Sunday, May 15, 2011

Starting on the wiring

I was finally able to get someone to help me roll the fuselage on its side (thanks, Honey!) so I can get started on the wiring. While having it on its side will make some of the smaller jobs to come more difficult, it was really the only way that I'd be able to get down inside there to work on the stuff down in the tunnel. I dread the day when I have to roll it upright again; despite my preparation prior to the roll, I still managed to miss one of the clecos stuck in the side. It got bent flat to the skin. I was able to reach in and remove it, but I couldn't see what damage (if any) that it caused.

So, working conditions are still pretty crowded and it's kind of dark back there against the wall, but at least I can get back to work.



The first order of business in the wiring is to put a conduit across the back of the center section. This conduit will protect various wires as they make their way out of the center tunnel and get routed to either side of the airplane. It's starts as a benign looking 36" long piece of plastic duct tube.


The tube needs to have a 7/16" hole cut in it to allow wires to enter at the center. I made a starter cut with a razor knife, then worked a 7/16" bit into the hole. Using the bit as a template, I then enlarged the cut out hole to the full 7/16". It isn't pretty, but it will be placed on the bottom of the duct where no one can see it.


Three strings get run through the duct to be used to pull wires through. One string goes all the way from right to left, and the other two go from either side and exit through the center. Dangling the string down through the duct worked fine for the left to right string, but it seemed that it might be a bit more of a pain for the strings that needed to exit through the center hole. I was able to grab a loop of the full-length string and pull it out of the center hole. I then tied the other two strings to each end of the full-length string and used it to pull the side-to-center strings through.



After that it was a simple matter to run the full-length string again. I tied a couple pieces of flange scrap to the strings exiting from the right and left sides, and secured the strings coming out of the center with the leftover piece of firewall grommet. The idea was to keep any of them from accidentally getting pulled out of the duct.


The duct is mounted to the back of the center section with four cushion clamps. These clamps also go by the name Adel clamps, or as I'm sure I will soon be referring to them, "the nutplates of the finishing kit." They're a royal pain to deal with, as it turns out. In any event, as I was perusing the drawings prior to getting the clamps ready I saw a bushing that I had either failed to install previously or was one of those cases where Van's figures you ought to know by now that you need to put in a bushing where there's one shown in the drawing.

In it went!


The clamps are held in with a screw and a locknut. The locknuts were tossed in a bag with three or four other sizes, so I had to play the figure-out-which-ones-you-need game.


The hard part about dealing with these clamps is getting them to close far enough to get the screw through. It's hard enough to do when you have them right there on the work bench; it gets downright irritating to have to do it in the tight confines of the airplane. I thought I'd try a little trick I've seen mentioned before. Basically you hold the clamp shut with a piece of safety wire, screw the clamp into place, and then remove the wire. I closed the first clamp down with a pair of Harbor Freight cheaper-than-dirt-and-a-bargain-at-half-that-price vise grips.


I wired it shut with safety wire, but in that state it was clamped too tightly to fit over the duct. I cut the wire and started over, this time with a lesser close.


That worked - I did all four clamps and was able to slip them all onto the duct.



I put the duct into the plane and had a scary moment. It looked like I had gotten the center strings caught under one of the clamps and that I'd have to take it all apart to get the string out. In fact, one of the upper clamps was so loose on the duct that it had slid down and caught the string. It was just a matter of pushing it back up into place.


Then I found that I had the wire so loose that it was useless.


The clamps in this location were accessible enough that it didn't matter that the safety wire was useless.  I was able to just squeeze them closed.


Next, the comm radio and transponder antenna cables get run down through the panel base, over the rudder pedals, and through the firewall bushings. The fit across the top of the rudder pedals was pretty tight, so I had to back out the bolts that hold them in place. There's also a really long "phone cord" that runs down the same length as the antenna wires, but it keeps going all the way back into the center hole of the wire duct and out to the right side of the fuselage. It will eventually connect to the Emergency Locator Transmitter, or ELT.  I had to use one of the pull strings to get it to go through the duct and I was careful to make sure that I pulled a replacement string through along with the phone wire.

