Making patterns for wing rib gussets

The gussets on a Baby Lakes biplane are unusual in that they are round instead of the rectangular type that's often times seen on other airplanes.

What I did to make this go a little quicker is I made patterns from some Aluminum scrap I had. At this point the rib jig is built and the nose rib assembly and all the pieces are installed in the jig. I fit the different pieces required on the jig until it was perfect. Then I took the aluminum and sanded it on the disc sander and buffed them smooth on the sanding sponge. Worked out really well.

Spar shim and wedges on the rib jig

Like I said earlier, the upper wings have a sweep back. In the builders manual it says to shim the front side of the front spar and the rear side of the rear spar .035". It also says to shim the front spar opening on the inside and the rear spar opening on the inside .005".

When I made my wing jig I accidentally made the spar openings a little too far apart so in my particular case I shimmed a little more than the what the builders manual says so I could correct it. My wing jig spar openings are extremely accurate now.

Regardless of my small mistake, the 5 photos below show how I shimmed the openings. I cut up post cards to shim the inside of the spar openings and used brass from Ace hardware to shim the other side.

NOTE: The lower wings on the Baby Great Lakes are straight and not swept. That means when assembling the lower wings the brass shims get removed and a .005" shim (paper) gets put in its place. The paper is so there's still a little wiggle room the spars. It's better to have a loose fit than a tight fit.

NOTE 2: In the first photo you can see where the pencil lines are on the spruce pieces. In the second photo I sanded them down to fit. I no longer do this, I just grind right to the line from the pattern and fit them in.

WEDGES: You can see why the wedges work well. And when switching to the lower wings, the ones without the .035" shim, it makes it easy.

Cutting out internal rib supports and making patterns

Once the pre-assembled nose rib assembly is in the jig and it's secure the internal pieces of cap strip can be marked and cut out.

People do this many different ways. Some cut all the parts out for all the wings and put them in bins. I decided I didn't want to do it that way.

What I did was make a set of patterns and number each piece at the the top of the pattern. I ordered them 1-14 starting at the front of the rib and moving down to the trailing edge.

Once I had these patterns I can simple keep the 14 numbered pieces in a zip lock bag and wne I want to assemble a rib I pull them out, lay them on a long piece of cap strip, mark them, cut them, then head out to the garage and grind each profile on the disk sander.

Below are the photos. No wedges are used at this time.

Below is my 9 year old son Henry taking patterns and marking them on a 4' long piece of spruce cap strip. After they are marked out I use a serrated bread knife and cut them up. Then I take them out to the 12" disc sander and profile them to the pencil marks. Because they are all marked 1-14 they are easy to put back in. Henry is also taking a sanding sponge (fine grit) and making sure the ends are prepared for a nice fit in to the jig.

Assembling the first parts in the rib jig

Now that the nose rib is glued to the upper and lower cap strips, and the cap strip trailing edges have been cut, and the rib jig is complete.....carefully lay the assembly in the jig. If you look at the photos closely you'll notice those wedges along the inside of the jig that keeps the upper and lower cap strip tight to the jig sides. I just made sure the wedges didn't interfere with the future gluing of the gussets and they were out of the way.

Wedges for keeping the rib parts tight in the rib jig

Wedges. I designed the rib jig around the idea that using a wedge driven between the nail and the part will keep everything tight while it's glued and makes it easy to remove the wedges and remove the assembly. It works great!

So cut a bunch of wedges, cut long ones, short ones, thin ones and thick ones. Be sure to have extra. I used my 12" disc sander for darn near everything so wedges take about 10 seconds a piece. As you'll see in future blog posts the wedges make a lot of sense.

Below is a photo showing just a couple I use. I think I made about 15 of theses and they are all different sizes.

Cutting the trailing edge of the pre-glued nose rib pieces

Now that the nose ribs are glued to the upper and lower capstrips and the rib jig is complete we can now take the glued assembly and shape the trailing edge. To make this happen the assembly is inserted in the rib jib. Starting with the bottom cap strip first I pushed that down tight and let the upper capstrip, which is glued, just kind of hang out. I then took a straight edge and lined it up with the cord line drawn on the rib jig. I made a mark with a pencil.

The same can be done with the upper. Simply pry up the lower cap strip and push down the upper. Lay the straight edge on it and mark it.

Another way to do it is after marking the bottom go ahead and cut/grind it off then reinstall it in the jig and use the cut line on the bottom cap strip as a pattern to mark the top cap strip. Then remove it again and cut the top cap strip.

Below are the photos showing the sequence and the end result.

Building the rib jig for the Baby Great Lakes Biplane

The following photos are self explanatory. The plans for the biplane come with both a template and coordinates and the builder can choose the best method. I decided to use the coordinates and I laid them out using a dial caliper and a pencil.

I then screwed down blocks the represent the spar openings. The wings on a Baby Lakes Biplane are unique because the top wings are swept at 6 degrees while the bottom wings are straight. One rib jig is used for both wings. That's accomplished by inserting shims next to the spar openings before assembling the ribs on the rib jig. I used brass shim stock available at any hardware store.

The nose ribs are pre-glued to the upper and lower capstrip so take that into consideration when building the rib jig. Instead of nailing down pieces to held the parts in place I simply used 2 long pieces of wood and followed the contour of the coordinates that define the airfoil shape and nailed them down. For the inside pieces I hammered some nails down and cut the heads off with a side cutter. Very simple and very easy.

Here are the photos of the rib jig. You will notice the red ink I used to draw where the wing rib gussets go. I did this so I could take a knife/file and open up the jig where the glue could potentially touch the jig. The makes it easier than cleaning the glue on the jig after I remove it.

You will also notice that I drove nails next to the spar blocks. I'll explain that in a different post but basically I ground some wedges on the disc sander and that holds the vertical pieces tight against the spar blocks.

Here are the photos of the rib jig for the Baby Great Lakes Biplane.