies, the web and root doublers and L stiffeners to permit the spars to lay completely flat on the drill press. Without these doublers, the spars are fairly stiff, but they are still long and challenging to move around the shop. Must be careful not to introduce any unwanted twist.
To accomplish cutting of the lightening holes on the drill press, I set the spar on a movable workstand at the one end:
Fly-cutter in the drill chuck. The yellow tape flag has a written note on it as a reminder that the cutter was already set for 95mm diameter, but I double checked anyhow. The spar web sits flat on top of a piece of plywood that fits between the bottom of the cleco pins. It supports the back side of the web as the cutter scribes it's circle:
I used a level on the web between the drill press and work stand to ensure the spar was completely flat for drilling:
Started cutting the lightening holes at one end of the spar, then worked inwards to the next, clamping the spar to the plywood and drill press work area. Cutting with the fly-cutter is always an adventure, but securing the piece, lubricating the cutting head with a bit of WD-40 and using slowly increasing pressure goes a long way to making good clean circles.
There are 5 lightening holes inboard of the web doubler and 4 outboard. With the inboard ones done, I flipped the spar end-for-end and drilled the outboard ones. The I repeated this whole (hole?) processes on the 2nd spar.
I'm really pleased how the process I came up with worked out. It wasn't complicated and went fairly quick, but I always have a certain amount of trepidation when using the fly-cutter. If the cutter jams or grabs the material it could damage the web material beyond repair, meaning redoing the entire spar (a very expensive mistake). Thankfully, I didn't have any issues with either spar. Here they are, back on the bench awaiting deburr and flanging of the holes. You can see in the bottom right that I hadn't trimmed the spar cap of the left wing yet, but that has been done since this picture was taken.
With the lightening holes deburred, I followed the same process as the wing ribs. The flanging die and two large C clamps worked well using the corner of the bench to reach from both sides of the spar.
In order to accommodate the length of the spars, I had to switch corners of the bench. Maggie the shop dog/chief inspector was kind enough to move out of the way for me when needed - even if she doesn't look impressed in this picture :)
Even more so than when the lightening holes are cut, it's important that the spar is lying flat for flanging the holes. I used another piece of thin plywood to support the spar at the opposite end.
I did get and answer about the rivet spacing on the spar web doubler from Zenith - my theory was correct and I can shorten the rivet spacing to 20mm without issue.
With most major fit up and drilling complete on the spars, next up will be pulling everything apart again for final deburring edges and holes and priming of the mating surfaces. Then I'll begin the process of reassembly with clecos in preparation for driving and/or squeezing the solid rivets. I want both spars complete and ready for wing ribs and skins. One spar with the assorted ribs and other parts will go into storage while I work on the other to make room on the bench.
Another item on my list is deciding on the best way to prevent dissimilar metal corrosion (sometimes called galvanic reaction corrosion) on the spar and root pickups. I'm considering some DIY anodizing of the aluminum parts using simple chemistry theory. More on this later :)
Thanks for following along!
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.