Cascoat did an outstanding job and all the metal was evenly coated with no runs and a beautiful overall sprayed finish. Careful preparation and professional finishing should result in a 100 year airframe without rust or corrosion. The two part urethane epoxy paint system is well suited for the attachment of the Poly Fiber Fabric system. The Poly Fiber Fabric system utilizes solvents that range from the mild 2210 fabric cleaner to the very aggressive MEK (methyl ethyl keytone) all of which have no effect on the Randolph epoxy finish. You can brush MEK on the Randolph coatings all day long without ever damaging the finish. The only way to really remove the paint is a torch. During the build project I found it necessary to add a bracket or tab or make a repair on the painted tubes and the easiest way to do this was to burn off the paint in the weld zone, clean it with MEK and repaint it with the same Randolph coatings. It was almost impossible to see where these repairs were made.
Before proceeding further with the Belly Panel project, I decided to move on to the Engine Mount installation.
There are certain welds on the airframe that deserve more attention and respect. These include the wing spar brackets, wing strut brackets, spar crossover tubes, landing gear brackets, tail feather attachments and the Engine Mount Brackets. Every weld is important but a a bad weld on the engine mount can ruin your day.
This project starts by first taking the fuse off the rotisserie to expose the front end of the airframe. The four airframe connection points must be accurately welded to agree with the chosen engine mount holes and the engine mount must agree with the engine you plan to use. My future plan was to use a Lycoming or Superior 180HP Engine and for now all I needed to do was decide on which type of Engine Mount to use. There are basically two types of mounts – conical or Dynafocal. The Dynafocal Mount is said to reduce noise and vibration inside the cockpit and the swing out feature sounded good in theory. The installation needed for the swing out feature will require careful alignment of the top and bottom brackets on each side so that the hinges will not bind and stay in alignment. There is no means of adjustment for a misaligned hole so careful tack welding and trial fitting is necessary to assure proper fit of the Engine Mount.
In later years I would discover that the swing out Engine Mount is not as practical for servicing the engine as it sounds. As you can imagine, the throttle cable, mixture cable, carb heat cable, magneto cables, oil lines and numerous electrical connections disallow any means of hinging the engine away from the firewall without first disconnecting everything. Only during a major service event will the swing out Engine Mount feature be utilized.
I decided to experiment with a material used in the display business called Alucabond. It is a 6mm panel consisting of two .020″ aluminum skins thermo bonded to a solid polyethylene core with an overall thickness of 6mm or 1/4″. It is a very durable material and easy to form. I chose the 6mm thickness to fit the standard 1/4″ set back of the “Z” channels however in retrospect I should have used the 3mm thickness and remade custom 1/8″ “Z” channels instead. The thinner panel would have been easier to form and be less weight.
My shop was not equipped with a metal forming machine so I designed my own contraption to form the bends. I used a cardboard tube from my local Home Depot that is used for making footings for decks. These come in various diameters and I used a slightly smaller diameter to compensate for springback. I filled the tube with concrete to make it as ridgid and hard as possible. A 1.5″ thick plywood panel was hinged at the edge of the work bench and was used for bending the Alucabond around the concrete filled tube. As crude as it sounds, this fixture worked amazingly well. There were of course a few R & D bends that did not fit right but I eventually developed a method that worked. Fitting the panels to the airframe was also a trial and error process. My only regret was that I did not make an extra set of panels. Ground looping the airplane during flight testing damaged two of the panels that I would later replace using an altogether different material and forming method that I will describe in a later post.