The main rib that you have to drill on the inside doesn't run parallel to the outside skin of the fuselage. If you try to drill it with the drill coming right out of the center of the hole you've already drilled, you're cutting it at an angle, and the hole saw has a tendency to get stuck. Even though the shorter configuration (picture 2) fits, the chuck part of the drill is in the way, so you've got to drill it with the drill closer to the center of the outside hole than is actually ideal. The longer configuration lets you get off more to one side. If this is confusing, that's okay - it will make sense when you try to do this.

There are actually four cuts you need to make - the outside skin, then two ribs that really just need to be trimmed, then another large hole. The outside rib hole is close enough that you can just do that at the same time you're doing the cut in the outside skin. The inner one isn't like that, so I just filed it down.

We've got a few questions about the way the steps fit in, and because we need to return Scott's can of primer and his hole saw (the one pictured above), it's time to pay Scott Millhouse a visit. Scott's just acquired an engine for his RV-9A - a O-320 B2C. The weird designation at the end means that it will use a conical mount instead of a dynafocal. This is because that it was previously in a helicopter. In any case, it seemed like a good idea to take pictures of the the areas on Scott's plane that he's just finished, and we're about to start working on, so we have engine pictures here (just because it was there) and a couple more pictures of Scott's project.