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Wing Assembly Tips

For this example we will assume that we need to build a turbulated, flat bottom three panel one piece wing.

Conventional Method

For building "built up" (stick and sheet) wings, the only instructions I have ever seen in a kit or on scratch buider's plans go something like this:

Build the center panel(s), including end rib at the joint.

Build each wingtip panel, including end ribs at the joint.

Join each panel to the next, end rib to end rib, inserting the dihedral brace at this time.

Since each panel will have a complete end rib the ribs will be doubled at the panel joint. It is difficult to get the angles of these ribs exactly correct so that they join neatly when the proper dihedral angle is set. It is also difficult to get the tip panel's top and bottom spars, top and bottom trailing edge sheets, and leading edge cut and sanded to exactly the right length to join neatly with the center panel. Two ribs at this location are more than is needed for strength and the extra rib adds weight, but improves stiffness when the wing covering is shrunk.

Improved Method

This method requires a stable bench set-up, with parts held in proper alignment with tape and/or pins.

Build the center panel without the end ribs. Insert and glue the main spar dihedral braces at this time.

Block up the center panel at the proper dihedral angle using a cardboard box. Note that it is the angle that is important, since the height at the end of the center section will be different from the height of the tip when building conventionally (if the panel lengths differ). If your plans specify a height of the tip above the bench, use the distance from the joint to the tip as your reference for elevating the center section. The end of the center section panel to be joined to the tip will rest on the plans at the dihedral break end of the tip panel. It is important that the spar lines of the center panel and the tip be in appropriate alignment (some aircraft will sweep the spar back at the panel break). Tape down the box to the bench and use tape or pins to secure the plans and center panel.

Glue the tip panel bottom spar to the dihedral brace, securing it in position on the plans.

Similarly, attach the lower trailing edge sheet (or triangular trailing edge stock).

Glue all of the tip panel ribs to the lower spar and trailing edge. Complete the leading and trailing edges. [Wing_Joint_Bottom_View]

(This picture shows the 1/32 inch plywood dihedral brace. A shorter brace stablizes the structure on the opposite side. The darker color is where the orange covering on the bottom panels overlaps at the capstrip described below.)

You can now add one rib (cut into two pieces) to complete the rib structure at the dihedral break. This rib will be cut back 1/16 inch at its top and bottom edges for addition of a 1/16 by 1/4 capstrip over its exposed edges. The capstrips are perpendicular to this rib, so the surfaces do not align exactly with the wing surface unless they are sanded. These capstrips provide more surface for attaching the top covering material and prevent bending of the rib when the covering is shrunk. Some sanding in the center of the top capstrip and at the edges of the bottom capstrip is required. Most plans and kits show this rib as being the same height as the center panel ribs. In fact, since it sits at other than a right angle relative to the spars, it should be a little taller (about 1/32 inch in this case) when the capstrip is added.

Complete the trailing edge and add the turbulators. If you are scratch building a Pussycat, be aware that the tip panel ribs in the kit are mispunched, resulting in a wavy path for the turbulators. If you are scratch building, a neater method is to cut the ribs out without the turbulator notches (other than the tip and joint ribs, then use a straightedge and pencil to mark the notch positions after the panel is built. Cut out the turbulator notches and add the turbulators.

Finally, sand the tip flat, removing any protruding spar, turbulator, etc, and add the wingtip blocks.

This improved method will result in a stronger, lighter, more accurate and more easily assembled wing, at the small cost of modifying the joint ribs for the cap strips.

If you have comments or questions, e-mail me (Attn: LGB)

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