Building the Stinson SR-9 (7)

OK…now it’s time to get started on something that will make it clear just how BIG this model really is…let’s build the wing. As it turns out, even if my workbench were long enough to lay out both the right and left panels of the wing at the same time, I would have to walk back and forth from one to the other to work on them. It’s a lot simpler to take the suggestion offered in the instructions and do one panel at a time, so we’ll do that and begin with the left.

We are going to follow the instruction book sequence as written. This model, while still of "conventional" design and engineering, is quite a bit different from the FlyLine Great Lakes in that virtually every step, including spacing and jigging and glueing up sub-assemblies, is spelled out in detail. You still get to do all the building, but Top Flite/Great Planes has defined every step for you in advance. First job is to assemble ribs W-1 through W-7...several of these are made up from two or three separate die-cut balsa pieces. It would have been possible for the kit designers to use wider than usual (3") balsa sheets and cut each of those ribs as one piece, but using wider sheets translates into higher costs. You get to glue up sub assemblies and save a few dollars. There are also reinforcing plates, or doublers, on each of these inner ribs. These will provide alignment and reinforcement for the wing mounting box structure. At this point, all the rib sub assemblies are together and the doublers are in place.

Here's an excellent example of the planning that's done for you in a kit like this one. The front(main) wing spar sweeps forward as it extends from the root ot the tip, and as a result each of the ribs crosses it at otjer than a square ( 90 degree) angle. The die cut slots in both the spar sections and the ribs must by definition be made square, so in order for the ribs and sparsto fit together properly it's necesssary to cut or sand three degrees of offset into each slot. The rib at the right has been "dry fitted" (without glue) and shows how the slots fit together in what is sometimes called "egg crate" assembly.

Here's the same angle being sanded into the next rib.

The Stinson Reliant wing is a very complicated shape to build. There is no single flat surface that will serve as a reference that allows you to build the rest of the wing square. To get around this, the kit is engineered with carefully measured offset shims added to the wing spars to hold them at exact angles in relation to each other. The builder’s job is to lock these spar shims in place on the building board to keep them from moving during assembly. This is the left wing tip. You can see where I have pinned strips of 1/4″ sq. balsa both front and rear of each wing spar, and added more scrap stock at the outside end of each spar to prevent spanwise movement. Using locating blocks in this way prevents sticking the actual structural parts full of pinholes.

This is the inboard end of the left wing with the ribs assembled in place on the front and rear spar assemblies. At this point I have used adhesive only to assemble the ribs...everything else is slotted and jigged together. The kit is designed this way to permit assembling the entire primary structure of the wing and confirming that everything fits and aligns properly before committing any of the joints to glue.

This is a closer look at the lower half of the wing mounting box assembly fitted into place through the various slots and holes in the rib reinforcements. No glue yet.

Here I have assembled the top portion of the wing mounting box. This structure will support a heavy aluminum tube that passes through the fuselage and out into both wing panels as the primary structure that holds the assembled wing panels in place.

Here's the whole deal from the front. Both the lower and upper front (main) spar caps of 1/4" x 1/2" basswood are in place and the entire assembly has been locked up using fast (thin) cyanoacrylate, but the leading edge has not been added.

The wing tip assembly is made up of a core and a series of die cut curved balsa edge sections, laminated to the lower and upper surfaces of the core.

Here's the tip assembly glued in place.

Here the front upper spar of 1/4" x 1/8" bass and the preshaped balsa leading edge have been glued in. I have also used an 80-grit sanding block to contour the top surface of the leading edge even with the tops of the ribs so the 3/32" balsa leading edge sheet will lie in place correctly.

Here's the outboard portion of the leadinfg edge at the same stage

The upper edges of every piece of structure that will contact the top surface sheeting as well as all the capstrips must be sanded flush...here is the top edge of the inner main spar.