Building the Stinson SR-9 (24)

Last time I finished what could be categorized as “the covering process”…with the Stits PolyFiber covering in place, shrunk tight and given its basic seal coat, and then given a complete “stitch-and-tape” treatment. As I have already suggested, “covering” and “finishing” with traditional fabric and paint materials are separate processes, but it’s not always easy to tell where one leaves off and the other starts.
Right now the next step will be building up a sanding base/primer coat of Stits PolySpray (silver-colored stuff), but before I do that I’m going to attach (hinge) all the control surfaces. WHEN to do this is usually a judgment call. If I keep the elevator, ailerons, etc., separate until the last coat of finish is on, I avoid the issues of paint jamming the hinges, stuck-together surfaces, and so on. But…then I have to deal with finding ways to HOLD each of those loose parts while I paint it AND while it dries. If I mess that up I get smears and smudges that will have to be fixed. On the other hand, after everything is covered, sealed and taped while I can get to the entire surface of each part easily, I can hinge them in place so, for example, each aileron becomes part of a complete wing panel and makes the “holding on to it” part easier. The catch here is to be able to reach every bit of surface with primer and color coats and find ways (like hanging trailing-edge-down while the paint dries) to keep them from getting stuck together.
That’s what’s getting started here. I pre-drilled all the holes necessary to install Robart Hinge Points and now I’m using a No. 11 blade to open them up through the covering. This is the trailing edge of the vertical fin.

This is a Robart Hinge Point. I’m going to use that ZAP-A-GAP for PART of the installation process.

Regardless of what adhesive I use to keep the hinges in place, I need to make sure none of it dries-hardens-cures in the moving hinge joint or the hinge will work poorly or not at all. I’m using a needle point oiler to put light machine oil into the working hinge. My rule is to get as much oil in there as I can without having it run out onto the mounting surfaces (and spoiling the adhesive joint where I WANT it to stick).

Here’s a hinge halfway installed. The ZAP-A-GAP is holding the hinge shaft securely inside the pre-drilled hole. The oil in the hinge joint prevented the adhesive from hardening THERE and I wiped the residue away.

Here I have the three hinges that go with the right elevator half all installed. If you look closely you can see that I’ve made a point of getting all three exactly in alignment and checked that they move freely. The next step will be to slip the assembly into place in the corresponding holes in the horizontal stabilizer and make whatever adjustments I need to get a perfect fit and full freedom of movement.

What you didn’t see off camera was my re-oiling each hinge joint and then putting a generous coating of 15 minute epoxy onto each of the exposed hinge shafts. At this stage of the job I prefer the delayed hardening of epoxy to guarantee that I have time to get the assembly into perfect alignment. (Yes, this is the vertical fin-rudder assembly, not the elevator). I’m using ordinary masking tape it keep it all that way while the epoxy cures.

Same game for the horizontal tail-elevator assembly.

This is the right wing flap seen from below. I’m test fitting the hinges for correct alignment, which is critical on this airplane because the pivot axis of the hinges lies outside/below the junction of the flap and the rest of the wing structure. Robart Hinge Points are perfect for a linkage assembly like this. Notice that the hinge nearest my hand has not yet been fully inserted into the trailing edge.

At this point I have ZAP’d one end of each hinge into the flap, just as I did with the elevator. I have re-inserted the hinges into the wing tailing edge holes to double-check the alignmnent and while the flap is temporarily mounted I’m oiling the joints prior to pulling out the flap, applying epoxy to the fronts ends, and re-assembling it permanently.

That has just happened , and I’m using more of that masking tape to ensure the assembly stays in perfect alignment while the epoxy cures.

Here’s something different. The flap and aileron servos have already been mounted to their plywood base plates. When I was doing the Stits covering job on the rest of the airplane I didn’t add any fabric to these plates. Now I’m doing a catch-up job using silkspan and clear dope. This simple covering step will permit me to hide the wood grain with far less sealer and sanding than if I’d left the bare wood exposed.

Here’s another quick change of subject. Back when I assembled the clear plastic windshield panels, I defined and protected the portions I wanted to remain clear with several layers of masking tape. Leaving the edges (framing structure) exposed, I then built up a generous fairing of Stits LiteFil epoxy extending out over the taped areas. Now I’m completing the job of sanding all of that to represent the sheet metal cover strips that define the windshield edges on the full scale airplane.

If I were to prime and paint those “cover strips” now, when I removed the masking tape there would be a narrow exposed line of bare epoxy where every built-up tape edge had been. To prevent that, now that all the shaping and sanding is done I’m removing all of the original masking. Then…

…I re-masked the whole windshield with fresh high quality, fine line tape with each tape line set back about 1/64″ from the simulated metal framing. This will allow the finishing paint coats to cover these bare edges and flow out over that 1/64″ gap to create a uniform, sealed-off finish.

Off camera I added a generous first coat of Stits PolySpray aluminum-based sanding primer. At this point I’m done with the sealing iron as a finishing tool along all those tape edges and I am beginning to sand them all gently to get rid of the still noticeable layer of “fuzz” that appeared as the PolySpray dried. For this job I’m trying something new and using a 320 grit abrasive pad. This functions as a sort of “soft sanding block” and gives me a gentle, even pressure all across the fabric-and-tape surface.

