Tuesday, April 27, 2010

In which I get my fill of nutplates

Having had a couple of days to rest up from the four building sessions over the weekend, I was ready to replace the worn down Dremel cutting wheel and remove the piece of metal from the seat rib that had to come out to make an opening for the autopilot servo control arm to fit through. Or something related to the autopilot, anyway. I really have no idea. It's ongoing mysteries like this that keep it interesting.

The Dremel is an absolute marvel for this kind of thing. I'm not sure how I would have done this without it.

At this point, the only thing being installed for the autopilot is a doubler that (I assume) one of the servos will get bolted to. The standard rib wouldn't have been strong enough to support the torque of the big servo motor pushing against the aerodynamic forces acting upon whichever control surface this part of the autopilot ends up controlling. Hence, this relatively beefy doubler. It required a few match-drilled holes first.

There are three holes that the plans insisted be left open, so I stuffed them full of clecos to remind me not to rivet them. That is anything but a foolproof method, of course, because the act of remove-cleco-insert-rivet is fully ingrained into my psyche at this point. Still, I thought I could manage to leave a measly three holes unmolested.

Just to help with the math, the separate page of autopilot bracket instructions called for six holes to be riveted in the case of what they call a PRECONST installation. The other option is POSTCONST; that's for the pitifully burdened people that are trying to install these things into a completed airplane. Not only do they have to drill out some very hard to get at rivets, they get to put in nine rivets for this step. I was happier to only have to deal with the six, thank you very much.

There were another three rivets after those six, but trying to determine that from the plans was a bit of a chore. I think Van's must have had Obscuro the Obfuscating Ostrich come in on Mondays to write some of these directions. Foreshadowing: it got worse. I finally figured out that the three rivets went in the flange of the bracket and the "aft intercostal." What's an intercostal? I have no idea. Ask the darn ostrich.

Here's where Obscuro really got me. See, I'm in the PRECONST clan, so I skipped ahead to Step 3, as directed, completely skipping over Step 2. Well, no, that's not right. I did my Step 2, which was to ignore the POSTCONST Step 2. Which, as it turns out, was not the right thing to do at all. Well, it was the right thing in that it's what I was told to do, but not the right thing in that one of the steps of POSTCONST Step 2 is also necessary for us PRECONST folk. Confused? Here, let me show you.

The part that I was instructed to skip but needed to do had to do with removing a rivet (one that I had just put in two days ago; I think they want me to skip this step out of embarrassment for making me remove something that I wouldn't have put in at all if they had thought to edit the directions on the prior page) in order to swing a nutplate out of the way of a screw that needs to be put in. With the nutplate still in place, that screw ain't going in, PRECONST or POSTCONST.

Of course, what with my having skipped the meatier of the Step 2s, I had no idea why this was the case. I figured I'd just have to remove the nutplate. I went back and read the real Step 2 and realized I only needed to drill out one of the rivets, so there is that. Fifty percent less rivet removal using their method. That ain't nothing.

Unfortunately, the drill bit went through the hole and nutplate as the rivet was drilled out and bent the nutplate down. To get it back where it belonged so I could rivet it back in, I had to clamp it.

I thought it might be a good idea to get the don't-rivet-here clecos out onto the other side of the rib so that I wouldn't end up building so much airplane around them that I couldn't get them out. That was also beneficial in reminding me not to rivet into those holes as I riveted all of the rest of them. Obscuro's drawing showing where rivets needed to go was obscured (or course) on the far side of the ribs and there was no "LP4-3, 12 places" (or whatever - I don't remember exactly how many it was) to tell me how many to expect - just "LP4-3 TYP." That usually means fill every hole you can find with a rivet, but doesn't necessarily countermand a "LEAVE OPEN" directive. Man, this stuff can get confusing!

So what's my beef with nutplates? Well, I thought that I was at a pretty good stopping point, but the next step was simple: put eight nutplates in the brackets that will hold one of the seat belts and rivet those brackets into the three holes that I had been obediently keeping open. How hard could that be?

Normally? Pretty easy. Especially since four of them used flush blind rivets - the easiest kind! Except this time, one of the nails broke off in the rivet puller, leaving an obnoxiously long remainder in the rivet. Obviously too long to just leave in there, but too short for the rivet puller to get a grip on.

That's never happened before!

But good things? They come in three. It was only a couple of rivets later that it happened again!

The third time it happened, I decided to remove the broken nails and call it a night. The only way I could get them out of there was to remove the tip from the rivet puller so that it could get a grip on them and pull them out. Without the tip, though, the head of the rivets extruded themselves up into the rivet puller. When that happened, they were no longer flush and had to be drilled out. When I was putting the replacement rivets in, I found that using the next smaller size tip would pull them without breaking them as the larger tip had, but the nails would jam in the puller. I had to take it apart after each rivet to get the nail out.

And that is how I came to have my absolute fill of nutplates.

I did go ahead and cleco the parts together, though.


Torsten said...

Dave, the last photo shows the ribs building the tunnel in the fuselage with two nutplates on them. These are supposed to be K1000-3 for AN3 bolts. They actually hold the blocks for the flap handle. I just read something about these nutplates being easily mistaken for K1000-08 nutplates as you handle so many of them in that section. That note triggered a bad feeling and I went outside and checked on those nutplates. Duh! I put -08 in there instead of -3. Just thought I let you know so you can check that now before you build more around it. I'll drill them out these days and probably put them in using CCR264 as I won't be able to get there with a squeezer anymore. Maybe tapping them could also work. I'll see :-(

DaveG said...

Do you mean the two nutplates on the left side of the far right rib, just under the seatbelt bracket? I wonder how hard it's going to be for me to get a look at those now that I had a lot of the floor in place.


Torsten said...

Yeah, those two. See if you can screw an AN3 bolt in there. If not then they are -08s. I can't. Started trying drilling them out but don't have the right tools. Have to get a right angle drill that's really small to not make this problem worse. Dang!

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