Building the Stinson SR-9 (11)

Assembly of the upper fuselage begins with the top portion of F-3, which was put together earlier and set aside until now. I’m using clamps made from ordinary clothespins to hold F-3T in place and a drafting square to ensure that it’s correctly aligned with the bottom portion of the former.

Because I made a point of squaring off the joining edges of the former assemblies, they fit accurately enough that I can use thin ZAP to glue the joint in place. Here I’ve removed the clamps and I’m putting an extra shot of ZAP into what might have been a dry spot in the joint.

Here the top portions of F-3 through F-7 are securely ZAP’d in place. I used that plastic square repeatedly to make sure each one was aligned before sticking anything together. This airplane is big enough that even a tiny misalignment at this stage of the building job would  show up to embarrass you later.

The next step is to add the 1/4″ x 1/8″ basswood top center stringers between F-3 and F-8. At this point I’ll suggest you stop trusting the accuracy of the parts cutting and be prepared to trim the  notches in each former in turn to get each stringer to run dead-straight front-to-rear. I have the camera slightly off center in this shot, so the curve in the side profile of the airplane shows up as if it were a bend in the stringer.

Here the three center top stringers are in place. I’ve left some overhang in the center one that got trimmed off later.

All five top stringers are in place. In this image you can easily see how they follow the curvature of the fuselage outline as viewed from the side.

The top longerons are cut from four pieces of 1/4″ x 1/2″ x 24″ balsa. Each longeron extends from F-3T to the top of F-9 and each one is made from two pieces of 1/4″ x 1/2″ balsa butt-joined at F-6. Here you can see the forward section of the top left longeron, which I have already ZAP’d into place at F-3, F-4 and F-5, ready for the slight bending pressure it will take to line it up at F-6.

The next step is to add the rear portion of the longeron, fitted into place as tightly and accurately as you can get it.

The tail gear mounting plate and the tail gear mounting doubler have to be glued together as a laminate before being installed. This is what the overlapped assembly should look like.

This is the left 1/8″ plywood inner stab saddle test-fitted in place against the left lower longeron and F-9.

Thin ZAP makes quick work of the job of glueing the left stab saddle into place.

This is the left outer stab saddle ready to be laminated in place directly outside (over) the left inner saddle.

I have cut a 1/4″ x 3/4″ balsa tail wedge to fit between the rear (vertical) ends of the stab saddles.

The next step was to clamp the entire assembly with wooden clothespins and thin-ZAP everything securely into place.

This is the entire stab saddle/tailpost assembly ready to be squared off and sanded smooth.

I used a long sanding block with 80-grit production paper for that job.

These are the die-cut forward fuselage sides ready for assembly. Each side is laminated from two identical 1/8″ plywood pieces to form a 1/4″ thick assembly…BUT…the right side is shorter than the left to create built-in side thrust offset. Join two “shorts” and two “longs” and mark them “right” and”left” to avoid confusion.

Although I won’t install it yet, I’m checking the fit of the left bottom deck. It’s at this point that all the 1/4″ sq. balsa temporary braces are cut out of the structure ahead of F-5 and wood is trimmed from the bottom deck and fuselage side assemblies as necessary for an accurate fit of all the parts. NOTE: trim the plywood parts, NOT the vertical and horizontal components of the formers OR the longerons.

Like this… Here I have marked a section of the right forward fuselage side assembly to be trimmed away to fit F-4 and F-3.

The next step was to add the 1/8″ plywood vertical former bracing at F-3, F-4 and F-5. This is the left F-3 doubler hand-held in place to check the fit before I glued it.

I have added all four F-3 vertical doublers – two each front and back – with ZAP-A-GAP and used clothespin clamps to hold them while it cured.

I’m trimming the 1/8″ x 3/8″ balsa main stringer at F-4 to provide clearance for the 1/8″ ply vertical former brace.

The next step is the addition of various 1/4″ x 1/8″ and 1/4″ x 3/8″ basswood reinforcing spacers to the top deck and fuselage side assemblies. Here they are all ready for installation. Next time we’ll assemble the nose structure and get ready to build a motor mount.