Back from Oshkosh

It was a long week, but it flew by (so to speak). My annual shopping spree netted four cases of Phillips 20w-50 oil and a Dynon D-6 for the RV-6, and a set of stubby wrenches for the RV-12. Darned if I didn't forget to get a set of nut drivers, though. Shamefully negligent, that. There were a handful of RV-12s there and I looked at each of them. Other than paint, they all look pretty much alike which is, of course, to be expected. I have to confess that I did look at the belly skins of a couple them to see how the edge breaking looked, something I swore that I wouldn't do.

With hundreds and hundreds and hundreds of airplanes there, I also spent some time just walking around looking at paint jobs. I'm still leaning towards a vintage air racer look - I really like that era. I'm sure it was a lot like early auto racing where fatal accidents were more common in any given race than not, which would make them very difficult and painful to watch, so it's lucky for me that my interest in them has the benefit of being viewed through the lens of nostalgia. From eighty years away, it looks like a glamorous, liberated era of pre-meddlesome government flying. The design of the planes is crude by today's standards, but is attractive and artful in the way a classic painting is. Face it, if the Mona Lisa were painted today, she'd have to be soaking in a jar of urine to be considered art. Back then the artistic flare was more subtle and evidenced in small details rather than in grand, swooping forms and gestures.

That level of artistic craftsmanship is by no means dead in certain areas. Where it thrives today is in one of the last bastions of aviation freedom, the Experimental category. While you won't see a lot of innovation and flare in the RV-12 world, a world in which we straddle the divide between regulatory rigidity and unfettered freedom to build what we want, you will still see in in the rest of the Experimental fleet. You will see it in spades in airplanes like this one, the 2010 Grand Champion kit built:

You can get a feel for the astonishing effort that goes into crafting an aircraft like that by viewing it from a distance, but it is the close-up details that really tell the story. There are hundreds of examples, some as seemingly mundane as the custom fuel caps. Every single part of that airplane was built or modified to be the best it could be. In my opinion, the very definition of art is beautiful artifacts created by supremely talented and dedicated people.

So, there I go, off on a tangent. Back to the paint schemes. Here are a few pictures that fit with the general look I will be going for, absent in all but one case the required distinctive logo somewhere on the side of the fuselage.

None of that will ever come to fruition if I don't get back into the business of building an airplane, so to that end I spent the last couple of evenings on finishing the fuel system. Tonight I put the final line into place. The last line to go in was the long length of 1/4" tube that runs from the firewall shelf back to the bulkhead fitting. Once installed, this line completed the fuel return line. I learned a little bit about the Rotax 912 up at Oshkosh and now know why a return line is necessary.

The Rotax is a low displacement engine relative to the normal Lycoming and Continental type engines found in most planes, my RV-6 included. More horsepower can be gained in two ways: increase the displacement of the engine, or increase the RPM of the engine. Or both, if you're made of money. The older engines have higher displacement but turn at lower RPMs. They turn relatively slowly because if they turned any faster, the tips of the propellors would approach the speed of sound and there is a whole lot of drag at those speeds.

The Rotax takes a different approach. It is a smaller, lighter engine with lower displacement and it makes up for the loss of horsepower by increasing the RPM. A lot. But what about the prop going too fast? Well, the Rotax has a gearbox called a PSRU: Prop Speed Reduction Unit. (I might be making that up - you can never tell with me) The engine runs fast (5,000 RPM), but because of the gearbox, the prop turns at a more sedate speed and avoids the high speed drag.

Running the engine that fast creates a lot of heat. If you shut the engine down and all of that residual heat causes the fuel in the fuel lines to boil, you get vapor lock. Good luck starting that engine, Bub. So what Rotax does is let the fuel in the lines vent itself back to the fuel tank through the return line.

Or so I understand. It doesn't really matter; the return line is in the plans, so I put it in.

Speaking of the plans, the directions for this particular line left me in a haze of what-duh-heck-are-they-saying?? The drawing was no help either; it seemed to show a complex pair of bends where the directions said there was a simple 90 degree bend. Well, a picture may be worth 1000 words, but I'm not sure even that many words could have described what was going on here. I finally just decided if the words say "make a 90 degree bend," well, that's what I'd do.  It worked out fine. So here's how it went.

First, remove the rudder pedals. They're just in the way. I took them out and set them back in the finished-but-not-yet-attached pile.

I cut a length of line a few inches longer than specified so as not to come up short. The plans suggest marking a line 14-ish inches to mark the start of a 90 degree bend. That's not the way my tube bender works, so that line would be useless, save for decorative value; I just made a bend that left me 14 inches of tubing to go up through the firewall shelf. That leaves about five or six feet of tube that has to be fed through the bushings and back out through the inspection port in the belly. Luckily, the tube bends easily.

