Remember how I said I was manually entering all the drawings from my plans into CAD? I've completed most everything and very happy about what I've learned.
I spent several hours trying to figure out how I'm going to print these items to scale for templates which will be used to trace out my aluminum parts. It's a careful balance trying to print the items to scale and within the borders of what a printer will print on a 8.5 x 11 sheet of card stock. I haven't decided yet if the card stock will be sturdy enough, or that I might transfer the patterns from card stock to a light gauge aluminum like an eaves trough flashing. This will be particularly important on multiple pieces where repeatable results are key.
LibreCad is the free program I used to digitize my plans, but like anything free it has some drawbacks such as a limited ability to print to scale right from the program. It does however export to PDF. There doesn't however seem to be any rhyme or reason to what scale the drawing end up in when exported.
To solve this problem, I found an online program that takes DXF files (the LibraCad file type) and converts them to PDF. It automatically scales them to the best size paper, not 1:1 scale (which I need).
I figured out however, that if I print the PDFs as is and hand measure them, I can calculate the scale percentage I need to up or down scale the PDF. The it's just a matter of entering that percentage in the final print and voila! 32 Perfectly scaled 1:1 drawings printed direct to card stock!
I'll be limited to those templates that fit on letter or legal card stock for now. Most of the larger parts are strait cuts anyhow. I'm more concerned with the complex curves of nose and wing ribs and some of the smaller parts. Maybe I'll do some research and see what size I can get card stock I can get.
The other item I've been trying to determine is the specs on my Corvair crankshaft. I've mentioned before it will need to be magnaflux tested for cracks, heat treated (nitride) for strength and the rod journals ground for bigger should radii. I happy to see the crank I have is within a couple of thousandths of stock meaning there is lots to room to have it ground properly.
Progress. Back into the shop I go!
To make up time I missed last week, I did back to back days in the shop this week.
The next step in the rebuild of this 701 wing is making new aluminum caps to reinforce the damage done by the original builder to the tops of the two fuel tank ribs. As you can see here, the holes are kinda randomly spaced and most aren't even clean:
We'll be doing a cap along the front edge as well for the same reason. This will strengthen the upper spar cap angle and make a much cleaner (and stronger) assembly. Before doing this, I did a test fit of the infamously missing replacement wing root spar doubler before measuring it for the bending of the flanges, and I'm really happy with the result of the fit:
Or at least I thought I was until I remembered the small bend in the upper spar cap that needs to be repaired. Looking along the top of the spar cap angle you can see the "wow" (bend) I'm talking about. It's not enough to change the fit of the spar root doubler, but it will affect how squareness of the wing to fuselage join-up::
So, using a bit of my recently learned knowledge about how aluminum "springs back" some when bent, I had to come up with an easy way to take this bend out. First, I taped some mahogany shims on opposite side of the spar cap and to either side of and equidistant to the bend:
Once these were in place, I carefully clamped a 2x2 piece of wood to act as a surface to leverage against:
Unfortunately, you'll have to use your imagination to visualize the next step as I don't have a picture.
Another C-clamp placed directly of the centre of the bend is gently tightened drawing the bend towards the gap and slightly beyond. Once released, "spring-back" takes over and the spar cap returns to the straight position. It took a couple of tries to get it perfect, but it worked. This wouldn't work if the spar cap was broken or kinked - it would have to be replaced at that point, a very time consuming and expensive process. Here is a picture of the now straightened spar cap. Very pleased how this worked out:
Next up, bending the spar root doubler and installing the new caps around the edges of the fuel tank bay. Progress!
I had hoped to get to the shop last week, but an unseasonably warm weather forecast was causing me some concern at home. With all the snow we've had through January and early February, we had about 3 feet of accumulation on the roof. Rather than go to the shop, we thought it better to remove the bulk of snow before the positive temperatures arrive and make the snow weight too much for the roof. It took several hours, but I got it done. Didn't feel like going to the shop (ok, actually I couldn't lift my arms for a couple of days).
Back to the shop today. Got right to work creating two new wing root spar doublers. These will be installed where they should have been in the first place. Using a template, I traced out the rough shape on the 0.032 aluminum:
I cut out the shape in rough and used a file and the grinder to get the final shape exactly right:
I repeated the same steps for the second one. The process is fairly simple as you can see from the wing root attachment brackets below. From top to bottom, a finished piece from inventory, a rough cut piece to be ground and the template from the plans:
First you trace the template onto the stock, and use (in this case) a bandsaw to cut it out close to the line. Comparing the two after the bandsaw, use a sharpie marker to trace it again, leaving a line showing the remaining material to remove by sanding or grinding:
Next, use the grinder or file to remove the balance of the material as defined by the trace line:
Last step, hand sanding all the edges to a satin smooth finish. Here is the stack of eight I finished (two for this repair and 6 for inventory) and below that the stack of wing root doublers for inventory:
More rain tomorrow, so back to the shop to start working these items into the repair.... and find more things wrong with this wing..... probably :)
Those that know me also know that I tend to stew on things. It's a trait I've always had and as I grow older, I've tried turning the energy that is wasted away worrying about the little things and more towards solving the problem or fixing the mistake. It doesn't always work, but sometimes, with a little thought and time to ponder it does.
