Sunday, August 26, 2012

Hot Air

One of my pet peeves (full disclosure: I collect pet peeves in the way lonely widows collect cats) when chained to my desk deep in the bowels of the data mines is interruptions. With my gamut of responsibilities running from IT Director all the way down to dish washer, help desk activities are an essential part of my job, but that makes it no less disruptive when I have to pull myself away from a particularly thorny piece of code to go handle a far more mundane issue. My typical trek across the office to the site of the problem is often accompanied by a muttered "This is why I never get anything done."

Did I say dish washer?? Well, yes, as I think I may have mentioned before, I am almost always the first one to get to the office in the morning. As such, I am the first to come across a packed-to-the-gills dishwasher. It's really up to one of the ladies in our Operations group to empty the dishwasher, but while almost dead, there is still a faint breath of life remaining in my chivalry gene. I usually go ahead and put the dishes away so they won't have to.

It's usually not even 6am when this is happening and since I am the only one there, the office is dead quiet. Disturbingly so, in fact. To the degree that I turn on the TV and put on the VH1 Classic channel. I think "classic" is their way of saying that they actually still play music as opposed to, say, MTV. Anyway, the commercials at the hour are always entertaining. I mostly tune them out, but the other day I heard one in which the narrator was saying, "By age 50, you may have lost up to 50% of your testosterone." I looked over just in time to see a despondent looking fellow sitting on the edge of a bed, accompanied by a woman (presumably wife or very close friend) who was looking somewhat disgusted.

The man said, "Well, that explains a lot!"

I looked over at my partially completed, not-very-manly domestic chore and said, "Yes. Yes it does."

As to not getting things done, though, I am going to provide an example of why building an airplane at the airport is a less than ideal situation when it comes to avoiding distractions. Pete and I typically meet at the McDonalds just up the street from the airport for a quick infusion of grease and caffeine before heading to the hangar. Once at the hangar we usually jump right into our respective jobs, but not this weekend. We first had to spend a goodly amount of time ogling the hot air balloons that were flying over, some of which came over the hangar quite low and landed at the soccer fields out by the airport road.

Oh, this? This is the stupidest cup holder on the face of the planet:

Here are the balloons:

I guess they're pretty in a way, and fun to watch as they try to land, but other than their work as artillery spotters in pre-airplane wars, I've never understood the point of them. If I wanted to be trapped where I couldn't get away from the irritating noise of expelled hot air while losing all control over my personal direction, I'd get married! [rim shot]

Once the novelty of the balloons had worn off, we got to work.

I'm still working on the replacement of the Dynon D-180 wiring with the new Skyview wiring. It's not just the wiring that has changed, though. The two units are configured in very different ways, and that includes the location of the box that samples the pressure in the pitot and static lines to calculate airspeed and altitude. With the D-180, those lines were fed into the back of a box way up in the front of the plane, in the avionics area. With the Skyview, those lines are plugged into a computer installed way back in the tail cone.

So with the old installation, the pitot tube came in through the firewall and stopped in the avionics bay, while the two static lines went through a T fitting into a single tube that ran forward up to the avionics bay.

With the Skyview, the pitot line now needs to go back to the tail cone, and the static lines are already there.

The secret to understanding the next step was to realize that the air that runs through the pitot and static lines really doesn't care what it is being used for; a tube is a tube is a tube. With that in mind, it's perfectly reasonable that the original tube that was carrying static pressure data from back to front will work equally as well as a tube carrying pitot data from front to back. All that has to happen to make that work is to connect the through-firewall tube to the old static tube up in the avionics bay. Now you have one long pitot tube running from the very tip of the front of the plane all the way back to the tail with hardly any effort at all!

There is one other change needed. That long pitot tube is still attached to the two static tubes at the T fitting in back. It needs to be removed.

That leaves two static lines (one on each side of the plane) in a bit of a mess. That's fixed by yanking out the short static line on the left side and replacing it with a longer one. That new longer tube will meet up with the right side tube up in the area where the air data computer will live. The two tubes get put back into the T fitting, and a third tube comes from the T fitting up to the input on the computer. That causes the left and right static pressures to be averaged before going into the computer.

So, two new tubes cut to length, the old static tube yanked out, new static tube cut to length, and another little tiny length of plastic tube that will be used to join the thin static tube to the thicker white tube that will plug into the computer.

This is the T fitting that will average the two static sources into the tube that goes to the computer:

The tubes get heated to make them expand enough to fit onto the nipple of the T fitting. More noisy hot air!!

Taa-daaa! Fits to a T. (So to speak)

This is where the fitting will be tie-wrapped into place once the computer is installed.

It is not a comfortable place to work. That's kind of the hallmark of this latest line of work. Very uncomfortable contortions required.

This is the new left side static line attached to the static port. If you're completely lost as to why all of this pitot and static stuff is going on, you can read up on it here.