I wrapped the flaperon mixer (I know the magic behind that thing now, having seen a completed one at Oshkosh. I'll share that with you some day) with duct tape to keep it from scratching, dinging, or gouging the fuel tube.

It took a few trips from the front of the plane to the bottom in order to get the tube to come out through the inspection port.

With the full length of the tube installed, I measured, eyeballed, guestimated, and SWAGed my way through cutting the excess length on each end to fit, flaring the ends, and installing the nuts to the various fittings. I installed the clamp that holds it into place on the firewall, a job that would have gone more smoothly if I had chosen the correct size screw out of bag 2727. For future reference, it's a stubby, fat little guy with a big head.

Insert favorite Napoleon joke here.

That's it for the fuel system. The longerons get bent next. I talked to a few people at Oshkosh about how it's best done but got no consistent answers. It's just something I'll have to work through.

I knew this would happen

Remember how I needed to order the fuel nipple that would pass fuel through the firewall and into the back of the gascolator because I had failed to do a complete enough inventory? Ans remember how I was missing two of the 3/8" sleeves to hold nuts onto flared 3/8" tube? Well, I knew it would turn out that these parts were, in fact, included in the kit and I had done all of that ordering of replacement bits and pieces for naught.  Well, I was right, and I was wrong. I found the sleeves.

The nipple has not yet been found, but its replacement finally arrived from Van's. You may also remember that I had attempted to order the nipple from Aircraft Spruce, but ended up getting the wrong size. Why, then, you ask, did you not just order it from Van's in the first place? Well, consider this: shipping from Aircraft Spruce was $1.28. Shipping from Van's was $8.50. They annoy me this way. Van's typically provides top-notch customer service, but they have yet to provide customer-friendly tools to allow the purchaser to make an informed decision regarding shipping method. In my opinion, that is something they could and should fix.

Do I seem a little crabby tonight? Eh, the paying job has a way of wearing me down towards the middle of the week. Some days go smoothly, others are pockmarked with unwanted interruptions, meetings that inevitably dump ever more work onto my crowded platter, and a crappy commute both ways. Two out of three, today. One bright point though was my sharing of an original, piquant, and pithy insight in one of the meetings: "The fact that I have a hidden agenda may make me duplicitous, but it does not follow that it makes me wrong." I don't think it worked, though. I ended up with the additional work anyway.

Nothing more relaxing than twisting a nipple, I figure, so I treated myself to a little shop time. You may recall that the hole that I drilled for the gascolator looked like it might have been a little off-center. Well, it was. It only took a little filing to get it rounded out to where it needed to be. Two bolts later, the gascolator was attached.

That was the final step in the outgoing fuel system. Now for the return line! The return line starts (well, the fabrication of it starts) at the fuel tank, follows the supply line around a little bit, and branches away to feed down to the bulkhead fitting that I enjoyed installing last Saturday. Because it is only 1/4" diameter tubing, it's a little tricky to get it to follow the 3/8" diameter around turns because the turn radius is a bit tighter. Or so it seemed to me; it's just as likely that I screwed up the math again. Either way, I found that the best thing to do was to be very careful to get the separation distance correct where the two tubes make their vertical climb up to where the fuel tank will be and just eyeball the rest. The two tubes will be clamped together for part of their run and I found it quite helpful to clamp them together early in the process to help maintain the required 1 5/8" separation.

The clamps are quite simple: they're just hose clamp and rubber tube.

I used the scrap of paper with the two Sharpie(tm) marks to set the spacing between the vertical tubes and used the first clamp to hold them in place. Then I just made the bends needed to shape the return tube to the path of the supply line. The hardest part was figuring out the bend required to angle the return line down to attach to the bulkhead fitting. I gave myself a few extra inches of tube to work with, and through a process of trial and error that saw the paired tubes in and out of the fuselage a dozen times, I finally got the length right, the tube flared (with the nut and sleeve on it!!), and the assembly installed for what will hopefully be the last time.

And now it's time for dinner!

Conniptions

It's beginning to dawn on me that there is a reason that people buy airplanes already built. It's just for the fuel systems, I think.

Having finished the rudder pedals, it was back to the fuel system. But a little housekeeping would be needed first. It's been awhile since I've straightened up and it was getting hard to find things that I had just set down moments before.

It's a cluttery process, this airplane building. Every tool has its place, but it seldom visits it. After a little rearranging, I was ready to start.

