Building the Stinson SR-9 (9)

It’s been a while since I have done any work that counts on this airplane…in fact, I have to confess that I’ve been letting it gather dust in my shop for about a year. I set the Stinson aside to work on the old FlyLine Great Lakes Trainer kit. That project turned into a twenty-nine-installment blog series…check the archives tab on my home page if you missed it. Just as that project ended up letting me finish it, it became clear that I needed to build a pre-production TigerKitten from the new kit my friends at Premier Balsa Kits are introducing, in order to help check out that new product for them. As you have probably figured out by now, I’m not capable of doing anything relating to model airplanes the quick way , so the Stinson spent several more months getting dusty on the back workbench.

At the point I made the last blog entry on the Stinson project I’d gotten the tail surfaces built up along with the left wing to the point of adding all the leading edge sheet and the capstrips. What was left to document was the final sanding to shape of the wing structure along with building the flap and aileron. Since building the right wing is essentially a mirror image operation, I planned to do that off-camera, intending to pick up the blog as I started work on the fuselage. All that worked out just as planned…but…while I was working on those two other airplanes I had to replace my old computer. The new one works way better, but in the process of changing to a new operating system and to different image processing software, guess what happened to all those images of building the aileron and so on?

So…I shot some after-the-fact images of one fully sheeted and sanded wing along with several views of the completed ailerons and flaps to give you an idea of what that part of the structure is supposed to look like. In the event you might be using my notes as a guide to building your own SR-9, don’t worry. The kit instruction book is more than sufficient to get you through without my help. Let’s have a look at these catch-up photos. I’ll get started with the fuselage in the next entry.

This is the outboard portion of the left wing as seen from the back. The rear spar extends from the root to the tip and here it serves as the front of the aileron cutout, or aileron well. All the outer sheet and capstrips are sanded to their finished shape so that I can build an accurate aileron using them as my reference.

This is the left aileron well seen from the bottom. At the upper right you can see the trailing edge portion of several ribs that extend all the way to the trailing edge, forming a fixed section between the aileron and the flap. The two cross members behind the main spar are the aileron servo rails.

This is the same structure looking out toward the tip. The wing as it is built to this point defines the aileron. Because this is a top-quality kit, it’s no big deal to presume that the component parts of the aileron are going to fit properly when it’s time to assemble them.

This is the completely assembled left aileron. The parts of the job I missed showing you go like this…you shape the aileron leading edge first, then spot-glue it into place against the rear spar. Next you fit the root and tip aileron ribs followed by the sheet balsa aileron core. You can see here that the leading edge is tapered, as viewed from the end, into a blunt VEE to permit deflection of the finished control surface. Also note where I have cut air passage holes through what will be enclosed space in each aileron rib bay to permit air pressure inside the structure to equalize when hot sunlight is doing its thing out at the field. The blocks you see are cut from basswood strip furnished in the kit to serve as aileron hinge mounting points and a control horn anchor.

Here’s the completed aileron hand-held in place. I block sanded all those rib, leading and trailing edge capstrips to a precise fit with the rest of the wing and then cut the assembled aileron free where I previously spot glued the leading edge to the main wing structure.

This is the inboard end of the left wing showing the open flap well. The front of the opening is defined by the inner trailing edge spar, which meets the inner rear spar at an angle. Here the top and bottom trailing edge sheeting and rib capstrips are in place and sanded to shape.

The flap well as seen from below reveals how the top trailing edge sheeting forms an overhang that will enclose the top of the trailing-edge-to-flap hinge line. You can see the three hinge blocks on the inner face of the rear trailing edge spar…these have already been drilled to accept the Robart Hinge Points that will be installed (at an unusual angle) after the covering and finishing are complete.

Here’s a look at the completed left flap with all the final shaping done. There is a complex taper cut and sanded into the leading edge…but…the instructions are clear about how to go about doing that job.

This is the completed left flap hand-held in what is close to the extended position. When the flap retracts the top surface will line up directly with the top of the wing and the hinge line will disappear under that extended sheeting.

This is the same flap as seen from the bottom. The gap created between the wing trailing edge and the flap leading edge by that taper will close up tight as the flap extends. We’ll get a better look at how the hinge installation works later on.