Friday, November 6, 2009

Late night Mulligan on left Flettner

Poor Anton Flettner must be doing pirouettes in his coffin over my ham-handed building of his eponymous anti-servo tabs. Last night, after buttoning them up for the final riveting scheduled for tonight, I was perusing a builder's log on the web and found that the guy had run into a problem when trying to install the tabs onto the stabilator. The problem was that the fit where they meet is very tight and he had gotten a gap between the control horn and the rib when he riveted them together. I thought that it might be a good idea to head back down to the shop and inspect mine.

What I found was that the right side was tight and flush with the edge of the skin, but the left side had enough of a gap that it was slightly outside of the edge of the skin. Rather than wait to find out whether it was going to cause a problem later after everything was all riveted shut, I decided to drill out the five rivets and re-do it while it was still easily accessible. Drilling the rivets out was easy-peasy, now that I've had a bit of practice at it, but when I clecoed the control horn back into place I saw that there were a couple of problems. One was the issue that caused the gap to form in the first place, while the second was caused due to the riveting problem.

The first was that the edge of the skin was not quite flush with the outside of the rib. This caused the control horn to not sit flat against the side of the rib. When I squeezed the rivet, this gap allowed the rivet to fatten up just a little bit between the two surfaces. That fat part of rivet in the gap caused the second problem: the hole in the rib got a reverse dimple in it. In other words, it was now an outie, not an inney. That prevented the horn from sitting flush against the rib and virtually guaranteed that I'd get the same result if I just tried to rivet the part back in place without some form of corrective action.

The first thing to do was to file down the skin to that it was flush with the rib. That didn't take much filing at all - it was a very small overhang, but just enough to cause the potential fitting problem. The second was to fix the outie. I did that by putting a very slight dimple in it with the dimple/die set that I used to dimple the holes in the vertical stab front fairing.

The control horn is now clecoed back into place and sitting tight against the rib - no more gap. I'll rivet it tonight just before going to the hangar for the final skin riveting.

No comments:

Post a Comment