The Return of the TigerKitten (6)

There’s a lot more work to do on the fuselage, but now we’re getting to the parts I find most interesting. Let’s build a top deck. When I designed the TigerKitten over twenty years ago, I used a combination of dowel pegs and a neat little custom made tube-and-wire latch to hold the top deck in place for flying, yet keep it easy to remove for battery charging and other access. Since that time those tiny rare earth magnets have become common and easy to find. Mike at Premier decided to simplify the deck retention mechanics by using several of them, and I am following his lead on this modification. It really does save time without compromising quality.

The top deck is really a removeable upper front fuselage. It provides excellent access to your battery pack as well as to whatever components of the radio system you choose to mount on the upper side of the inner tray. It's big enough and important enought that a good fit and a neat appearance really matter. Premier has made the job of building it quite a bit easier by providing a laser cut base/outline to which everything else gets glued. I began assembly by gluing the 1/8" x 3/16" balsa base strips along either side of the ply base plate. These lie flush with the outer edge of the plywood, and must be bent gently to follow the curve at the front end of the base plate. For this part of the assembly I am leaving everything pinned to the building board, nice and flat.

Building the cowl structure "in place" on the existing fuselage is the best way to ensure that it fits perfectly. I used a piece of food wrap to keep glue from sticking where it's not supposed to and assembled the laser cut formers C-1 through C-6 in place on the plywood hatch base. Notice that C-5 is installed at an angle to serve as the instrument panel base, whether or not you choose to add a fake panel later on for appearance.

Formers C-1 through C-5 are laser cut with notches to accept the 1/8" x 3/16" balsa stringers that will support the 1/16" balsa sheet outer skin. These lie flush against the back face of F-1 at the front and end at C-5 at the rear. It's a good idea to extend the top center stringer temporarily all the way back to C-6 to act as a brace during assembly.

The outer skin of the top hatch is 1/16" balsa sheet, which fits over the top of the C-1 through C-5 formers and along the outer edge of the base plate. Here you can see how the edge of the base plate is cut to fit 1/16" inside the outer face of the fuselage side so the top skin will lie flush when it's installed.

The outer surface of the top deck (the part you see) consists of two pieces of 1/16" balsa sheet, each cut to fit one half of the structure and meet in the center of the top/middle stringer. You can measure directly from the deck structure onto a sheet of balsa to mark cutting dimensions, or make a paper pattern and trace that. Either way the lower edge of the sheet must lie flat against the building board and fit tightly against the lower edge of the ply base plate to fill the 1/16" space we saw in the last step. Just as I did with the forward fuselage side sheets, I sprayed the outer surface of the deck skin with water prior to assembling it the way you see here to permit it to bend easily and prevent the possibility of cracking along the grain. You'll need to do some careful trimming to ensure that the edge of this portion of the sheet skin lies right down the centerline of the top stringer in order to leave room to attach the other side. I used ZAP A GAP here to allow time to bend the wetted skin carefully into place and then press it down to bond.

This is a better look at the centerline attachment of the left side of the deck skin. The right side will go into place in exactly the same way. In an assembly like this there is no substitute for careful measuring, trimming, and then going back to trim or sand off a little more to get it right. The smart trick in cutting the edge of a part like this where the fit must be perfect is to make your first cut knowingly oversize, so you can recheck and remeasure and go back to sand away more wood cautiously until the fit is just right. If you let yourself be satisfied with a sloppy fit in a place like this, no amount of filler or covering will ever hide it completely, and your mistake will be preserved right there for the world to see.

I have added the right half of the 1/16" balsa sheet deck covering, let the water that I sprayed on to help with the bending dry thoroughly, and done some preliminary trimming of what will become the cockpit opening. You can see that the top stringer still extends all the way to C-6 as a reinforcement brace during assembly. I have marked a rough outline to which I will trim with a No. 11 blade. I have done this job many times and I'm comfortable making the final cut and trim by eye. If you have any uncertainty about where to cut, make a paper pattern using the plan sheet as a reference and trace an exact line onto the wood before you go near it with a knife.

We're making the finished cut into the top deck sheeting that will define the cockpit opening. There is nothing about this that's critical to the structure; however, you need an opening of some sort because this is where your cooling air exits the fuselage. The big deal is the esthetic one...the appearance of the finished airplane depends in part on how you decide to shape this opening. As I mentioned in an earlier note, I've done this one before and I know exactly what I want. For your airplane, you get to choose. Whatever you do, it's not practical to try cutting the opening with just a No. 11 knife...you need to sand it. Here I am using an old can as a backing for 40-grit production paper to rough-cut the opening to the shape I want.

The top deck assembly is mounted to the fuselage by two 1/8" diameter pegs that fit into holes in F-7 and a couple of those little rare earth magnets at the front that we'll get to later. Here I'm drilling the 1/8" I.D. (internal diameter) holes that will match up with short lengths of 1/8" O.D. (outside diameter) carbon fiber rod (those pegs) that will be part of the removeable deck. Just drilling holes into the wood former will not provide a secure mounting base that will hold up...the holes would "hog out" in use and become sloppy.

I'm using thin (fast) ZAP to harden the wood all around the holes. The top deck gets removed every time you fly this airplane, and you don't want the working surfaces of the removeable deck arrangement to wear out from heavy use.

Using the holes already drilled in F-7 as guides, I marked and drilled more 1/8" holes in C-6 to accept the 1/8"carbon fiber pegs. Here they are in place, glued with fast ZAP. Using the holes in F-7 to locate the pegs ensures that everything will line up.

I'm using 3/16" diameter rare earth magnets (I got mine at Radio Shack) to hold the front of the top deck in place. I drilled a shallow hole in the top longeron on each side of the fuselage and a corresponding hole in the bottom of the top deck. Here I am using SLO ZAP to mount the left lower magnet. When both lower magnets are in place and the ZAP has cured, I'll cover the entire area with clear plastic wrap, ZAP the two upper magnets into their holes in the top deck assembly, and assemble everything.

Here's what that looks like. The lower magnets are stuck in place, the plastic wrap is keeping the fresh SLO ZAP from sticking to anything except the upper magnets and the holes they fit into, and assembling the top deck in place and holding it with that masking tape permits the top magnets to align themselves perfectly against the bottom ones before the SLO ZAP grabs.