The forward end of the fuselage was easy to attach to the rotisserie fixture. Several metal strap clamps were formed over the fuse tubes and simply attached with wood screws to the plywood panel that was used to spin the frame. The rear end of the fuselage was more problematic. Several protruding parts such as the rudder stops and hinge bushings were in the way of trying to flush mount the tail end of the fuse to the spinning plywood disk. I discovered that a drill press vise had a sizable clamping area and was already “V” grooved for tubing. A good snug turn on the vise handle kept the fuse nicely attached to the rear rotating disk of the rotisserie.
The fuse became noticeably heavier to turn as I continued to attach more parts. Without redesigning the rig I attached a hoist motor at the base of the rotisserie and strung the winch cable to a pulley at the top of an 8 foot aluminum mast. I then redirected the cable downward and attached it to an “L” channel that spans the rotating plywood panel. This arrangement allowed me to spin the fuselage from zero to ninety plus degrees in one direction. To spin the other direction all I needed to do was disconnect the cable and reattach it to the other side. This proved to be very helpful especially when it came to the Poly Fiber Fabric attachhment and painting process.
Later, after the airplane was completed I used the same motorized mast to help raise the tail for tailwheel repairs, weight and balance computations and adjusting wing dihedral angles. In this case, I attached the hook and cable directly to the welded lift handles on the fuselage.
With the fuselage painting completed, it was time to reattach it to the rotisserie and it would stay that way for the next two years. Over that time I would complete the belly panel installation, floorboard project, interior sheet metal attachment and the complete fabric attachment and painting process.
The belly project continued with the trimming and fitting of the fixed and removable belly panels. The fixed sheet metal panels were attached with Avex pop rivets to the “Z” channels. The removeable panels were designed to slip fit into a forward slot created by an overlap of the adjacent fixed sheet metal panel and secured to the sides and rear edge of the openings with #8-32 machine screws that connected to fixed anchor nuts on the “Z” channels. It was at this time that I made a deliberate decision to standardize on #8-32 machine screws and anchor nuts on all detachable sheet metal skins versus using sheet metal screws. This would add time to the project since anchor nuts are time consuming to install but for as many times as I had to take these panels on and off it has been well worth the effort. Sheet metal screw holes would have enlarged and become an unreliable means of connection over time.
The forward belly panel was fabricated with clear Lexan. I originally tried clear acrylic (Plexiglass) but it turned out to be too brittle. The Lexan is very tough but is easily scratched and is not as optically clear as the acrylic. The clear Lexan panel is located just below the control sticks and my thought at the time was to have a glass port in the floorboard that could be used for targeting a belly camera or for general observation of the passing landscape below. During flight testing I quickly discovered the oil from the breather line would cover the Lexan belly panel and make it useless to see through, even with an Air/Oil Separator. This was more likely to occur when I filled the crankcase with over 6 quarts of oil. If I maintained a maximum of 6 quarts there was no oil blow back on the belly.
Another very useful purpose for the clear Lexan panel was for preflight inspection of components that would otherwise be unobservableable. I could easily inspect from above and below the torque tube, push-pull tube, aileron pulleys, brake line connections, hydraulic lines, fuel lines and fuel selector valve.
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.
With all the welding complete, it was time to paint the fuselage. The preparation began with protecting the inside of all the tubes with a bath of hot linseed oil. Small holes were drilled at various tube locations and hot linseed oil was injected into the tubes while also rotating the fuse on the rotisserie. The hot linseed oil helps you determine if the oil has reached all the places in the tubular structure by feeling the tubes for heat. Excess oil was drained off and the 3/32 inch holes were closed with pop rivets.
I discovered during the build process that sandblasting was very messy so I left the fuse on the rotisserie and hired a flat bed tow truck to deliver it to Southwest Sandblasting in Grand Rapids. They used a fine bead media and cleaned off and blasted every tube, joint, tab, and nook and cranny of the fuselage.
From there, I had the fuse delivered to Cascoat for painting. They specialize in an electro-static process where the paint and the metal are electrically coupled so that all surfaces can be evenly coated. They first cleaned the fuse with a bath of MEK and then two coats of Randolph two part epoxy primer followed by two coats of Ranthane two part epoxy 146 J3 OEM yellow finish coat. Along with the fuse, I had them also paint the landing gear components, engine mount and numerous other individual parts.
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.