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| Top drawing of the Horizontal plans |
Place 8 cross blocks evenly spaced between the two main members. Cut and fit the construction surface 112" long by 11.5 wide. Rip a full sheet of MDF or Particle board 11.5” wide and stack up the two boards together. Stagger the joints such that they do not line up with each other; Glue both boards together using Titebond Glue. After they glue sets, lay the construction surface on top of the back up ladder frame. Stretch a chalk line from one edge to the opposite side. Space the chalk line off of the construction surface with a block of ¾” thick wood. Use a spacer block at both ends. The idea here is to shim the construction surface such that the gap is exactly ¾” all along the surface. After the shims are in place along one edge, secure the construction board to the ladder frame by driving some sheet rock screws through the shims and into the ladder frame. Once one edge is level. Use some more door shims to level out the aligned edge. Place the shims under the ladder truss. Once the aligned edge is level, start leveling the construction board in the perpendicular direction, using door shims between the construction board and the ladder frame. Once the construction surface is perfectly level, it can be used for the build up of all of the spars.
The spars of the Horizontal, Elevator, rudder and Vertical fin are all built up on this assembly board. All of the spars have some degree of taper to them (relative to a 90 degree angle) All of the spars are first constructed from square stock spruce. After the assembly is bonded together, the bevel angles are cut on a table saw. Use a hollow ground planer blade for all of these cuts.
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| One spar of the Horizontal being assembled |
I use 3/8 x 3/8 corner molding for the locator blocks. I will stretch a chalk line to locate one surface and then make a template that locates the opposite side. Usually my template consists of a parallel board that spans at least 2 of the opposite locating blocks. Glue the blocks in place with Titebond glue
After the spars are built up, the blocks can be chiseled and sanded off and the jig board reused.
Since the horizontal is a constant section, all of the ribs are identical. Because of this, it pays to make a more durable cutting template. I am using galvanized tin sheet here. A tracing of the rib shape is first made by either copying from the plans using a copy machine calibrated to the correct scale, or the full size loft or laser cut paper templates are used. Drill some #30 holes in the template, this is an approximate size, experiment with the round toothpicks such that they will wedge into the holes after sticking out about 3/8". Use these toothpicks to locate and hold the foam blanks. Use a band saw to cutout the foam. As mentioned earlier, I always use a metal cutting blade with minimal kerf and guide off the back of the blade. This ensures that the ribs are easily cut and repeatable.
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| ribs located to the spar |
After the ribs are cut and the spars built, assembly begins on the Horizontal. Again, 5 minute epoxy is used to bond the ribs to the spar, this greatly simplifies and speeds up construction.Use a 90 degree wooden triangle as a guide to set the ribs perpendicular to the spar. The ribs here are shown being assembled to the front spar. If a rim sits on a plywood doubled , trim the rib equal to the thickness of the doubler.
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| Front spar being added |
The Front spar is located to the standing ribs. 5 minute epoxy is used to bond these ribs again. The cans were added for weight. Only contact pressure is required between the rib and the spar. If a rib sits on a doubler, trim away the thickness of the doubler before bonding.
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| Nose rib template |
The nose ribs are constructed similar to the main ribs.
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| Nose ribs being added to front spar |
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| Learing edge splice sheet |
The leading edge is spliced at 3 points along its length. At each location the outside contour of each rib is reduced by the thickness of the splice sheet.. This is done by carefully sanding. At each splice location the nose ribs are also doubled up. The splice plate is pinched together as shown with a clamp. It is then sprayed with unscented Ammonia and allowed to soak through and dry.
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| splice plate being bonded to nose splice ribs |
After the Ammonia drys, bond the splice plate to the ribs with 5 minute epoxy as shown.
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| start of construction of leading edge form tool |
The leading edge skin nose radius must be formed into the plywood sheet. Its important that before you actually form this skin that it was cut out with the face grain running the length of the part. The assembly jig table is used to construct the forming tool. Standard hardware rafter or truss brackets were used to mount two parallel 2 x 4 walls. This photo shows one wall installed. Use a chalk line to set one edge and then make a tool that locates the opposite side, similar to the spar jig block procedure
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| completed forming tool |
a series of "Broken arm" clamping fixtures were made from 2 x4's and piano hinges. These will be used to apply pressure on the leading edge tube used to form the inside surface. The precut leading edges are all wetted with spray ammonia and then folded in the center and shoved between the two walls.
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| leading edge being formed |
The whole idea in forming the skin is to impress the leading edge radius. The remainder of the skin will wrap over the nose ribs and form to contour. I could have made a smaller former and formed one skin at a time, but that would have added 3 additional days to the process.
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| formed leading edge |
This is what the skin looks like after 24 hours. There was a little spring back, so I will use a smaller radius forming mandrel (tube) the next time I do this. This part was OK and it wrapped and bonded to the nose ribs with the correct contour.
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| Complete empennage assy |
This the final empennage assembly, all of the other components are built similar to the horizontal and Vert Fin. After the leading edge was formed and bonded to the nose ribs (I used epoxy and Micro balloon mixed to a consistency of peanut butter for the foam to wood bond) The reason 5 minute wasn't used is because of the working life. Before the skin is attached the 1/8" thick cap strips were bonded to the foam ribs.
Everything in this empennage assembly weighs 9.8 lbs and took 2 weeks to build.