I still don't have the nipple for the gascolator, but I did somehow manage to order the correct sleeves so I could finish the fuel supply line that runs from the fuel tank to the fuel pump. I had already made the first 90 degree bend in that line, but progress came to a screeching halt when I went to get the nut sleeve from the parts bag. As it turns out, even if the sleeves hadn't been missing, I was in for a rude awakening. You see, in my fervor to get the first 90 degree bend up tight to the end of the tube (as shown in the apparently fictional rendition in the plans) I hadn't put the sleeve that I didn't have on the tube. Had I done so, I would have realized that the flaring tool wouldn't work with the short length of tube left after making the bend. With the sleeve pushed back as far as it would go, the end of the tube fell 1/8" short of where it needed to be for the flaring tool to work. BAM! Two feet of aluminum tube tossed aside as ruined.

Fortunately for me (but not so much for the fellas I was going to donate my extra fuel line to - better order some, Kyle) I had a lot left over from the spare length that I had bought. I rolled out another two feet (plus two inches, just in case), put the nut and sleeve on and made the flare, then did the first 90 degree bend. Which, oddly enough, is the exact order written in the directions. Imagine! Still, my tube bender can't get the bend where Van's wants it, but the extra two inches of tube I had to work with would cover the extra distance the tube would have to run. And the best news is that there would still be enough tube left to give at least a couple of feet to Kyle.

For the second 90 degree bend, I did the measuring to find the location of the 'L' line as specified in the instructions that came with the tube bender. That bend went perfectly. Then there is a slight fifteen degree bend that I had to do by eyeballing - the tube bender instructions are notably mute on the topic of bends less than 45 degrees. That left only one more bend: another 90 degree bend that would turn the line up from the plane of the first three bends to attach to the bottom of the fuel tank. I measured an 'L' line, very, VERY carefully made sure that I was bending in the right direction (it's surprisingly easy to go the wrong way), and made the bend. I set the finished line down on the plans and found the the last bend was about 1/2" out of position. Argh! That's way more than can be waved away, besides which using the extra length of tube to get the bend to the wrong location had eaten up enough tube that the vertical part would be too short to reach the tank.

Remember the old adage "measure twice, cut once?" I've amended it for fuel line fabrication: "Measure twice, bend once, start over."

I grabbed the last of my tubing, made the flare with the nut and sleeve installed, made the first 90 degree bend, measured the 'L' line for the second degree bend, and confidently made the second 90 degree bend in the wrong place. Yep. The wrong place. I got something wrong in either marking the 'L' line or getting it positioned in the tube bender and the distance between the first and second 90 degree bends ended up being too far. Desperate, I decided to try to save the tube by making the fifteen degree bend a 30 degree bend, my thinking being that the vertical 90 degree bend only had to be in the right point in space, no matter how convoluted its path in getting there.

That seemed to work. If I could only make the third 90 degree bend in the right place this time, all would be well. I didn't bother with an 'L' line this time, that method having failed me twice already. I eyeballed the last bend and very, VERY carefully ensured that I was bending in the right direction, drove to KFC for a bucket of chicken to sacrifice at the altar of all deities affiliated with tube bending just to increase my chances of getting it right, and made the bend.

Success!

Well, you'll have to take my word for it. All of the stuff described above is hidden under the baggage floor.

Flush with victory, I went on to the next step. With the fuel delivery line completed, I now have to build the fuel return lines. It would seem that not all of the fuel that leaves the tank ends up getting burned, or at least not on that particular trip. Some apparently gets returned to the tank. Not as much as leaves the tank, though; these are 1/4" lines, not the 3/8" of the delivery lines.

Step 1: put a fitting through a bulkhead. A bulkhead that is now accessible only through an inspection port in the belly skin. The belly skin that hasn't always been there. It's the belly skin that I put there. I put it there when I was told to. You know what would have been nice? If I had also been told to put this fitting in before putting the belly skin on. It would have taken two minutes. Instead it took hours.

Putting it through the bulkhead wasn't so bad.

Getting a nut and washer tightened onto the other side was. It ended up taking hours and giving me a painful case of conniptions. Whatever those are. I think it's something my grandparents had, back in the day. We get vaccinated for it now, but even modern medicine has its limits.

The first problem that I ran into was that I needed a way to hold the fitting in place while I wrenched on the nut. I tried having Co-pilot Egg hold it, but she couldn't get enough of a grip on it. Also, when she held it flush the corners of the flats on the nut would hit the belly skin and I wouldn't be able to turn it. I was at a loss. It was time for the last resort, which is to search the forums on the Vans Air Force web site to see if anyone else had run into this problem. Someone had. The rest had been smart enough to put the thing on before riveting on the belly skin.

Show-offs!

The trick is to hold the fitting in place with a pair of needle-nosed vice grips clamped to the side of the bulkhead. Then you go to Harbor Freight and buy a set of Crow Foot (I think they're Native American technology, going by the name) wrenches.

With the vice-grips holding the fitting, I was able to reach up into the inspection port with the Crow Foot wrench and tighten the nut. It still wasn't easy, but it was manageable.

All I have to do now is see if those clever Crow Foot indians ever came up with a cure for the conniptions.