While this is more of a construction technique, joining the wing panels correctly is critical to how your plane will fly. Have you ever had a plane that got a small warp in one wing and required some aileron to offset the roll? If the warp was pretty bad, every time you changed speed, you had to retrim. For years I went through this same thing, trying to build the perfectly straight wing. I finally figured out the procedure, and now my planes fly straight (mostly).

Here are the rules:

1. Build as straight as you can to start with.
2. Use an incidence meter (I have the oldest Robart there is).
3. LINE UP THE WING TIPS.
4. LINE UP THE WING TIPS.
5. I'm going to say it again, guys, because this is the biggie,
6. Don't worry how the roots line up, LINE UP THE WING TIPS

Is that enough emphasis? Here are the details. Generally, when you construct an airplane, you make two wing panels, a right and a left one. I say this because I have made two right ones before, along with two of the same fuselage sides. I did it once on the same plane. Keeps you humble. The wing panels should be built as straight as possible, without warps or twists. After construction, and before covering, you then join them at the root chords and reinforce the joint with fiberglass cloth and epoxy. You may or may not use a plywood dihedral brace, depending on the design and your preference for construction. The key to a good flying airplane is the joining.

In order to join the wings properly, you will need an incidence meter. Robart makes an inexpensive one that is invaluable to the RC flier. I can emphatically state that all my planes started flying noticeably better after I started using an incidence meter.

Don't worry about how the roots join up, get the tips aligned. On a giant Spinks Akronmaster I have, one wing ended up with a 5/8 inch warp in it. I aligned the tops with a Robart incidence meter, filled in with scrap balsa where the roots didn't match and it flew with negligible aileron trim. The area of the wing near the root chord has very little influence of the roll sensitivity of the plane compared to the top area.

Here's how you do it. Lay some Handi-Wrap or other glue proof covering on a flat table. Lay the two wing panels down on the table with the roots together like you will join them, so that the tops hang over the edges of the table. This is so you can get the incidence meter on the wing tips without interference. Lay old magazines on top of one panel to keep the wing from shifting, and prop or shim this panel until the incidence meter on the top reads zero. Now, go to the other wing panel and prop it up to the correct dihedral. Lay old magazines or other weight on it to keep it from shifting and then shim it until it is also at zero incidence. Note where the roots are. If you have a perfectly straight wing, they will also be aligned. More than likely, there will be a small difference. Don't worry about this and don't believe that you can pull a warp out with Monokote. If the difference is really great, you can cut sheeting and reglue to try to straighten, but shrinking the covering on a diagonal will not permanently remove a warp. On the next hot day, your twist will start coming back in.

Once the panels are aligned, carefully remove one panel from the table, being careful not to disturb the shims, coat the root with 5 minute epoxy and replace the panel. Recheck the incidence of both panels while the glue is still soft and realign. When the epoxy is hard, sand, fill in as necessary and cover the center section of the wing with heavy weight fiberglass cloth and epoxy. This method of alignment, using an incidence meter will assure you of a straight flying airplane. Once you have started using an incidence meter and see the results in the air, you will never build without one again.

If you had any error in the alignment of the roots, you will have to make an adjustment to your wing saddle area on the fuselage. I usually do this when I build the fillet, filling any gaps at this time. You should also be sure to use the incidence meter for aligning the stabilizer and engine thrust line. In this alignment, use the wing tips as the check point.

The bottom line is to get the plane as aerodynamically correct as possible. The wings, tail, and engine thrust should exactly match the values given by the designer. Take that little extra time to use an incidence meter and I know your planes will fly better.