Wing Mating

by Dick Rihn

I have just finished mating my wing to the fuselage. I did not put the front surface crush pad plywood on but instead cut out a 1/16th mahogany plywood shim which fit on the aft surface of the forward wing saddle . It was cut out for the truss wing mount pin bushing and associated end flange. These pieces of plywood were then contact cemented to the saddle to prevent scarring of the front surface of the spar during the many slide ins and outs associated with mating. I used 0.026 aluminum for the dams and worked that down even finer so that it would just slide in - dry. I was very carefull to make the hole a very tight fit. I also "biased" the aluminum dam so that it was automatically pushing against the front surface of the spar. I turned down the two inside corners to give purchase for a pair of pliers to pull it out later. I also obtained some plain steel rod (5/8th and ground a bullet nose on one end to assist in centering the hole of the dam. I used a first coast of carnuba wax and then lots of K-Y jelly to slide the dams into position. After location the "bullett" pins were removed and the well wax and K-Y jelly protected wing pins were placed with ease. The dams did not leak. Taping of the edges was not necessary. Final fitting of the 0.002" stainless steel shims could then be done between the wing pins and the truss bushings. The bushings had been reamed to 0.005" oversize. After final reassurance of proper levelling, angle of incidence, tramming and all of that time consuming but very important activity the epoxy was poured. I used 205 hardener for the first small amount to make the dam a reality. After it had begun to exotherm I began pouring the rest. I tried to use the 404 high density bonding filler but found it was impossible to prevent a myriad of micro-bubbles. So I used the regular flox and avoided air bubbles almost completey. In talking to Gougeon service rep. he suggested the best bond between their product and aluminum is obtained with a freshly anodized surface. He also suggested a method to obtain better wood penetration which I used. I heated the big holes in the spar with a heat gun and applied 206 activated resin until it wouldn't accept anymore. Then I began the mating process described above. The logic is that when the wood heats, water vapor is expelled . As the wood cools it sucks back into its grains whatever is on the surface. It seemed to work as an awfull lot of resin went into the wood. Having previously done some test samples on end grain penetration and being somewhat dissapointed I was glad to have this technique. The most usefull shop tool in mounting the wing was the construction of a small oblong stool covered with carpet. It should be large enough to comfortably support the wing when out of the truss and wide enough to keep the bushings from falling out on the floor as you wiggle the wing into the saddle. One person can safely and easily mount and demount the wing once the wing has been placed on this stool. It was screwed to the 2 x 4 s that were attached to the firewall and were firmly on the floor of the shop.