I was feeling pretty good today, I managed to get the trim tab clamped and the opposite side hinge flange match drilled to ultimately mount the trim tab this evening. Everything was going along well, I had it lined up perfectly with the trailing edge as viewed from above. I was just about to start riveting the first few rivets for the hinge on the trim tab side when I started to notice that the trim tab itself, once it was all cleco'd together, had a very slight warp to it that showed at either the inboard edge or outboard edge depending on which side you held firm against the straight edge. Maybe 3/16" out from being true. Hmmmm..... how did this happen and is it a big deal??

So therein began several hours of internet searching for others that have had this issue and it's actually not that uncommon. This trim tab..... I tell ya.... Worse yet, there really isn't an easy way to fix this (especially if the bottom side has already been riveted) When you order the new skin for the trim tab their description for the part literally says, "So, your #*!@ tab didn't quite come out the way you wanted it? Just use our handy trim tab skin and get the thing right next time." You think they know it's a poor design lol!

Long story short, somewhere in the build up of the trim tab, perhaps the initial bend to shape, perhaps when I had to hold it open to rivet or bend over the tabs, somewhere in there, the trailing edge bend isn't quite right and it's manifesting itself as a slightly short inboard portion of the skin. The pictures show it more clearly but here's what is going on and why it's not awesome.

The outboard portion of the trim tab skin, topside, (bottom already riveted closed) line up with the holes on the trim tab spar very well. When you lay the skin on the spar, the holes naturally lay on top of their match. The further you move inboard, the more the holes are mismatched naturally, IOW when you lay the skin down on it, it doesn't naturally match the hole below. They are close, but as it turns out, just far enough away to be a problem. You can easily get them to line up with clecos so at first it looks like everything is ok. But due to the structure of the trim tab, not having any internal bracing or ribs, if the holes along the top side of that spar are not pretty much dead on in alignment with their matched holes underneath, this causes the skin to be 'pulled' or 'pushed' in direction fore/aft just in that one little area. That little 'pull' in my case draws the skin on the inboard portion of the trim tab just slightly with more force which causes that portion of the skin to have less distance between the trailing edge and rivet line which thus introduces just enough uneven force to cause the warp that I'm seeing in the trailing edge. Since there are no internal rib to 'fix' the distances from the trailing edge to the rivet line, this is prone to happen if you're not careful with it. HEY VANs, HELP A BROTHER OUT HERE, MAYBE A BETTER DESIGN?? Wouldn't it be nice to have pre-made trim tabs! Hmmm... might go into business building trim tabs after all this lol...

So sigh..... I know that many, many builders build multiple trim tabs for various reasons, the little tabs on the end, warping of the trailing edges (in my case) or a whole host of other possible flaws. Now in my case, this little approximately 3/16" warp may not be a big deal, it may not even be a reason to build another one. However the tab bends on the outboard portion of my trim tab came out slightly curved as viewed from above. It's just the way the metal got folded over. I stared at that little gap between the outboard edge of the trim tab and the edge of the cutout of the elevator for a while this afternoon with the trim tab mocked up. I decided I could live with it, perfection is after all the enemy of progress in this process. However, once I realized the whole piece was slightly warped, well that tipped the scales in favor of a rebuild. It will give me a chance to fix all of my previous errors that I've made along the way of building the trim tab.

I read about all these people rebuilding their trim tabs and now I have a better understanding of why. You could argue this is partially Van's fault as the instructions for building the trim tab are lacking much in the way of detail and the parts themselves could be better designed. Anyone that builds a Harman Rocket (RV-8 on steroids) builds the trim tab using mostly the same parts except their trim tab is made from thicker sheet I believe and they add stiffeners to the inside of their version. Maybe I'll do the same, we'll see how the next one comes out.

So the learning curve on this one was steep. Turns out I can read about these issues all I want but until I experience them for myself, I don't seem to heed the advice. Here's what I will do differently on V2 after priming the part first:

1) Before bending the trailing edge or end tabs I will match drill and dimple the holes for the E-717 and E-718 control horns for the trim motor push rod
2) Then I will bend the trailing edge to final shape, I think I didn't bend it far enough on V1 figuring the rivets would make up for any shortcoming (not realizing that warping could occur if the bend isn't good enough). I will use the spar as a better guide and be a lot more picky about how close the bend rests to the spar naturally.
3) I will make sure the bend line on the inboard tabs has enough edge distance with the inboard most holes that attach E-717 and E718. The holes will already be there now so I can actually judge the distance before the tab gets bent over.
4) I will bend the bottom inboard tab to shape and then rivet on the control horns if I can (TBD), then bend the top tab to shape after those are riveted in place.
5) I will ensure a straighter bend line on the outboard tabs to give a better edge result.... I hope!

So lots of lessons learned on this, can't say you don't gain experience while going along on this journey. Fortunately I can get back to a few things on the elevators while I wait this week for new parts from the Mother ship. I still have to finish rolling the leading edges on both elevators, there is still fiberglass tips to add and both of the elevators need their trailing edges tweaked just a little bit as in most cases where the bend isn't quite right, they are underbent which is fairly easy to address, more squeeze!

Anyways off on a nice trip for a few days to Florida for work. Time to order those new parts and regroup.