The Return of the TigerKitten (10)

In the TigerKitten the servos, receiver, ESC and battery pack all mount to a 1/16" aircraft plywood tray that fits into the center portion of the fuselage. This requires that you build in these 1/4" square bass (or spruce) rails along the inside of the fuselage doubler on either side and then provide for hold-down screws. This involves a bit more work than simply glueing the tray in place, but it offers the real advantage of being able to remove the tray...and leave the entire center area of the fuselage open...for repairs or modifications. The difference in weight might be measurable, but it's inconsequential. When I got the 1/4" square rails installed I wasn't satisified that the fit between the plywood tray and my fuselage as I had built it was going to provide enough area for the mounting screws to hold securely, so I added the doubler/reinforcement blocks you see here, made from leftover 1/4" square. (Note that there are two more out of the image near the nose.)

Here I have measured and cut out the opening at the rear of the tray for the rudder and elevator servos and added a pair of 1/4" sq. bass rails across the tray to hold the servo mounting screws. I chose to mount these servos upside down so that the rudder and elevator control tube connections will be accessible when the wing is off. My mounting hardware is No. 4 x 1/2" button head sheet metal screws (DuBro Cat. No. 527)

I'll have more to do inside the model later. Now it's time to add the rudder and elevator control horns. I'm using DuBro nylon control horns (Cat. 107), which are intended to be attached flat against one side of the control surface with two screws extending to a backing plate on the opposite side. There is nothing wrong with doing it this way...but...I am a fussy all-out scale fanatic and I like to reproduce credible "scale" appearance even on my sport models. To get rid of the clunky-looking backing plates I chose to inlay each horn base into its respective surface. Here I have traced the "footprint" of the rudder horn.

I used an ordinary No. 11 blade to trim around the marked outline down to the thickness of the base (about 3/32"), and then a curved miniature wood chisel to create an opening for the horn to slip into.

Once I had checked that the rudder horn rests squarely in place in the opening, I wet the inside of the cutout generously with ZAP-A-GAP, pressed the horn into place, then flowed in more ZAP-A-GAP to create an outer surface flush with the rest of the structure.

A shot of Zip Kicker ensures that the thick application of ZAP will cure quickly and thoroughly. NOTE: This method of control horn installation works well for small, light airplanes, but may sacrifice some of the strength of the screw-through feature. It's fine on a three pound sport model like this, but once the model in question gets much bigger you need to be using plywood insert horn bases along with nuts and bolts to hold everything together.

It's time to provide an opening for the control connection to the servo. This happens to be the marked location, per the plan, where the elevator push-pull tube assembly will exit the fuselage.

I'm going to use a concentric tube-within-a-tube connector system here. The hole through the side of the airplane must allow the outer (thicker) tube to fit snug, but also to lie straight in a line from the control horn to the servo output. To get this right you start with the locations marked on the plan, measure and fit and check, and adjust as necessary. Be sure your hole is elongated enough that the outer tube won't try to make an "S" curve as it passes through the sheet balsa. I'm using a round wood rasp (file) to cut the clearance I need. NOTE: I can't assume that every "new guy" knows this...that sheet balsa insert is absolutely necessary to provide an anchor for the tube and to support whatever covering you use...film, fabric or whatever...around the tube exit. The control connection can't be allowed to flop around loose.

These concentric control tubes won't support themselves over the distance between the servo output and the exit hole...unless they are braced securely they will flop around under air load pressures and cause erratic control responses. Here I've drilled a simple piece of 1/8" sheet balsa cut to fit at the F-6 station, to support the front end of the rudder and elevator tubes. (I have the inner tube "dummied" in place and lined up with the servo output at the front.) Thin ZAP will work best here to hold everything in place once I have it located correctly.

This is the outer tube for the elevator. With everything aligned, I ZAP'd it in place in the balsa sheet support insert and then cut off the end to form a neat control exit that will blend into the finished covering as a streamlined fairing.

Same deal as seen from the bottom. The tube on the airplane's left (it's upside down) is for the elevator; the other is for the rudder. The tubes cross inside to permit as straight a run as possible from servo to control horn.

I'm using DuBro pinned nylon hinges (Cat. No. 117) for all the control surfaces. This is the rudder. You can just see a temporary wrap of masking tape at the right of the hinge...this holds the surfaces in alignment while I mark hinge locations as per the layout shown on the plan. I'll extend these simple pencil lines around the edges of the surfaces once they are separated.

Here I am working on the vertical stabilizer, using a 1/32" bit to drill a hole all the way through at the exact center of trailing edge at each end of all the hinge locations I just marked in pencil. These will define the hinge slots. With the holes drilled, it's easy to cut out the balsa between each pair of holes with a NO. 11 blade.

Back at the rudder...I've drilled and opened up all the hinge slots and dry-fitted the DuBro No. 117 hinges in place. NOW is the time to sand, trim, or otherwise fix the control surfaces so they all fit like this without forcing or binding.

Here's another look at the tail with the rudder and elevator in place. Everything is fitted dry (no adhesive) at this point. I'll install the hinges for keeps after all the covering and finishing work is done.

I'm using the same pencil line technique to mark the hinge locations on one of the ailerons.

As with the rudder and elevator, I'm drilling 1/32" holes at each end to define the hinge slots.

After drilling, I use the No.11 blade again to cut out each hinge slot. There are various "machines" around to do this job for you, but I have discovered that I prefer the blade and drilled stop holes as the easiest way to make controlled cuts and open each hinge slot exactly where I want it to be.

Because the front of the aileron includes an angle that creates a narrow leading edge, it's easier to get the aileron to fit snugly against the wing cutout/trailing edge if we cut a relief slot in which the center pinned section of the hinge can rest. I'll sand the surface of this cutout smooth after I finish trimming.

This is the right aileron in place with the control horn and the inboard hinge dry-fitted. You can see how the hinge nestles into the shallow slot I just made for it.