Ribs and Spars

Build hours: 697

Progress has been made since the last update in August. We decided to build our ribs for the experience, weight savings and to use up all of the accumulated cutoffs instead of buying 2 additional 4' x 12' sheets. So far, the rights side ribs and spars are completed and the left side rib parts are made.

This is the particle board jig to hold the rib parts in place during assembly. The top and bottom caps were bent in the brake and then shrunk to the rib pattern. An endless number of braces were folded (enough for 2 sets of ribs).

Alignment dowels were inserted into the jig to allow the pattern pieces to be moved to the opposite side of the build board to make left or right ribs.

A form was made to bend the nose pieces over and a particle board flanging die made to make the lightening hole flange. Shrinking of the flanges manually and with the shrinker was required.

Finished rib assemblies.

We used 3/32" solid rivets to assemble the ribs. After you get the rivet driving going, its as fast as pop rivets and gives better edge distances.

These are the 4" or 4 1/2" flanging dies for the spar lightening holes. The flanges stiffen the web considerably even though all of those holes only remove 3.7 ounces from each spar.

A 14' jig was made that would hold the spar center section and one outer spar at the correct angle. The spar fittings were prepared and clamped. The jig was set at the correct height for the drill press. All spar fitting holes were drilled undersized and reamed to .002 or .001 under as required.

Additional rounding and cleanup on the spar fittings was completed. All spars are done.

Spar braces

Build hours: 577

The spar has been positioned and attached temporarily to the bottom angle. The outer spars have to be made and matched to the center spar before the center spar can be fastened permanently. The spar braces were made and ready to rivet. The edges of the spar braces were rolled over to give a more finished look and provide additional stiffness in the process.

The spar brace edge required notching to set on the spar caps.

This shows the spar brace bend angles required to match the fuselage and the bend on the outer edge. The blank had additional width for bending in the brake. After bending, the extra material was cut back.

The wooden brake works well for aluminum up to .025 and even short pieces of .040 but it was not up to the task of bending .062 2024T3 across the grain. A 17" brake made from leftover 1/8" steel angle was cobbled together. The platten has a 3/16" radius which is required when bending .062 2024 in the T3 condition (3X thickness).

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.