Working on the Elevator

Friends,

The last couple weeks have seen some progress. I was able to get the elevator skins bent properly (working on a video about those), and started drilling the skins. I like to pre-drill the skins so that I have pilot holes that allow me to see the center line of the ribs/spars underneath. This is similar to how Zenith used to ship their kits before they started CNC match-drilling everything. There are ways to drill the skins and ribs blind, but I prefer being able to visually ensure the ribs are in alignment. Plus, with the pilot holes drilled, I generally don't have to worry about the bits wandering.

However, if you use this method, you absolutely must ensure that you've measured your rib stations onto the skins properly. Somehow, I'd managed to locate a rivet line about 3/8" offset from one of the rivet stations. I think I accidentally had the tape measure hooked on something off the edge of the skin, but I don't know for sure. Maybe I just measured wrong. It was a duplicate measurement to the bottom side of the skin, and the exact same mirrored measurements for the co-pilot's side rear skin. It was just the top rivet line of the one side that I'd messed up. I'm going to re-make the skin and use it as a template to pilot hole the new one (without using the bad rivet line, of course). So it'll add an hour or so to the elevator (and scrap the original skin), but I'd rather take care of it now than just fill the holes with rivets.

Elevator Right and Left side Trailing Edge Skins:

Homemade gauge for checking the bend angle:

Elevator Nose Skins roll-formed manually with a 2x4:

 

Test layout of skins:

Center overlap of rear skins for strength:

Rear skins cleco'd to the spar and ribs:

Another thing to which you have to pay close attention is the rivet pitch and size specified in the plans. The overlapping skins in the center get drilled for A5 rivets at a pitch of 25. I missed that part on the plans, and accidentally drilled them to 40 pitch, which is what the rest of the elevator takes. I compensated by doubling the pitch to 20, with only results in an extra rivet on the front and rear rows, but it also means I have to remake the upper and lower control horns for the elevator to be able to use the existing rivet holes to mount the horns. With the 40 pitch, the rivets fall in slightly the wrong position, causing there not to be enough flange material on the horns. I'll remake the horns with longer flanges to solve that problem.

3D Printing For Prototypes

Friends,

I've been curious about 3D printing technology for several years. While at AirVenture 2016, I was able to visit the 3D printing display in the drone exhibit. I'd been involved in a few discussions about the viability of 3D printing for aviation. Regarding my STOL CH 750 project, I've identified some key things I'd like to design, and 3D printing is convenient when paired with EAA's Solidworks CAD member benefit. I'm considering using a DIY EFIS/PFD system based on the Raspberry Pi computer and commercially available ruggedized displays. As such, I could end up with a need for custom bezels, mounting brackets, etc. At the very least, I could print custom mounting hardware for GoPro cameras to use while filming flight footage for my subscribers!

I have some other ideas for parts for the airplane, and a distant goal may include manufacturing parts for sale. But let's not put the cart before the horse. Right now, I just want to experiment with the technology as an intellectual exercise. After that, I probably will apply non-structural designs to the airplane. Following that, if the process seems viable, I may turn it into a business venture. Anyway, it's a sort-of project-related idea that I'm excited to share. I even shot a short video about it:

My printer kit:
http://www.gearbest.com/3d-printers-3d-printer-kits/pp_343643.html?wid=21

Prusa i3 Printer, upon which mine is based:
http://www.prusa3d.com/#our-printer

EAA Solidworks Member Benefit:
https://www.google.com/search?q=eaa+solidworks&ie=utf-8&oe=utf-8

Thingiverse 3D Printer File Database and Resource Website:
http://www.thingiverse.com/

Cheers,

Greg

Slat Skin Forming Videos are up!

Friends, I've edited and uploaded the Slat Skin Forming Videos to YouTube. Check 'em out:

Forming the Slat Skins - Part 1/2:

Forming the Slat Skins - Part 2/2:

Stay tuned for an update on forming the elevator skins!

Cheers,

Greg

Got skins?

Friends,

After finally getting my assembly table rebuilt and getting back to work, I spent the last several days cutting skin blanks for the elevator, slats and flaperons. I decided to go ahead and bend up the slat skins first, as they are the most complicated skins to bend. The nice thing is that they can all be done on the brake, but there is a lot of setup time in between certain bends. And with 4 bend lines on each skin, there is a lot of time laying out the part for bending. 

As always, with the complicated bends and large pieces, I made a test strip about 20mm wide to determine my bend pattern. I got very lucky on the first try (although now I'm so familiar with how the brake bends, that it was a sort of "educated guess" about where to put the bend lines). Here are the results:

Test skin pattern next to slat rib and slat tip. Not the opposing flange bend at the lower right:

Test skin pattern clamped around rib to check measurements:

The first inboard slat skin bent to tolerance (it's perfect!). I bent this skin up from start to finish without bending anything on the other three skins, so to ensure the part would turnout correctly. It is approximately 6 feet long:

 Another view of the first slat skin. These skins are made in .016" and they are extremely flimsy. Care must be taken to avoid kinks and smileys:

 

All four slat skins bent to tolerance...2 inboard and 2 outboard skins (the outboard skins are nearly 7 feet long). Once the first skin was completed, I switched to "assembly line" mode, and performed the same bend on each skin before setting up the brake to perform the next bend. This saved a lot of setup time compared to how I bent the first skin:

 

Another view of the slat skins:

I shot a full video on how I bent these skins and it details the bending brake setup issues. The video also includes some of my reasoning on the "how and why" I did things the way I did. I'll get that video cut together soon and post an update with it. I also still have hours of other videos to cut together, particularly the remaining parts of the Horizontal Stabilizer Build. That's all for now!

Cheers,

Greg