The wording of the directions was rather unclear as to which of the bushings the antenna cables were supposed to go through; basically it said "pick one." I stuffed everything down the same hole. The plans mention that it might be necessary to remove the snap bushings (which kind of sucks - they're called 'snap bushings' because they snap into place and thus become very difficult to remove) and cut a slit in them in order to get the wires to go through. This was the case with the second antenna wire because the wire from the first took up so much of the open room in the bushing that the BNC connector of the second couldn't fit through. I took out the bushing and used the band saw to cut a slit in the side. With the slit done, the bushing could be opened enough to slip the wires into place.


Unfortunately, that also had to be done with the other bushing that I had just put in. With that one, I couldn't use the band saw because I couldn't get the bushing out of the airplane without removing the wire duct and the strings. There was no way that I was going to do that! I just used a hacksaw instead. I sure wish they had mentioned the need for the slit before I put it in! I was kind of angry about that, at least right up until I found the spot in the directions where they actually tell you to install the bushing four or five steps later.  I was ahead of the game on that one!


The next bundle of wires includes the wires that go to the fuel flow transducer, the electric fuel pump, the stall warning vane, a couple of things I haven't figured out yet, and the electric pitch trim servo. This bundle also has the two power wires for the avionics cooling fans. In fact, it's those that get done first.


The plans have us separate out the RED/WHT wires. These are wires that are alternating red and white, not two separate wires that are red and white. That's an important distinction because there are both in the bundle. At this point, all that was required was to strip their ends.


I just hung the whole bundle on the plane while I figured out what to do next.


Actually I was separating out the wires by length. Starting with the shortest length first and working my way back to the longest, I fed them through the bushing, across the top of the rudder pedals, and through as many fuselage bushings as they'd reach. The plans suggesting taping the end down to keep a sufficient length for reaching the radios and such that they will connect to behind the panel.


When it came time to get some terminal fittings to attach the cooling fans, I got to play another game of find-what-you're-looking-for with a pile of electrical fittings.



A hoop terminal gets crimped onto the ground wire of each fan.


With the terminal attached to the ground wire and thus no longer able to be fit down into the ground socket on the only 12V battery I had handy, I had to stuff a piece of safety wire in there in order to run the fan to determine which way the wind blew. This is a required piece of information since one fan will be installed blowing up into the avionics bay and the other will be installed blowing down. In case you're interested, the fans blow away from the label on the fan blade hub.


The fans are held in with two screws each, and each screw uses an AN960-6 washer. Those little washers led me a merry chase! First, it took forever to find them in the inventory sheet because I'm in the habit of reading the part number in the first column. Consider the way bag 2776-1 is displayed as compared to bag 2777-1.


If that wasn't bad enough, it was followed by an extraordinarily frustrating hangar-wide search for bag 2777-1, which being just a thin little bag of washers was eventually found snugged up under the flap of bag 2796.


I was finally ready to install the fans. I set them in place on the avionics shelf while I gathered up my tools. That also gave me time to ponder the less-than-helpful directive in the plans: "Do not over tighten the screws....because this can break the fans!" An exclamation mark!! Probably the first I've seen in the plans! THIS MUST BE IMPORTANT!!! So, how do I know if I've over tightened a screw? Is there a torque value provided?

Nope.

The answer is quite simple: if you break the fan, you've over tightened the screw. What could be simpler?


I marked the shelf with a Sharpie(tm) to make sure I got the fans oriented correctly. Doing so reminded me of the old José Jiménez skits on the Ed Sullivan show. Those were, of course, way before my time, but I remember seeing them in the movie The Right Stuff.
Jose Jimenez : "My name, Jose Jimenez."

Ed Sullivan : "Well, now I see you have some of your space equipment with you. Uh, what is that called, the crash helmet?"

Jose Jimenez : "Oh, I hope not."
Fan Blows Up? Oh, I hope not!


Another cushion clamp gets installed on one of the fans. This one uses an AN960-8 washer, which again caused a bit of angst during the prolonged search through the inventory list. I finally found them in bag 2775-2, but note that this time there is not even a hidden explanatory entry like there was for the AN960-6 washers.


After an exhausting game of which-is-the-right-one, I narrowed it down to two options. I took a chance and went for the one on the right.