The new computer is also going to want a bundle of wires run back to it from the avionics bay. This will allow it to compute digital values based on the pitot and static information and transmit them up front to other computers and to the display unit. The holes that currently (heh - electrical current. Get it?) carry electrical wires through the bottom of the cockpit are already full with other wires, so new holes get drilled to handle the additional wires.

There were measurements provided to correctly position the new hole, but it was hard to get down inside there with a ruler to get a precise location marked.

Another problem was the location of other wires right behind where one of the holes was to be drilled. It's a 3/4" hole, and that means Uni-Bit. And Uni-Bit means long, angry, looking-for-trouble bit. I had to keep those wires out of harm's way. I lassoed them with some twine and yanked them out of the way while I drilled with the other hand. Well, no, that doesn't sound right. I guess I held the wires with one hand and held the drill with the other.

Good thing the markings for the hole location weren't super precise or I'd be all upset with myself for missing the spot so badly.

Back up front, there is a connector on one of the harnesses that was to be plugged into a little external box that did nothing but provide knobs for setting things on the autopilot built into the knob-less D-180. That function is now built into the knob-enabled Skyview, so the connector is no longer needed.

There was also a pair of wires that I had to verify had been installed by Van's. That meant that I had to pop open the back shell of the connector and take a look.

The wires were there, so all I had to do was chop off the old connector and cover the exposed ends of the wires. I covered each individual wire with thin heat shrink tube, then covered the entire bundle with bigger tube. Having plenty of heat shrink tube on hand is really paying off!

There were two big bundles of wire in the avionics bay that had to be long enough to reach the back of the D-180. Rather than have us remove those bundles entirely to be replace with new Skyview bundles, Van's has developed a series of adapter bundles to transition from one system to the other. These adapter bundles will take up a lot of room in the avionics bay and will moot the need for the original bundles to take up so much space in the bay. Therefore, we are instructed to pull them back down into the tunnel and bundle them up. I did the pulling down part, but deferred the bundling up part.

While I was working in the tunnel, I came across a lone, orphaned wire. It is one of the wires that used to be connected to the autopilot disconnect switch. It had to be cut loose since it was hard-wired to a switch in the now obsolete lower instrument panel. I had to refer back to the plans to find out which wire it used to be spliced to, then re-do the splice.

This is why I never get anything done!

Then it was time to install the first adapter bundle, Hmmm, bit of a problem here: male to male threads? That ain't gonna work! At least in the Midwest.

That sent me back to the build manual where I discovered that I had overlooked the part where it said I would have to use gender matchers.

That will work much better!

I couldn't help noticing that these adapter bundles had a hella lot more wire than they needed just to span the 10 inches across the avionics shelf. That did not bode well. That wire was gonna have to go somewhere!

Meanwhile, Pete was drilling a hole in the cooling shroud over the engine. A cooling hose was to be installed to provide cooling air to the expensive-and-failure-prone Ducati voltage regulator/rectifier mounted on the firewall shelf. It was too tight of a fit to get a drill in there, so he had to improvise.

You may remember that I was going to part ways with Van's and not remove the pitot hose, thinking that by removing one of the wire bundles that they would have us abandon in place I would have enough room to push new wires through without removing the pitot tube. Well, I pulled out the wires, compared them to those much thicker bundles still coiled up on the adapter harnesses, and decided to pull out the pitot tube too.  I was quite a bit of wire to leave in place. I'm not sure why they did that. I think I had better hold onto it, just in case....

With those wires pulled out and the connector chopped off, I again had to shrink some tube over the remaining stubs.

Which gave me an idea. I saw that I would be pulling wires through that had little gold pin connectors on them. This was just like the trim motor wires that I had pulled through ages ago when I first did the wiring. I had read case after case of other builders breaking those gold pins off and struggling to replace them. I wrapped mine in masking tape to protect them, and patted myself heartily on my back for successfully pulling them through without breaking a single one. The tape had been a chore to pull through the bushings, though, because I had gotten wrinkles in it. I decided that this time I would try bending the pins back and covering them with heat shrink before trying to pull them through tight, crowded areas.

It worked perfectly!

There was quite a bit of wire to be pulled:

It was a miserable job, but I finally got all of the new wires down through the avionics bay floor, over the rubber pedal bars, and through the first new hole. It's amazing how desperately those wires want to tangle up with each other, tangle up with themselves, and snag on pieces/parts of airplane. Truly a frustrating job, but eventually I was able to sit back and look at a completed task.

I looked too close. There, sitting on the floor of the cockpit, was a little gold plug. All by its little lonesome - nothing attached to it. There was only one place it could have come from: the bundle of trim wires that I had ever so carefully pulled all the way up from the very back of the airplane without breaking one. One must have gotten broken off when it got snagged by one of the new wires.

This, THIS is why I never get anything done!

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