Ok so I have joined the multiple trim tab builders club. This will make my third one. The original tab bends were never really that good and have always bugged me. So I sent off to Vans to get the four parts to rebuild it. After reviewing the construction manual I dove in to building my second tab. It came out worse than the first. So what to do??? I started researching the forum to see what other builders have done. WOW what an eye opener! A lot of guys have tried at least twice and some departed from the plans to cut and build small "riblets" for the ends. Good grief, after slow building the wings I cant believe this is that hard !! After rereading Vans instructions again and again I started to get a picture of just how they did it. There are several steps and materials that are a must. Vans says to use MDF or equivelant hard wood and CLAMP the material down with carpet tape to hold the tab from moving. I purchased some poplar hardwood blocks from Home depot and some 3M thin carpet tape to hold the pieces. I decided to disassemble and cut up the original tab and make a paper template of the original unbent tab and trace it on the cut end. Then after edge dressing the material, and marking the bend line I was ready to bend the new ends.
After doing two practice bends I felt ready to build the third trim tab. The pieces arrived from Vans and I was off and running. The third tab came out perfect!
Things I learned and steps I did different on on the third build.
1. Match drill the trim tab horns before the trailing edge bend.
2. Complete the trailing edge bend per the plans
3. The trim tab spar comes pre-bent from Vans but must be slightly adjusted with hand seamers to fit perfect between the skin. If that adjustment is not made it pulls the skin and creates a concave situation on the top skin after the bottom skin is riveted.
4. Match drill the skin to the spar and the trim tab horns.
5. Complete the tab end bends per pp 6-15 in the const. manual.
6. Dimple,counter sink,debur and prime all parts per the plans.
7. Follow the Vans construction manual for the remainder of the trim tab build picking up on pp 6-12 under "prepare the parts".
8. When setting the blind rivets in the tab ends I substituted an MK319BS for the CS4-4 for edge distance concerns. I read another builders log who said this was approved by Vans.
Making the wood blocks out of a good hard wood is a must to getting a nice 90* bend. Clamping the whole assembly to a table very solidly will keep it from moving. Using a flush rivet set with the pressure turned down low for the final pass makes a nice bend. Hopefully this write-up will help a new builder put some money into his future panel than a bunch of trim tabs!!
Trim tab follies....
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