Yet another clamp gets mounted onto the fuel flow transducer. This one required the removal of one of the bolts that hold the transducer in place - the clamp gets attached to that bolt and the bolt is then replaced. Three terminals were also required to be added to the ends of the wires so they could be attached to the wires from the transducer. The plans said that I'd need to attach six terminals, but the three on the transducer were already installed. That must have been done as part of the fuselage kit.  I dimly remember doing it.


The next wire was one of those that's mildly inconvenient because of the fuselage being on its side. I had to get to the contact panel for the left wing to attach the wire that will power the stall warning vane.


Then I had to feed the wire up through the grommets in the seat ribs and grab it through the opening in the fuselage.


It was a bit if an aerobics exercise to crimp the terminal on in that location, but once that was done it was an easy matter to attach it to the terminal in the contact block.


By this time, it was getting harder to run the wires over the rudder pedals as it was getting pretty crowded up there. It was unpleasant working down in the rudder area too; someone in there hadn't had a shower yet.


The last step of the day was to attach the power wire to the electric fuel pump. Just as with the fuel flow transducer, this required the removal of a bolt and the installation of a clamp. Also, the ground wire would get attached to the bolt with a hoop terminal. It was a tight reach down into there, and I couldn't help noticing that if I were to accidentally drop the bolt, it could fall through the lightening holes in those ribs and end up way down against the side skin of the fuselage where it would be next to impossible to retrieve.

The thought process went exactly like this:

"Geez, be careful not to drop that bolt... it would be an absolute....... CRAP!!!!;

Well, not exactly like that. I don't think the actual word was 'crap', although the part about it falling all the way down to the side skin was 100% accurate.


I remember that day I bought this little extend-o-grabber as an impulse buy at Harbor Freight. Well, now I remember it even more fondly!


The dropping of the bolt happened because I hadn't used the safety wire trick with this clamp, having found it to be unnecessary with the wire duct. Clearly it would be needed now, so out came the wire. I wired it up and was ready to try again.


The bolt went right in! Piece of cake, and all I had left to do was remove the safety wire and I'd be done for the day.

You'd think by now that I would know better than to ever think "this will be easy."

It took twenty minutes to get that wire out of there, primarily because I couldn't find a tool that would fit down there, and I tried a lot of tools!


I finally got it out of there and put the wire bundle in place through it. You can hardly tell that an epic battle had been fought and won here just minutes before.


It wasn't an easy fight, as the marks on my wrists show. It looks almost as if I'd spent twenty minutes trying to slash my wrists with the wrong side of the knife.


Another ten minutes and I might have considered turning the knife over!

Update with a missive from the mail bag:

Torsten said...
I hate to say it, Dave! Do you remember how I read ahead and followed Joe's fuselage hints and installed that darn clamp next to the fuel pump when running the plumbing? That's why!

Well, I'll start by saying that Torsten makes a fair point and I guess I could have / should have done that, but then I wouldn't have had an interesting story to share, right? Or maybe I'm a Van's purist: I want the full, unadulterated Van's experience. Reading ahead would be just like watching "Scenes from Next Week's Show," something I studiously avoid.

Okay, while those seemingly facetious reasons are actually at least partially true, they're not true enough for me to deliberately ignore simple, labor-saving advice. I read through the notes Torsten refers to while I was still building the fuselage and I'm sure I read one about installing the clamp on the fuel pump while it was still easily accessible, but I didn't have the clamp at the time. It was months after I installed the pump that I ordered the finish kit, and by that time it wouldn't have mattered anymore. One could argue that it would have been worth ordering the $.34 (or whatever) clamp ahead of time in so as to avoid the hassle of installing it later, but that's only obvious in hindsight.

It might be a good time to see if Joe has a list of finish kit notes, though. I'm sure there are more pitfalls just over the horizon!

3 comments:

Torsten said...

I hate to say it, Dave! Do you remember how I read ahead and followed Joe's fuselage hints and installed that darn clamp next to the fuel pump when running the plumbing? That's why! SCNR!!

Anonymous said...

Dave, I installed the rudder pedals after the wiring was finished. Much easier. I got the clue from the forum on Van's Airforce website.

Bill

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