El Gato Dos

I’m almost finished with assemby of the left elevator. It’s a bit more complicated than the right one since the left one has a trim tab and houses the trim servo. The skin is riveted to the skeleton and the final step is to close the leading edge of the elevator. To do that I need to roll the skins so they meet and can be riveted together. Rolling is done by attaching the skin along it’s edge to a dowel (a broom handle works well). You use duct tape along the edge of the skin to attach it to the broom handle, then you use the broom to create a nice rolled bend to the skin.

You can see the rolled edge ready to river together in the above picture. In the next photo you can see the opening in the botom of the elevator where the trim servo will mount and the notch in the trailing edge is where the trim tab will fit. More on this when I start bending the trim tab and fitting the servo.

Now that the empennage is built, I have to add the tips to the rudder, stabilizers and elevators. They are supplied in the kit as rough fiberglass parts that have to be fitted, cut to size and attached.

Below is a picture of the tip drilled into place on the horizontal stabilizer. At the moment it’s simply drilled and held with 3/32 clecos and is open on the back side.

In the following steps I’ll be setting it up to be attached with #6 stainless screws and closing up the open back side for drag reduction and to keep anyting from nesting in there when the plane is hangered. Since the open end doesn’t hold the tip to the shape of the opening we’ll have to create a support to allow it to keep it’s shape when removed. Below you can see a small former that I’ve made with fiberglass and place in the open end to cure after the tip has been cut to fit.

After this cures I’ll remove the tip and add fiberglass to cover the entire opening then sand the tip to have a nice streamlined shape. Below is the tip removed and I’m laying fiberglass cloth with resin into the open end to close it.

The resin I use is a West epoxy resin, it is available with mixing pumps that meter the resin and catalyst in proper ratio for mixing.

After the fiberglass sets it requires a lot of filing and sanding to create a nice smooth finish. Below is one tip in progress after one application of filler and a bit of sanding. Lots of fill and sand operations to go yet until this is finished.

Building a plane sometimes means you goof…you drill a hole in the wrong place, bend a rivet, make a ding in a skin or some such misadventure. It happens, the thing you need to do is recognize it and fix it. Glossing over it is not a proper choice when building an aircraft.

Repairing can mean simply buying new parts and building that section over again or sometimes it means a repair. The proper means to repair aircraft are documented in a publication of the Federal Aviation Administration (FAA) entitled; Aircraft Inspection, Repair & Alterations: Acceptable Methods, Techniques, and Practices, publication AC 43.13.

My current goof wasn’t a bad one, it was just ulgy work and I decided that the cosmetic flaw didn’t belong on my airplane. In the photo below you can see two small tabs that need to be bent over by hammering them over the wooden form to overlap and make the inner edge of the trim tab on the left elevator.

In forming the bend I scratched the metal and the bend wasn’t crisp or well done. So I elected to fix this by first removing the tabs and making a rib to fit into the end in their place. Below are photos of the trimming and finishing of the tabs and of the rib I made to fit. More pictures and descriptions later as I make the final fitting and drill it.

Here is the rib I made to take the place of the tabs.

The elevator skeleton is a little different from the skeleton of the horizontal stabilizer (HS) that they attach to. The HS skeleton has ribs that form the edges and an internal structure to support the skin. The skin of the HS is thicker also, so when it is riveted to the skeleton it forms a strong rigid structure. The curvature of the HS to create the airfoil also contributes to it’s strength.
No so the elevator which has a much thinner skin, a skeleton that only forms the perimiter and has a flat surface profile. The elevator’s surface is given rigidity by means of small stiffeners made of angle aluminum that are riveted to the skin.

Here’s a photo of the right elevator skin with the angles cut to the correct shapes and match drilled to the skin.

After cutting to shape and drilling to match the skin the ribs need to be sanded to remove sharp edges and the holes need to be deburred. Cracks start from the little nicks and cuts left by the forming operations. So the next step is to use an abrasive wheel and a deburring tool; seen at the right.

In the last step the ribs are attached to the skin. In the photo the skin has been deburred, dimpled and primed and is ready for attachment of the ribs. The ribs are attached by a method known as backriveting. The rivets are inserted into the skin and taped in place with ordinary celo tape. The skin with the rivets is places upside down onto a smooth metal plate (a backriveting plate) and the rib placed over the rivets. The last step is to use the rivet gun to peen the heads of the exposed rivets.

The trailing edge of the rudder is a somewhat complicated step. The right and left side skins of the rudder are joined using a method called ‘double flush riveting’. This involves pounding a rivet against a back plate to form the head and tail of the rivet flush with the skins on both sides. The big deal here is that the edge of the rudder remains straight within 0.1 inch - anything more and you invite handling issues in flight.

So the edge is glued with a goop called ‘Proseal’ that is also used to seal the fuel tanks against leaks. It is a sticky gooey two part mixture that all builders hate since it sticks to everything and is an unholy mess to clean up. Frequent rubber glove changes minimize the amount you end up spreading around.

Mixing proseal

Here’s a shot of the Proseal mixed and ready to be applied to the trailing edge of the rudder.

Proseal applied and the rudder clecoed to a piece of angle aluminum to keep it straight whilst the Proseal cures.