When installing your wings, no matter what the airplane, you are probably going to have to set the incidence—the angle between the mean chord line and the fuselage—before drilling permanent mounting holes. In the case of an RV-style aircraft, this will probably involve drilling the aft spar bolt attach hole. There are various ways of measuring incidence, and your kit instructions should tell you how the designer wants it done.
In the case of the F1 Rocket, you measure the incidence by leveling the fuselage (flight deck sills level) and then making a long measuring stick. With the leading edge of the stick over the forward spar, the vertical distance between the line of rivets on the aft spar bolt attach and the stick—if the stick is level—is supposed to be 2.95 inches. That is a pretty precise measurement, so rather than simply clamping a ruler at right angles to a level, we used a piece of square aluminum (to ensure it was straight and wouldn’t sag) and bolted a vertical with a precisely scribed line—then riveted on a little “step” to make sure that it was square to the stick. This was then clamped in place, and our digital angle finder used to match the stick to the flight deck sills. These little angle finders have a resolution of 0.05 degrees—the long-established method of leveling things with a bubble level isn’t quite that close, so it’s a good device. You raise and lower the aft edge of the wing to get level, clamp, then drill. Make sure to do each wing separately—don’t trust them to be symmetrical, or identical!
