This article was written for the Sig 1/4 scale kit. Please read through this article before you begin.
Items you will need to complete this project
- 1/16-ply 1/8-ply 3/16 or 3/8-5ply
- 36″ storm door turnbuckle brace
- A plastic wing nut that will fit the rods from the door brace above
- 2-ton or slow setting epoxy
This requires you to cut a few extra parts. Make a copy of R2 and W1A out of 1/16 ply. Cut two 1/8-ply plates that will fit between ribs W1 and W2 and 6 and 7/8 long. Take a trip to your local lumberyard and pick up a brace for a 36″ storm door. This is two metal rods with a turnbuckle in the middle. Also pick up a plastic wing nut that will fit the rods. Come in about 5 inches from the threaded end and make a 1-inch C bend. Then cut the rod off (see fig. 1). Do this for both rods.
If you have 3/8 ply cut two 1 x 1.5 strips, if not cut two 1 x 3 x 3/16 strips of 5-ply plywood and glue together with slow setting epoxy to form a 1 x 3 x 3/8. After the glue has dried, cut and make two 1 x 1.5 strips. Now lay the rod on top of the ply, draw the image of the C onto the ply (see fig 2) and then cut the section out. Next, you will need to cut two 1 x 1.5 x 1/16 ply rectangles out.
Now for the building.
Build the center section as it is on the plans (excluding P3, WS2 and 6-32 bolt). Glue the copy of R2 on the left side of the center section. Build the wings as plans require (excluding P2 and Blind nut) on the right wing and add the copy of W1A to the left wing as it was to the right wing. You will need to duplicate the box that is located on the right wing that accepts the feed through-front brace. This duplicate will be installed on the left wing. When finished the left side will be a mirror image of the right side.
From now on, use slow setting epoxy in the next few steps, if used wisely, you will not use much and weight will not be a problem. Before sheeting the wing, glue the two large 1/8-ply squares to the top of the bottom hard wood spars on each wing. Now slide both wings on to the center section. Feed the two rods, one on each side, through the holes that are cut for servo wires to the center. Install the turnbuckle and tighten it about 15 turns. This should position the C bend in the middle of the large ply plate. Glue the two 1 x 1.5 x 3/8 blocks down fill the C section with glue, insert the C rods and apply the 1/16 cap. Let it set over night. Disassemble the wing and finish your build.
Install the plastic wing nut onto the rod, it will only fit one side as one rod is a left-hand thread and the other is a right-hand thread. When you install the wing together to fly, I install the left wing first. Next install the turnbuckle 1 turn. This starts the turnbuckle on the threads. Mark your turnbuckle with a strip on the end that goes on the left-hand wing. Now install the right wing until the rod contacts the turnbuckle. Tighten it until it’s a good snug fit. Now back the plastic nut up to the turnbuckle and tighten 1/16 to 1/8 turn against the turnbuckle. This keeps the turnbuckle from unscrewing in flight. This might be over kill is some areas but this is the set up used on a lot of stunt planes.
In the diagram above (not to scale) you are looking at the right wing from the front with the first rib missing and the second rib shown in red. Two Hardwood spars are shown in purple. The rod is shown in gray. 1/8-ply plates that fit between the ribs are shown in brown. The 1 x 1.5 x 3/8-ply is shown in blue and the 1 x 1.5 x 1/16-ply rectangle is shown in green.
Thanks to fellow club member Ron Acker for providing the above photo of the center section of his Sig Cub. This is what the section should look like. Note that the sheeting on the wings have not been installed yet.
This design is preferred for use with an opening door. If you build your model without an opening door, you will need to make a removable hatch on top to allow you to attach the wings. If you have any questions about any of these tips, feel free to contact us.