ELEVATOR SERVO INSTALLATION
My servo selection for this airplane was based on prior experience with airplanes of this size and also because of the servo selection published by CPLR. When I was opening up the covering for various holes in the fuselage, I saw immediately that the provided hole for the elevator servo was too small. Opening this up is much easier accomplished before stab installation than it is after, so I made a command decision to break the normal order of operations and resize the hole to accommodate the servo as the first thing in this build. A discussion with the factory confirmed that they are aware that the class servo I chose is more important for setting the airplane up as a precision airplane, and are looking to integrate this into future production runs of the airplane. For guys in the first production run, you’ll need to do this. It takes about ten minutes to do and is not difficult at all to perform. You’ll need the following:
Calipers
Ruler
Low tack masking tape
Fine point pen, mechanical pencil
Knife handle with #11 and #18 heavyweight chisel tip
Various sanding blocks
Pin vise with 1/16-inch drill bit
Plywood servo shims
Servo
Covering iron
Thin CA
First, remove the covering from the hole. You can simply trim the covering flush with the opening as there is no point folding it in and then outline the hole with ¾” low tack masking tape. Take your calipers and measure the overall length and width of the body of the servo. Add 2mm to the length measurement and a millimeter or so to the width to ensure that the only portion of the servo that makes contact with the airframe when installed are the mounts themselves. I am not a fan of mounting a servo directly onto soft wood, therefore, I measured the overall length of the servo with the grommets installed and added about 2mm to this measurement and removed the balsa underneath that the servo insets into the skin of the fuselage slightly. This gives a much nicer aesthetic, as well as prevents the balsa from crushing underneath the servo when you tighten it down. Once you remove the top balsa sheeting, you can begin to resize the plywood mount to accept the servo.
Carefully cut through the sheeting of the fuselage to reveal the plywood mount. Use a ruler to keep the side cuts straight, but don’t go all the way to the corners. Use the #18 chisel blade to accomplish this. Once satisfied that you have cut the perimeter of the opening down to the plywood mount, take the chisel blade and remove the sheeting to reveal the inner plywood mount. Take your calipers and measure the overall length of the servo case and add two millimeters to this overall dimension. Measure the difference in the pocket you created and the new dimension, and make marks from each end to denote your actual servo mount opening. Again, carefully and with a very sharp blade, cut along your marks through the plywood to enlarge the mount to accept your servo. Don’t try to cut all the way through at once; in fact try to only make very shallow cuts and always cut away from the corners so that you don’t create stress risers or risk slipping and cutting covering. Patience and a steady hand will soon reveal a properly sized servo opening for your servo. Clean up the sides with some sanding blocks. I will glue sandpaper to pretty much anything to the shape I need. I’ve got some scrap pieces of thick brass sheet in various widths that I glue sandpaper to for the purpose of shoring up small openings. Permagrit tools are very nice, but I don’t have anything of theirs small enough to work in an opening this size. Now is also a good time to take your covering iron and give the area a good once over one more time to ensure that the covering is well-adhered since tape was lifted from the area.
Using double-sided tape, tape some thin plywood shims (I believe mine were 1/32” for the elevator servo) to each side of the servo so that it is perfectly centered in your opening. Center the servo longitudinally in the opening, and mark the mounting holes with a mechanical pencil or pen. Remove the servo and use your pin vise to drill the mounting holes. Thread the servo mounting screws through the holes, and saturate the holes with thin CA. I got a little zealous with the CA and actually saturated the entire area of exposed plywood to give a little extra strength to the corners and the remaining sheeting. Remove the shims from the servo and put it to the side for now.