Sunday, July 20, 2008

Center Spar

Build Hours: 542
The spar is labor intensive and the plans require a lot of study to catch all of the details (hope we didn't miss any)! We finally found the answer to "Where's the beef?" - it's in the center spar.
This is the spar cutout. An air nibbler was used for the bulk of the cut. Shears were used to clean the straight cut lines and a drum sander was used for the large radius. Lots of filing and sanding completed the cutout.

These are 2024 T3 3/16" blanks cut from the carry thru stock. The stock plate was cut with the grain in 1 1/16" strips with a jigsaw and then put in an X-Y vise. A 1/4" endmill was used in the drill press to square the blanks to 1". The 2024 aluminum is really hard on jigsaw blades and 10 tpi was found to do the best job.

Here's the center web with the spar tangs and upper and lower caps. The caps have already been notched and the tangs have been radiused. The other 2 pieces are the cap spreader and spacer.

The assembled end of the spar ready for riveting. The end cap notch radius has been carefully sanded up to 800 grit and polished. The last 4 holes for the tang bolts will go to the drill press for drilling and reaming to get the best fit. The outer spars must be built next to set the dihedral and complete the spar tang drilling.

The carry thru was cut per the plans with a jigsaw. The plate was cut across the grain. A holesaw in the drill press was used for the lightening holes. More filing and sanding to cleanup the edges!

The web stiffeners were bent in the homemade brake after a modification to the platen for the 1/2" channel width.