The Return of the TigerKitten (14)

It’s time to attach (hinge) the control surfaces…the rudder, elevator and ailerons. When to do this relative to covering, preparing a base finish, and adding the color coats is always a judgment call. I can’t imagine doing a final installation of the hinges before covering…there’s just too much stuff you can’t get to that way. I also like having my base finish work…clear dope, sanding base coats and any final primer…done while I can still get to every component from every angle. On the other hand, on an airplane of this size I like the control of having all the various small parts attached so I don’t have to hang, or jig, them someplace in my painting area and worry about bumping into them while I’m concentrating on an airbrush or a spray gun. The down side to this is that I’ll have to worry that when I hang each painted assembly up to dry the wing, for example, is oriented leading edge up so that the ailerons hang straight down to ensure that the wet paint won’t grab adjacent structure and stick them against the wing in a deflected position…and I’ll also have to take time to clean dried paint from the hinges. On a larger airplane I would take the time to rig holding fixtures for each control surface and spray them with the color coats separately. None of this is an issue if you use pre-finished, iron-on coverings, but here we are talking about the real thing…traditional model building skills…and you need to know this stuff if you want to play in that league.

Prior to covering the structure I used a fine drill bit and a No. 11 blade to open slots for all the control surface hinges. After the last primer coats were dry and sanded out, I opened up each slot with the same No. 11 blade and dry-fitted a hinge (DuBro No. 117) into each slot to check the fit. I'll push this hinge all the way in to make sure it fits without binding before I go anywhere near it with adhesive.

Regardless of the adhesive you use to assemble pinned hinges to the airplane structure you must make sure it doesn't infiltrate the working portion of the hinge and cause it to bind, or stick, or worse yet, lock up. OIL is the answer...any adhesive you are likely to use won't stick to it. I'm using a needlepoint oiler with ordinary light machine oil on the entire mating portion of the hinge. Get the hinge line WET with oil, but don't let it run out onto the flat attachment tabs.

I'm using ZAP A GAP to set the first side of each hinge...here I'm working on the elevator...because I'm dealing with one hinge at a time and I can concentrate on getting it aligned without worrying about it's neighbors. If you're not confident you can do this, use slower setting epoxy instead.

Here's the hinge pushed all the way into place with any excess "squeezeout" of adhesive wiped away.

I'm pressing the elevator leading edge against my flat work surface to make sure each hinge assembly in turn is parallel to the leading edge. (On a larger airplane with removeable-pinned hinges I'd do this by inserting an alignment rod through each hinge and into the next as I installed it.)

The hinges are in place in the elevator, recessed into the slots I cut for them, and aligned as neatly as I can get them. At this point I wipe each hinge assembly CLEAN of any remants of oil and cured adhesive, double-check it for freedom of movement,and re-oil the working joint before the final step.

Now we are looking at one of the ailerons. ALL of the hinges on this surface will have to fit into the trailing edge at the same time, so I chose a thirty minute epoxy to guarantee that I'll have time to get all of them lined up exactly and any dribbles of excess epoxy cleaned up before it starts to cure. This is one of those no-second-chance deals. If you ever have to cut misaligned hinges out of an assembled control surface you'll find out what that means.

I'm slipping the entire left aileron into place FOR KEEPS...the outboard hinges are doing just what this one is, with wet epoxy on them. The control horn is slipping into the pocket prepared for it in advance. You can be sure I double-checked THAT as well before mixing any epoxy.

Last chance...I'm using my trusty old artist's pallette knife to lift away any little globs of epoxy that squeezed out as the hinge was pushed into place. A little squeezeout is good...it ensures that the internal joining surfaces are fully wetted with adhesive. You can't see a dry joint, but you'll recognize one when it fails.

I use strips of masking tape wherever I need them to lock the aileron...and the other surfaces...into exactly the alignment I want, and then go away to do something else for a while to be certain the epoxy has had time to cure hard before I move anything. All the hinges on all the control surfaces go in the same way on this airplane.

Cockpits, canopies, windshields and so on are FUN. They are also attention grabbers on any model where the builder has invested some effort beyond a plastic bubble taped to the top of the fuselage. The TigerKitten is not a scale model, but I designed it to look like one...you really need a cockpit, and in this case a windshield, that looks believeable. The cockpit cutout and backrest are pretty much dictated by the way I designed the airplane, but the details can make all the difference. On this model I'm going to represent a simple unframed single curvature plexiglass windshield which in the real world would be molded to shape and attached to the top deck with a formed metal or plastic base fairing secured with either rivets or screws. On the model I can hand form the plastic windshield, attach it with ZAP, and then build up a fairing strip using filled epoxy. And...I'm going one step further. If this were a full scale airplane there would be some sort of matte, anti-glare feature on the top deck inside the windshield above the instrument panel. I'm going to represent that with a piece of brown suede-finish paper from the craft store. At this point I have marked the line where the windshield will meet the cowl by tracing the dry joint with a pencil, then rough-cut a piece of my suede paper big enough to cover the inside surface with a safe margin for error.

The next step is easy. I used spray-on contact adhesive on the back of the suede paper, positioned it to cover the area I marked out, and pressed it into place.

Now I can go back, dry-fit the windshield again, and mark onto the suede paper where the attachment line will be. With that done I ran a strip of masking tape along the INSIDE of the curve to serve as a cutting guide and protective covering.

Put a fresh (sharp) blade into the knife for this job...you want to be able to make a clean cut through ONLY the paper without having to press down hard. I'm trimmimg away the excess suede...the part that would have been outside the windshield...so I'll be able to attach the clear plastic to the cowl, not to paper.

Now I can peel away the extra paper.

I cut the windshield to shape using the pattern on the plan, then covered the entire outside face with several layers of masking tape leaving only a narrow margin...about 3/16"...for attachment. Here I have fixed the outer edges of the plastic in place with masking tape and I'm using ZAP A GAP to build a neat fillet along that exposed edge of the plastic where it meets the cowl.

The sides of the windshield are firmly ZAP'd in place. Now I'm pressing the front edge firmly in place against the cowl, ready for more ZAP A GAP. Zip Kicker accelerator is a must for an assembly like this.

With the entire bottom edge of the windshield fairing ZAP'd in place, I ran a single strip of 3-M Blue fine line automotive masking tape along the bottom of the masked area to ensure a sharp definition, then added a double strip to define the outer edge of where I want the the fairing to be.

There are all kinds of lightweight epoxy putty/fillers around. In this case I made my own by adding talc (baby powder) to some thirty-minute epoxy. I'm using that same artist's pallette knife to build a fillet of epoxy putty up and over all the tape edges. NOTE: Do not use a solvent-based balsa filler product for a job like this. It will shrink as it dries, crack, and ruin your best efforts to do a neat job...and...it will impart zero strength to the joint.

A WET finger is an excellent tool for smoothing the fresh epoxy putty to a smooth contour as close as possible to the finished shape you are looking for, in order to save sanding later.

The cured epoxy can be sanded to a finished contour. Here I'm using 220-grit silicon carbide paper wet. There is no substitute for care and patience doing this part of the job.

Ready for a primer coat. I have finish sanded the fairing strip to form the smooth, concave curvature I want and to cut the surface of the epoxy putty material down level with the top of the various strips of masking tape. That way when I pull the tape I get a crisp edge equal to the thickness of the tape buildup. This simulates the edge of a sheet metal fairing. I'll leave the tape on the windshield until after all the paint is on and then pull it to get a similar raised edge on the opposite side of the fairing.