Originally Posted by Stockmanreef
2. Why can't you just make the opening for the prop in the top cowl is aligned versus spinner plate?
You can use what ever procedure you want. The instructions were written in a way that helps builders position the cowl accurately in ways that they might not realize could be an issue.
The instructions do have you align the upper cowl to be centered on the spinner, but the cowl can be mis positioned in the roll direction even if it is properly centered on the spinner.
This can be for numerous reasons that I won’t go into because following the instructions negates the issues.
Since the instructions had you level the fuselage laterally (roll direction) the placement of the level on the floor is to assure that the surface below the cowl that you are referencing height measurements to, is also level (many shop floors are far from being level).
The use of the plumb bobs is to mark a point directly below the front corners of the cowl, to assure that you are measuring to the same point below the cowl every time.