Chapter 14 - Section 1

Center Section Jig

What's up?

In this chapter, we will build the center section spar which joins the wing to the fuselage. The center section spar is the heart of the wing structure, so accuracy is important.  Note that the top of the spar is flat: that it sweeps aft and that the bottom has positive dihedral in order for fuel to run inboard while in level flight.



[Hindsight] This chapter is not as difficult as some of the previous ones. However, some sessions take a LOT of effort and time to complete. Stopping mid-stream is not recommended. Therefore, one of the most important preparations for this chapter is to smooch up to your better half or someone who can give you a hand down the road, not once, but at least 3 times...unless, you plan to work on these sessions by yourself, non-stop for a minimum 12 hours!     


Center Section Jig

The first step of this chapter is to make a particle board jig which will be used to support the center section spar. The first thing I did was to set up my work table so that it can accommodate this long (12') fixture. I prepped the surface so that it is nice and flat and re-leveled in all directions to 0.0 degrees. With the help of my laser, I drew a straight reference line along the full length of the table.


My neighbor (at work) is a cabinet maker and buys his particle boards (coated) at wholesale. As a result, my jig has a high-gloss quality look, though it functions the same as the regular particle boards . I cut up the boards per plan and assembled them on its back (part D) because I know my table surface is nice and flat. Besides, I can get to the undersides of part A, B and C with Bondo much easier. Once the Bondo sets, I stood them right side up per plan.


I re-measured all dimensions of the jig and found that 8.48" on the width of part A (instead of 8.51") and 6.80" width on part B & C (instead of 6.83") - an overall of .03" short all around. With all the concerns I read from the Cozy forum regarding the thickness mismatch between the center section spar and the main wings, I wasn't too sure how critical these dimensions were (since the plan specifies down to .01" in dimension). I decided to post the questions to the Cozy forum. Feedback from Marc Zeitlin and Dennis Oelmann were basically "good enough" - I decided to go forward without further ado.


Part E of Jig Support

I wasn't quite sure how part E was suppose to look per Chapter 14, Page 6. I decided to make 2 support legs instead of 1 for better stability. Based on the slope of part C relative to A, the angle equates to 8 1/2 degrees. I just trimmed the top edge of part E to 8 1/2 degrees and they fit perfectly.













To ensure the resultant center section spar is straight and level, I confirmed the leveling of the jig with my digital level. Note the Bondo used for holding the jig legs together. The boards, butting against part D are to make sure it stays straight and level throughout the assembly process.