The Return of the TigerKitten (3)

It’s taken me a bit longer than I would have liked to get this blog entry posted…I bought a new computer and have had to go through the drill of learning a new operating system. Now that’s done and we can get back to building model airplanes. There are a few more details to finish up on the tail surfaces, but I am choosing to wait until the rest of the structure is built to go back to those. For now, let’s get started building a wing for this flying machine.

As with the tail surfaces, I chose to cut my own balsa strips for the wing. This is a 3/16" sq. which will become a wing spar.

It's always good to make as accurate as possible a cut. Here I am using a miter saw and box to get an exact 90-degree cut on one end of a 3/16" sq. spar.

 

I'm going to build the right and left wing panels one at a time. This is the left, with the ribs dry-fitted in place over the lower 3/16" sq. balsa spar, the upper 3/16" sq. spar in place, and a strip of 3/16" sq. balsa placed as a spacer to elevate the trailing edge so that the spar assembly will be perpendicular to the building board.

Making sure that the top and bottom 3/16" sq. balsa spars are aligned perpendicular to the building board is critical to building an accurate wing. I check the alignment with a square and move the 3/16" sq. balsa spacer under the rear ends of the ribs to adjust as necessary.

The Premier kit includes laser cut spar web pieces. To do their job correctly, these web inserts must fit tight against the ribs. To be sure this happens I used a web insert to define the rib spacing before glueing anything in place. If you use the spar web pieces to space the ribs for assembly, there may be a tiny discrepancy in respect to the plan. That won't be a problem...it's much more important to get all the ribs and web inserts fitted properly together for structural integrity.

This is another look at how the ribs, spars and spar web pieces should fit together. (Note that W-1 will not be glued in place until later on in the assembly sequence.)

 

I have used one of the spar web inserts to space the ribs, but the instructions don't call out glueing them in place yet. Here I'm using thin ZAP to bond the top 3/16" sq. balsa spar into one of the W-2 ribs.

More ZAP attaches the 3/16" sq. balsa leading edge to the front end of each rib.

I suggest that you include washout (a twist in the wing that raises the trailing edge slightly at the tip, to help control tip stalling). The easiest way to do this is to build it into the wing during initial construction. By moving the 3/16" sq. balsa trailing edge spacer forward just enough to raise the rear of W-5 about 1/8" and completing the wing structure around this adjustment you can lock in the required washout.

This is the 3/16" x 7/16" balsa trailing edge that I stripped from 3/16" balsa sheet. I am using a square to mark exactly where to cut it off to match the W-1 rib.(notice the little pencil mark...measure, never guess)

I am using the miter saw and box again to get an accurate cut-off of the trailing edge.

I'm using glass headed pins to hold the 3/16" x 7/16" balsa trailing edge in place against all the ribs before I add any adhesive. Setting up an assembly "dry" like this allows you to double check everything before glueing if you are using a thin (fast) CA adhesive like ZAP

 

Here's another look at the trailing edge/rib assembly laid out prior to glueing...you can see how the 3/16" sq. balsa spacing strip is angled forward near the tip to provide washout.

With all the ribs W-2 through W-5 glued to the leading and trailing edge and both 3/16" sq. balsa spars, it's time to set the angle at which W-1 must lie for the correct dihedral. Check out the scrap block under the spar at the left...it's holding the panel at the required angle with the tip rib 3" off the plan per the directions. With this set-up the W-1 is glued in place square to the board.

This is the left wing panel with all the ribs in place. I have removed the dihedral spacer block to rest the panel flat on the building board again.

The new kit offers the option of building up the wing tip outlines using laser cut parts rather than laminations. I'm building this airplane that way. Here I have the three outline section parts pinned in place over the plan. I have already used thin ZAP to glue up the assembly...note the clear plastic wrap underneath everything.

An insert of 1/16" balsa sheet is added to the rear portion of the tip outline to prevent distortion under the tension of the covering material. Here I am using the assembled tip parts as a template to mark a piece of sheet balsa for cutting.

The tip outline gets glued in place using more thin ZAP. The front and rear ends of the outline assembly center on the 3/16" sq. balsa leading edge and the rear tip of rib W-5.

The 1/16" balsa sheet insert is in place here. You can see how it is going to prevent the tip assembly from being subject to lateral twisting, especially where that otherwise unsupported rear section hangs out there all alone to match up with the aileron we haven't built yet.

We add a short piece of 3/16″ sq. balsa as an extension of both the lower and upper spar to support the 1/16″ balsa leading edge sheet that will extend all the way to the tip.

Adding the tip assembly completed the basic assembly of the left wing panel. With that done I repeated the process and built up the right panel to the same point...here it is.

The main, front and rear spar joiners are laser cut plywood. The main and rear fit into slots defined by precut openings in several ribs. The front joiner may require that you trim a bit of balsa at W-1 and W-2. Here I have the main and rear clamped in place in the right wing panel.

I used thin (fast) ZAP to glue the spar joiners in place. The precut slots in the ribs make it easy to ensure that each joiner is properly centered before you commit to this step.

 

With the ply spar joiners glued I have replaced the right wing panel on the building board, lined up with the plan.

With the right wing panel on the board, I assembled the left panel onto the previously installed spar joiners and checked that the resulting dihedral angle raised the bottom of the left wing at W-5 exactly 3" above the work surface.

Once again thin ZAP is the adhesive of choice to join the assembled wing panels together. The big building weight (a lead block) is extra insurance that everything stays in line during this part of the assembly.

The 3/16" sq. balsa leading edge "as installed" is supposed to be a bit oversize to allow sanding it to a perfect fit.

I used one of those "big long sanding blocks" to dress the top and bottom edges of the 3/16" sq. balsa leading edge to match the front of each rib exactly.

This is what that part of the job looks like. Sanding operations like this one work out best if you use the biggest, longest sanding block you can control.