There are ALWAYS going to be bumps, dings and other odd flaws at this point. One of the advantages of using a “silver” (aluminum) primer is that it displays the finish you are creating in the most critical light possible…EVERY flaw will stand out. On this job I used a tube of ordinary auto body red lacquer-based spot putty/primer to cover all of them. After letting it dry thoroughly I’m using another abrasive pad…80 grit this time…to smooth and blend the edges of each spot of primer.

More loose ends… just beneath the horizontal stabilizer trailing edge on each side of the fuselage, my full scale reference photos show a sheet aluminum access panel. I represented these with .007″ aluminum sheet (more of that litho plate) stuck to the primed fabric surface. Here the left plate is in place and I’m holding the one that will go on the right side. I want these plates to look like a painted piece of sheet metal screwed in place over finished, painted fabric , so I waited until all but the final primer coat was on the fabric and then added the plates before spraying one final coat. This gives a convincingly “real”, functional appearance once the color goes on.

It’s pretty much the same game with the openings for the cabin side windows. On the full scale airplane a piece of aluminum sheet covers the entire window outline and extends, or overlaps, about 1/4″ into the open area to cover the window panel edge. I’m going to replicate this on each of the rear windows with more of that aluminum sheet. (The front windows, which are part of the doors, are already taken care of by the aluminum outer door panels). Using the existing window openings as a guide, I’m making a card stock pattern of the exact size required for the side window panel.

This is one of the two rear window cover panels partially cut out. You can see from the pencil line where I’m going to finish the cutting job.

As with the access panels at the tail, I used a thin coat of 15 minute epoxy to hold these window frame plates in place. When that was thoroughly cured I used one of my favorite “custom sanding guides” and some 320 grit paper to do some final shaping and cleaning.

As with the windshield, I wanted to do some fairing and shaping where the front end of each of the wing root gap covers (more .007″ aluminum) join the top of the windshield fairing. I did the primary shaping with a curved block and now I’m touching up with a loose piece of 100 grit.

When I had that fairing just the way I want it, I pulled the 3-layer masking tape strip that defines the edge of the fairing.

Off camera again, I’ve inspected the entire airplane to satisfy myself that ALL the little details like that last one have been finished just the way I want them. Again, as with the access panels, I want the underlying surface almost finished so that I can complete the finish base (all the primer, etc., that goes on before the color) with ONE final coat of primer over those last details. What this accomplishes is to give those last bits of plastic, aluminum, etc., just a touch of primer to make the paint stick without building up so much material that it obscures the fine edges I just created.
With all that taken care of, it’s time to get out the spray gun again and give the entire airplane a full, wet coat of PolySpray on which I’ll be able to do some serious sanding.

Now we’re getting someplace! This is the tail end of the airplane with the final (third) coat of Stits PolySpray primer all dry. From here, after some last light touches of sanding, the base finish is ready for color.

On this airplane the trim color (orange) goes on first, and the areas that will remain orange then get masked off. (If I were going to spray and mask the final white pinstripes I’d put the white paint on first. I’ll explain more about that in a moment). For now I have sprayed a double wet coat of Stits PolyTone International Orange generously over, around and beyond EVERYWHERE the design scheme wants orange to show on the finished airplane.

More stuff has been happening off camera. Remember my explanation that I was going to condense my description from time to time in this installment? What you missed seeing was my masking off all the orange as I said I would, then spraying the entire airplane with the primary color (Stits PolyTone Insignia Blue) . When all that was dry, I pulled all the masking tape and added all the white pinstripes using 1/16″ white trim tape. At that time I also added the custom markings that had been made for me by Cal-Graphics…more on these in the final installment. With all THAT done I gave the entire airplane a top coat of Stits PolyTone Clear to seal all the edges of the tapes and markings. I left the windshield masked off until now to keep the clear coat from spoiling the clarity of the plastic and then pulled the last of the masking tape away. That’s what you see here. (Worth waiting for, wasn’t it?)

Now there’s a lot of assembly work left to finish up. This is the underside of the horizontal tail assembly showing the aluminum streamline section strut I built earlier all screwed into place.

Now it’s starting to look like an airplane, but there’s plenty of work left to do with final assembly of components I’ve already built and finished. There’s a special story behind the extra help I’m getting. Katya is one of three feral cats we rescued a couple of years ago. It took a long time to get to this point…she’s up here now just to demand attention from me…but it was worth it.

This is one of those details components I’ve worked on separately and can now assemble once the painting is done. This is one of the landing gear strut upper fairings that came out of the kit as a plastic molding. I did a fiberglass reinforcement job on it (and the one on the opposite side as well), primed and painted it separately, and now it’s time to fix it in place. The plans/instructions suggest that it might either be glued or screwed in place…I chose to replicate the full scale arrangement by using LOTS of 3/16″ flat head wood screws. These are going to seat into the fiberglass cloth reinforcement I added to the fuselage sides with this in mind. Here I’m countersinking their holes in the fairing using a scrap wood block to support the work.

This is the left fairing fitted into place and held with tape. At this point all the screw holes in the fairing are drilled and countersunk. The next step is to (very carefully) drill a pilot hole through each hole into the underlying fuselage side.