Compression Ribs

I built the second of the short compression ribs. One thing I forgot to say, it's easy to lightly unbend the stick slightly to fit the nose rib nearly perfectly which makes getting a tight glue joint easier.

I have one more of the full light compression ribs to build for the lower wings, they get sticks added to both side.

The compression rib for the lower wing at the tip is not made like the short one for the upper wings. It uses the same nose rib from 1/4" spruce but that's all. There also is no drawing for it. The factory assigned a part number and then some how used that number for a different part on a totally different plane, good job guys. The rib does not show up in the factory photo because all you can clearly see in it are upper wings. The drawings I have that the Air Corps made in late 1926 some how missed that rib also. They show all the other rib types for each wing. Both the factory drawings and the Air Corps drawings show the cap strips made from 1/4" x 3/4" spruce with a web in hidden lines about 1/4" thick, like the nose ribs and root ribs.

I found this photo (only the tip end shown here) in Foster Lane's book about Miss McKeesport. The picture, about the size of a credit card, shows an upper and lower wing for C116 in a stand after repairs when he restored it. I scanned it, descreened it and enhanced it enough to see that the rib is clearly solid spruce and from the amount of overhang of the cap strips it clearly is 1/4" thick. The trailing edge section looks shortened but I suspect they used the same rib as for the aileron cut out on the upper wings and the shortening is due to shaping to fit the tip bow. The Aileron cut out rib aft of the spar is also 1/4" spruce with 1/4" x 3/4" caps strips.

This rib isn't used on the WACO TEN (improved NINE) because the TEN has ailerons on both upper and lower wings. Why on earth they made every compression rib different is beyond me. They Clayt and Sam were not engineers so it's hard to imagine any precision knowledge of different loads at each rib. They did work at Aeromarine during the war which is where they got the airfoil. I've seen other planes designed with this airfoil and the details are identical on the full light ribs. I suspect all or much of this came from some Aeromarine report which we just have not yet discovered. Ah, the quest for knowledge!