I got to thinking about the Rear Wing Root channel that I made the "oops cut" on last week. Looking over the plans, not all is lost. I'd already made the flange end longer than what the plans called for. Beefing things up in this manner is an accepted practice. This larger flange means that I still have room to correct my mistake and salvage the piece.
Here is the damage I did. You can clearly see where the cut extended beyond the relief hole:
By trimming the flange end a little bit narrow and creating a new relief hole, I eliminated the bad cut and still met the requirements for size on both. The corrected mistake is shown on the top in this picture and my second proper length "no damage beyond the relief hole" cut at the bottom:
Once I dressed and deburred the edges of the entire piece, off to the bending brake we went.
Unfortunately, I went a bit far with the lower edge. It ended up with a full 90 degrees of bend, but needed to be less than 90 to match the curvature of the wing skin.
No big deal, I just made up a jig to bend it back a bit (you can't undo bends in the brake). The key is to bend it all at once to maintain a consistent edge on the flange. You can see in the next picture that I placed the channel on the workbench and used a two-by-four and C-clamps to secure it. Ron has an excellent flanging tool just perfect for adjusting things (painted red):
Worked like a charm... my oops is no more!
Fit up seem good. Plenty of room for new rivet location and flange matches top of the rib:
Next I worked on making a new wing root attachment bracket to replace the damaged original. This required cutting thick aluminum with the band saw, a new experience for me (although I've cut wood many times on the bandsaw). It went well. The secret is to cut the piece out slightly larger, allowing room to sand/grind the piece smooth to it's final dimension:
Next up will be to make a replacement forward wing attachment bracket and the new wing root spar doubler that we discovered was missing on the original build. Luckily we have a traceable template for this:
With each repair and new fabrication I'm making, I'm getting the courage up to start bending and shaping metal for my own plane. I CAN do this!
Back in the shop again Monday. I got some more repair work done on the 701, but like home renovations one thing leads to another.
Talked over the latest issues with Ron. We decided we didn't like the original builders efforts on the rear wing attach point either. Damage to the rear root channel is also too much to accept as is, so we'll replace it too.
Drilled out the rivets holding the root rib and the first outboard rib, then started removing the rivets to separate the channel from the wing attach bracket:
With the rivets removed, it becomes easier to see the damage done by whomever drilled the wing root skins. The wing root skin is one of the last things to be fitted during a build and one might understand the desire to "hurry up" and get done, but this is done terribly, even if they weren't in a hurry. None of the holes are measured right and at least one critically damaged the wing attach bracket:
The hole for the wing attach bolt has a few issues too. According to the plans, it should be drilled directly centered in the channel. A random second hole on this attach bracket shouldn't even be there and look how close it is to the main bolt hole. This is a fatigue crack waiting to happen. Corrosion protection certainly wasn't considered either. Regular old white paint ain't going to cut it!:
I spent some time cleaning up the skin edges around the fuel tank bay. This will go a long way to making the skins sit flat. We are also putting L brackets over the top of the ribs and spar web in this area. This has the dual benefit or strengthening the ribs and providing a better place to rivet the tank skin on later - with the proper rivet spacing! These look like Swiss cheese.
The overriding goal of this repair is to learn the fine skills required for my build. I definitely learned one when preparing the new rear channel. I measured very carefully, and made sure to drill the corner relief holes in the correct position. This material is 0.032 thick, something I really haven't cut before with hand tools.
Reminder to self.... when cutting with hand shears, the tool will jump ahead when reaching the relief hole. A cut past the hole is the inevitable and regrettable result, ruining a well measured part:
I originally circled the excess cut and was pretty angry for making this simple mistake. Then I reminded myself the goal is learning. As long as I don't forget next time when cutting towards a hole, making a 2nd replacement rear channel isn't a big deal.
I added the rest of the word "OOPS" as a humorous reminder that life is good as long as I'm learning. I'm going to salvage the majority for other small parts and leave this part propped up on the bench as a reminder.
Back into the shop in a few days. Thanks for reading.
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.